Groupe Psa

Computer-Aided Styling DMU Digital Mock-Up PLM Product Lifecycle Management CAE

Keywords:

A B S T R A C T

Industrial design reviews benefit from emerging interactive technologies to become more Realistic, Immersive and Collaborative. The industrial product review is a vital process for project members to assess aesthetic properties, user satisfaction, and technical feasibility of the product before physical prototyping. Particularly, reviewing digital mock-ups in a realistic context with one-to-one scale enriches their reviewing experience, and a shared workspace facilitates discussions across distinct experts. However, modifying the product data during the reviews is still challenging. Although research in the integration of Virtual Reality (VR) and Computer-Aided Design (CAD) has proposed a range of systems for design reviews, only a very few of them support direct modifications of original CAD data within immersive systems. Engineers, therefore, need to apply post modifications on the CAD data from a workstation to adjust the design based on discussions during the design reviews. This iterative process causes delays in the design verification process.

I argue that current distinct processes of design reviews: discussion and design adjustment should merge-so thus it could reduce the iterations, facilitate discussions and empower all users to directly apply modifications on CAD data. In this dissertation, I propose a new industrial design reviewing paradigm in which project members can adjust and compare a final design of the product within interactive systems. Considering various traits of experts involved in the review process, the interactive systems should be configurable to meet their requirements. Also, the design review practice should be collaborative between remote locations concerning the current trend of decentralized work organization.

The accessibility of native CAD data is the cornerstone of the new design review process. I first designed a back-end server, namely VR-CAD Server, which can update the CAD data with an embedded CAD engine and transmit it to the interactive systems. I implemented VR-CAD Server in a distributed network architecture that makes the system highly configurable to support heterogeneous systems and multi-user interactions between remote locations. This structure is a basis of the design preview process, which empowers project members to modify the product design on top of the current design reviews.

Based on the distributed architecture, I explored interaction techniques for novices to modify parametric CAD data in large interactive systems. Since targeted users include non-CAD experts, interactions with the 3D-CAD model should be straightforward to learn, i.e. without the interaction on parameters, over various systems. The choice of v interactive systems differs according to the expertise and their purpose. In actual practices, ergonomists prefer to use a 3D environment to assess the spatial feeling, whereas project managers prefer discussing with a large format 2D display. I therefore designed two interaction techniques on 3D and 2D interactive systems to cover diverse reviewing scenarios, and conducted user studies for each: a Cave Automatic Virtual Environment (CAVE) system and a wall-sized display.

For the former case, I designed a 3D interaction technique on parameter modifications of the CAD data, namely ShapeGuide. With ShapeGuide, users can implicitly manipulate parametric constraints of a CAD part with a co-localized shape-based interaction. This technique prepares a set of shape variations from an original design at run-time to guide users' hand gestures. To stabilize the gestures in 3D space, I also tested force feedback during manipulations. I performed a controlled experiment to evaluate how ShapeGuide affects a CAD data modification task in comparison to a standard one-dimensional scroll technique. Results of the experiment demonstrate that ShapeGuide is significantly faster, more efficient and preferred by the users than the scroll technique.

As for the wall-sized display, I designed ShapeCompare, an interaction, and visualization technique in which users can modify and compare multiple designs of CAD models on a large space with touch interaction. The technique of ShapeCompare is based on ShapeGuide, which generates and presents multiple design alternatives deviated from an initial CAD model on the wall. I performed a experiment to evaluate how a large number of design alternatives displayed on a wall-sized display affects on collaborations between different experts. Results of the experiment showed that with ShapeCompare, paired participants finished the collaborative reviewing task faster, preferred and found it more helpful in communications across pairs. Lastly, I summarize these findings and conclude with an illustration of future collaborative design review scenarios across heterogeneous systems. Both ShapeGuide and ShapeCompare are designed based on the distribution of design alternatives. This method does not only supports the direct design refinement during the review but also adapts the interaction technique to a specific system platform. This approach can be extended to other contexts, which involves collaborative discussions on parametric data. vi R É S U M É Les revues de projets en conception de produits industriels bénéficient des technologies interactives émergentes pour devenir plus réalistes, immersives et collaboratives. La revue de produit immersive au cours de la conception est un processus essentiel pour les membres d'un projet afin d'évaluer les propriétés esthétiques, la satisfaction de l'utilisateur et la faisabilité technique du produit avant le prototypage physique. En particulier lors de la prise en compte du cycle de vie des produits (Product Lifecycle Management (PLM)), examiner des maquettes numériques dans un contexte réaliste à échelle 1 : 1, enrichit leur expérience en matière de revue du produit, et un espace de travail partagé facilite les discussions entre experts distincts. Cependant, la modification des paramètres de conception du produit au cours des examens reste difficile. Bien que les recherches sur l'intégration de la réalité virtuelle (VR) et de la conception assistée par ordinateur (CAO) aient proposé une gamme de systèmes pour les revues de conception, aucune d'entre elles ne prend en charge les modifications directes des données de CAO d'origine au sein de systèmes immersifs. Les ingénieurs doivent donc appliquer des modifications après modification aux données CAO d'un poste de travail pour ajuster la conception en fonction des discussions tenues lors des revues de conception.

Je soutiens que les processus actuels de revue de projet, de discussion et d'ajustement de conception doivent être fusionnés afin de réduire les itérations, de faciliter les discussions et d'autoriser tous les utilisateurs à appliquer directement des modifications aux données CAO. Dans cette thèse, je propose un nouveau paradigme de révision de la conception industrielle dans lequel les membres du projet peuvent ajuster et comparer une conception finale du produit dans des systèmes interactifs. Compte tenu des caractéristiques et préférences des experts impliqués dans le processus de revue de conception, des systèmes interactifs hétérogènes, éventuellement distants, doivent pouvoir être configurés de manière à répondre efficacement à leurs besoins en terme de capacités interactives et collaboratives.

Un premier cas a été la conception d'une technique d'interaction 3D sur les modifications de paramètres des données de CAO, à savoir ShapeGuide, dédiée à des systèmes immersifs (CAVE ou Head Mounted Display (HMD)). Avec ShapeGuide, les utilisateurs peuvent implicitement manipuler les contraintes paramétriques d'une pièce CAO avec une interaction basée sur la forme et co-localisée avec celleci. Cette technique consiste à préparer un ensemble de variations de forme par rapport à une conception d'origine pendant l'interaction temps réel pour guider les déformations réalisées par les utilisateurs et d'assurer la validité des changements de valeurs de paramètres CAO vii sous-jacents. Pour stabiliser les gestes dans l'espace 3D, j'ai également testé le retour d'effort lors des manipulations. J'ai effectué une expérience contrôlée pour évaluer l'impact de ShapeGuide sur une tâche de modification de données de CAO par rapport à une technique de défilement unidimensionnel (scroll) de la valeur du paramètre à modifier. Les résultats de l'expérience démontrent que ShapeGuide est nettement plus rapide, plus efficace et est préféré par les utilisateurs que la technique de défilement. Un second cas concerne l'affichage 2D sur grand écran mural, pour lequel j'ai conçu ShapeCompare, une technique d'interaction et de visualisation dans laquelle les utilisateurs peuvent modifier et comparer plusieurs conceptions de modèles CAO sur un grand espace avec une interaction tactile. La technique de ShapeCompare, basée sur ShapeGuide, génère et présente plusieurs variantes de conception déviées par rapport à un modèle de CAO initial sur le mur. J'ai effectué deux expériences pour évaluer l'impact d'un grand nombre de variantes de conception affichées sur un écran de la taille d'un mur sur les collaborations entre différents experts, et en quoi cela facilitait l'exploration de leurs conceptions. Les résultats des expériences ont montré qu'avec ShapeCompare, les pairs de participants finissaient la tâche d'examen collaboratif plus rapidement, qu'ils préféraient et la trouvaient plus utile pour leurs communications.

viii A C K N O W L E D G M E N T S

First and foremost, I wish to express my sincere gratitude to my advisor Patrick Bourdot. He gave me this great PhD journey in France and continuous and tireless support-not only on my dissertation but also on countless administrative issues I encountered throughout my PhD. I also would like to express my deepest gratitude to my second advisor, Cédric Fleury. He gave me great help on experiment design, analysis, brainstorming, and in particular-paper writing for which he was always with me until the last minutes of the deadline. I appreciate both of my supervisors for their patience during my thesis writing.

My sincere thanks also goes to Nicolas Ladevèze and Olivier Gladin for all of their supports on my experiments. Nicolas often stayed with me until after dark for the maintenance of CAVE and gave me tremendous assistance in every difficult time over my whole PhD study as a colleague-but also as a good friend. Olivier's door was always open, and his help on implementations and experiment setup with WILDER enabled me to get over the last step of my PhD. Without their supports, I could not imagine completing this dissertation.

I gratefully acknowledge my jury members, Thierry Duval and Theodore Lim, for taking their time on reading my thesis and their invaluable feedback, as well as Caroline Appert, Alexis Paljic, Regis Kopper and Jean-Claude Martin, for being on my orals committee and their insightful comments.

In my journey towards this degree, I have been fortunate to have worked with people in VENISE and ExSitu teams. I would like to thank everyone for their supports, encouragement and giving me motivations when I require them. A lot of my teaching activities were undertaken with the help of Jeanne Vezien and Nicolas Férey. Jeanne always gave me a hand whenever I look for hardware and also colorful stories during coffee time. I also would like to express my sincere gratitude to Wendy Mackey and Michel Beaudouin-Lafon for giving me various knowledge in the field of HCI during PhD seminars. I appreciate the help of Theophanis Tsandilas in statistics to analyze experiment results. It was always my great pleasure to work with my fellow labmates in pursuing PhD together. I thank Yiran, Nawel, Mengchen, Iuliia and Valentin for making the office and coffee time always delightful and sharing all up-and-down moments with me. Yiran and Nawel, my fingers are tightly crossed for the completion of your dissertations. I also thank Carla, Germán, Michael, Stacy, Philip and Liz for their kindness, encouragement and great surprises at my thesis defense. Stacy, I cannot count how many times we figuratively described our PhD life at Panifique. I was always grateful for your ix support during my thesis writing. I am finally on my return trip to the planet where I was and hoping these lines will find you the same.

My thanks also goes out to the people from whom I received the courage to embark on this journey in the first place. Special thanks to Lian and Maya for giving me the strength to go abroad, always hilarious but thoughtful teaching, and a wonderful time we had in Cebu. I also thank Philippe and Hélène for introducing me to a number of amusing nightlife in Paris and inspiring me to go for PhD path.

I would like to say a heartfelt thank you to my family in Japan, Sachiko, Takanobu, Kotaro, Chieko and Kinari for always giving me peace of mind whenever I am home. Their undying support and encouragement as well as the ceaseless food shipment from Japan to France.

Finally, my life in France would not have had happened without staying with my French family. To my foster family in France, Kiyoko, Dominique, Akemi, Louise, Seiji and to the cutest cat Tsuki, thank you for making your home homey for me. For those delicious food you served on the table and for making me feel that I am a part of your family. Being in your house refreshes my mind after my busy days. I could not have reached where I am now without your support. Merci beaucoup.

Kiyoko, I finally finished my long journey! Application of the V-model to the product development (BMW). Left side of the V-model shows System design phase, and the right side shows System integration phase [START_REF] Weber | Automotive Development Processes[END_REF]. The System design phase is divided into Conceptual design and Detailed design. . . . . . . . . . . . . . . Figure 2. [START_REF] Ball | Move to Improve: Promoting Physical Navigation to Increase User Performance with Large Displays[END_REF] "Over the wall". The designer throws the designs over a wall to the manufacturing engineers who then have to deal with the various manufacturing problems [START_REF] Boothroyd | Product design for manufacture and assembly[END_REF]. . . . . . . . . . . Figure 2. [START_REF] Beaudouin-Lafon | Multisurface Interaction in the WILD Room[END_REF] Concurrent engineering as expressed by prime European region [START_REF] Sohlenius | Concurrent Engineering[END_REF]. Each process is overlapped each other in comparison to traditional sequential process. . . . . . . . . . . . . . . . . Figure 2. [START_REF] Beaudouin-Lafon | Lessons Learned from the WILD Room, a Multisurface Interactive Environment[END_REF] Traditional design process explicitly divided into three different processes (left). Proposed product development process (right) which various teams involve throughout the overall process [START_REF] Buxton | Sketching user experiences: getting the design right and the right design[END_REF]. . . . . . . . . . . . . . . . . . . . . . . Figure 2.9

Manual exterior rendering of BMW 3 Series (BMW) [START_REF] Weber | Automotive Development Processes[END_REF]. . . . . . . . . . . . . . . . . . . . . Figure 2. [START_REF] Berg | An Industry Case Study: Investigating Early Design Decision Making in Virtual Reality[END_REF] Translation of sketch into tape drawings [START_REF] Weber | Automotive Development Processes[END_REF]. Figure 2

.11

Manufacturing of 1:1 exterior clay models (BMW) [START_REF] Weber | Automotive Development Processes[END_REF]. . . . . . . . . . . . . . . . . . . . . . . . . Figure 2. [START_REF] Bi | Comparing Usage of a Large High-resolution Display to Single or Dual Desktop Displays for Daily Work[END_REF] Informal selection of concept sketches. This session would involve a number of designers, the section leader and studio manager [START_REF] Tovey | Intuitive and objective processes in automotive design[END_REF]. . Figure 2. 13 Detailed virtual car (BMW) [START_REF] Weber | Automotive Development Processes[END_REF]. . . . . . . . . Figure 2. [START_REF] Boothroyd | Product design for manufacture and assembly[END_REF] During entire PLM, multiple experts work with one unique Digital Mock-Up (DMU) [START_REF] Li | Multi-user interface and its use for collaborative work with multiple representations of Digital Mock-Up[END_REF]. . . . . Figure 2. [START_REF] Butterworth | 3DM: A Three Dimensional Modeler Using a Headmounted Display[END_REF] Example of interior review with a cray model and detailed illustrations [START_REF] Happian-Smith | An introduction to modern vehicle design[END_REF] Example of various project reviews during product development: SGR (Specification Gate Review)-the requirement review, PGR (Preliminary Gate Review)-the preliminary design review, CGR (Critical Gate Review)-the detailed design review, FEI (First Equipment Inspection)the prototype review, and IQA (Initial Quality Approval)-the industrialization review [START_REF] Li | Multi-user interface and its use for collaborative work with multiple representations of Digital Mock-Up[END_REF]. . Figure 2. [START_REF] Buxton | Large displays in automotive design[END_REF] Sketchpad [START_REF] Sutherland | Sketch Pad a Man-machine Graphical Communication System[END_REF] (left) and Sword of damocles [START_REF] Sutherland | A Head-mounted Three Dimensional Display[END_REF] (right), Ivan Sutherland. . . . . . . . . . . . . . Figure 2. [START_REF] Xiang 'anthony' Chen | Forte: User-Driven Generative Design[END_REF] Igarashi et al.'s Teddy [START_REF] Igarashi | Teddy: A Sketching Interface for 3D Freeform Design[END_REF]. . . . . . . . . . . . . Figure 2. [START_REF] Choi | ONESVIEW: An Integrated System for One-Stop Virtual Design Review[END_REF] Example of 3D drawing applications . . . . . . Figure 2. [START_REF] Chu | Multisensory user interface for a virtual-reality-based computeraided design system[END_REF] Digital tape drawing techniques . . . . . . . . Figure 2. [START_REF] Vincent | Resolving Nonuniqueness in Design Feature Histories[END_REF] Surface modeling applications . . . . . . . . . . Figure 2. [START_REF] Herbert H Clark | Grounding in communication[END_REF] Interface of CATIA V5. . . . . . . . . . . . . . . Figure 2. [START_REF] Clark | Designing Surfaces in 3-D[END_REF] Definition of Boundary Representation (B-Rep) model. On the left (a), the complete solid object; in the middle (b), its representation in terms of topological surfaces; on the right (c), its representation in terms of edge and topological vertices. . . . . . . . . . . . . . . . . . . . . . . . Figure 2. [START_REF] Coffey | Design by Dragging: An Interface for Creative Forward and Inverse Design with Simulation Ensembles[END_REF] Example of Constructive Solid Geometry (CSG) tree. The final solid object is actually the result of a subtraction between two objects: the first object, on the left, is the intersection between a sphere and a cube; the second solid, on the right is the result of the union of three cylinders. Figure 2. [START_REF] Convard | History Based Reactive Objects for Immersive CAD[END_REF] Immersive solid modeling . . . . . . . . . . . . Figure 2. [START_REF] Convard | Managing Deformable Objects in Cluster Rendering[END_REF] Design reviews on large displays . . . . . . . . Figure 2. [START_REF] Joseph | Fardier à Vapeur[END_REF] Design reviews on immersive systems . . . . . Figure 2. [START_REF] Czerwinski | Toward Characterizing the Productivity Benefits of Very Large Displays[END_REF] Collaborative design reviews between distant locations . . . . . . . . . . . . . . . . . . . . . . Figure 3.1

The use of VR during the design process at PSA.

The figure is translated into English from the original one [START_REF] Martin | Modéle pour la conception immersive et intuitive: application à l'industrie automobile[END_REF]. . . . . . . . . . . . . . . . . . Forte is a 2D design tool that takes a userdriven approach of generative design:a user sketches a reading chair inspired by the painting 'The Great Wave off Kanagawa' (a) with specified loading scenario (red arrow forces, blue ground); Forte then generates structures (with real-time feedback) to support the loads while resembling the user's sketch (b), which can then be post-processed to create a 3D fabrication-ready model (cd). [START_REF] Xiang 'anthony' Chen | Forte: User-Driven Generative Design[END_REF] . . . . . . . . . . . Figure 3.5

Dreamsketch: the user navigating through the resulting solutions by directly manipulating the bike handle (top). [START_REF] Habib Kazi | DreamSketch: Early Stage 3D Design Explorations with Sketching and Generative Design[END_REF] . . . . . . . . . . . . . . Figure 3. [START_REF] Ball | Move to Improve: Promoting Physical Navigation to Increase User Performance with Large Displays[END_REF] Shape generator in Autodesk Inventor [START_REF] Xiang 'anthony' Chen | Forte: User-Driven Generative Design[END_REF] . . . Figure 3 Interaction with ShapeCompare: when a part is selected (Selection), the system generates a set of design alternatives on a row of the wallsized display (Display). All alternatives can be scrolled up and down with a three-finger drag (Slide shapes), rotated in 3D with a widget (Rotation), and displayed on the external screen with a two finger long press (Update 2nd screen). Brainstorming session with participants. . . . . Figure 6.7

Usability study setup: the target shape is displayed with a transparent yellow color in a realistic environment on an external screen next to the wall-sized display. . . . . . . . . . . . . . Figure 6.8

The mirrors modified by each participant during the study. . . . . . . . . . . . . . . . . . . . Figure 6. [START_REF] Berg | An Industry Case Study: Investigating Early Design Decision Making in Virtual Reality[END_REF] Igarashi et al's Suggestive Interface [START_REF] Igarashi | A Suggestive Interface for 3D Drawing[END_REF]. . . . . . Figure 6.9

Selection widget, users can select a thumbnail of the two extreme shapes to generate the corresponding design alternatives. . . . . . . . . . . Figure 6.11

Two solutions for visualizing the design history: the similar shape appears just above the selected shape (top), or the similar shape always appears in the central column (bottom). . Figure 6.12 Interaction flows of two conditions: after shape selection (1), Selection Widget helps users to select a CAD parameter by displaying shapes corresponding to parameter extrema (2). Then users can explore design alternatives using Shape-Compare or ShapeSlide. . . . . . . . . . . . . . . . Figure 6. 13 Pairs of participants are exploring the design to find the one meeting their design criteria with ShapeCompare (top) and with ShapeSlide (bottom). Figure 6

A C R O N Y M S 1 I N T R O D U C T I O N
The review process of industrial products is a critical part for verifying aesthetic properties, user satisfaction, and technical feasibility. Oftentimes such process is driven by heterogeneous interactive systems where project members can discuss the final design of the product. In most cases, this process is iterative. The project members first review the digital mockup within a large interactive system. Then, engineers need to apply postmodifications on the product data with CAD systems based on remarks and annotations from the design reviews. I argue that these two distinct steps should merge-so thus all members in a multidisciplinary team can apply modifications and review the updated product instantly, which would facilitate communications and give more design inspirations. In this dissertation, I introduce a new approach for industrial design reviews in which they can collaboratively discuss, modify, and validate the product altogether in large interactive systems: a CAVE and a Wall-sized display. My dissertation describes three key contributions to achieve such an approach: (i) native CAD data modifications, (ii) interaction techniques, and (iii) study on collaborative design activities.

Immersive product reviews of digital mock-ups are increasingly becoming a vital process in industrial companies [START_REF] Lawson | VR Processes in the Automotive Industry[END_REF]. These reviews let various specialists (e.g. designers, engineers, and ergonomists) assess the design of the product and conduct numerical or manufacturing simulations in a virtual environment before creating physical prototypes. Depending on the purpose or users' requirements, the interactive systems used for review sessions can be heterogeneous: e.g. designers may want to check the aesthetic properties with a highresolute visualization while ergonomists may want to assess the users' satisfaction within a 3D environment. Such large interactive systems make a conventional reviewing activity more Realistic, Immersive and Collaborative. Verifying the digital mock-up in a realistic context with one-to-one scale enrich virtual reviewing experience, and a shared reviewing workspace facilitates discussions across distinct expertise. With this goal, the use of VR platforms or large displays for design reviews have been explored since more than two decades [START_REF] Berta | Integrating VR and CAD[END_REF][START_REF] Buxton | Large displays in automotive design[END_REF][START_REF] Raposo | Environ: integrating VR and CAD in engineering projects[END_REF], and industrial companies now more often use such displays-especially at the end of the industrial design process.

The industrial design process stretches from ideation of the product to its realization [START_REF] Buxton | Sketching user experiences: getting the design right and the right design[END_REF]. Throughout the process, representation forms of the product turn from conceptual representations-e.g. sketches or drawings-into more technical representations-e.g. blueprints with design specifications-before becoming physical prototypes. Engineers (i.e. drafters) conduct such data transformations with CAD systems, which can define the product by parameters and geometric constraints with a set of operations (e.g. Extrusion, Sweep and Boolean operations) to consider manufacturing feasibility. The CAD systems permit them to quickly prepare variations of a design with respect to design intents defined in the earlier design process.

Project members belonging to a multidisciplinary team therefore often review and discuss the product with CAD models in large interactive systems. After the review meetings, engineers apply modifications based on remarks and annotated documents by other specialists on the CAD system from a workstation. Consequently, the current design reviewing activity encompasses two processes: design adjustment and discussion. This process is often iterative. It delays the design verification process and does not allow other specialists to directly explore and reflect their ideas. A side-by-side setup of VR and CAD systems [START_REF] Techviz | [END_REF] could reduce the iterations, but still, the design adjustment task is only limited to engineers.

The goal of this dissertation is to propose a new approach for design reviews in which project members can adjust and discuss the product within a large interactive system at once-in other words; I ambition to merge two distinct processes during product reviews. In such a way, project members can directly apply modifications on a CAD model during a collaborative reviewing session. That would shorten the iterative process and reduce miscommunication between experts. This dissertation contributes to the advancement of industrial design reviews by considering three different research questions:

1. How can immersive design review systems access and update native CAD data?

2. How can non CAD-experts efficiently modify the CAD data with heterogeneous systems (e.g. 2D or 3D visualization systems)?

3. How can project members effectively collaborate on design explorations on-site or across heterogeneous systems?

Even though previous studies enabled users to create or edit 3D models in a virtual environment, loading and modifying native CAD data is still challenging. The first question concerns Data pipeline between CAD systems and a virtual environment.

Then, the second question is concerned with Interaction technique for 3D CAD data modifications. The design approach I propose involves non-CAD experts in a design adjustment process. As mastering CAD skills is complex, time-consuming, and costly [13], the interaction has to be straightforward for the non CAD-experts.

Lastly, the last question focuses on Collaboration. Design review meetings are organized with a multidisciplinary team either on-site or across geographically distant locations. The design reviews system should be designed to encourage collaboration between distinct experts.

research approach

Previous works on integrating CAD to VR have started since the 2000s, and various 3D interaction techniques on virtual prototyping have been studied since the 90s. However, the convergence of these fields has not received much attention. One of the difficulties of these studies comes from huge limitations of the data access on commercial CAD systems. By following three research questions, I first investigate previous works on CAD-VR integration and implement a VR-CAD Server as a core functionality to support the project review where project members can directly modify CAD data. Then I explore research directions through brainstorming sessions with researchers from automotive industries. These work sessions inform the scenario of a new process for design reviews: remote users collaboratively generate and review design alternatives within heterogeneous systems. Based on this scenario, I design a technical framework to build technological prototypes with which I design and implement two interaction techniques for 3D CAD data modifications on large interactive systems: a CAVE and a wall-sized display. To evaluate these techniques, I conduct a controlled experiment on the CAVE system and a user observation study with civil engineering students on the wall-sized display. In a second step, by running two controlled experiments, I investigate how a large number of design alternatives displayed on a wall-sized display fosters collaboration among various experts and encourages design explorations.

thesis contribution

This dissertation provides technical contributions in the form of CAD data editing tools within heterogeneous systems, empirical findings from multiple user studies, and theoretical contributions that introduce a new approach for design reviews which could facilitate the collaborative reviewing activity across different expertise.

technical contribution: I designed and implemented:

• a distributed CAD design architecture in which remote users can collaboratively review and modify the native CAD data with heterogeneous interactive systems;

• ShapeGuide, a 3D interaction technique that enables users to modify a parametric CAD model with a shape-based interaction; and

• ShapeCompare, an interaction and visualization technique that distribute multiple design alternatives derived from an initial CAD model on a multi-touch Wall-sized display.

empirical contribution: I found that:

• shape-based 3D interactions on CAD model provides users more efficiency and less frustrations on the deformation task;

• non-CAD experts, interviewed during the user observation study, are interested in applying their modification ideas on the product by themselves even if the user interface is more limited compared to traditional CAD software;

• the visualization of multiple design alternatives enhances the discussion between different experts by increasing the use of deictic instructions; and

• design inspiration can be drawn by multiple design alternatives displayed on a Wall-sized display.

theoretical contribution: I derived:

• clues on how users collaborate during design reviews from controlled experiments on constraint solving and negotiation tasks.

thesis overview

The rest of this dissertation is organized as follows:

Chapter 2 presents the context of this thesis. In particular, it describes the sequential process of the industrial design and the previous works on design tools with large interactive systems for each step of this process. I discuss how and where previous systems contribute to the design process and position my work within this process.

Chapter 3 explains the motivation and the targeted scenarios. In particular, it describes a collaborative design review scenario where remote users can review and modify the data across heterogeneous interactive systems. I then describe a use-case of the collaboration between a CAVE and a Wall-sized display.

Chapter 4 introduces a VR-CAD Server that communicates with a CAD engine and a virtual environment to update native CAD data. The VR-CAD Server is embedded in a distributed network architecture. This system supports configurable interactive systems and multi-user interactions between remote locations. Chapter 5 introduces Shapeguide, an interaction technique that enables users to modify a parametric CAD model with a shape-based 3D interaction. Shapeguide provides a direct interaction with a shape in a 3D environment, which simplifies the interaction with CAD systems for the purpose of design adjustments. This chapter reports a user study that investigates the effect of Shapeguide on CAD data deformation task.

Chapter 6 introduces ShapeCompare, an interaction and visualization technique that distribute multiple design alternatives of a CAD model on a wall-sized display. ShapeCompare allow users to generate many derived shapes from an initial CAD model with touch interaction. This chapter reports a usability test of the first prototype with civil engineering students and describe a controlled experiment with ShapeCompare that investigate how a wall-sized display supports collaborative design negotiations between different experts.

Chapter 7 concludes the dissertation with a summary of the main contributions and future perspectives for the industrial design review process.

Design is the first step in manufacturing, and it is where most of the important decisions are made that affect the final cost of a product.

-Geoffrey Boothroyd [START_REF] Boothroyd | Product design for manufacture and assembly[END_REF] This chapter begins with an introduction to industrial design. Particularly, I detail the traditional industrial design process and highlight the earl design stage, where the preliminary design concept is transformed into a physical artifact. I then review previous studies which present design systems offering users various design activities-conceptual design, detailed design, and design reviews-within a large interactive space. Finally, I summarize the previous literature and discuss how this PhD thesis contributes current industrial design process.

introduction

A technological breakthrough in computing systems has radically developed an industrial design. Over 100 years, the industrial design process has been discussed and optimized to reduce the cost and time during the whole design cycle. In this chapter, I first introduce the industrial design process with an example of automotive design, whose development mostly affected the current mass-production process. I then detail each step of design activity with the role of participantsvarious specialists are involved in the each step during the design cycle. After that, I review previous studies on industrial design systems in terms of Human Computer Interaction (HCI)-especially VR-and introduce how and which design stage those systems can contribute. Despite the fact that a vast number of systems have already explored since the 90s, there is still room for further optimization. At the end of this chapter, I summarize the literature reviews and position this PhD thesis within the industrial design process.

industrial design

Industrial design is concerned with the vast array of goods manufactured by serial-or mass-production methods [START_REF] Heskett | Industrial design[END_REF].

The history of industrial design is closely linked to the industrialization from the late eighteenth century, in the period of Industrial Revolution, which is most commonly associated with the introduction of mechanization, steam-power, and large-scale manufacturing and commercial organization. It is said that the word, Industrial design, began to be used in the USA since the 1920s, which was mainly affected by the development of mass-production methods of automobiles.

Figure 2.1: Simon Stevin's sailing chariot in 1600 [START_REF] Wardhaugh | Magic is no magic': The wonderful world of Simon Stevin[END_REF] In the history of automobiles, the earliest experiments in individualized powered transport took place in France [START_REF] Arthur | Early Australian automotive design 1895 -1953[END_REF]. In 1600, Simon Stevin proposed a first two-masted sail carriage (Fig. 2.1). Ninety years later Denis Papin invented the steam digester, a type of pressure cooker, which was the first concept of a steam engine. Then Nicholas Joseph Cugnot presented a tricycle driven by the steam engine in 1769 (Fig. 2.2). While this is currently regarded as a first automobile in the world, it was designed to transport cannons for the French army, which was close to the "truck" than the "car".

The practical automobile came in 1885 form Karl Benz. He produced a tricycle driven by a petrol engine (Benz patent Motorwagon, Fig. [START_REF] Joseph | Fardier à Vapeur[END_REF] This is not only acknowledged as the world's first "true" automobile, but also considered to be the first "production" vehicle. Afterward, America trailed behind Europe, and Henry Ford started the first mass-production of the automobile. The Ford Model T (Fig. 2.4a), which first appeared in 1909, was manufactured on an assembly line [START_REF] Weber | Automotive Development Processes[END_REF]. Ford developed a moving production line, in which the vehicles move along a track at an unending steady stream, then workers did not need to move from one task to another (Fig. 2.4b) [START_REF] Happian-Smith | An introduction to modern vehicle design[END_REF]. The manufacture of the Model T involved new concepts of the standardization and integration of the production line, which profoundly affected the practice of industrial design [START_REF] Heskett | Industrial design[END_REF]. The arrival of the mass-production boosted the productivity of industrial products from the previous hand craftsmanship. However, it also increased the importance of design activities in the early stage.

Interestingly, although hand-crafting is always associated in the public's mind with high quality, mass production actually requires higher standards of accuracy and consistency of dimension, because in mass production, all similar parts must be completely interchangeable [START_REF] Happian-Smith | An introduction to modern vehicle design[END_REF].

Henry Ford was also conscious of the need to consider the maintainability and ergonomic features of the product from the early design stage to decline the total cost and time for whole manufacturing processes.

Currently, the industrial design method varies for each manufacturer. Nevertheless, as common grounds, their main focus on the design process is to comprehensively think of the design from the early design stage before manufacturing the physical product.

Industrial design process

The industrial design process is a "secret recipe" for each manufacturer [START_REF] Weber | Automotive Development Processes[END_REF]. They have a specific design process according to the company's organization and management policies, the role of participating experts and their manufacturing facilities, which is usually strictly confidential. However, there is a commonly accepted base structure for automobile development. The V-model (Fig. 2.5) is the established process model in systems engineering but also adopted in most vehicle development [START_REF] Weber | Automotive Development Processes[END_REF]. The V-model shows the interplay of verification and validation processes throughout the development project. Verification is an objective set of tests to confirm that the product meets the metrics of the requirements (left side of V-model), while validation seeks to demonstrate that the product meets the original intent (right side of V-model) [START_REF] Fowler | Chapter 1 -Introduction to Good Development[END_REF]. The left side of the V-model is the system design phase, which starts with design concepts based on requirements, system designs and simulations, then parts specification, design, and evaluations. Whereas the right side of the V-model denotes the system integration phase where designed components are assembled and tested from components over sub-systems up to the complete vehicle.

The central concept of the V-model is to consider user satisfaction, ergonomics aspect, and mechanical feasibilities from the design stage. As the importance of the early design stage has been discussed since the arrival of the mass-production, Boothroyd also claimed that taking careful account of manufacturing and assembly problems in the early stages of product design leads to shorter design-development cycle, reduce the cost, and increase productivity [START_REF] Boothroyd | Product design for manufacture and assembly[END_REF]. Once the product is designed, at least 70% of the cost is already committed [START_REF] Happian-Smith | An introduction to modern vehicle design[END_REF]. Left side of the V-model shows System design phase, and the right side shows System integration phase [START_REF] Weber | Automotive Development Processes[END_REF]. The System design phase is divided into Conceptual design and Detailed design.

Sequential design process

The system design phase is divided into two processes: Conceptual design and Detailed design. Conceptual design is where a preliminary design concept is defined, and the aesthetic design of the automotive is drafted. Whereas, Detailed design is the time when the conceptual design draft turns into a blueprint, more specific and precise description, to focus on the manufacturability of the product. Traditionally, this design process was sequential. Each process was strictly divided each other, so thus the attitude of designers tend to make an order to engineers [START_REF] Boothroyd | Product design for manufacture and assembly[END_REF]. This is known as Over the wall design (Fig. 2.6). The designer throws the designs over a wall to the manufacturing engineers who then have to deal with the various manufacturing problems [START_REF] Boothroyd | Product design for manufacture and assembly[END_REF].

Even though the design process is unique at each company, there is no hierarchy between designers and engineers. However, the designers' voice can be very powerful, given the importance of their role in selling vehicles [START_REF] Happian-Smith | An introduction to modern vehicle design[END_REF]. This sequential approach increases the time and cost for the development and lowers the overall product quality [START_REF] Robert | Deciding between sequential and concurrent tasks in engineering design[END_REF].

Concurrent engineering

The sequential design approach leads to the necessity of collaboration among various experts involved in the whole design process. For this aim, Concurrent Engineering, or sometimes called Simultaneous Engineering were introduced from US defense in 1989 [START_REF] Robert I Winner | The role of concurrent engineering in weapons system acquisition[END_REF]. US National Institute for Defense Analysis defines concurrent Engineering as:

Concurrent engineering is a systematic approach to the integrated, concurrent design of products and related processes, including manufacturing and support. This approach is intended to cause the developers, from the outset, to consider all elements of the product life cycle from conception through disposal, including quality, cost, schedule, and user requirements [START_REF] Robert I Winner | The role of concurrent engineering in weapons system acquisition[END_REF].

They reported how concurrent engineering could improve quality, decrease the cost, and reduce the time to develop weapons systems. As opposed to sequential engineering, concurrent engineering focuses on parallel processing of each design phase (see Fig. ) by that to decrease the development lead time and increase quality by integrating product and process design [START_REF] Sohlenius | Concurrent Engineering[END_REF]. As well as automotive companies, the aeronautic company, Airbus, has successfully applied Concurrent engineering to all the aircraft's design since 1999 [START_REF] Mas Morate | Collaborative Engineering: an Airbus case study[END_REF]. As a similar approach, Toyota adopted a new system of mass-prodution in 1930, making multi-skilled workers more collaborative within a team, which is defined as Lean production in 1996 by Womack [START_REF] James P Womack | Machine that changed the world[END_REF]. The difference between concurrent engineering and lean production is dicussed in [START_REF] Koskela | Re-Engineering, concurrent engineering, lean production: What is the ideal antidote for the construction industry's ailments?[END_REF]. Basically, the concurrent engineering is based on same conceptualizations as lean production.

The essence of Concurrent engineering is not only the concurrency of the activities but also the cooperative effort from all the involved teams [1]. Buxton [START_REF] Buxton | Sketching user experiences: getting the design right and the right design[END_REF] suggested that the business, technical, and creative elements in the product life cycle must be active in all three phases instead of braking into three independent silos (Fig. 2.8). "design" includes the design of the business and engineering plans, as well as the product itself." [START_REF] Buxton | Sketching user experiences: getting the design right and the right design[END_REF]. As Buxton noted, the word "design" can be interpreted in various ways in the domain of industrial design. Particularly, several types of design activities are involved during the system design phase, being managed by dedicated experts.

The noun 'designers' refers to individuals or groups engaged in the activity, whose background, talent and achievement need to be described and understood [START_REF] Heskett | Industrial design[END_REF]. which various teams involve throughout the overall process [START_REF] Buxton | Sketching user experiences: getting the design right and the right design[END_REF].

In this dissertation, to clarify the word used to describe experts during the design stage, I define the role of people engaged in Conceptual design as Stylists, and for those in Detailed design as Engineers or CAD engineers. The following part details the traditional system design phase, where an initial concept is transformed into a physical artifact.

Traditional system design process

The system design process encompasses various steps from ideation to realization of the product. Particularly the first step, product planning is essential to steer whole design processes toward the final design that meets initial design requirements. The project organization, comprised of senior management, marketers, design directors, etc., establishes the product requirement 'brief' based on analysis of the current market, target users, competitive companies and their sales. The documented brief is provided to stylists, which gives design specifications. Afterward, all the stylists and the modeling supervisors brainstorm the design concept based on the given requirements.

Conceptual design

One of the main procedure of conceptual design is introduced by Harley Earl, who built a styling department in General Motors in 1927 [START_REF] Happian-Smith | An introduction to modern vehicle design[END_REF]. The stylists first make a preliminary design concept on a paper as 2D sketches, then convert it to full-size orthogonal 2D sketches. Finally, they make a full-size 3D model usually with a clay. The stylists are responsible for the initial conceptual thinking in the creation of the new product, and they give it to the detailed design stage with fully defined surfaces [START_REF] Tovey | Intuitive and objective processes in automotive design[END_REF]. concept sketch: based on the given specifications, the stylists make up to 50 distinct sketches either with hand-made sketches Figure 2.9: Manual exterior rendering of BMW 3 Series (BMW) [START_REF] Weber | Automotive Development Processes[END_REF].

or with Computer-Aided Styling (CAS) software [START_REF] Weber | Automotive Development Processes[END_REF] (Fig. 2.9). The design does not need to be accurate in this step. The primary requirement is a fundamental concept portrayed on the sketch [START_REF] Happian-Smith | An introduction to modern vehicle design[END_REF]. Many stylists and project managers compare between each design proposal on a large display board (Fig. 2.12), then only a few designs stay for the next step [START_REF] Tovey | Intuitive and objective processes in automotive design[END_REF]. full-size 2d sketch: the chosen design concepts are drawn as full-scale with tape drawings. The sketches have to be accurate before this process. The sketches are placed on the display board, and stylists place adhesive tapes along contour lines of sketches (Fig. 2.10). While this process can transform a simple sketch to a full-size concept, the design is still 2D. clay model: to make a transition from 2D drawings to 3D model, a full-size clay model is created from the tape drawings by Highly skilled specialists. The clay model is indistinguishable from the real thing at first glance [START_REF] Buxton | Sketching user experiences: getting the design right and the right design[END_REF]. It gives a first realistic impression of the new vehicles visual (Fig. 2.11) and ergonomic appearance [START_REF] Weber | Automotive Development Processes[END_REF]. The full-size model is used as the basis for all body surface information required by the engineering departments for structural design and analysis, etc. [START_REF] Tovey | Intuitive and objective processes in automotive design[END_REF]. Most importantly, the 3D CAD model is created based on the clay model in Detailed design stage.

Detailed design

Styling is apt to be regarded as a more vital factor to appeal to customers than detailing. However, the success of the design depends on the proper integration of the detailed design and style design. Good detail cannot save a bad design, but bad detail can ruin a good one. [START_REF] Happian-Smith | An introduction to modern vehicle design[END_REF]. The engineering design ensures that the product has quality and reliability, is well made and will not break down [START_REF] Tovey | Intuitive and objective processes in automotive design[END_REF].

In the detailed design stage, the physical mockup is transformed into the DMU. Dolezal [START_REF] Walter | Success Factors for Digital Mock-ups (DMU) in Complex Aerospace Product Development[END_REF] defined the DMU as "A Digital Mock-up is a digital 3D representation of a product together with its product structures and attributes". The DMU does not only contain geometrical data of the product but also meta database for the appearance (e.g. materials, textures), physics simulations, assemblies, human resources, etc., which are all related to various activities during the product life cycle. Engineers build such digital mockup with CAD software based on the design concept created by the style department.

computer-aided design: the development of CAD systems has significantly reduced the time and cost of the industrial design process. Provision of prototypes for the evaluation of complete vehicle characteristics is one of the major cost factors: for example, an early prototype can cost up to one million euro [START_REF] Weber | Automotive Development Processes[END_REF]. Once the DMU is built with CAD, various assessments traditionally performed on the physical model can be conducted on the virtual vehicle within the system design phase. Unlike the aesthetic design focus of stylists, CAD engineers focus on the manufacturability of the product. As such, the DMU needs to be precisely designed with parameters, rather than freeform drawing. Typically, relevant capabilities of automotive 3D CAD systems, such as CATIA and Solid Works, include advanced surfacing, advanced solid modeling, the ability to handle large assemblies [START_REF] Weber | Automotive Development Processes[END_REF]. Also, feature-oriented modelers are essential for engineers to apply their design intent on the product. Engineers firstly build each component of the vehicle, then integrate them into one full design at the end (Fig. 2.13).

product lifecycle management: each activity during the product life cycle require specific computer tools, such as the planning and management tools (PPS/ERP), CAD, Computer-Aided Engineering (CAE) for physics simulations, and Computer-Aided Manufacturing (CAM) for all manufacturing operations [START_REF] Li | Multi-user interface and its use for collaborative work with multiple representations of Digital Mock-Up[END_REF]. The DMU can offer a various representation of the data to adapt specific needs from distinct experts during the product design cycle (Fig. 2.14): e.g. for assemblies, physics simulations, design quality analysis. For physic simulations, the DMU can provide CAD geometry data for assembly process design, maintenance design and CAE data, such as structure analysis, crash tests, thermal simulation, aerodynamics and Computational Fluid Dynamics (CFD). Those data can be stored and managed in PLM database, where all experts can load, update, and share across different departments.

Design reviews

Throughout the whole design processes, often a number of project review meetings take place at each step with several experts. Regular project reviews can strongly summarize the current work and assign the work of the next stage by making modifications and proposing solutions to both strategies and technical details [START_REF] Li | Multi-user interface and its use for collaborative work with multiple representations of Digital Mock-Up[END_REF]. Also, at some points, management intervention needs to ensure that the project is going in an appropriate direction to meet the initial requirements or design concepts. As an example, Fillatreau depicts how industrial companies intend to project review checklists as many as possible during the product life cycle (Fig. 2.15). More often than not, project teams use more virtual prototypes for design reviews than physical prototypes during the design cycle to reduce unnecessary costs for operations of a production line. Particularly, a detailed design review (CGR in Fig. 2.15) is critical to steer the final design of the product with various assessments or verifications (e.g. aesthetic properties, ergonomics, user satisfaction, technical feasibility) based on CAD data before building the physical prototypes. In current industrial design practices, engineers need to adjust the design with a CAD system after the design review meeting and prepare the updated version for the next meeting (the detailed process of one of the automotive company is described in chapter 3).

Figure 2.17: Surface evaluation on virtual surface models (BMW) [START_REF] Weber | Automotive Development Processes[END_REF].

Usually, the design review meetings are organized by gathering multiple experts in the same room (e.g. Fig. 2.12). Large space allows multidisciplinary team members to review and discuss various design concepts (e.g. design sketches, small miniatures) or a full-scale prototype (Fig. 2.16), which varies for each step of design reviews. Traditionally, physical prototypes or a large projected image (Fig. 2.17) are employed for the review meeting. Today, with advances in information technology, various presentation methods of the prototype have been developed, so thus a project team can choose the one that suits the purpose of the design review meeting and needs from experts. The following section will describe research works and applications, which assist design activities and design reviews.

related studies and applications

Development of the industrial design process has been discussed and advanced since Henry Ford took the first step of mass-production for automobiles in the early 20 century. This advancement has been mostly affected by the technological progress of computing systems.

In 1963, Sutherland presented Sketchpad [START_REF] Sutherland | Sketch Pad a Man-machine Graphical Communication System[END_REF] (Fig. 2.18a), which is considered to be the ancestor of CAD system where users can design geometric data with Graphical User Interface (GUI). The notable contribution brought by Sketchpad is not only a fundamental design of modern CAD system but also a notion of HCI. Timothy claimed "If a computer system is to work in partnership with a designer, the system must be able to accept, interpret, modify and remember shape description information introduced graphically" [START_REF] Johnson | Sketchpad III: A Computer Program for Drawing in Three Dimensions[END_REF]. Since then, various design systems have been studied for the domain of industrial design. Most of them enhanced the intelligence of CAD systems and interactions with it. Sutherland presented another technological breakthrough in 1968 regarding user interaction and visualizations, which transfers both interactive and visualization space from 2D to 3D environment [START_REF] Sutherland | A Head-mounted Three Dimensional Display[END_REF] (Fig. 2.18b). The Sword of Damocles is known as the first HMD, offering the user's head tracking and adaptive stereoscopic rendering, designed based on the concept of "ultimate display" [START_REF] Sutherland | The ultimate display[END_REF]. Those achievements realized essential concepts of VR and Augmented Reality (AR). Using The Sword of Damocles, in 1976, Clark presented a first 3D design system in which a user can design the 3D model within a 3D visual environment [START_REF] Clark | Designing Surfaces in 3-D[END_REF]. After that, especially from the beginning of the 90s, a number of researchers explored industrial design systems that allow users to interact with various display systems supporting large, and/or an immersive environment.

The visualization of the DMU in a large space make the traditional industrial design process more:

• Realistic: high resolution visualization of full-scale digital mockup enhance the assessment of affective design properties of automobiles.

• Immersive: various user-oriented simulations, e.g. ergonomics, assembly chain, maintenance, can be conducted with the digital mockup. Also, user interactions would be more intuitive (i.e. gesture-based) in 3D space.

• Collaborative: a large space of visualization and interaction space can afford multiple users for design reviews or design activities.

Those contributions drastically increase the use of digital mockup for design verifications at each step in the early design stage. In the following, I introduce various systems in a large space intended to improve specific design activity.

Sketching and drawing

Aesthetic design property of the product is mostly considered during the conceptual design stage (Section 2.2.2.1). In this stage, the design can be coarse, and it does not have to be precise. Various studies aimed at replacing physical tools for the design activity-e.g. pencils and papers-with computers.

From physical to digital tools for 3D design

Traditionally, people preferred using pencil and papers because of the low overhead of a single-tool interface, the lack of specialized knowledge needed to draw, and the ease with which many kinds of changes can be made [START_REF] Zeleznik | SKETCH: An Interface for Sketching 3D Scenes[END_REF]. However, as designers often need to draw a number of design alternatives, especially for showing the model from different viewpoints in 3D space, it becomes tedious to draw all from scratch. The advantages of digitalized sketches are also the ease with which images can be stored, printed, projected full size, or transmitted to any location in the world [START_REF] Happian-Smith | An introduction to modern vehicle design[END_REF]. With 3D computer modeling systems, users can create a 3D sketch, but it requires specialized expertise and does not provide much freedom for users to explore the design.

To bridge the gap between hand sketches and computer-based modeling programs, Zeleznik et al. [START_REF] Zeleznik | SKETCH: An Interface for Sketching 3D Scenes[END_REF] presented SKETCH, a drawing interface that can automatically transform 2D strokes to 3D primitive objects based on predefined specific types of lines. Igarashi et al. [START_REF] Igarashi | Teddy: A Sketching Interface for 3D Freeform Design[END_REF] enhanced this approach with Teddy (Fig. 2.19) to adapt users' freeform strokes to construct 3D polygonal surface models. Those applications helped users' 3D design activities without demanding specific knowledge of 3D-CAD systems. Nevertheless, interaction and visualization of models were two-dimensional. Some other studies explored conceptual design activities in full-3D space.

3D interactive systems

Immersive drawing applications offer users full-scale design capability of 3D models. 3D interaction can foster design inspirations and enhance spatial thinking. Israel et al. [START_REF] Israel | Investigating three-dimensional sketching for early conceptual design-Results from expert dis-cussions and user studies[END_REF] presented the system in which users can draw 3D lines within a CAVE system freely using a 6 DoF pen device (Fig. 2.20a). Today, such 3D drawing application can be easily seen in the market: e.g. a 3D drawing application with HMD, Tilt Brush (Fig. 2.20b), has been developed for artistic design [START_REF] Skillman | Tilt Brush application[END_REF].

To digitalize the actual interaction conducted during the conceptual design stage in the automotive industry, Balakrishnan et al. [4] presented a digital tape drawing system (Fig. 2.21a) based on traditional tape drawing practices (Fig. 2.10). They proposed a bimanual interaction method that is potentially easy for stylists to adopt a computer-based workflow in their activity. Grossman et al. [START_REF] Grossman | Creating Principal 3D Curves with Digital Tape Drawing[END_REF] extended this interaction method to support 3D surface modeling on a large scale display (Fig. 2.21b). Also, Fleisch et al. [START_REF] Fleisch | Strokeinput methods for immersive styling environments[END_REF] and Keefe et al. [START_REF] Daniel F Keefe | Drawing on Air: Input Techniques for Controlled 3D Line Illustration[END_REF] (Fig. 2.21c) presented it with stereoscopic displays.

While these systems focused on free and preliminary drawing activities, some previous works presented geometric modeling applications. 3-Draw [START_REF] Sachs | 3-Draw: a tool for designing 3D shapes[END_REF] is the first application for free-form modeling ) presented surface modeling tools in 3D visualization spaces, by using a 6 DoF mouse [START_REF] Butterworth | 3DM: A Three Dimensional Modeler Using a Headmounted Display[END_REF], a set of pinch gloves [START_REF] Kuester | 3DIVS: 3-dimensional Immersive Virtual Sculpting[END_REF] or the stylus [START_REF] Fiorentino | Spacedesign: a mixed reality workspace for aesthetic industrial design[END_REF]. 3DIVS and SpaceDesign enabled co-located interactions with digital mockups between the users' real hands and its visualization. Paljic et al. [START_REF] Paljic | A Study of Distance of Manipulation on the Responsive Workbench[END_REF] confirmed that manipulation of the digital mockups at a closer distance is significantly more efficient in 3D space.

Summary

In general, design systems for conceptual design put importance on intuitive interactions with the digital mockup. One of the limitations of 3D interaction is the lack of accuracy and increase of physical fatigues due to the lack of support of the user's arm in 3D space. Some previous researches addressed these issues with force feedback, which I detail in Chapter 5.

Parametric Design

At a later product design stage, the conceptual model has to be built as a solid model to meet precise design specifications in consideration of its engineering feasibility. The solid model is a 3D model defined by mathematical operations. Unlike wireframe and surface modeling, solid modeling systems ensure that all surfaces and structure of the model is geometrically correct. In the detailed design stage, CAD engineers transform the conceptual model to the solid model using CAD systems (Section 2.2.2.2). With the CAD system (Fig. 2.23, CATIA V5), the 3D model is created based on a 2D sketch. Once the 2D sketch is drawn, the solid model is formed by 3D operations (e.g. extrusion, revolution) applied on the sketch. Several Boolean operations are performed between solid models to shape the final design. The creation of the solid model is based on two complementary geometric modeling methods:

Computer-Aided Design

• B-Rep: method for the representation of the model, which is a based on a collection of connected surface elements, the boundary between solid and non-solid (Fig. 2.24)

• CSG: this model representation is based on a succession of Boolean operations between geometric primitives such as cylinders, spheres, cones, tori, illustrated by the binary tree (Fig. 2.

25).

In most cases, the representation of the 3D model used during conceptual design is mesh format, which is easy to import, edit, and export in an immersive environment. Whereas, the data structure of CAD data is difficult to maintain and modify outside of the CAD system. Some previous works challenged this issue-which I detail in Chapter 4. Nevertheless, most studies need to (i) convert CAD data to a different format or (ii) develop an immersive solid modeling tool. The first one (i) is a conventional method to project the design data in a large interactive system for design reviews. To empower users to design the solid model in the immersive environment, most previous studies proposed solutions with (ii)-which are described below.

Immersive solid modeling -simple object -

One of the challenges for immersive solid modelings is to allow users to modify the solid model with 3D interaction. JDCAD [START_REF] Liang | JDCAD: A highly interactive 3D modeling system[END_REF] (Fig. 2.26a) is one of the first VR-CAD application in which users can create or edit primitives and perform Boolean operations by 3D interaction. JDCAD proposed Region-based reshaping technique: the users can manipulate specific parameters by dragging relevant control points mapped on the surfaces of the primitives. ARCADE [32, 109] (Fig. 2.26b) extended this approach and proposed a Topological-context-based modification: this technique considers not only the selected region on the surface but also the users' subsequent 3D gesture to determine the optimal object behavior according to users' hand stroke. However, it was difficult to meet all users' expectations for the object behavior from various users' input. Moreover, these works cannot address complex solid models, including internal geometric constraints, which makes more difficult to anticipate the object behavior. More recently, De Araújo et al. developed Mockup Builder [3] (Fig. 2.26c), which provides the ability to create and manipulate the solid model with co-located bimanual finger interaction technique for rapid 3D prototyping.

Immersive solid modeling -complex object -

To deal with such complex models, Gao et al. [START_REF] Gao | An approach to solid modeling in a semi-immersive virtual environment[END_REF] presented a 3D interaction technique to create and modify solid models containing different geometric constraints. Their VR-CAD system stores each prim- itive, parameters, and operators within customized CSG, to recognize the related constraints from a selected element and enable consistent shape deformation with users' 3D hand motion. Ma et al. [START_REF] Ma | A hierarchically structured and constraint-based data model for intuitive and precise solid modeling in a virtual reality environment[END_REF] and Zhong et al. [START_REF] Zhong | A methodology for solid modelling in a virtual reality environment[END_REF] also tackled this issue with a hierarchical constraintbased data model. The idea of these approaches is to create a new design system in an immersive environment, which is not for modifying existing CAD data designed by commercial CAD systems. As the CAD data is not merely a mesh but composed of B-Rep and CSG, it is challenging to load and modify the design within the VR system while keeping the original data format. Particularly, it is even harder with a 3D user interaction. Some previous works focused on integration between CAD and VR systems to avoid the data conversion (detailed in Chapter 4). Nevertheless, none of them can modify native CAD data using a 3D interaction in the immersive environment.

Summary

Various VR systems have been proposed to change the interaction for solid modeling from an alphanumeric input to direct shape-based interaction. Yet, there is no complete system that can import and modify native CAD data within a large interactive system. Although previous studies would improve prototyping activity within an immersive environment, it would not be suitable for the later stage of industrial design where users need to adjust the product design with a CAD system.

Design Reviews

The ability to display and interact with large-scale representations of vehicles has always been a fundamental requirement of the automotive design industry [START_REF] Buxton | Large displays in automotive design[END_REF].

The use of large-format displays for industrial design reviews offers a full-scale design visualization, large interactive space, and a collaborative environment with colleagues. Portfolio Wall [START_REF] Buxton | Large displays in automotive design[END_REF] (Fig. 2.27a), which displayed multiple different designs as tiled thumbnails on the screen, was designed to compare various concepts in design offices, like a traditional wall-mounted corkboard. Khan et al. [START_REF] Khan | Spotlight: Directing Users' Attention on Large Displays[END_REF] (Fig. 2.27b) also studied a tool that highlights the area of the user's attention on large wall-sized displays to facilitate group meetings.

Immersive system

A number of previous works of design review systems also support a 3D visualization and interaction space. Such virtual product reviews are becoming a vital factor during product development process [START_REF] Lawson | VR Processes in the Automotive Industry[END_REF][START_REF] Zimmermann | Virtual Reality Aided Design. A survey of the use of VR in automotive industry[END_REF], significantly reducing the time and costs for manufacturing a physical mock-up. Previous works on VR-CAD integrations enabled to load the native CAD data and render it within VR environment [START_REF] Berta | Integrating VR and CAD[END_REF][START_REF] Rantzau | The integration of immersive Virtual Reality applications into Catia V5[END_REF][START_REF] Raposo | Environ: integrating VR and CAD in engineering projects[END_REF]. One of the preliminary idea on VR-CAD integration was presented by Fakespace and Dassault Systèmes [START_REF] Berta | Integrating VR and CAD[END_REF] (Fig. 2.28b). They had ambitions to embed VR rendering in an industrial CAD system (CATIA V5 R ) to deliver fast and seamless VR reviews of a product to users. Raposo et al. [START_REF] Raposo | Environ: integrating VR and CAD in engineering projects[END_REF] (Fig. 2.28a) proposed a real-time CAD data visualization and interaction on a large immersive display for oil and gas industry. This system can load a high resolute and massive size of data for Plant Design System and allow users to navigate and ma-nipulate virtual objects. Schilling et al. [START_REF] Schilling | CAD-VR geometry and meta data synchronization for design review applications[END_REF] (Fig. 2.29c) presented a middleware framework in which the users can also edit properties of the product (materials or textures) during immersive reviews.

Collaborative environment

The VR design review systems also became collaborative. CALVIN [START_REF] Leigh | CALVIN: an immersimedia design environment utilizing heterogeneous perspectives[END_REF] (Fig. 2.29a), for example, focused on collaborative architectural design for multidisciplinary experts, such as architects and engineers. The experts could explore and manipulate objects in a shared virtual environment. They were supported with distinct viewpoints according to their expertise: an inside-out view for engineers, and an outside-in view for architects. Lehner et al. [START_REF] Valerie | Distributed virtual reality: supporting remote collaboration in vehicle design[END_REF] (Fig. 2.29b) developed a collaborative review system for vehicle design across two distant CAVE systems. Previous works and an existing application support heterogeneous systems for collaborative material or texture editions [START_REF] Choi | ONESVIEW: An Integrated System for One-Stop Virtual Design Review[END_REF] and manipulations of the global position/orientation of the CAD model [START_REF] Mahdjoub | A collaborative Design for Usability approach supported by Virtual Reality and a Multi-Agent System embedded in a PLM environment[END_REF].

Summary

Now that studies on VR design reviews have shifted from research to application domains. Visualizing CAD data in a HMD is becoming one of the common functionality in commercial CAD systems. Also, many private companies offer VR design review applications. For example, improov 3 (MiddleVR) [START_REF] Kuntz | improov 3 , The VR collaborative meeting room[END_REF] support various functionalities for design reviews, such as remote collaboration, annotations, object manipulations with imported native CAD data. However, those applications do not support any modifications of the native CAD data within the virtual environment.

position of this phd thesis

The industrial design has been improved to optimize productivity with advances in the design process and computing systems. The traditional sequential design process became more concurrent, involving various experts in each design step-which results in decreasing the time for product development and increase the quality of the product. Design practices with physical tools have been replaced with computers or heterogeneous interactive systems-which makes the design environment more immersive, realistic, and collaborative. In particular, a design review meeting with a multidisciplinary team benefit from a workspace where project members can discuss the product from various perspectives within a large interactive system. However, while it facilitates and shortens design discussions between different experts, design review meetings need to be conducted at each design refinement until they reach a consensus on the product design. As the CAD model is not directly modifiable outside the CAD system, the virtual prototype has to be updated by engineers after each design review meeting. This iterative process causes delays in the design verification process.

The focus of this thesis is to optimize a detailed design review by merging those design discussions and design refinement steps. I argue that direct modifications of CAD data during the design review meetings would shorten the design verification process. In such workspace, all project members-including non-CAD experts-can apply modifications to the CAD model, which would give them more design inspirations and facilitate communications between various experts. In this thesis, I will propose the new industrial design review process based on the development of a technical framework for CAD data modifications within heterogeneous interactive systems and studies on user interactions and collaboration.

conclusion

I described in this chapter:

• History of industrial design: industrial design is largely affected by the development of automotive design at the beginning of 20 century,

• Automotive design process: traditional design process, Vmodel, is divided into two phase: System design and System integration. To comprehensively consider the later design process from System design stage with a multidisciplinary team is important to reduce the cost and time of the whole design cycle,

• System design process: design concept made during the conceptual design stage is transformed into digital mockup with CAD systems in the detailed design stage. Once it is built with the CAD system, it can be used for various physical simulations,

• Previous works on design activities with large interactive systems: various interactive systems have been developed to assist the design process.

-Conceptual design: 3D design activity foster spatial thinking and increase intuitiveness on drawing, which is useful for design ideation process, -Detailed design: while some research approaches enabled immersive solid modeling, users cannot work on CAD data within the immersive environment, -Design reviews: a number of studies and now commercial CAD systems support visualization of CAD data in heterogeneous systems. Some applications also support remote collaboration. Yet, no modifications on CAD data are suppored during the design review,

• Position of this PhD thesis: this thesis proposes a new design review practice where a multidisciplinary team can discuss and modify the CAD data within a large interactive system. It would shorten the detailed design review process by merging a design discussion and design refinement steps.

The next chapter introduces a design review practice with large interactive systems in an actual automotive company. Based on their current design review practices, I propose and detail the scenario of the new design review process.

If we have a tradition it is this: everything can always be done better than it is being done.

-Henry Ford [START_REF] Boothroyd | Product design for manufacture and assembly[END_REF] Today the review sessions of industrial products are conducted among multidisciplinary experts within heterogeneous systems. My PhD work proposes adding a modification capability of the product data during such sessions. In order to narrow down this goal to specific use cases, I had some discussions with research engineers who manage the VR or interactive systems for design reviews in an automotive industry. This chapter details their design review process and describes the targeted scenario.

discussions with research engineers at an automotive industry

Now that the use of large interactive systems for design reviews is getting indispensable process for automotive companies. I had discussions with research engineers at PSA, France (called PSA in rest of the manuscript) and visited the VR center where they conduct design review sessions. They manage design review systems of PSA and prepare datasets for visualizing the product data in immersive systems before the actual review processes of vehicles.

In their company, the industrial design encompasses two distinct processes: product design (or system design) and process design (or system integration). The former process is during which an industrial product is conceptualized with aesthetics, end-user oriented ergonomic studies and engineering feasibility considerations. The following addresses many issues of product manufacturing, such as the design of assembly procedures, including ergonomic studies, to prevent workers' health disorders, up to the full design of the modern lines. PSA integrates VR reviews into their design process (Fig. 3.1). This enables project members to review both product design and process design in parallel once the detailed architecture and dimensions of the product are defined.

In the VR center, there are different types of immersive systems according to dedicated purposes:

• CAVE: the system consists of five back screens with stereoscopic projections for each, and a seating buck (a physical driver seat) can be installed at the center in the CAVE (Fig. 3.2). The system shows a cockpit with the exterior details to assess the visibility from the driver's viewpoint and test the moving items in the passenger compartment (e.g. a door, a rear-view mirror). Also, ergonomists can evaluate the feasibility of manual operations by displaying a virtual production line with full-body tracking. Project members experience the simulated environment within the CAVE and communicate with other members outside who monitor the operations via other screen and update data when necessary.

• Stereoscopic wall-sized display: a wall-sized stereoscopic display shows a scale one vehicle in a realistic environment. This system is used for group discussions in the large meeting room. Project members compare several vehicle architecture concepts, assess the perceived quality and check results of physics simulations: e.g. they can visualize computations of air flows inside the cockpit to evaluate thermal comforts for passengers.

With these systems, project members can conduct various assessments with DMU without building physical models. In the following, I describe the detailed design review processes for product design at PSA.

Current design review process at PSA

PSA split the product design process into three main stages (Fig. 3.3): Conceptual design, Detailed design and Perceived quality analysis. At each • Conceptual design: stylists sketch a preliminary draft of the product based on expectations of end-users and requirements from executives of a company. They create a conceptual model using dedicated tools specialized at aesthetic design (e.g. Alias R , Autodesk). After several design iterations, some of the conceptual models are checked through Style review meetings with Chief Executive Officer (CEO) and other executives in a company.

• Detailed design: CAD engineers build a DMU using parametric CAD software (e.g. CATIA R ) from the conceptual model designed at the previous stage. Several design alternatives of the initial design are compared and reviewed in Design review meetings with a multidisciplinary team which consists of architects (who usually lead the meeting), CAD engineers, ergonomists and stylists.

• Perceived quality analysis: stylists and CAD engineers tune rendering materials and textures on high-quality meshes exported from the CAD data to create a realism-oriented virtual scene using a high-rendering system (e.g. Deltagen R ). In Industrial style review meetings, stylists, CEO, and other executives analyze the perceived quality of the car to validate the final DMU. If modifications are required, it is mandatory to go back to the Detailed design stage to apply these modifications to the CAD data.

Throughout these stages, review meetings are often conducted within immersive VR platforms to allow experts to collaboratively review the virtual prototype at full scale and/or in a realistic environment. Also, these experts can be geographically spread, so thus, these meetings often require collaboration between remote locations. The DMUs are stored and exchanged through a PLM database under various formats according to the dedicated software used at each product design stage. Consequently, this data heterogeneity imposes conversions to pass from one stage to another. Also, the use of VR environments usually imposes time-consuming conversions and/or transcriptions between the virtual environment and the PLM database.

design comparison during design reviews

Within the three product design stages The goal of this thesis is to propose a design review process in which users can directly modify CAD parameters. However, based on the review process of PSA, the complex CAD operations would not be necessary during the design review. Their key practice during the review meeting is a design refinement by comparing multiple design alternatives. As the essential design concept is already discussed in the previous design stage, project members do not have to or want to change the design intent. Therefore, in this thesis, I will focus on this design refinement scenario and investigate the method to dynamically generate design alternatives from the initial design to compare them on a large interactive display during product reviews.

Generation of design alternatives

Generation and visualization of multiple design alternatives is a core functionality of Generative design. The Generative design is a design technique that originated to fill a gap between conceptual design and detailed design stage. In other words, the Generative design encourages engineers to think more like stylists, and stylists to think more like engineers. In Generative design, users express their design intent with high-level specifications, then the computer helps them explore solution designs with various design alternatives based on topology optimization.

There are two possible directions for Generative design, which is whether to build a bridge from conceptual design toward detailed design or vice versa. In the former case, designers can explore multiple ideas based on sketching and make better-informed decisions without using extensive parametric modeling system, such as CAD [START_REF] Xiang 'anthony' Chen | Forte: User-Driven Generative Design[END_REF][START_REF] Habib Kazi | DreamSketch: Early Stage 3D Design Explorations with Sketching and Generative Design[END_REF] (Fig. 3.4, 3.5). For the latter case, engineers can get design inspirations from generated design alternatives based on the CAD model (Fig. 3.6).

In my targeted design review scenario, the DMU is already created with the CAD system during detailed design. Hence, the latter case fits my objective. In this thesis, I do not explore the intelligence of variable design generations with regards to given high-level user inputs. Rather, I focus on a system framework for design reviews which can distribute multiple design alternatives on large heterogeneous interactive systems and how the users can interact with those alternatives considering specific configurations of the interactive systems.

research direction

Based on the consideration of the design process of PSA, I am interested in studying a design review system which supports:

• Interaction with design alternatives: all users-including non-CAD experts-can generate intended design alternatives of initial CAD model during review meetings.

• Visualization of design alternatives: the system visualizes multiple design alternatives to meet the purpose of expected users and configuration of interactive systems.

• Heterogeneous systems: users can conduct design reviews using appropriate interactive systems considering their expertise.

• Collaboration: on-site or remote users can collaboratively review the CAD model.

Targeted scenario

The ideal scenario of design reviews would be that remote users can collaboratively review the shared DMU from distinct interactive systems. Within this scenario, both users can generate and compare design alternatives from each interactive system. To cover various interactive systems which are likely to be used for most industrial design reviews, I investigate design review practices using two interactive systems: CAVE-like system, 3D visualization with gesture interaction; and Wall-sized display, 2D high-resolution large screen with multi-touch interaction.

Targeted interactive systems

Both platforms are located in campus of Universitè Paris-Sud: CAVElike system is in building 512, Limsi/CNRS and Wall-sized display is in building 660, Inria. These platforms are not on the same local network.

• CAVE-like system: the CAVE-like system (Fig.

Design review scenario

The needs for the interactive system varies depending on the purpose. Based on the literature reviews and the design process of PSA, the 3D environment is mostly required to conduct ergonomics simulations for end-users and manual labors in manufacturing lines, and to test assembly. Whereas the large 2D visualization environment is often used for management reviews where mostly senior project memberssuch as project manager, design manager, and engineering managerobjectively check the current design if it meets the initial concepts. Therefore, given the expected contexts and characteristics of these systems, the design alternatives would be better to be presented in a specific way on each interactive system:

• EVE: the DMU is displayed with a surrounding environment in the EVE system. Users-mostly ergonomists-can review the DMU considering the relation with surrounding environment in 3D space. Also they can generate design alternatives with 3D interaction, which they can select and deform the part where they want to modify with a simple manner.

• WILDER: the DMU is displayed on one of the tiled screen. Once users select the part where they want to modify with touch interaction, multiple design alternatives are generated and distributed over the screen. All generated designs are accumulated as design history. Users-senior managers and stylists-can discus and compare between all generated different design.

Users between each platform could remotely collaborate within a shared virtual environment. All generated design alternatives can be visible from both sites without interfering remote users' interaction. Also, they can make a video conference in a virtual environment.

Based on all illustrated system functionalities, I envision making the following scenario for next step of industrial design process.

An industrial company is divided into several departments over the world. Stylists work at the parent company in France, while ergonomists work in Japan. With the proposed system, stylists and executives check the design or perceived the quality of an automotive through a large screen with a high-resolution visualization system, while ergonomists evaluate the customer comfort (e.g. driver seat, cockpit space, the field of view) in a 3D visualization system. All users can directly generate design alternatives from both sites, and get instant feedback to compare them on each site using a specific interaction technique dedicated at the configuration of each interactive system. They can communicate between remote sites by streaming video and audio, then conclude the design direction to ask CAD engineer to apply last minor modifications or complete the final design by themselves.

The above scenario facilitates communication across geographically distant locations and different experts within distinct interactive systems that suit their needs. Today, most industrial companies adopt a decentralized organization, spreading departments across borders, which requires frequent remote discussions on the decision-making of the product. With the communication with the use of shared design alternatives, project members would have a better understanding of mutual design ideas compared with the use of verbal or text-based communication, especially between different languages or distinct experts who do not have common vocabularies. Therefore, the illustrated scenario is expected to enhance the quality of the decision-making process as well as reduce a number of design reviews thanks to direct modifications of CAD data.

To make this scenario possible, I follow the research direction formulated based on the design review process of PSA (Section 3.3). The following chapters will descibe main contributions of this thesis: a system architecture supporting a generation of design alternatives of a CAD model within heterogeneous systems and user studies on interaction techniques and collaborative design review for a comparison of multiple alternatives.

conclusion

I described in this chapter:

• Design reviewing process at PSA: they hold three different design review sessions consist of distinct experts using various VR interactive systems,

• Focused design review practice: project members compare several design alternatives during a detailed design review. Engineers need to prepare the alternatives based on remarks from several experts with CAD systems before each design review meeting,

• New design review process proposed in this thesis: a design review environment where users can collaboratively generate and compare design alternatives of the initial CAD model within heterogeneous systems,

• Illustrated scenario: remote experts-ergonomists and senior managers-can generate, compare, and validate design alternatives from native CAD data on a CAVE-like system or a Wall-size display, and they can collaborate across them.

In the next chapter, I describe an essential technical contribution to the proposed scenario, a system architecture supporting a generation of design alternatives based on native CAD data.

T E C H N I C

A L F R A M E W O R K F O R V R -C A D I N T E G R AT I O N
Integrating CAD into VR has been studied for two decades, yet full modifications of native CAD data are not possible from VR systems. This chapter presents the VR-CAD Server, a backend server that can load and update semantic information of CAD data. The VR-CAD Server modifies native CAD data based on modifications requests from VR systems and transmit the tessellated meshes in return. I also present a distributed network architecture to support heterogeneous interactive systems and remote collaboration. The technical framework described in this chapter is a core technical contribution of this dissertation and is used in the following studies.

introduction

CAD systems play a central role in the design and manufacturing industries. As introduced in the previous chapter, conceptual design data is transformed into CAD data during the detailed design process. The CAD data is then integrated into the PLM database, which is a common data hub used for several design verification processes. Consequently, various studies and applications for design reviews in VR focus on loading CAD data to reduce the time of data conversions and/or transcriptions between the PLM database and the virtual environment. However, CAD and VR environment are not fully integrated. VR-CAD data integration still suffers from data interoperability. Notably, the semantic information of the CAD model is lost during CAD-to-VR conversion. Most design review systems use static meshes generated by tessellations of the CAD data, which do not contain information of design history, CHG, and B-Rep. Because of this data conversion issue, the system can visualize-but not modify-the CAD data from the virtual environment.

To address this issue, I firstly analyzed and stabilized the research prototype on VR-CAD integration, cRea-VR, designed by a predecessor. I then designed and implemented a VR-CAD Server, which can load and update semantic information of CAD data to link the CAD and VR systems. With this VR-CAD Server, users in the VR system can request modifications on visualized CAD data and receive tessellated meshes in turn. Also, I implemented the VR-CAD Server on a distributed architecture to support heterogeneous interactive systems and remote collaboration between distinct interactive systems.

In this chapter, I begin by reporting related works on VR-CAD integrations and distributed network architectures. Also, I present cRea-VR, which was used as a basis for developing the VR-CAD Server. Finally, I detail the VR-CAD Server and the distributed network architecture used for this PhD work.

native cad data parsing

Most of the studies on VR-CAD integration focus on project reviews (see Section 2.3.3) or assembly simulations. Only a few previous works tackled the integration issues for parameter modifications of native CAD data. [START_REF] Jayaram | VADE: a Virtual Assembly Design Environment[END_REF] (Fig. 4.1a), was one of the first VR assembly simulation, which users can import CAD data into VR environment with automatic data translations. One of the main challenges in studies for assembly simulation is to link CAD and VR data to avoid manual data translations between each session. Wang et al. [START_REF] Wang | Live parametric design modifications in CAD-linked virtual environment[END_REF] proposed a system that can link semantic information of CAD data (e.g. constraints, design features, and parametric settings) with VR session, so thus users can perform assembly simulation on the (c) User study in the CAVE with project members in a hydraulic pump manufacturing company. [START_REF] Berg | An Industry Case Study: Investigating Early Design Decision Making in Virtual Reality[END_REF] (d) VR assembly session with a leap motion and HMD. [START_REF] Freeman | A bi-directional interface for improved interaction with engineering models in virtual reality design reviews[END_REF] Figure 4.1: Various VR assembly simulations original data file. As the other approach, some studies used Product Data Management (PDM) or PLM database as a medium between CAD and VR systems [START_REF] Lorenz | CAD to VR -A Methodology for the Automated Conversion of Kinematic CAD Models to Virtual Reality[END_REF][START_REF] Mahdjoub | A collaborative Design for Usability approach supported by Virtual Reality and a Multi-Agent System embedded in a PLM environment[END_REF][START_REF] Vr | A Tool to Co-Ordinate a Collaborative Product Development Process in a Virtual Environment[END_REF]. By doing so, it would offer a collaborative working method where multiple experts can conduct specific simulations using the shared database from various systems: e.g. ergonomists conduct analysis with a 3D human model while engineers perform assembly simulations in VR system. Freeman et al. [START_REF] Freeman | A bi-directional interface for improved interaction with engineering models in virtual reality design reviews[END_REF] (Fig. 4.1d) and Berg et al. [START_REF] Berg | An Industry Case Study: Investigating Early Design Decision Making in Virtual Reality[END_REF] (Fig. 4.1c) conducted case studies to investigate how VR-CAD integrations affect the decision-making process during the design stage. They found that the VR session helps users to understand the geometry of the product, spatial relationships between product components and interactions required to assemble the product. Most notably, it increased the engagement of design team members more actively with compared to the passive conference room environment of traditional design review. 1 www.spatial.com/products/3D-acis-modeling 2 www.opencascade.com tory of CAD objects [START_REF] Convard | History Based Reactive Objects for Immersive CAD[END_REF], such as operators, parameters, transformation matrices, etc. Today, major CAD systems use CHG to store all the history of CAD models. Some works have attempted to keep that information for design activity in an immersive environment. Toma et al. [START_REF] Mȃdȃlina | A comparative evaluation of human interaction for design and assembly of 3D CAD models in desktop and immersive environments[END_REF] (Fig. 4.3a) proposed a geometric design in an immersive environment using Solidworks R thanks to VRSolid module which provides a VR interface for this CAD system. This system supports creating virtual objects in a VR environment but not loading the CAD model already designed by CAD systems. Whereas, Meyrueis et al. [START_REF] Meyrueis | D3: An Immersive Aided Design Deformation Method[END_REF] (Fig. 4.3b) proposed a system in which users can deform the mesh of 3D objects created in CAD systems before the VR session. This system stores the deformation information in a customized CHG for VR session, and then it requires merging them with the original CAD data after the VR session. The immersive modifications of existing operators and their parameters are not addressed. As one of the previous VR-CAD system, Bourdot et al. [START_REF] Bourdot | VR-CAD integration: Multimodal immersive interaction and advanced haptic paradigms for implicit edition of CAD models[END_REF] presented a CAD data management technique for a VR representation, which makes and stores a link between each element of B-Rep and relevant CHG nodes of the CAD model. This technique aimed to allow users to implicitly modify the parameter of the CHG node from a surface selection of the represented CAD model in an immersive environment. They implemented a proof of concept with OpenCascade. Later, Martin et al. [START_REF] Martin | Modéle pour la conception immersive et intuitive: application à l'industrie automobile[END_REF] extended this model to address commercial CAD systems used by industry. A proof of concept, cRea-VR (Fig. 4.4), has been implemented with CATIA V5 R (Dassault Systémes) in a CAVE system.

Assembly simulation VADE, a Virtual Assembly Design Environment

previous vr-cad system: crea-vr

cRea-VR is one of the successful system for the VR-CAD integration, which enables users to directly modify parameter values of native CAD data within the immersive environment. I firstly stabilized the operation of cRea-VR, then analyzed and organized its system architecture to publish this work as a research paper [START_REF] Martin | A VR-CAD Data Model for Immersive Design[END_REF]. Based on the CAD data management process implemented in cRea-VR, I designed and developed a new system architecture to support the design review scenario described in Section 3.3.1.2. • Data pipeline between VR and CAD systems: the system can parse native CAD data designed by commercial CAD systems and update it at run time based on user interactions from the VR system.

• Simplified parameter selections: users can select parameters defined in the CAD model by directly selecting a shape, instead of exploring a design tree.

cRea-VR can parse all the necessary CHG nodes of the CAD object (operators and its parameters, constraints and 2D elements of sketches) and B-Rep elements, then associate each B-Rep element with a list of relevant CHG nodes. This information is stored in VR-CAD data model, which can be updated at each modification process. This enables interactive modifications of existing CAD objects from VR systems. Particularly, the implicit parameter selection from shapes is a benefit for non-CAD experts to avoid understanding the full design history of a complex model or extensive project database. The system architecture of cRea-VR is composed of four main components: Interaction engine, Visualization system, Inference engine and Encapsulations (Fig. 4.5).

• Interaction engine: receive Virtual Reality Peripheral Network (VRPN) data: tracking data of user's head and pointing devices (FlyStick or wiimote) and its button states. Interaction engine triggers events based on the user input and send information to Visualization system to update scene rendering.

• Visualization system: manage immersive rendering of the scene. A proof of concept is implemented with a CAVE-like system run by four cluster PCs. Visualization system thus uses DRS (Distributed Rendering System) [START_REF] Convard | Managing Deformable Objects in Cluster Rendering[END_REF] for clustering renderings.

• Inference engine: identify the relevant CHG information from a selected shape by the user. Inference engine then propose a list of parameters that the user can choose and modify. The data set in Inference engine is updated at each modification step after parsing the updated CAD model.

MIDDLEWARE CAD SYSTEM

BRepElements (Map)

Operator Labels Naming Reference Ancestors Children • Encapsulation: load CHG of the CAD model and prepare data lists for each Operator, parameter, constraints, and sketch element in design history. B-Rep data map is also managed in this step.

Targeted CAD model

As a proof of concept, cRea-VR supports CATIA V5 as CAD systems and target a specific CAD model, Rear-view mirror of a car (Fig. 4.6).

The Rear-view mirror is designed by actual CAD engineers in PSA. This Rear-view mirror is generated from a sweep operation following a guide curve (green lines in Fig. 4.6), which is defined by different parameters (radius, lengths) and geometric constraints (tangency and symmetry).

For example, the red colored constraint (60 mm in Fig. 4.6) defines the distance to the bottom of Rear-view mirror.

Interaction flow

When the cRea-RV is launched, the system loads and parse specified CAD data (a proof of concept only supports CATIA V5, *.catpart) then starts a VR session. In the VR session, user interactions can be divided into three steps:

• Shape selection (Fig. 4.7c): the user can select a shape with a casted ray from a controller (yellow lines). When the shape is selected (colored in red), the relevant information are displayed on the left panel: e.g. name of geometry set, name of operator, parameters (constraints) related with the shape.

• Target selection (Fig. 4.7c): the user can select one of the listed constraints (e.g. Distance: Constraint.46, Radius: Constraint.5) to modify it with buttons if more than one constraints are accessible.

• Parameter modification (Fig. 4.7d): the user can modify the parameter value of the selected constraint with horizontal scrolling: decrease the value by moving to the left, and vice versa. Current parameter value is displayed above the shape with white color. For example, the user is modifying the distance of the top part of rear-view mirror. The green dotted line shows the updated 2D sketch.

• Validation (Fig. 4.7e): when the modification is validated, the CAD data is updated and displayed in the scene. The user can save the CAD model with the original format.

User feedback

Senior CAD engineers of PSA tested cRea-VR and highlighted its strength: real-time visualization of updated CAD objects, deep access to the parameters of CATIA objects from a VR system, and conversion-free immersive project review. However, they mentioned the interaction technique-horizontal scrolling-needs to be improved to become more straightforward to users. Although the horizontal scroll motion allows users to manipulate selected parameters easily, users cannot expect the shape modification due to the constraint definition in the CAD model. For example, when the user selects Distance constraint tied to the bottom part of the Rear-view mirror (red-colored parameter in Fig. 4.6), the height of the mirror will be deformed as opposed to the user's horizontal hand motion. This inconsistency between the direction of shape deformation and user interaction might confuse users with no experience in parametric design.

Summary

cRea-VR introduced the VR-CAD integration method, in which the user can modify parameters of CAD parts from VR systems without any data conversion. With cRea-VR, users can implicitly select the parameter from 3D surface-without interacting with design tree-and modify it with horizontal gesture interaction. These features would achieve the new design review process where project members can discuss and modify the data within an immersive environment. However, the current interaction technique and the system architecture is limited to a specific configuration of interactive systems. To support various users' needs and available equipment of the industrial companies, the increase of the scalability is the first requirement. Therefore, I extracted the core architecture of cRea-VR (Inference engine and Encapsulation, Fig. 4.5) and designed a VR-CAD Server, which serves as a back-end server where users can access and ask for modifications from various interactive systems.

vr-cad server

The VR-CAD Server relies on the data flow illustrated in figure 4.8. This server is designed to be used as a CAD data processing node, which runs in the back-end to receive data modification commands and transmit the output data to front-end applications.

The VR-CAD Server first loads a specified CAD data based on the encapsulation method of cRea-VR, then generates meshes and a linkage information file (.xml), which is a map between each mesh and relevant B-Rep. The generated meshes often have some defects (e.g. non-manifold geometry) during the tessellation process, so that Mesh cleaner handles these post-tessellation issues using VCG library 3 . The cleaned meshes are converted into a Wavefront standard format (.obj). After these processes, the meshes and linkage file are transmitted to the distributed systems.

When the VR-CAD Server receives the modification command, with the given B-Rep ID, Constraint and Requested parameters, the CAD engine generates the updated meshes and the linkage file then transmits them back to interactive systems.

For example, when the user wants to change the curvature of the bottom left corner of the Rear-view mirror (Fig. 4.6) from 15 mm to 45 mm, the information "B -Rep ID = 4", "Constraint = Radius" and the new "parameter value = 45" are transmitted from the user's VR platform to the VR-CAD Server. Then, the CAD engine communicator asks the CAD engine to edit the parameter of the specified CHG node with the new value. The CAD engine updates the whole CHG and generates new meshes from the computed B-Rep. This process takes 700 ms on average. After all these processing, the new meshes and the updated linkage file are delivered to each platform. The VR-CAD Server is attached to the distributed network architecture, which needs to be designed carefully, especially for Collaborative Virtual Environment (CVE), not to add latency and inconsistency between interactive systems.

distributed architecture

The design of distributed architecture should step on the numerous previous works to choose a proper network architecture and data distribution according to system requirements.

The state of the virtual environment between different nodes has to be synchronized for remote collaboration. Previous works studied several distributed architectures for CVE since the 90s. In a survey, Delaney et al. [START_REF] Delaney | On Consistency and Network Latency in Distributed Interactive Applications: A Survey-Part I[END_REF][START_REF] Delaney | On Consistency and Network Latency in Distributed Interactive Applications: A Survey-Part II[END_REF] highlighted that the main goal of the distributed architecture was to maintain the consistency of the CVE, while enabling users to observe or interact with the same objects at the same time.

The following criteria are important to ensure this consistency:

• Synchronization: time synchronization; each event should simultaneously happen on all nodes, and spatial synchronization; all entities or objects should be at same locations on all nodes.

• Causality or Ordering: all events should run with same order on all nodes.

• Concurrency: system should manage a conflict access to a same object from multiple users at same time.

In addition, Delaney et al. [START_REF] Delaney | On Consistency and Network Latency in Distributed Interactive Applications: A Survey-Part I[END_REF][START_REF] Delaney | On Consistency and Network Latency in Distributed Interactive Applications: A Survey-Part II[END_REF] explained that the system should also provide good responsiveness to the users when they interact. This responsiveness can be defined by the latency of the system to respond to user inputs. Consistency of the CVE and responsiveness of the system are usually two contradictory aspects: a system, which ensures a perfect consistency, could probably have bad responsiveness, and vice versa. Each CVE must find an adequate trade-off between consistency and responsiveness, which suits its requirements. The way nodes are connected over the network and how the data of the CVE are distributed among these nodes have a strong impact on this tradeoff. Consequently, I describe in the two following parts, the different network architecture, and the data distribution and emphasize their effects on consistency and responsiveness.

Network architecture

Fleury et al. [START_REF] Fleury | Architectures and Mechanisms to Maintain efficiently Consistency in Collaborative Virtual Environments[END_REF] identified three different types of the network architectures: peer-to-peer, client/server and hybrid architectures (Fig. 4.9). The peer-to-peer architecture ensures fast interaction between a few users, while the global consistency is difficult to maintain, especially with large groups of users. In contrast, the client/server architecture can easily maintain the consistency, but it may decrease the responsiveness. The hybrid architecture can combine the two previous network organizations to reach a good trade-off: it ensures a high communication speed between nodes (peer-to-peer), while maintaining a good consistency through the server (client/server). Some applications for CVE use the hybrid architectures to meet the user requirements [START_REF] Leigh | CAV-ERN: A distributed architecture for supporting scalable persistence and interoperability in collaborative virtual environments[END_REF][START_REF] Margery | Openmask:{Multi-Threaded| Modular} animation and simulation {Kernel| Kit}: a general introduction[END_REF].

Data distribution

Several data distribution models were originally discussed by Macedonia et al. [START_REF] Macedonia | A taxonomy for networked virtual environments[END_REF]. Fleury et al. [START_REF] Fleury | Architectures and Mechanisms to Maintain efficiently Consistency in Collaborative Virtual Environments[END_REF] classified them in three categories: shared centralized world, homogeneous replicated world and partially replicated world (Fig. 4.10). The shared centralized world stores all the data of the virtual environment in a central server. This server also manages the modification requests on each virtual object. This model ensures a good consistency between each node, but it might decrease the responsiveness of the system due to the time required to request data from the server. The homogeneous replicated world stores all data and executed all processing on each node. It gives good responsiveness, but inconsistencies might occur between each node. The partially replicated world is a hybrid model that can overcome some drawbacks of the other models. It distributes the data and the processing to specific nodes to avoid duplication of data and reduce the computing load on each node. For example, the referent/proxy mechanism used in OpenMASK [START_REF] Margery | Openmask:{Multi-Threaded| Modular} animation and simulation {Kernel| Kit}: a general introduction[END_REF] is a partially replicated data distribution. In addition, an adaptive data distribution mechanism [START_REF] Fleury | A New Adaptive Data Distribution Model for Consistency Maintenance in Collaborative Virtual Environments[END_REF] can be used to dynamically switch between these three data distribution models during a collaborative session in order to select the most appropriate one according to users' tasks. Based on prior surveys, I designed a distributed architecture which allows multiple users on heterogeneous systems to modify shared CAD data through the VR-CAD Server. This architecture should meet the following requirements:

• Modification of native CAD data at runtime: the system should be able to load and modify existing CAD data without any data conversion before/after the review session.

• Interconnection between heterogeneous platforms: the system should deal with various visualization systems and interaction devices of each platform.

• Collaborative modification of CAD parts: multiple users should be not only able to modify different parameters of a part but also the same parameter of this part.

• Distribution of CAD data among remote locations: the system should dynamically update the CAD data on each remote platform.

To support these features, I use a hybrid network architecture which combines both a centralized architecture to connect remote platforms to the VR-CAD Server and peer-to-peer connections to allow fast communication between platforms. This architecture is independent of the technical specifications of each platform and can connect heterogeneous platforms with different visualization systems and interaction devices.

In the following, I first detail the distributed architecture that connects each interactive platform and the VR-CAD Server. Then I illustrate how multiple users could collaboratively manage parameter modifications on the shared CAD part. Lastly, a proof of concept of this VR-CAD system is described as a use-case between EVE system and WILDER.

Network architecture

I propose a hybrid network architecture to connect the remote platforms and with the VR-CAD Server (Fig. 4.12). All information about non-CAD objects (e.g. avatars, pointers) are transmitted with a peerto-peer architecture between each platform; whereas, all the data relative to CAD objects (meshes and linkage files) are transmitted with a client/server architecture between the platforms and the VR-CAD Server.

A Workspace server (WS server in Fig. 4.12) is used for authentication and for establishing the connection between each platform and the VR-CAD Server. This notion of Workspace allows the storage of a particular configuration of a work session and to retrieve it later in order not to have to redo the network configuration for each similar work session. Each user has to connect to a specific Workspace to be connected to the other user. The WS client is the communication layer which manages the network communication on each platform and the VR-CAD Server. The communication between the WS server and the WS client is managed by the WebSocket protocol, which allows real-time full-duplex communication.

The communication between each WS client is handled by WebRTC4 protocol allowing peer-to-peer connections. I choose this open protocol to be able to connect various remote locations with different network architecture and deal with network constraints such as firewall and security issues. The WS client running on each platform streams application data to all other platforms for synchronizing interaction events and non-CAD object positions in the CVE. The VR-CAD server also exchanges the CAD data or the modification requests with each platform through a WS client.

For the internal communication inside each platform, the WS client uses the TCP to interact either with the application running on each platform or with the CAD engine. Each application sends information about the local elements (e.g. positions/orientations of user's head and hand, events) to the local WS client which transmits updates about the state of the CVE to the remote platforms. Conversely, information on the remote platforms is transmitted to the local application by the local WS client. If the platform is composed of computer clusters (such as for CAVE systems), the WS client only communicates with a master node of its local clustering system.

Each platform can also stream media data (audio and/or video) with the WebRTC protocol through a Media manager. The Media manager is connected via WebSocket to the local WS client which controls the media streams. The audio and video stream can thus be delivered to all the other remote platforms.

As the communication module is independent from the platform, this architecture can easily be adapted to several visualization systems and interaction devices. Figure 4.12 describes the architecture with two platforms, but additional platforms can be included with the same communication scheme.

This distributed architecture is implemented as a proof-of-concept. Yet, a user interaction layer is still under discussion. Interactions with the shared CAD model between remote places are discussed below.

Collaborative interaction

Cooperative activities in the CVE can be classified into three levels [START_REF] Margery | A General Framework for Cooperative Manipulation in Virtual Environments[END_REF]. The first level is defined as basic cooperation: each user can perceive each other in CVE through an avatar or with other communication tools.

The second level, mostly used in collaborative product reviews [START_REF] Leigh | Multi-perspective collaborative design in persistent networked virtual environments[END_REF], allows users to act on an individual scene by changing the visual contexts of the scene (e.g. change the location and properties of objects). At the third level, multiple users can act on the same virtual object for manipulations or modifications. This last level can be further divided into two sub-levels: (i) the users can act on the independent properties of the same object (e.g. location and color) and (ii) the users can concurrently act on the same or linked properties of the same object. In many research works [2,[START_REF] Pinho | Cooperative object manipulation in collaborative virtual environments[END_REF], this sub-level (ii) is called cooperative manipulation.

The proposed distributed architecture was designed to support all levels of cooperative activities, with media streaming (first level), by allowing multiple users to act on individual visual context (second level) and to concurrently modify the same or linked parameter values of a specific CAD part (third level). Illustrated below are the example of interaction flow for CAD parameter modification with two categories of cooperative activities: independent and cooperative modification.

Example of interaction flow

The user interaction for CAD parameter modification with the proposed system can be divided into three steps:

• Selection: the users start by picking a specific part of the 3D model using a virtual tool. Once they have selected a part, they need to pick a specific constraint in a list of constraints (e.g. distance, radius) linked to the part.

• Parameter modification: the users can then modify the selected parameter value using a dedicated manipulation metaphor to increase/decrease the value, e.g. in cRea-VR [START_REF] Martin | Modéle pour la conception immersive et intuitive: application à l'industrie automobile[END_REF] used a horizontal scroll technique.

• Validation: when the users validate their modification, the resulting modification request is sent to the VR-CAD Server which updates the CAD data and distributes the new version over the network. If the value is not acceptable for the CAD engine (i.e. exceeds the limit of the constraints), the users receive an error and have to continue the parameter manipulation.

Conventionally, each remote user is allowed to act on different CAD parameters to avoid a conflict in parameter manipulation. But, it would also be interesting scenario for multiple users to simultaneously modify the same parameter to support different types of cooperative activities. This cooperative manipulation could be adjusted by considering the expertise and roles of the collaborators. For example, a CAD engineer could assist the parameter manipulation conducted by a stylist to refine its modification by either providing possible discrete solutions or constraining its manipulation range in real-time. Both of these interactions with CAD parameters could be implemented with the proposed system, and users can use both techniques according to their parameter selection:

• Independent modifications which occur when each user modifies a different parameter of the CAD data at the same time. Each user can see the visual proxy of the other users' hand and can thus check their actions. When one of the users validates its parameter value, the CAD data will be updated regardless of the ongoing parameter manipulation on the other platforms.

• Cooperative modifications which happen when more than one user simultaneously select the same CAD data parameter. One of the interaction techniques that can achieve such cooperative manipulation is a Mean technique: the system averages the parameter values of each user after their validation. This is a simple way to combine users' action [START_REF] Ruddle | Symmetric and Asymmetric Action Integration During Cooperative Object Manipulation in Virtual Environments[END_REF], and some other techniques have also been discussed [2,[START_REF] Pinho | Cooperative object manipulation in collaborative virtual environments[END_REF]. But, some previous studies do not fit our scenario: for example, I cannot use DoF separation [START_REF] Ruddle | Symmetric and Asymmetric Action Integration During Cooperative Object Manipulation in Virtual Environments[END_REF] since the targeted parameter manipulation is only in one-dimension. The interaction technique for cooperative modifications has to be carefully chosen or designed not to reduce the work efficiency or disturb the collaborator.

Interaction Between Heterogeneous VR Platforms

As a proof of concept, I implemented the distributed architecture with two platforms: EVE and WILDER (Fig. 4.12). In this specific system configuration, the VR-CAD Server belongs to same network group as the EVE system, so two WS client run on platform 2. Each VR system communicates with the WS client through a master node of clusters. All of the CVE data (e.g. tracking data, the object data, CAD data) pass through the master node. When the WS client receives the CAD data from the VR-CAD Server, the CAD data is saved on a local data server, and the master node copies this data to deploy it to the slave nodes.

In WILDER the information of the user's touch inputs and the tracking data are directly transmitted to the master node of the clusters. Unity scene gathers all information and distributes it to slave nodes.

In EVE, the VH Server, Visio-Haptic Server (detailed in Chapter 5), receives haptic handle's position/orientation and user's head tracking data, then broadcasts them as VRPN format to the master node of clusters. MiddleVR for Unity handles the VRPN data over the cluster nodes. When the CAD data is distributed to each platform, this CAD data is loaded in VH Server and used for the force feedback computation. The video of each user can be transmitted through the WebRTC protocol to each other. Each IP camera streams the video to the Kurento media server 5 which distributes the received data to cluster nodes. In this proof-of-concept, remote users can collaboratively modify the shape of a rear-view mirror while standing in the virtual cockpit of a car, instead of using the interface of CAD software. As illustrated in Section 3.3.1.2, a stylist could use the wall-sized display to check the quality of the product with a wide field of view and a high-resolution visualization. In contrast, an ergonomist could use the CAVE-like system to verify the driver experience in a 3D environment. Currently, cooperative interaction techniques are not implemented. However, the proposed distributed architecture is highly configurable, supporting various data transmission, multi-user environment, and heterogeneous platforms, which would serve a base system for further studies on collaborative interaction.

Summary

I designed a distributed architecture for collaborative VR-CAD system based on hybrid network architecture. This architecture would make the illustrated scenario (Section 3.3.1.2) possible, but still, this is a proof of concept. The interaction techniques on each platform and collaborative interaction methods should be explored and investigated with user studies.

conclusion

I described in this chapter:

• Previous works on native CAD data parsing: many studies have investigated VR-CAD integration for assembly simulations, whereas only a few studies focused on parameter modifications of native CAD part within immersive systems. One of the successful work is cRea-VR,

• cRea-VR: cRea-VR enables parameter modifications of native CAD data in the immersive system with a direct surface selection instead of interacting with design trees. Since the cRea-VR is designed on specific system configurations, I redesigned the system architecture to increase the scalability,

• VR-CAD Server: I extracted core functionalities of cRea-VR and designed a back-end server which can be accessed from various interactive systems. This server output meshes and CAD-VR data link information based on given modification requests,

• Previous works on distributed architecture: The design of distributed architecture affects the synchronization and conflict issues between each connected interactive system. To keep fast communication and better consistency between nodes, I used a hybrid network architecture,

• VR-CAD system architecture: I designed a distributed architecture with VR-CAD Server to support new design review scenario. Multiple users can collaboratively review and modify the native CAD data from each interactive system. The proof-of-concept is implemented on EVE and WILDER. This system architecture is a basis for further studies described in the following chapters.

This chapter presented the core technical contribution to VR-CAD integration and distributed architecture for design reviews. From the following chapter, I describe the investigation of interaction techniques with CAD data on EVE (Chapter 5) and WILDER (Chapter 6).

D I N T E R A C T I O N T E C H N I Q U E F O R C A D D ATA M O D I F I C AT I O N

3-D computer-aided surface design is best done in real-time with 3-D tools.

To expect a designer of 3-D surfaces to work with 2-D input and viewing devices unnecessarily removes a valuable degree of freedom.

-James H. Clark [START_REF] Clark | Designing Surfaces in 3-D[END_REF] Various 3D interaction techniques have been explored since 90s, yet none of them target detailed design stage. This chapter presents ShapeGuide, an interaction technique which allows users to modify parameters of native CAD model with a shapebased 3D interaction. I also present a user study which investigates the efficiency of ShapeGuide on parameter modifications of CAD models, and the add-value of force feedback assistance. This study shows that ShapeGuide is more efficient, less frustrating and preferred by participants compared with a standard interaction technique.

introduction

Preliminary work on the VR-CAD system focused on carrying design activities from 2D to 3D space. Clark [START_REF] Clark | Designing Surfaces in 3-D[END_REF] demonstrated 3D interactions on design activities using a first prototype of HMD with a 3D wand in 70s. Afterward, studies in this field have mostly advanced since 90s, and many design systems have been developed aiming at providing coherent dimension between visualization and interaction space.

Most of those studies targeted conceptual design applications in which designers make initial designs by drawing, sketching or geometric modeling with 3D interactions [3,[START_REF] Fiorentino | Spacedesign: a mixed reality workspace for aesthetic industrial design[END_REF]. For detailed design, most of the VR-CAD applications allow users to visualize CAD data in an immersive system, but not to modify them. Although 3D interactions are not beneficial for creating full CAD models, such interactions can be valuable for small adjustments during design reviews. However, most of current VR-CAD applications still do not support 3D interactions for modifying native CAD data. One of the main limitation is complexity on CAD data management as highlighted in a previous section.

Even if a previous study, cRea-VR, allows users to modify native CAD data within an immersive system [START_REF] Martin | Modéle pour la conception immersive et intuitive: application à l'industrie automobile[END_REF], the interaction was still on one-dimensional scrolling for a parameter tuning, which was not consistent with 3D shape deformation. Transferring alphanumerical input to 3D interaction is challenging, especially for a complex CAD model that contains internal geometric constraints. The 3D interaction would simplify the CAD data interactions on a workstation and provide straight-forward methods on design refinements for non-CAD experts.

To improve the interaction technique for modifying native CAD data, I proposed ShapeGuide, a technique to modify native CAD data through a shape-based 3D interaction. It allows users to implicitly manipulate parametric constraints of CAD parts by grabbing and deforming its surface. I conducted a controlled experiment to compare the efficiency of ShapeGuide on parameter modifications of CAD model with a onedimensional scroll technique, used in cRea-VR. Also, I investigated the add-value of force feedback assistance on these two techniques.

In this chapter, I begin by reviewing previous works on 3D interaction techniques in the context of industrial designs. I then introduce ShapeGuide, a technique to modify native CAD data through a shapebased 3D interaction. Finally, I detail the controlled experiment which evaluates ShapeGuide.

3d interaction techniques for detailed design

As introduced in Section 2.3, various 3D interaction techniques have been studied for design activity in immersive environment. Most studies focused aesthetic design purpose, for which users conduct drawing or surface modelings. Precision does not matter for this stage, but interaction has to be straightforward for users not to limit their ideation process. Those studies generally offer shape-based interaction techniques in which users can directly grab and drag or draw the surface with one-to-one scale by gesture interaction. However, it is difficult to realize such interaction technique on modifications of CAD part-particularly the constraint-based CAD model.

JDCAD [START_REF] Liang | JDCAD: A highly interactive 3D modeling system[END_REF] and ARCADE [START_REF] De Amicis | Parametric Interaction for CAD application in Virtual Reality Environment[END_REF][START_REF] Stork | Efficient and Precise Solid Modelling Using a 3D Input Device[END_REF] first tried to achieve the 3D interaction technique on parametric model by defining the possible user's hand motions at each selectable region. To deal with the complex models, Gao et al. [START_REF] Gao | An approach to solid modeling in a semi-immersive virtual environment[END_REF] presented a 3D interaction technique to create and modify solid models containing different geometric constraints. Their VR-CAD system stores each primitive, parameters and operators within customized CSG, to recognize related constraints from a selected element and enable consistent shape deformation with users' 3D hand motion. Ma, Zhong, et al. [START_REF] Ma | A hierarchically structured and constraint-based data model for intuitive and precise solid modeling in a virtual reality environment[END_REF][START_REF] Zhong | A methodology for solid modelling in a virtual reality environment[END_REF] also tackled this issue with a hierarchical constraint-based data model. These approaches improved previous VR-based solid modelings to support constraint-based CAD models; however, the number of supported constraints and operators are limited, and they cannot directly apply 3D interactions on existing CAD data since their approaches lay on custom data structures.

More recently, some researchers argued that desktop-based CAD systems are more suitable tools for detailed design stage. Stark et al. [START_REF] Stark | Towards hybrid modelling environments-Merging desktop-CAD and virtual reality-technologies[END_REF] listed three reasons why productive VR-based detailed design (e.g. solid modeling) systems do not exist yet:

• Usability of current VR-based user interfaces for CAD systems is limited.

• 2D interaction techniques of current CAD systems cannot be transferred one-to-one to VR systems for various reasons. E.g. alphanumerical input is difficult to realize in VR systems while additional sensumotor coordination effort due to the third dimension makes it difficult to navigate and interact precisely, even if snapping functions are provided.

• Additionally, the accuracy of modelling operations cannot be assured. Thus, only a limited set of available CAD systems' functions can be provided in a VR-based CAD system.

In other words, the previous VR-based system for detailed design could not satisfy functionality, interaction, and accuracy for CAD operations in comparison to the desktop-based system. Especially, limited functionality sounds critical issues for CAD engineers. But, my targeted scenario for design reviews do not require any complex CAD operations. As the design intent is already discussed and built as the digital mockup, project members can focus on the design refinements, rather than the modeling of the digital mockup. Hence, the accuracy would not be important neither, since project members may not adjust the size precisely during the review session.

Traditionally, for the purpose of increase the accuracy on 3D manipulations, haptic feedback has been studied. The benefit of providing haptic feedback is also to reduce the physical fatigue of the user's arm. Ye et al. [START_REF] Ye | An investigation into the implementation of virtual reality technologies in support of conceptual design[END_REF] compared the usefulness of each sensory feedback (vision, audio, and haptic feedback) on surface modeling task, and found that the haptic feedback marked the second highest place following the visual feedback. Haptic feedback can be used in both aesthetic and solid modeling applications. For aesthetic design, Snibbe et al. [START_REF] Snibbe | Springs and Constraints for 3D Drawing[END_REF] and Gregory et al. [START_REF] Arthur D Gregory | in-Touch: interactive multiresolution modeling and 3D painting with a haptic interface[END_REF] (Fig. 5.1a) provided the force feedback to drawing and painting activities in 3D space. Dachille IX et al. [START_REF] Dachille | Haptic Sculpting of Dynamic Surfaces[END_REF] and Liu et al. [START_REF] Liu | Virtual De-signWorks-designing 3D CAD models via haptic interaction[END_REF][START_REF] Liu | Manipulation of CAD surface models with haptics based on shape control functions[END_REF] (Fig. 5.1b) presented surface deformation with pulling/pushing interaction using force feedback devices. For solid modeling, Picon et al. [START_REF] Picon | Haptically-Aided Extrusion for Object Edition in CAD[END_REF] applied the force feedback to extrusion task to increase the 3D gesture accuracy. In this chapter, the main challenge I focus for VR-CAD system is Interaction, how to transfer the alphanumerical input to shape-based interactions in 3D environment. While parameter oriented interaction techniques meet CAD engineers' needs, such interaction does not fit to non-CAD experts. Coffey et al. [START_REF] Coffey | Design by Dragging: An Interface for Creative Forward and Inverse Design with Simulation Ensembles[END_REF] developed an interface in which designers could refine the design of a medical device built with SolidWorks R by directly dragging the parameterized surface or simulation results (e.g., Finite Element Analysis (FEA), CFD) on 2D screen. This study allowed designers to interact with the simulation results to modify CAD data.

Similarly to their concept, shape-based 3D interaction techniques could provide non-CAD experts more straightforward interaction method and empower them to perform modifications of native CAD data during immersive reviews.

shapeguide: shape-based interaction technique

This section describes a 3D interaction technique for CAD data modifications, ShapeGuide. ShapeGuide is designed to make users feel that they can deform a CAD model with pulling/pushing interactions. The method of ShapeGuide is based on a generation of a set of design alternatives. The consecutive design alternatives superposed in 3D space are displayed one by one according to the user's hand motion. I also investigated force feedback assistance during a deformation task.

In the following, I detail the methodology of ShapeGuide and the computation of force feedback assistance.

Mesh computation

The main difficulty of shape-based interaction with a constraint-based CAD object is the "unpredictability" of the shape deformation from a given parameter change. In parametric CAD systems, 3D models are usually defined by a set of operations (e.g., Extrusion, Sweep, Boolean operations) applied from primitives and 2D sketches, based on many parameters and geometrical constraints, like a sketch of Rear-view mirror (Fig. 4

.6).

To modify parameter values of such complex CAD objects with the shape-based interaction, first several possible design alternatives are generated from a set of discrete parameter values. For example, when the user selects the bottom part of Rear-view mirror in a virtual environment, the VR-CAD system lists accessible constraints related to the bottom part (i.e. distance: 60 mm and diameter: 2300 mm, Fig. constraint, the VR-CAD Server computes several design alternatives of the corresponding parameter value (Fig. 5.2). Due to tessellations of its B-Rep, Rear-view mirror is composed of nine sub-part meshes.

While the system render the complete Rear-view mirror (full meshes in Fig. 5.2) for visual feedback, only sub-part meshes are used for physics computation to reduce computation cost. For this physic rendering, the distance between the user's hand and sub-part meshes are computed at each frame for both visual and haptic rendering. For the visual feedback, only the closest full mesh is rendered in the virtual environment to make the user feel that the CAD object is deformed through a pushing/pulling interaction regardless of its hidden internal geometric definition. Haptic feedback can be computed from distances between the user's hand and closest two meshes to assist the shape selection process as described in section 5.3.3.

Tessellation of B-Rep takes time according to CAD model size and complexity. In the ShapeGuide methodology, sub-part meshes generation impose a loading time after each selection to guarantee a real-time interaction while the user is modifying a parameter value. While com-plete update could be achieved on primitives or simple CAD object in real-time, updating a complex CAD model at each frame during parameter modification could delay system response that strongly impacts user's performances. Indeed, the real-time sensory feedback to users (60 Hz for visual feedback and 1 kHz for haptic feedback) is one of the critical criteria to maintain their immersion in a virtual world. Even if ShapeGuide requires some loading time, it ensures realtime system responsiveness during modifications for any CAD model regardless of its complexity. As an example, tessellations of the six sub-part meshes of the bottom part of Rear-view mirror presented in Fig. 5.2 takes between 0.9 to 1.2 seconds.

The number of shapes N shapes and parameter step size ∆p need to be specified at sub-part selection stage to define the parameter set surrounding current parameter p 0 of the constraint. These values can be changed at each selection during the simulation to be able to set any parameter value with the required precision. After the sub-part selection, users can choose the constraint to modify if more than one constraints are linked to the selected part. In the current system, I did not implement a user interface to allow the user to tune these values, N shapes and ∆p as well as the one to select the constraint within the list fetched by VR-CAD linkage. For the experiment purpose described in section 5.5, I did not let users manipulate these values during the experiment. Instead, I imposed static values for N shapes and ∆p and specified a default modifiable constraint for each sub-part to control the loading time fitting our experimental hardware capabilities and time limitation for immersive experiments.

3D shape-based interaction

Once the design alternatives are computed from a given parameter set, users can select one of them from their 3D hand position P hand (Fig. 5.3). Algorithm 1 performs this selection by computing each nearest point P i and minimal distance D i on each mesh within a set of generated sub-part meshes (MeshSet). Nearest3DPointOnMesh(M, P) in Alg. 1 computes the nearest point on each triangle of M mesh from a given P(x, y, z) position based on the computation algorithm described in [37, p. 141-142]. Then it returns two closest points (P closestA and P closestB ) and nearest mesh Ids (MeshId A and MeshId B ). After this computation, the closest mesh Id (MeshId A ) is sent to VR simulation to display the selected nearest shape in a virtual environment.

Force feedback assistance

An additional benefit of ShapeGuide is to be able to convey haptic feedback while modifying CAD part. The force feedback model is inspired by force feedback grid [START_REF] Yamada | Desk-sized immersive workplace using force feedback grid interface[END_REF] (Fig. 5.4), which stabilizes user's

(P i , D i ) ← Nearest3DPointOnMesh(MeshSet[i],P hand ) 5: if (D i ≤ D minB ) then 6:
if (D i ≤ D minA ) then 7:

(MeshId B , P closestB ) ← (MeshId A , P closestA ) 8:

(MeshId A , P closestA ) ← (i,P i ) 9: else 10:

(MeshId B , P closestB ) ← (i,P i ) 11:

end if 12:

end if 13: end for Output: MeshId A , MeshId B , P closestA , P closestB hand onto attractive points distributed on Cartesian axis. As a visual proxy comes close to the attractive point, the amount of the force becomes higher. Yamada et al. [START_REF] Yamada | Desk-sized immersive workplace using force feedback grid interface[END_REF] explain this force concept as "This is analogous to the force by which a piece of iron would be attracted to a magnet.". I extended this magnet metaphor from homogeneous Cartesian grids to arbitrary axis in 3D space. This force feedback attracts the user's hand onto the surface of the nearest sub-part mesh during the shape edition to hold the user's hand steady and to guide the hand toward neighbor meshes. The attractive point on the surface (P closestA ) is acquired from the distance computation process (Alg. 1). Then, the amount of magnetic force F m (Fig. 5.5) is computed as:

F m =    F max * d min d min ∈]0, ] (F max -F min ) * D-d min D- + F min d min ∈ [ , D[ (5.1)
The distance D is the half distance between the two closest shapes:

D = || ---------→ P closestB P closestA ||/2 (5.2)
F max is the maximum force value, and F min is the continuous force applied on the user's hand independently of his position. The force is modulated by the velocity of the user's hand with dumper model in order to avoid the vibrations nearby p closestA .

F d = -b * d dx d min (b > 0) (5.3)
b is a viscosity coefficient used for force feedback stabilization. Thus, the force feedback norm F is defined as:

F = F m + F d (5.4)

system architecture

The ShapeGuide technique lies on the VR-CAD system composed of VR-CAD Server, VH Server-Visuo-Haptic Server-, and VR Platform).

The distributed architecture (Fig.

Data flow of ShapeGuide

When a user selects a sub-part of the original shape in a virtual environment, the system runs following processes until the user validates the modification.

Step 3 and 4 are iterative processes while the user switches meshes computed based on the user's selection information.

1 . Part selection: VR Platform finds constraint Id related with the selected sub-part using a linkage file. After the constraint selection, it transmits selection information (part Id and constraint Id) with a list of N shapes and parameter step size ∆p from the current parameter value p 0 to VR-CAD Server.

2 . Shape computation: VR-CAD Server computes and generates several meshes of the selected sub-part based on the given parameter set. All generated meshes are saved to the Shared data server.

3'. Physics computation: VH Server imports the sub-part meshes from the Shared data server to compute the nearest distance between the meshes from the user's hand position. The computed distance is used for haptic rendering, and the closest mesh Id is transmitted to VR Platform to switch the current visualized mesh at each frame.

4'. Update visualization:

VR Platform loads the full meshes from the Shared data server, and display only the closest mesh from the user's hand in the virtual environment during modifications.

. Validation:

Once the modification is finished, VR Platform transmits a chosen parameter value to VR-CAD Server. VR-CAD Server exports an updated linkage file onto Shared data server and VR Platform.

experiment

In order to assess the efficiency of ShapeGuide on a CAD deformation task, I conducted a controlled experiment in the CAVE system (Fig. 5.7) to compare it with a scroll technique, named Scroll. I also wanted to assess the effect of force feedback that could enable participants to "touch" the different parameter values during the modification on both interaction techniques. The Scroll technique allowed participants to manipulate a parameter value of the CAD object by scrolling their arm onto a horizontal axis. The parameter value increased with the arm motion towards the right, and vice versa. The direction of Scroll was static, which means that it did not rely on the direction of the shape deformation; therefore, the direction of Scroll may not be consistent with the shape in most cases. In this experiment, I limited the number of computation shapes to N shapes = 10, and parameter step size as ∆p = 10mm to avoid participant related variability regarding these settings and to focus on a fair comparison of the two interaction techniques. As an example, generating ten full meshes of Rear-view mirror takes between 1.5 to 2.0 seconds, which was acceptable loading time for participants according to our pilot test.

Consequently, I chose the real space range of the scroll to allow users to reach any of the ten available alternative parameters values from a one hand motion (0.5m). The step in that range (real size of 5cm), equally distributed on the horizontal axis, allowed to easily perform parameter value modification with stable force feedback from the gathered results of a pilot test. Also, I provided visual feedback displaying the corresponding modified shape during the manipulation. For stability purposes, the user's hand was snapped onto the scroll axis using attractive force feedback.

From assumptions based on the related works and some first pilot tests, I formulate the following hypotheses: H1: participants achieve the deformation task faster with ShapeGuide than with Scroll, H2: participants are more likely to start the deformation in the correct direction with ShapeGuide than with Scroll because of the consistency of the gesture with the deformation direction, H3: participants prefer ShapeGuide to Scroll, H4: the magnetic force feedback helps participants to reach the desired parameter values with more precision, especially with ShapeGuide.

CAD Part

Four parts of the Rear-view mirror (Fig. 4.6) were used for the deformation task: LeftBottomCorner, RightBottomCorner, Bottom and RightSide (Fig. 5.8). In Scroll condition, shape evolution was consistent with user's hand motion in RightSide and LeftBottomCorner: right-hand motion led to shape deformation towards the right for both parts.

On the contrary, it was inconsistent in RightBottomCorner and Bottom: right-hand motion led to shape deformation towards the left for the RightBottomCorner and towards the bottom for the Bottom. I chose these four parts (two consistent ones and two inconsistent ones) to analyze how consistency between the interaction and the deformed shape effects on the modification task. Moreover, I applied scale factor of three on the virtual scene to suit to the experimental VR setup. After scaling, the real-world perceived width of the Rear-view mirror was 75cm, and the distance between two sub-part meshes computed by ShapeGuide was from 0.5cm for the corners up to 6cm for the side parts. Consequently, I chose two corners to investigate precision issues, and two side parts to assess the efficiency of both techniques since the distance between consecutive shapes with ShapeGuide was similar to the Scroll step size.

Method

The experiment had a [2x2x4] within-subject design with the three following factors:

• Technique, with two levels: ShapeGuide and Scroll.

• Feedback, with two levels: NoForce for which the magnetic force feedback is not available, and Force for which the magnetic force feedback is available.

• Part, with four levels: the four deformable parts of Rear-view mirror (LeftBottomCorner, RightBottomCorner, Bottom and Right-Side).

The techniques used in each Technique×Feedback condition can be described as follow:

• Scroll, NoForce: the CAD part is modified with a horizontal scroll of users' hand.

• Scroll, Force: in addition to Scroll, the magnetic force feedback attracts the users' hand to some attractive points distributed on the horizontal axis. Users can thus feel each discrete parameter value.

• ShapeGuide, NoForce: the CAD part is modified in the direction of users' gesture according to the ShapeGuide algorithm.

• ShapeGuide, Force: in addition to ShapeGuide, the magnetic force feedback attracts the users' hand to the closest shape proposed by the ShapeGuide algorithm. Users can thus feel each possible shape corresponding to a specific parameter value.

Technique and Feedback are the two main factors, and trials are grouped by Technique×Feedback. The order of Technique×Feedback was counterbalanced across participants using a balanced Latin Square; the order of Part was counterbalanced for each Technique× Feedback.

Participants

I recruited 16 participants, aged between 20 and 63 (11 men and 5 women). Only one person was left-handed. 11 participants had experience of VR system (mostly head-mounted display or CAVE system), and 9 out of 11 participants had used a haptic device before. 2 participants use 3D modeling software on a daily basis (Blender R , SketchUp R and CATIA V5 R ), 2 on a weekly basis (3DS Max R ), 2 on a yearly basis (SolidWorks R , Maya R and 123D Design R ) and 10 almost never.

Ethics approval

An ethics approval was not required at the time the research was conducted as per our Institution's guidelines and national regulations. However, participants were recruited and treated in accordance with the principles outlined in the Declaration of Helsinki. All participants signed consent forms that details: purpose and procedures, risks and benefits, voluntary participation (they were free to discontinue their participation at any time, without providing a reason and without penalty) and data confidentiality. All collected data were anonymized.

Deformation task

I asked participants to perform a deformation task of the Rear-view mirror. A virtual representation of a Virtuose handle was displayed in the virtual environment (Fig. 5.9). This virtual handle was co-localized with an actual handle of Scale1 in the CAVE system. This virtual handle was used as an interaction pointer allowing the users to interact with the Rear-view mirror.

The deformation scenario was composed of the following steps:

• Selection of a part: the participants could select the part by pressing a button on the handle while the virtual handle was colliding on the surface.

• Modification: after selection, the scenario automatically switched to modification mode. The participants could start switching between possible shapes by their hand motion after some waiting time for the shape computation. Once they reached the desired 3D shape, they could validate the deformation by pressing the same button once again.

For each trial, participants had to deform the Rear-view mirror to fit a target shape, i.e., from an initial parameter value to a targeted parameter value. Only this part of Rear-view mirror was modifiable at each trial, colored with Orange (Fig. 5.9). The targeted shape was displayed with a transparent yellow color (Fig. 5 failed to deform the shape with the correct targeted parameter value, they had to select the same part and attempt to deform the shape again. We counted this as an error. Once participants achieved the task, the next targeted shape appears. The participants were instructed to accomplish the task as fast as possible.

.8). If participants

Procedure

Participants were welcomed and given paper instructions on how to perform the deformation task. They walked then inside of the CAVE system, followed by an instructor who explained them how to operate Scale1.

For each Technique×Feedback condition, the participants first performed a training phase before the experimental test. The training phase was composed of two steps:

• Interaction training: the participants could deform a part of the Rear-view mirror as many time as they wanted to learn the interaction technique.

• Task training: the participants accomplished deformation tasks for each one of the 4 Parts of the Rear-view mirror to learn the deformation task.

In the experimental test, the participants performed 16 trials: Four repetitions for each one of the Four Parts of the Rear-view mirror. For each repetition, the initial and targeted parameter values were different. I controlled the offset between the initial and targeted parameter values to have the deformation in both directions and to have comparable parameter modifications for each Part. The order of the different offsets was chosen in a random order among -40, -30, +30 and +40. The same initial and targeted parameter values were used for each Technique×Feedback condition and presented to participants in a random order to avoid learning effect between conditions.

The participants were encouraged to take a break after each block of trials corresponding to a Technique×Feedback condition. At the end of the experiment, the participants filled out a questionnaire. The whole experiment lasted around 40 minutes including the time to fill out the questionnaire.

Data Collection

I registered 1024 trials: 2 Techniques × 2 Feedbacks × 4 Parts × 4 repetitions × 16 participants. For each trial, I logged the time, the evolution of the parameter value and the number of attempts to complete the task. From this data, I extracted four different measures:

• Task Completion Time (TCT): the TCT measured the total duration of the modification step during the deformation task. The measure started when the participants selected the part to deform and when all possible shapes were loaded. It stopped when participants validated the deformation with the correct parameter value. If the participants made some errors, the TCT aggregated the time of the different attempts to reach the correct parameter value. The selection step was not considered since it was similar to all the conditions.

• Wrong Direction Starts (WDS): I considered that the participants started their motion in the wrong direction if they started by deforming the part in the opposite direction to the targeted parameter/shape. The WDS rate was computed according to the total number of attempts required to achieve the task. For example, if a participant made one error and if the motion of the first attempt were in the correct direction, while the motion of the second was in the wrong direction, the WDS rate would be of 0.5 for this trial.

• Overshoots: an overshoot was counted when the participants reached the targeted parameter/shape, but continued their gesture further away to a higher or smaller parameter value. Several overshoots can be accumulated during one attempt. Consequently, the number of Overshoots is the mean value of overshoots over all the attempts of the same trial. For example, if a participant made one error and if she did 2 overshoots on the first attempt and 3 on the second, the number of Overshoots would be of 2.5 for this trial.

• Errors: the number of Errors was computed from the number of wrong parameter/shape selections in a trial (i.e., number of attempts minus 1).

Finally, the questionnaire assessed the participant preferences. It was designed based on the NASA Task Load Index (TLX) [START_REF] Hart | Development of NASA-TLX (Task Load Index): Results of Empirical and Theoretical Research[END_REF]. Effort was replaced by the Difficulty to achieve the task, and Time pressure was not asked. I included one extra factor: Consistency (i.e., Did you find the interaction technique consistent with the shape deformation?). Consequently, the factors of the questionnaire were Mental Demand, Physical Demand, Difficulty, Frustration Experienced, Consistency and Performance Level. Participants had to grade each factor using a 5-point Likert scales, and they could also give open-ended comments.

results

Task Completion Time

To minimize noise in our data, I averaged the TCT of the 4 repetitions for each Technique×Feedback×Part condition. We tested TCT for normality on the whole aggregated data set using a Shapiro-Wilk W test1 and found that it was not normally distributed2 . I tested for goodness-of-fit with a log-normal distribution using Kolmogorov's D test, which showed a non-significant result. Therefore, I ran the analyses using the log-transform of TCT, as recommended by Robertson & Kaptein [START_REF] Robertson | Modern Statistical Methods for HCI[END_REF](p. 316). In addition, I did not find any significant learning effects due to technique presentation order.

I ran an analysis of variance on TCT with the model Technique× Feedback×Part×Rand (PARTICIPANT) with a REsidual Maximum Likelihood (REML) analysis. The result of the full factorial analysis revealed significant effects of Technique (F 1,225 = 394.20, p < 0.0001) and Part (F 3,225 = 8.90, p < 0.0001), but no significant effect of Feedback, as well as no significant interaction effects between factors. For Technique, a Student's t-test showed that ShapeGuide (avg. 2.41s) was significantly faster than Scroll (avg. 4.14s, p < 0.0001) (Fig. 5.10, left3 ). For Part, a post-hoc Tukey HSD test indicated that the task was significantly longer to achieve for the RightBottomCorner (avg. 3.64s) than for the RightSide (avg. 2.94s, p < 0.0001) and the Bottom (avg. 3.18s, p = 0.0017). It was also significantly longer for the LeftBottomCorner (avg. 3.34s) in comparison to the RightSide (avg. 2.94s, p = 0.0112).

To check if the consistency between the gesture and the shape deformation had an impact on TCT, I also analyzed the data by grouping parts which produced a consistent and an inconsistent deformation motion according to the gesture direction with the Scroll technique.

Rightside and LeftBottomCorner were considered as consistent, RightBot-tomCorner and Bottom as inconsistent. I thus ran a REML analysis on TCT with the model Technique×Feedback×Consistency×Rand (PARTICIPANT) with Consistency as a factor with two levels: Consistent and Inconsistent. I observed the same main effects than in the previous analysis, but I detected an additional interaction effect of Technique×Consistency (F 1,233 = 4.36, p = 0.038) (Fig. 5.10, right). A post-hoc Tukey HSD test indicated that the task was significantly longer to achieve with Scroll on Inconsistent parts (avg. 4.42s) than with Scroll on Consistent parts (avg. 3.86s, p = 0.0328). Both Scroll conditions were also significantly longer than both ShapeGuide conditions (p's < 0, 0001).

Wrong Direction Starts

In conformity with the nature of such count data, the WDS rate did not follow either normal or log-normal distribution. Consequently, I computed the mean WDS rates of each participant by levels for each factor and I used non-parametric tests to compare these values. For Technique, a Wilcoxon Signed Rank test showed that ShapeGuide led to significantly fewer WDS (7% of WDS) than Scroll (35% of WDS, p < 0.0001) (Fig. 5.11, left). For Feedback, a Wilcoxon Signed Rank test did not reveal any significant differences. For Part, a Friedman test was conducted and rendered a Chi-square value of 31.38 which was significant (p < 0.0001). A post-hoc analysis detected that the RightBottomCorner induced significantly more WDS (45% of WDS) than the RightSide (8% of WDS, p < 0.0001), the LeftBottomCorner (13% of WDS, p < 0.0001) and the Bottom (19% of WDS, p = 0.0266).

In addition, I used the Aligned Rank Transform (ART) procedure proposed by Wobbrock et al. [START_REF] Wobbrock | The Aligned Rank Transform for Nonparametric Factorial Analyses Using Only Anova Procedures[END_REF] to analyze the data and have hints of the interaction effects between factors. Data were aligned with the ARTool, and I ran a REML analysis on WDS rate with the model Technique×Feedback×Part×Rand (PARTICIPANT). It confirmed the main effects described previously and detected an interaction effect of Technique×Part (F 3,225 = 40.23, p < 0.0001) (Fig. 5.11, right). A post-hoc analysis revealed that Scroll on the RightBottomCorner led to significantly more WDS than all the other combinations (p's < 0, 0001). It showed that Scroll on the Bottom induced significantly less WDS than Scroll+RightBottomCorner, but significantly more WDS than all the other combinations (p's < 0, 04).

Overshoots

A similar analysis to the one for WDS rate was conducted for Overshoots. For Technique, a Wilcoxon Signed Rank test showed that ShapeGuide led to significantly more Overshoots (avg. 0.54) than Scroll (avg. 0.23, p < 0.0001) (Fig. 5.12, left). However, for Feedback, a Wilcoxon Signed Rank test revealed that Force significantly reduced the number of Overshoots (avg. 0.33) in comparison to NoForce (avg. 0.45, p = 0.0240) (Fig. 5.12, right). For Part, a Friedman test was conducted and rendered a Chi-square value of 14.71 which was significant (p = 0.0021). A post-hoc analysis detected that the RightSide induced significantly less Overshoots (avg. 0.26) than the RightBottomCorner (avg. 0.52, p = 0.0023) and the LeftBottomCorner (avg. 0.45, p = 0.0189).

I also ran a REML analysis on Overshoots with the model Tech-nique×Feedback×Part×Rand (PARTICIPANT) after that the data was aligned with the ART procedure. It confirmed the main effects described previously and detected an interaction effect of Technique× Feedback (F 1,225 = 4.01, p = 0.047) (Fig. 5.13, left) and an interaction effect of Technique×Part (F 3,225 = 36.60, p < 0.0001) (Fig. 5.13, right). For Technique×Feedback, ShapeGuide with Force seemed to significantly reduce the number of Overshoots (avg. 0.47) in comparison to ShapeGuide with NoForce (avg. 0.62, p = 0.0103). ShapeGuide with and without force was also significantly different from both Scroll combinations (p's < 0, 002). For Technique×Part, ShapeGuide on both the RightBottomCorner and the LeftBottomCorner led to significantly more Overshoots than all the other combinations (p's < 0.0015). Scroll+Bottom was also significantly difference from Scroll+RightBottomCorner and Scroll+LeftBottomCorner (p's < 0.03).

Errors

I used the same method than for WDS and overshoots to analyze the number of Errors, but I did not observe any significant differences for Technique, Feedback and Part.

Subjective questionnaire

In the questionnaire, participants had to grade each one of the four Technique×Feedback combinations on a 5-point Likert scale. To avoid confusion for participants, I phrased the questions so that they always had to give a good grade if they appreciated the interaction technique for all the criteria. Consequently, I asked them if they found the interaction technique not mentally demanding, not physically demanding, not difficult to use, not frustrating and consistent with the deformation of the shape (from 1: strongly disagree to 5: strongly agree). They also had to give an overall evaluation (from 1: bad to 5: good). Fig. 5.14 illustrates the results of the subjective questionnaire.

To analyze the data, I computed the mean grades of each participant by levels for Technique and Feedback. I used a non-parametric Wilcoxon Signed Rank test to compare each level. For Technique, ShapeGuide was perceived less mentally demanding (avg. 4.28 vs. 3.16, p = 0.0046), less frustrating (avg. 4.56 vs. 3.44, p = 0.0098), less difficult to use (avg. 4.28 vs. 3.56, p = 0.0093) and more consistent (avg. 4.5 vs. 2.88, p = 0.0005) than Scroll. In general, ShapeGuide was also preferred by the participants in comparison to Scroll (avg. 4.28 vs. 3.06, p = 0.0040). For Feedback, Force was considered more physically demanding in comparison to NoForce (avg. 3.06 vs. 3.62, p = 0.0293).

discussion

The results of the experiment provide evidence that ShapeGuide technique significantly increases user performance on parametric modification of CAD data in comparison to a one-dimensional scroll technique used as a baseline. More precisely, participants were able to achieve the deformation task 42% faster with ShapeGuide than with the Scroll technique, which supports H1. This improvement can be explained by a better consistency between shape deformation and user hand motion with ShapeGuide. In particular, I observed that ShapeGuide reduced of 80% the chance that participants move their hands towards the wrong direction at the beginning of their gesture, in comparison to Scroll. This is especially true on parts which produce an inconsistent deformation motion according to the gesture direction (RightBottomCorner and Bottom): Scroll on the inconsistent parts led to significantly more wrong direction starts than on the other parts. This has a certain impact on performance since the task with Scroll took longer on Inconsistent parts than on Consistent parts. Conversely, I did not observe any similar effects with ShapeGuide: the WDS rate was more consistent between parts (Fig. 5.11, right), and there was no time difference between Inconsistent and Consistent parts. This is beneficial for users because they can thus expect the same behavior in every part. The subjective questionnaire also confirmed that the participants perceived ShapeGuide as more consistent that the Scroll technique. For all these reasons, H2 is validated.

In the subjective questionnaire, most of the participants reported that they preferred ShapeGuide to the Scroll, which supports H3. In particular, they found ShapeGuide less mentally demanding, less frustrating and less difficult to use. This can be explained by the better consistency of ShapeGuide: users have to think less about the direction towards which they need to move their hand, and they can more easily predict what will be the result of their actions. The efficiency of ShapeGuide has probably also a positive impact on the user preference.

The main limitation of ShapeGuide is that it significantly increases the number of overshoots in comparison to the Scroll technique. I observed this phenomenon mainly on the corner of the Rear-view mirror: ShapeGuide on both the RightBottomCorner and LeftBottomCorner led to significantly more Overshoots than ShapeGuide on the two other parts and than Scroll on any parts (Fig. 5.13, right). However, ShapeGuide on the RightSide and Bottom was not significantly different from the Scroll on any parts. The distance between consecutive shapes proposed by ShapeGuide is smaller for the corner than for the other parts. Consequently, a possible explanation for the higher number of Overshoots is that it is harder to reach the desired shape with ShapeGuide when this distance is small: users are more likely to encounter unwanted switches between the targeted shape and the next one if the gap between these consecutive shapes is small. On the contrary, the distance between two consecutive parameter values on the scroll axis is always the same for the Scroll technique. This distance is especially defined to avoid unwanted switches; therefore Overshoots have less chance to occur with the Scroll technique less than ShapeGuide (see section 5.5.1).

The introduction of scale management into ShapeGuide may significantly reduce Overshoots. To implement such function, the scale value should be computed to guarantee that the minimal distance between available shapes fits human hand motion precision capabilities.

With respect to this issue about Overshoots, the results show that magnetic force feedback can be a effective solution to reduce the number of Overshoots and thus, improves the precision of both techniques, and especially ShapeGuide. During the experiment, participants achieved the deformation task with 27% fewer Overshoots with the magnetic force feedback than without, which supports H4. Force feedback also led to a reduction of 24% Overshoots for ShapeGuide, while the reduction was no significant for the Scroll technique. Finally, it seems that the magnetic force feedback has a small drawback: participants perceived both techniques more physically demanding with the magnetic force feedback than without.

In this experiment, I did not let users to choose the number of shapes N shapes , neither the parameter step size ∆p nor the target constraint related to his sub-part selection. Indeed, these features are necessary for designers to reshape the model precisely and to address the complex CAD model containing parameters defined by multiple constraints. The VR-CAD system can easily support these features by providing a user interface for the parameter tuning although the user interaction on that interface have to be carefully designed to consider the usability. Those feature limitations in the experiment eliminated any biases on comparison of the two interaction techniques for the shape modification task as the task completion time should not be affected by these parameter tuning. A user modifies the shape of Rear-view mirror within a realistic virtual environment of a car's cockpit while perceiving modification impact from a first person perspective in real time.

As a VR scene configuration, I chose to use a simple visual context (Fig. 5.7) to let the users focus on experimental tasks. But, the VR-CAD system supports real-time context switching during the VR session. It would be useful for project members to experience the product considering different contexts specified in PLM, such as end user-oriented environment 4 (Fig. 5.15), manufacturing lines, maintenance scenario, external observer. As several experts are involved in immersive product reviews, these environments could facilitate their arguments based on the mutual experience to support their design choices.

In comparison to the work by Coffey et al. [START_REF] Coffey | Design by Dragging: An Interface for Creative Forward and Inverse Design with Simulation Ensembles[END_REF], the VR-CAD system can provide users a extensible 3D workspace and support a run-time computation for sampling possible shapes before each modification, instead of pre-processing all the data beforehand.

conclusion

I described in this chapter:

• ShapeGuide: I presented a shape-based interaction technique for parameter modifications of CAD data. The method of Shape-Guide is based on a generation of design alternatives. Those alternatives are superposed in 3D space, and only the nearest shape to users' hand is displayed. With ShapeGuide, users can modify the CAD model with pulling/pushing its surface,

• Force feedback assistance: to assist user's hand gesture in 3D space, force feedback is given during the shape deformation. The force feedback attracts users hand on to the nearest surface of design alternatives,

• Controlled experiment: I compared the effect of ShapeGuide with Scroll interaction for CAD data deformation task. Scroll is a traditional interaction technique to manipulate parameter values as used in cRea-VR. The effect of force feedback was also investigated. The experiment demonstrated that ShapeGuide is faster, and more preferred by participants than the Scroll technique for a deformation task. Force feedback assistance did not show significant difference.

• Limitation: the experiment also showed that ShapeGuide could be less precise in selecting the desired shape when the gap between consecutive shapes is tiny. I am currently exploring solutions to solve this problem. A work in progress extends the 3D based distance computation approach (see Alg. 1) by taking into account the orientation of the users' hand regarding a pseudo-normal vector at the closest point on the surface. Furthermore, I plan to scale the scene according to the detected distance between sub-part meshes on shape computation.

This chapter presented one way of showing design alternatives in 3D environment, and how users can generate and interact with them. With ShapeGuide, project members do not have to go back to workstations to update the digital mockup. Instead, anyone in project members can simply touch and drag the surface of the digital mockup to assess different designs within immersive environment. This would be especially useful for ergonomists who wants to check usabilities of the product considering the surrounding environment.

In next chapter, I introduce another example of the use of design alternatives in a Wall-sized display.

publication

PA R A M E T R I C D E S I G N D I S C U S S I O N W I T H A WA L L -S I Z E D D I S P L AY

The ability to display and interact with large-scale representations of vehicles has always been a fundamental requirement of the automotive design industry.

-Bill Buxton [START_REF] Buxton | Large displays in automotive design[END_REF] A wall-sized display is a powerful tool to enable multiple users to collaborate and work in groups with large datasets. I take advantage of such large interactive space to enhance design review processes by showing collaborators multiple design alternatives to facilitate discussions. This chapter presents ShapeCompare, an interaction and visualization technique that users can generate and compare multiple design alternatives on a wall-size display. I detail the usability study which aimed to assess and improve this technique. I also present user studies which investigate how ShapeCompare can foster collaboration among various experts and encourage design explorations. Lastly, I will describe design recommendations for other types of alternative exploration with a wall-sized display.

introduction

As illustrated in Chapter 3, the goal of this thesis is to merge design discussion and CAD data adjustment step in order to enable various experts to discuss, modify and validate a design of the industrial product. In Chapter 5, I explored the review scenario within 3D environment, where users can review and modify the CAD model in an immersive and realistic environment. Such system might be interesting for ergonomists who need spatial perceptions to assess the usability of the product. However, the 3D environment would limit a number of users and time for review meetings. For example, with a CAVE system, only a few users could have proper adaptive views, and stereoscopic renderings may induce their eye fatigues and cybersickness. This would be an obstacle for a multi-user context.

In 2000s, Buxton et al. [START_REF] Buxton | Sketching user experiences: getting the design right and the right design[END_REF] introduced a Portfolio Wall (Fig. 2.27a) that serves as a traditional wall-mounted corkboard where multiple users can throw ideas and compare between each design concept on a large space. Wall-sized displays [START_REF] Beaudouin-Lafon | Multisurface Interaction in the WILD Room[END_REF] are promising in such a context because they offer new ways to collaborate and interact with large data sets. Previous work demonstrated their benefits over traditional desktop displays for a co-located collaboration, as several people can simultaneously interact with information [START_REF] Ball | Move to Improve: Promoting Physical Navigation to Increase User Performance with Large Displays[END_REF][START_REF] Mikkel | Up Close and Personal: Collaborative Work on a High-Resolution Multitouch Wall Display[END_REF][START_REF] Liu | Shared Interaction on a Wall-Sized Display in a Data Manipulation Task[END_REF].

I investigate how wall-sized displays can improve the review process in industrial design. In particular, this chapter presents ShapeCompare, which allows users to generate and distribute multiple alternatives of CAD data on a wall-sized display using touch interaction. ShapeCompare enables non-CAD experts to modify native CAD data by directly retrieving multiple design alternatives from the linked CAD engine. Users are thus able to explicitly express their design ideas and compare the proposed alternatives. To assess the benefit of wall-sized displays for collaborative design tasks, I ran a controlled experiment that compared ShapeCompare with a visualization technique suitable for standard screens. It evaluates whether comparing many design alternatives on a wall-sized display is more beneficial than exploring them one by one, as it can be done on a standard screen.

In this chapter, I firstly examine how wall-sized displays foster collaboration on complex data sets. I then detail the design of ShapeCompare based on the feedback from a usability study. Lastly, I describe the controlled experiment, discuss the results, and present design recommendations that generalize the use of a wall-sized display to other types of alternative exploration in various contexts.

wall-sized displays

The benefits of wall-sized displays have been demonstrated on various tasks. Ball et al. [START_REF] Ball | Move to Improve: Promoting Physical Navigation to Increase User Performance with Large Displays[END_REF] showed that users' physical navigation induced by a large display improves performance on navigation, search and pattern finding (Fig. 6.1a). Ball and North found that peripheral vision offered by wall-sized displays contributed to task performance [5]. The large amount of data displayed improves task efficiency and accuracy [START_REF] Yost | Beyond Visual Acuity: The Perceptual Scalability of Information Visualizations for Large Displays[END_REF]. Larger screens provide better performance on complex and cognitively loaded tasks [START_REF] Czerwinski | Toward Characterizing the Productivity Benefits of Very Large Displays[END_REF][START_REF] Liu | Effects of Display Size and Navigation Type on a Classification Task[END_REF] (Fig. 6.1b), and enhance peripheral application awareness [START_REF] Bi | Comparing Usage of a Large High-resolution Display to Single or Dual Desktop Displays for Daily Work[END_REF] compared to workstations. Wall-sized displays also enhance collaboration among co-located users. Previous studies investigated how user interaction affected collaboration [START_REF] Dostal | SpiderEyes: Designing Attention-and Proximityaware Collaborative Interfaces for Wall-sized Displays[END_REF][START_REF] Langner | Multiple Coordinated Views at Large Displays for Multiple Users: Empirical Findings on User Behavior, Movements, and Distances[END_REF] (Fig. 6.1c) for data analysis tasks. Liu et al. [START_REF] Liu | Shared Interaction on a Wall-Sized Display in a Data Manipulation Task[END_REF] compared various collaboration strategies on a wall-sized display. They also showed that cooperative interaction improves close and loose collaboration [START_REF] Liu | CoReach: Cooperative Gestures for Data Manipulation on Wall-sized Displays[END_REF].

Since wall-sized displays are powerful tools for displaying and interacting with large data sets, they can allow visualizing multiple alternatives by creating "small multiple" representations of an object. For example, Beaudouin-Lafon [START_REF] Beaudouin-Lafon | Lessons Learned from the WILD Room, a Multisurface Interactive Environment[END_REF] proposed to distribute a large number of brain scans on the screen (Fig. 6.2). This enables neuroscientists to compare and classify this brain scan according to specific brain fold patterns. For industrial design reviews, the "small multiple" approach can be valuable for exploring and comparing design alternatives.

While some previous works on VR-CAD explored CAD data modifications for non-experts, they focused on the deformation of one particular CAD model and did not consider the generation of multiple design alternatives. Other works investigated reviews of static design alternatives, but they did not allow users to modify these alternatives or to generate new ones. As wall-sized displays are efficient to show multiple variations of a same object and to foster collaboration, they could be an ideal tool for design discussions where a multidisciplinary team can review, compare, and also generate design alternatives without using a conventional CAD system.

design of shapecompare

To assess the benefit of a wall-sized display for collaborative exploration of design alternatives, I firstly designed a system allowing non-CAD experts to modify native CAD data and distribute alternatives on the screen. I created ShapeCompare by using an iterative design process involving potential users. The prototypes and the usability study used during this process are described in this section.

First prototype

The first prototype was designed to meet three criteria: i) interaction in a large space, ii) native CAD data modification and iii) multipledesign comparison. Based on the technical framework developed for native CAD data modification (Chapter 4), I implemented a service that generates multiple alternative shapes by varying parameter values of a native CAD model. This service communicates with a front-end application running on a wall-sized display (WILDER, Fig. 3.9). This application, handling user interaction, shape distribution, clustering rendering and network communication, is implemented with Unity.

User Interaction

Various interaction techniques have been studied on a wall-sized display: such as pen-device interaction [START_REF] Forlines | Hy-bridPointing: Fluid Switching Between Absolute and Relative Pointing with a Direct Input Device[END_REF] (Fig. 6.3a), distant interaction by finger-pointing [START_REF] Vogel | Distant Freehand Pointing and Clicking on Very Large, High Resolution Displays[END_REF] (Fig. 6.3b) or using handheld device and head orientation [START_REF] Nancel | High-precision Pointing on Large Wall Displays Using Small Handheld Devices[END_REF] (Fig. 6.3c). However, as the interaction technique in itself is not the main focus of this study, I decided to simply use direct touch to interact with the CAD data displayed on the screens. If the part can be modified, it turns green. Each part is tied to an internal parameter defined in the native CAD data. The system then prepares a set of parameter values for the selected part and asks for the corresponding shapes. In this first prototype, I defined a minimum and maximum parameter value for each part and chose a predefined number of values equally distributed in the range. As CAD models are defined by multiple geometric constraints, the CAD engine cannot always perform the modification for the full range of values. If a shape is not successfully generated, a "cross" is displayed to inform users of the failure. shape visualization: The set of newly generated shapes is displayed on a full row of the screen, above previous versions of the CAD model. In this manner, each row represents a set of design alternatives for a specific part of the CAD model. WILDER consists of 75 tiled screens (15 columns and 5 rows), and each shape is displayed at each tiled screen to make use of borders shown by bezels. Consequently, 15 shapes are displayed at each shape generation at maximum.

design history: Users thus accumulate design history below the current design alternatives and can navigate with a three-finger interaction to scroll up or down the design alternatives (Fig. 6.4). Users can select a part of any shape in the design history and start over modification from this shape.

3d rotation: To interact with 3D objects, I implemented the In(SITE) technique [START_REF] Louvet | Combining Bimanual Interaction and Teleportation for 3D Manipulation on Multitouch Wall-sized Displays[END_REF] (Fig. 6.5). It allows users to perform 3D rotation on a wall-sized display with bimanual touch interaction. The rotation of displayed alternatives is synchronized to maintain a similar view angle for all of them. While the In(SITE) technique can also manipulate translation of a 3D model (xy and z translation in Fig. 6.5), I did not implement them.

usability study

To assess the usability of the interaction technique proposed in the first prototype, I invited potential users to test it and observed their behaviors while achieving an individual CAD modification task. After the task, I had short individual debriefings and a brainstorming session with all of them (Fig. 6.6).

Participants

The 5 participants (1 female), aged 21 to 24 (mean 22.8), are students at the civil engineering department. 4 rated their expertise level of CAD system as 2 out of 5, and 1 rated as 1 (1: Never used before -5: Use almost every day). All students have experience in AutoCAD1 to read construction plans and design. Although they are not CAD experts, they provided us relevant feedback as they are knowledgeable about parametric modeling and design process.

Task

I asked each participant to modify a CAD object with ShapeCompare to reach a given target shape within a time limit of 5 minutes. The CAD object is a rear-view mirror (Fig. 4.6) designed by an industrial designer at PSA. An external screen next to the wall-sized display was used to display a design alternative of the mirror within an automotive cockpit. Participants could display a particular alternative on this external screen by selecting it on the wall-sized display with a twofinger long-press. The target shape was shown with a transparent yellow color overlaying the design alternative on the external screen (Fig. 6.7). This simulated the fact that participants have design skills to evaluate the design alternatives in a realistic environment.

To investigate if the interaction technique used for CAD modification was straightforward, I did not provide any CAD parameter-related information (e.g. geometric constraints of the sketch, linkage between each parameter and displayed shape) to the participants. I just explained to them that the mirror is a parametric CAD model designed with a commercial CAD system, and what are the actions to modify it.

Results

As a result, all participants could not reach the target shape (Fig. 6.8) within the given time limit. P1 reached the same width of the target mirror, but the height and radius did not match. Based on the interviews and observations of participant behaviors, I extracted the main issues they encountered. First, all participants mentioned that it was difficult and frustrating to figure out how the part selection affects the shape deformation. P2 explained, "I didn't know the link between the parameter map and shapes. Without this information, I was afraid to modify the shape wrongly". Most participants expected that each "length" of the selected part would change. For example, P3 said, "I was surprised when I selected the right side. I expected that it would get higher, but it got wider instead. I had to adjust my mind after each system response". The links between parts and parameters are defined by the CAD data, and each parameter is mapped to the part that constrains the parameter. For example, when the right-side part is selected, it changes the parameter that constrains the width (Fig. 4.6). They were also confused by symmetry constraints in the mirror. The left width parameter is symmetric to the right side-the mirror width changes to both sides with the modification of the right-side parameter, which also surprised them after the shape selection.

Second, all participants often needed time to find out how the generated shapes on the new row are different from the one they selected. P3 detailed, "I expected that the same shape would appear just above the selected shape, but it didn't. I was surprised at this behavior. I had to take a step behind to look for the exact same shape" in the new row. In fact, as the parameter values used for generating shapes are always distributed between a static minimum and maximum, the initial shape in the range of variations is not displayed above the previously selected shape, but at a random position.

Aside from these critical issues, participants often had difficulties in finding the difference also between neighbor shapes, especially on radii of corners, top and bottom parts. Some of them claimed that the difference of 4 shapes on a row was not noticeable. They needed to step back from the screen and check the smallest and the largest shapes (leftmost and rightmost ones) to grasp the global difference of the shapes on the row. P2 commented, "I was looking at the first and the last shapes of the list to understand the modification. Then looked in the middle to find the one I want".

Despite the above issues, I had positive reactions of all participants. Although it was difficult for them to understand the shape modification, they liked the simple interaction which does not require to understand and manipulate parameter values. In particular, they found it useful for novices. P5-rated own CAD expertise level as minimum-said, "I found that it is very difficult in AutoCAD to find parameter values, remember the parameter information and how it affects the shape modification, but this app made it much easier", "I like this app that I can modify a design by myself. I want to design by myself, not by other people". They also appreciated the proposed shape visualization: "Seeing many different designs on the wall-sized display, comparing them, and visualizing them within the realistic context was nice to generate new ideas" (P1). As a common ground, all of them agreed that ShapeCompare cannot be a substitute for traditional CAD software due to the limited functionalities, but it is valuable for a design adjustment task which does not require to change the whole design intent.

Updated prototype

Based on the usability study results, I identified two main issues in the first prototype with respect to: (i) Understanding of shape modification and (ii) Visualization of design history. I addressed these issues as described in the following.

Understanding of shape modification

To solve this issue, I drew inspiration from the Suggestive Interface proposed by Igarashi [START_REF] Igarashi | A Suggestive Interface for 3D Drawing[END_REF] (Fig. 6.10). This interface offers small thumbnails presenting results of geometric operations and encourages novice users to explore a new system and find unknown operations. I decided to compute and displayed a preview of the minimum and maximum shape modification for each part. As participants often checked the smallest and the largest shapes to understand the current modification during the usability study, these extreme shapes would have a similar effect and give a hint to the users before selecting the modifica-Figure 6.9: Selection widget, users can select a thumbnail of the two extreme shapes to generate the corresponding design alternatives.

tion. In the updated prototype, when users select a shape, a selection widget appears and displays thumbnails of the two extreme shape modifications for all parameters of each part (Fig. 6.12, (2)). Users can then select a thumbnail to generate the corresponding design alternatives. They no longer have to touch the parts directly, which prevents problems of selecting a small part.

Visualization of design history

To improve the shape visualization, I changed how the system generates design alternatives to ensure that I have the same number of design alternatives with lower and higher parameter values compared to the selected one. Instead of defining a static minimum and maximum for the parameter values, I defined a specific offset for each part.

The system thus generates half of the shapes with lower parameter values by incrementally decreasing by the offset the parameter of the selected shape, and conversely for the other half with higher parameter values. Consequently, the selected shape always appears in the middle of the alternative range, and not at a random position as in the first prototype. I then explored solutions to display each row of new design alternatives. I first showed a similar shape just above the selected one (Fig. 6.11, top) in order to meet the expectation of the participant of the usability study. However, it creates unused screen space and requires an additional interaction for horizontal scrolling. For these reasons, I shifted the new alternatives to the center of the screen to always fit them in. This solution displays all the selected shapes always in the central column (Fig. 6.11, bottom), which is beneficial for keeping track of the modification history. I highlighted the selected shapes with a green color and the central column with different saturation.

Figure 6.11: Two solutions for visualizing the design history: the similar shape appears just above the selected shape (top), or the similar shape always appears in the central column (bottom).

experiment

I conducted a controlled experiment to assess the benefit of a wallsized display in the context of collaborative design reviews. In particular, I investigated how simultaneous visualization of multiple design alternatives affects the collaboration between participants. I compared ShapeCompare to another technique called ShapeSlide, which displays only one shape at a time (Fig. 6.12). With ShapeSlide, users can change the shape displayed at the center of the wall-sized display with a sliding gesture on the screen. Although ShapeSlide is suitable for a standard screen, I implemented it on the wall-sized display to avoid bias which could be introduced by the devices, user positions, or interaction techniques. Consequently, I used the same device (i.e. the wall-sized display) for both conditions. Only a small portion of the wall-sized display was used for ShapeSlide, simulating the use of a smaller screen. This reduces bias that could be introduced by different devices or standing-sitting positions. It also simplifies the experiment since participants did not have to change devices. In addition, I decided to use the exact same widget and interaction technique for selecting the part to modify on the CAD model for both conditions (Fig. 6.12). Only the way to browse the generated design alternatives differs in the two conditions: users had to walk in front of the wall-sized display with ShapeCompare, while they had to use a sliding gesture with ShapeSlide. Finally, to fairly compare the conditions, I provided the same functionalities in both cases. In particular, I imitated the design history of ShapeCompare by implementing an "Undo" button in ShapeSlide, which allows users to go back to the set of design alternatives that were previously generated. Selection Widget helps users to select a CAD parameter by displaying shapes corresponding to parameter extrema (2). Then users can explore design alternatives using ShapeCompare or ShapeSlide.

Task

I designed the experimental task based on actual industrial practices collected through interviews with engineers at PSA (Chapter 3). The task was to modify a car rear-view mirror and simulate expert negotiation on several design criteria (Fig. 6.13). Since it was difficult to find and invite real experts involved in an actual industrial design process, I controlled users' expertise by giving individual design criteria to pairs of participants. I simulated two distinct expert: Specialist 1 who focuses on general shape properties of the mirror, and Specialist 2 who focuses on reflections from the mirror face.

Specialist 1 had to consider two criteria (Fig. 6.14):

• Aspect ratio: Aspect ratio (A) is the balance between the height H and the width W of the mirror such as A = H/W.

• Asymmetric balance: Asymmetric balance (B) is the balance between either left-and-right (B LR ) or top-and-bottom (B TB ). One of the two asymmetric balances was chosen for the tasks. In both cases, the asymmetric balance was defined from the four corner radii: left-top (LT R ), left-bottom (LB R ), right-top (RT R ) and right-bottom (RB R ). Specialist 2 had to consider two criteria (Fig. 6.14):

B LR = |LT R -RT R | + |LB R -RB R | (6.1) B TB = |LT R -LB R | + |RT R -RB R | (6.2)
• Rear visibility: participants had to follow a given guideline that specifies which objects should or should not be visible in the reflective part of the mirror.

• Surface size: Surface size (C) is the geometric area of the reflective surface of the mirror (computed in cm 2 ).

These criteria are good representatives of design challenges for each role. The Aspect ratio and the Asymmetric balance represent criteria used by designers to influence the overall appearance, whereas the Rear visibility and the Surface size are important factors for ergonomists to assess user experience. For A, B and C, participants had to reach a value within a given range. To help them, the current value of each criterion was displayed with different colors next to each design alternative: red for A, yellow for B and blue for C (Fig. 6.14).

To ensure a proper counterbalancing and avoid bias, I designed two tasks which resulted in different mirror shapes (Small and Large). I verified through pilot tests that they had similar difficulty and contradictory criteria which require pairs to find a trade-off. The criterion values are A: 2.0 -2.3, B: > 50 (top-and-bottom), C: 110 -140 for Small, and A: 3.1 -3.5, B: > 55 (left-and-right), C: 200 -230 for Large.

Once participants agreed on a design, they saved it with a double tap gesture. They were instructed to finish the task as quickly as possible. I encouraged pairs to communicate together, but strongly forbade them to tell their own design criteria. For example, Specialist 1 was not allowed to say "Aspect ratio" or "Asymmetric balance" to express requirements. Instead, they could use shape-related vocabularies: e.g. "I want to make the mirror higher/wider/smaller/curvier/etc.".

Hypothesis

I formulated hypotheses based on the usability study and previous work about collaboration on wall-sized displays:

• H1: participants find the right design faster with ShapeCompare than with ShapeSlide;

• H2: participants find the right design with fewer iterations with ShapeCompare than ShapeSlide;

• H3: participants prefer ShapeCompare for communicating with their partner;

• H4: overall, participants prefer ShapeCompare to achieve the task.

Method

The experiment is a [2×2] within-participant design with the following factors:

• Visualization with the two techniques: ShapeCompare and ShapeSlide;

• Task with two set of design criteria resulting in different target shapes: Small and Large.

I first counterbalanced the order of the two Visualization conditions among pairs, then for each condition, I switched the Task. To allow all participants to do the two Tasks with both Visualization conditions, but to avoid them remembering the task, I ran the experiment in two sessions separated from two to three weeks. For example, if participants did Small with ShapeCompare and Large with ShapeSlide in the 1st session, they did Small with ShapeSlide and Large with ShapeCompare in the 2nd session. Participant roles remained constant across the two sessions.

Participants

I recruited 24 participants, aged 20 to 32 (mean 25.4), with normal or corrected-to-normal vision. Pairs were formed at the time of recruitment leading to 6 male-male, 4 female-male and 2 female-female. 6 participants had previous experience with AutoCAD, 4 with Solid-Works, 2 with CATIA, 3 with other CAD systems, and 9 had with no experience.

Procedure

For each session, participants received written instructions. They filled out demographic questionnaires. They sat in distant places in a room and received design criteria for Specialist 1 or Specialist 2. They could ask questions to the instructor without being heard by the partner.

At the beginning of the experiment, each participant had a dedicated training to understand the given design criteria. For example, the instructor asked Specialist 1 to modify the mirror and reach a specific Aspect ratio with two different sizes. During this training, the partner waited in a different room. For each Visualization condition, pairs also performed a common training to learn the interaction, followed by a measured trial. They filled out a questionnaire after each trial. Whole sessions lasted about 60 minutes including the time to fill out the questionnaires.

Data Collection

I registered 48 trials: 2 Visualization×2 Task×12 pairs. I logged the Task Completion Time (TCT) and the number of selections (Selections). For TCT, the instructor gave the starting signal and measurement stopped when pairs agreed on a design or after 30 minutes. Selections correspond to the number of iterations performed by the participants during the task. I also recorded video. The questionnaire was designed based on the NASA TLX [START_REF] Hart | Development of NASA-TLX (Task Load Index): Results of Empirical and Theoretical Research[END_REF], Effort was replaced by the Difficulty to achieve the task, and Time pressure was not asked. I also added three questions regarding their communication during the task: "How difficult was it for you to explain your design intention to your partner?", "Was the communication with your partner frustrating?" and "Did the interaction technique help you to communicate with your partner?". Participants graded each factor using a 5-point Likert scales or open-ended comments.

Data Analysis

I analyzed the video recording to investigate communication and the use of speech and gestures. I first transcribed participants' discussions. Based on the transcripts, I ignored the utterances which were not relevant to the task and grouped their design-related conversation into 5 categories:

• Deictic instructions: participants used deictic gestures to show something on the screen to the partner. This category has two subgroups:

-Deictic-specific: participants indicated a specific shape (e.g. "I want to modify the mirror like this"). Most of the time, they used a pointing gesture.

-Deictic-range: participants indicated a range of shapes (e.g. "...from this shape to this one, it is OK").

• Design expression: participants expressed ideas either verbally or with gestures (excluding deictic gestures). This category has two subgroups:

-Expression-verbal: participants used shape-related vocabularies (e.g. "...wider, more curved, etc.").

-Expression-gesture: participants described the desired shape with hand or finger motions.

• Magnitude: participants quantified the size of the modification they wanted (e.g. "much more..." or "a bit less...").

6.6 results

TCT

I tested TCT for normality on the whole data set using a Shapiro-Wilk W test and found that it was not normally distributed2 . I tested for goodness-of-fit with a log-normal distribution using Kolmogorov's D-test, which showed a non-significant result. Therefore, I ran the analysis using the log-transform of p = 0.033) and Task (F 1,47 = 4.66, p = 0.036) but no significant interaction effect. Pairs achieved the task faster with ShapeCompare (6.04±1.76 min) than with ShapeSlide (7.83±1.59 min) (p = 0.0333) (Fig. 6.15, left). Large (5.95±1.49 min) was faster than Small (7.91±1.91 min) (p = 0.0364) (Fig. 6.15, right).

Number of Selections

In conformity with count data, Selections did not follow normal or log-normal distribution. Consequently, I computed the mean Selections of each participant by levels for each factor and I used non-parametric tests. For Visualization, a Wilcoxon Signed Rank test did not reveal any significant differences (p = 0.78)(Fig. 6.16, left). For Task, a Wilcoxon Signed Rank test showed (p = 0.009) that Large (6.13±1.66) led to fewer Selections than Small (8.19±1.66) (Fig. 6.16, right).

Conversation analysis

I analyzed the communications between participants during the design exploration tasks. 2591 sentences were tagged for all trials (Fig. ShapeCompare (39.4% for Deictic-Specific, 10.22% for Deictic-Range) than with ShapeSlide (28.77% for Deictic-Specific, 0.27% for Deictic-Range). On the contrary, they used less Shape-related expression and Magnitude with ShapeCompare (33.17% for Expression-Verbal, 5.99% for Expression-Gesture and 11.22% for Magnitude) than with ShapeSlide (42.74% for Expression-Verbal, 10.42% for Expression-Gesture and 17.8% for Magnitude).

Qualitative Feedback

In questionnaires, participants graded each Visualization on a 5point Likert scale. To avoid confusion, I phrased the questions so that they always had to give a high grade if they appreciated the condition. I asked them if they found the condition efficient, not mentally demanding, not physically demanding, not difficult to use, not frustrating and helpful for communication (1: strongly disagree, 5: strongly agree). They also gave an overall evaluation (1: bad, 5: good) for the technique itself and the communication with their partner.

I computed the mean grades of each participant and used a nonparametric Wilcoxon Signed Rank test (Fig. 6.18). ShapeCompare was perceived more helpful for communication (avg. 3.96 vs. 3.13, p = 0.00014) and preferred in general (avg. 4.08 vs. 3.25, p = 0.014) and for the communication (avg. 4.25 vs. 3.375, p = 0.004) in comparison to ShapeSlide. I did not find significant differences for the other criteria.

SC SS

discussion

ShapeCompare enables non-CAD experts to easily generate multiple design alternatives of native CAD data. Unlike the conventional design process, all project members can participate in design adjustment tasks (Fig. 6. [START_REF] Xiang 'anthony' Chen | Forte: User-Driven Generative Design[END_REF]). This new capability is complex to evaluate since no comparable systems exist. However, I can draw inspiration from some evaluation criteria proposed by Olsen [START_REF] Olsen | Evaluating User Interface System Research[END_REF] to verify the contribution of this system: "Expressive Match"-users can interact with the final shapes of the CAD object instead of a 2D sketch and a parameter tree as in a CAD software, and "Empowers new design participants"-non-CAD experts can achieve design adjustments which are currently done by CAD engineers in the industrial design process. ShapeCompare also takes advantage of a wall-sized display to distribute design alternatives across the screen space. To assess the benefit of this visualization technique for collaborative design tasks, I examine the results from the controlled experiment with respect to initial hypotheses.

• TCT shows that participants found the right design significantly faster with ShapeCompare than with ShapeSlide. This supports H1.

• Selection indicates that there was no significant difference in a number of iterations between ShapeCompare and ShapeSlide. H2 is not supported.

• From the questionnaires, ShapeCompare was perceived more helpful for communicating with the partner than ShapeSlide. This supports H3.

• From the questionnaires, ShapeCompare was generally preferred. This supports H4.

The smaller TCT and better communication with ShapeCompare could be explained by the large number of Deictic instructions used by participants. During the task, the multiple alternatives of ShapeCompare were often used as references for communication: participants used the displayed shapes to convey their design idea (e.g. "I want a mirror like this"), to show limitations (e.g. "only shapes between this and this one") or to ask for partner opinion (e.g. "what do you think about this one?"). Whereas with ShapeSlide, they needed to describe their requirements verbally (e.g. "I want this mirror flatter and curvier on right bottom corner") or with their hand gestures. The words related to Magnitude were also more used with ShapeSlide when they instructed their partner acting on a modification (e.g. "Can you increase it more?"). With the multiple design alternatives of ShapeCompare, participants were probing partners' design requirements and increasing common grounds through their discussions. According to Clark [START_REF] Herbert H Clark | Grounding in communication[END_REF], communication costs can be minimized by generating common grounds, which can explain the smaller TCT.

The same iteration numbers in both Visualization could be due to the task design and the fact that these iterations may be necessary to reach the right design. In addition, I made two different sets of design criteria (Small and Large). Even if I tried to make these criteria as equivalent as possible, it seems that Large was easier than Small. I was concerned that displaying lots of alternatives with ShapeCompare could increase the cognitive load. However, I did not find significant difference in the NASA TLX, which suggests ShapeCompare do not overload participants.

Although most participants preferred ShapeCompare for the ease of communication, some others prefer ShapeSlide in terms of interaction: e.g. "ShapeSlide is interesting because it allows to have instant feedback and to cycle through all possible design while swiping". It seems that these users prefer to have more initiatives on the design activity, instead of dealing with solutions given by the system.

ShapeCompare is a first prototype, but additional functionalities would be required to allow the user to feel more in control of the alternative generation. In particular, it would be important that users can define the minimum, maximum and step size of the generated alternatives. This would allow them to achieve fine or coarse modifications. Moreover, with the current implementation, the generation of new alternatives can take up to 5 seconds. A solution to improve this could be to use several CAD servers to parallelize the computation of 3D meshes.

Finally, I believe that the proposed system can be extended to any CAD objects as long as they require collaboration among multidisciplinary experts. For large objects, the number of displayed alternatives or the scaling could be adjusted.

design recommendations

While I studied alternative exploration in a specific context, the approach of visualizing "small multiples" on a wall-sized display could be extended to other contexts as soon as parameter variations are involved. For example, it can be suitable for generative design (see Section 3.2.1) in which users can specify preferred designs to the AI, or physical simulations such as weather predictions in which users can run several simulations with different parameter variations. Based on the observations of the usability study and the results of the controlled experiment, I draw some generic recommendations which can be applied to other contexts:

• A large number of alternatives can be displayed on the wall-sized display without overloading the users.

• Allowing users to generate/compare alternatives can help them to solve constraints and reach a trade-off.

• Users need to understand the effect of all possible modifications before generating new alternatives to facilitate exploration. One option could be to display previews of the most extreme modifications.

• Users need to keep track of the design history and the link between each alternative selection to understand the design evolution.

• The difference between side-by-side alternatives should be big enough to be perceived by users. An automatic solution to tune parameter steps can be valuable.

conclusion

I described in this chapter:

• ShapeCompare: I presented a system which enables users to generate and distribute design alternatives of a CAD model on a wall-sized display. ShapeCompare relies on "small multiple" representations of a CAD object to allow multidisciplinary teams to collaboratively explore, compare alternatives and reflect their ideas on a wall-sized display,

• Usability study: I invited civil engineering students to assess the usability of the interaction technique proposed in the first prototype. Based on the study, I identified and addressed two main issues in the first prototype with respect to: (i) Understanding of shape modification and (ii) Visualization of design history,

• Controlled experiment: I investigated how simultaneous visualization of multiple design alternatives affects the collaboration among experts during a constraint-solving task. I compared ShapeCompare with another technique named ShapeSlide which shows only one design alternative at a time, but enable users to quickly switch the displayed alternative. ShapeSlide could be used on any standard screens since it does not require a large screen space. The results showed that participants reach a consensus respecting the design constraints significantly faster with ShapeCompare than with ShapeSlide. I also found that participants used more deictic instructions and less verbal or gesture-based design expressions with ShapeCompare than with ShapeSlide. It suggests that the multiple alternative visualization helps collaborators during design exploration and negotiation by increasing the common grounds among them,

• Limitation: There are still many limitations in ShapeCompare.

-Computation time: the time for the generation of design alternatives could be costly depending on the shape complexity. This computation can be minimized using several VR-CAD Server in parallel.

-Multi-user interactions: multiple users cannot interact with the generated object at same time. To let each user explore the design individually would produce diverse designs, and it helps mutual understandings between them.

-Parameter tunings: currently, the parameter offset between each design alternative is static. Users could adjust this parameter according to their needs for precision. Like generative design, it would be valuable for users to request designs with high-level vocabularies.

The current technique, ShapeCompare, is still a research prototype. There is a lot of space to explore and improve the way to visualized alternatives and interact with them. However, to our knowledge, it is the first study to demonstrate the benefit of the "small multiple" concept on a wall-sized display.

The highlighted finding from this study suggests that multiple design alternatives would help bridge the gaps in communicationsespecially between distinct experts who do not have common vocabularies. The proposed approach would facilitate discussions in the new industrial design reviews described in this dissertation.

C O N C L U S I O N A N D F U T U R E P E R S P E C T I V E S

This dissertation addresses a new approach for industrial design reviews. Design review is an essential process to comprehensively evaluate industrial products at an early design stage. Various experts and project managers assess the end-user satisfaction, aesthetic property, and engineering feasibility with prototypes. Traditionally those prototypes are physical models created with clays by stylists. Over the years, since the CAD software was invented in the 1960s, most of the physical models have been replaced by digital models, which led to drastically reduce the cost and time for manufacturing the prototypes.

Today, digital platforms for design review are increasingly becoming large interactive systems rather than workstations. Various types of such systems are used to satisfy the particular expert needs. For example, ergonomists or engineers conduct usability tests or assembly simulations in VR systems which offer an immersive 3D environment. Whereas, executives, project members, and stylists evaluate the user satisfaction and design concept in large interactive displays where they can discuss and compare design alternatives collaboratively.

These advances for design reviews have enriched reviewing practices. However, the design reviews could still take time because of the back-and-forth between the workstation-where CAD engineers modify the design with CAD interface-and the large interactive systemwhere multiple experts discuss the design. Although the users can change the viewpoint, manipulate the design, or put annotations within the large interactive system, current systems used in the industry do not support any modifications of the CAD data.

In this thesis, I argued that the current two steps of this iterative process-design modification and design discussion-should be merged. It will reduce the number of iterations, which would lead to shorten the time and facilitate the discussion among a multi-disciplinary team. I believe that the ideal design review environment would be the collaborative workspace, wherein any experts can directly apply design adjustments on the displayed CAD data within the heterogeneous interactive system. Also, as experts can be geographically spread in today's globalized world, the review meetings should also support collaboration between remote interactive systems.

contribution

To understand the current design review process, I started this PhD work by discussing industrial design practices with research engineers from an automotive company (Chapter 3). They use several interactive platforms for simulating car designs and later manufacturing processes. For example, various experts compare several design alternatives of A-pillars within a realistic environment using a CAVE system. Those design alternatives are prepared by CAD engineers before the meeting and updated afterward. Based on these practices, I envisioned a scenario in which project members can directly generate a set of design alternatives and compare them during the design reviews. For the design platforms, I focused on the two different types of interactive systems mostly used for collaborative design reviews: the CAVE and the wall-sized display.

To implement prototypes of the pictured scenario, I first designed a technical framework which supports direct design modifications of native CAD data, heterogeneous interactive systems, and collaboration between remote locations (Chapter 4). I developed a VR-CAD Server, which manages the interaction with native CAD data based on a previous work named cRea-VR. The VR-CAD Server transmits several design alternatives according to specific requests from users and is embedded in the distributed network architecture to support heterogenous interactive systems and multi-user interactions. A proof of concept is implemented between a CAVE and a wall-sized display.

One of the challenges of direct design modification is to enable non-CAD experts to achieve parametric data modification. I designed ShapeGuide, a shape-based interaction technique which allows users to explore several design alternatives with directly dragging the 3D surface of the CAD model (Chapter 5). ShapeGuide help users to modify the native CAD data without interacting with the CAD interface. A controlled experiment shows that ShapeGuide is significantly faster and preferred by users than a traditional parameter modification technique in the CAVE system. With the example of a real Rear-view mirror from industry, I demonstrated the value of the proposed technique in a review scenario, in which project members can check the reflected scene in the mirror from different angles while modifying the design at run-time.

With the wall-sized display, I studied different approaches to generate and visualize design alternatives which take advantage of the large display area. I designed ShapeCompare, a technique allowing users to generate and distribute a set of design alternatives on the screen with touch interactions (Chapter 6). I assessed this prototype during a brainstorming session with civil engineering students. Based on the improved prototype, I ran a controlled experiment to investigate how simultaneous visualizations of multiple design alternatives affect discussion and communication across experts. The results show that ShapeCompare is significantly faster than a single shape visualization to reach a consensus considering several design constraints. I also found that participants often used deictic instructions and less verbal or gesture-based design expressions with ShapeCompare.

The technical contribution of this dissertation is a set of interaction techniques based on design alternative generation, which can be adapted to specific design review platforms. The empirical findings showed that these techniques allowed users to modify digital mockups without any expertise in CAD and facilitated the communication among experts. In agreement with the current trends of industry which aimed to unify distinct steps during design process, this solution would increase collaborative work opportunities in design reviews.

enhancements and future work

Of course, the solutions investigated in this PhD have some limitations. While a previous work on VR-CAD integration enabled native CAD data modification, current proof-of-concept of cRea-VR can manage only specific CAD parts. Since this PhD work steps on the cRea-VR implementation, I had to use a Rear-view mirror throughout my whole thesis. However, various kinds of CAD data which are defined by multiple operators (e.g. extrusion, torus, boolean operations) should be tested. In addition, the proposed VR-CAD integration approach could be applied to other CAD systems, such as SolidWorks and Inventor, instead of CATIA V5.

One drawback of design alternative generation is the computation time. This approach assures fast system responsiveness during manipulation of the alternatives, but users have to wait for the generation at the beginning. This computation time depends on the complexity of CAD data and the number of alternatives. To decrease the computation time, I am currently working on parallel processing of CAD data by using multiple VR-CAD Servers. These VR-CAD servers communicate with a Job handler, which distributes the computation requested among each VR-CAD server. Any number of VR-CAD servers can be registered on the Job handler with a configuration file. This approach can significantly reduce the computation time.

In the proposed interaction techniques, the parameter set used for the design alternative generation should be adjusted to users' requirements. Currently, ShapeGuide allows users to set the number of alternatives and the step-size between them before the generation, but ShapeCompare does not provide any controls of these parameters to users. The users should be able to tune the parameters to compare the shapes both coarsely and precisely. Presumably, users should be able to specify these parameters with high-level input (e.g. "rough" or "precise") instead of explicit parameter tunings, since they have no knowledge of the parameters defining the CAD data.

The proposed techniques could be interesting for Generative design. The concept of Generative design is to encourage engineers to think more like stylists, and stylists to think more like engineers. With this goal, the computer helps users explore design solutions by proposing design alternatives based on give criteria. Distributing the design alternatives on large interactive systems makes this process more interactive and collaborative. This dissertation illustrates a collaborative design review scenario between remote locations. While the proposed system architecture makes such a scenario possible, it needs to be implemented and tested through user studies. With the use of ShapeGuide and ShapeCompare, remote users working within a 3D environment or a large format display can compare design alternatives generated from both platforms. They could work on either different or same parameter constraints in the CAD model. To do so, the VR-CAD Server should support concurrent data access. The simple way is to lock the access from specific users while the other is exploring the design alternatives. The more interesting way would be that multiple users can concurrently modify the object together. They could modify either the individual parameter or the same parameter of the CAD model. It allows users to form various types of collaboration, which would be especially valuable in a multidisciplinary or hierarchical collaboration context. Currently, a proof-of-concept is implemented between a wall-sized display with ShapeCompare and a HMD in which users can check the specific design in a 3D environment (Fig. 7.1). The further study on such collaborative CAD data modifications and also the awareness of remote users would enrich the design review experience.

In recent years, various options of visualization systems and interactive devices appear. It allows us to choose the system that satisfies our needs, instead of adapting ourselves to the available system. Therefore, designing a system for collaborative activities, particularly including several experts-like industrial design reviews-should consider to cover these heterogeneities for smooth communication and collaboration.

colophon

This document was typeset using the typographical look-and-feel classicthesis developed by André Miede and Ivo Pletikosić. The style was inspired by Robert Bringhurst's seminal book on typography "The Elements of Typographic Style". classicthesis is available for both L A T E X and L Y X: R ésum é : Les revues de design industriel b én éficient des nouvelles technologies interactives pour devenir plus r éalistes, immersives et collaboratives. Toutefois, la modification des donn ées de conception (CAO) est toujours effectu ées depuis un espace de travail traditionnel par des ing énieurs qualifi és. Des probl èmes de communication entre les diff érents experts peuvent apparaitre lors des r éunions de revue de projet et engendrer des erreurs d'interpr étation des modifications. J'estime que les processus actuels de r évision de la conception impliquant it érativement des discussions sur la conception et un ajustement des mod èles 3d devraient fusionner. Cela pourrait r éduire le nombre d'it érations de correction sur les mod èles durant le cycle de d éveloppement en facilitant les discussions et en permettant à des utilisateurs non sp écialistes CAO de modifier les donn ées. Dans cette th èse, j'ai commenc é par interviewer des ing énieurs de l'industrie et j'ai esquiss é un sc énario de revue de conception dans lequel tous les membres d'un m ême projet peuvent g én érer et comparer plusieurs alternatives de conception depuis des syst èmes interactifs adapt és pour r épondre aux besoins de leurs diff érents expertises. J'ai d'abord conc ¸u un syst ème de couplage entre un environnement interactif temps r éel et des donn ées de CAO (RV-CAO) capable de modifier et de mettre à jour au format CAO natif. J'ai ensuite propos é des techniques d'interaction pour permettre à des utilisateurs non experts en CAO de modifier les donn ées CAO param étriques en utili-sant des syst èmes depuis un syst ème CAVE et un mur d'image. Pour le syst ème CAVE, j'ai cr é é Sha-peGuide, une m étaphore d'interaction bas ée forme permettant aux utilisateurs de g én érer et de choisir parmi des alternatives de conception en agissant indirectement sur les valeurs des param ètres d'un mod èle CAO. J'ai étudi é comment ShapeGuide peut affecter la qualit é d'une t âche de modification de donn ées CAO par rapport à un r églage de valeur de param ètre bas ée sur un d éfilement unidimensionnel . Les r ésultats ont montr é que ShapeGuide permettait une modification plus rapide, plus efficace et pr éf ér ée par les utilisateurs. Pour l'interaction depuis un mur d'images, j'ai cr é é ShapeCompare, qui permet à plusieurs utilisateurs de g én érer et de comparer plusieurs alternatives de design. J'ai étudi é comment ShapeCompare affecte la collaboration entre experts par rapport à une technique de visualisation adapt ée aux écrans standard. Les r ésultats ont montr é qu'avec ShapeCompare, des paires de participants effectuaient plus rapidement une t âche de r ésolution de contraintes multiples et utilisaient plus d'instructions d éictiques. Les r ésultats pr ésent és d écrivent des propositions de nouvelles pratiques de r évision de conception, se basant sur l'utilisation d'interactions immersives et de murs d'images, qui permettent la modification directe des donn ées de conception d'origine par tous les membres du projet quelle que soit leur expertise en CAO.

Title : CAD Modification Techniques for Design Reviews on Heterogeneous Interactive Systems

Keywords : Virtual reality, Interactive surface, Collaborative interaction, Distributed architecture, Computeraided design Abstract : Industrial design reviews benefit from emerging interactive technologies to become more Realistic, Immersive and Collaborative. However, the modification of design data is still managed in traditional workspace-Computer-Aided Design (CAD) systems on a workstation. As only engineers can apply modifications in such a workspace after the design review meeting, miscommunication between various experts could occur, resulting in unnecessary iterations. I argue that current processes of design reviews-design discussion and design adjustmentshould merge. It could reduce the iterations, facilitate discussions and empower non-CAD experts to modify CAD data. In this dissertation, I started by interviewing engineers at an automotive industry and drew a new design review scenario in which project members can generate and compare several design alternatives in heterogeneous systems that can support needs from various experts. Based on the scenario, I firstly designed a VR-CAD system that can update the native format of CAD data in highly configurable interactive systems. I then explored interaction techniques for non-CAD experts to modify parametric CAD data with 3D and 2D interactive systems: a CAVE system and a wall-sized display. For the CAVE system, I created ShapeGuide, which allows users to generate and switch design alternatives of CAD data with a shape-based 3D interaction. I investigated how Sha-peGuide affects a CAD data modification task compared to a standard one-dimensional scroll for parameter manipulation. Results showed that ShapeGuide was faster, more efficient and preferred by the users than the scroll technique. For the wall-sized display, I created ShapeCompare, which allows users to generate and distribute multiple design alternatives of CAD data using touch interaction. I investigated how ShapeCompare affects the collaboration among experts compared to a visualization technique suitable for standard screens. Results showed that pairs of participants performed a constraint solving task faster and used more deictic instructions with Shape-Compare. The presented findings for new design review practices using immersive systems and a wallsized display, allowing direct modification of the original CAD data by all project members regardless of their CAD expertise.

Universit é Paris-Saclay

Espace Technologique / Immeuble Discovery Route de l'Orme aux Merisiers RD 128 / 91190 Saint-Aubin, France

Figure 3 . 2

 32 Figure 2.17Surface evaluation on virtual surface models (BMW)[START_REF] Weber | Automotive Development Processes[END_REF]. . . . . . . . . . . . . . . . . . . . . Figure 2.15 Example of various project reviews during product development: SGR (Specification Gate Review)-the requirement review, PGR (Preliminary Gate Review)-the preliminary design review, CGR (Critical Gate Review)-the detailed design review, FEI (First Equipment Inspection)the prototype review, and IQA (Initial Quality Approval)-the industrialization review [74]. . Figure 2.18 Sketchpad [110] (left) and Sword of damocles [112] (right), Ivan Sutherland. . . . . . . . . . . . . . Figure 2.19 Igarashi et al.'s Teddy [56]. . . . . . . . . . . . . Figure 2.20 Example of 3D drawing applications . . . . . . Figure 2.21 Digital tape drawing techniques . . . . . . . . Figure 2.22 Surface modeling applications . . . . . . . . . . Figure 2.23 Interface of CATIA V5. . . . . . . . . . . . . . . Figure 2.24 Definition of Boundary Representation (B-Rep) model. On the left (a), the complete solid object; in the middle (b), its representation in terms of topological surfaces; on the right (c), its representation in terms of edge and topological vertices. . . . . . . . . . . . . . . . . . . . . . . . Figure 2.25 Example of Constructive Solid Geometry (CSG) tree. The final solid object is actually the result of a subtraction between two objects: the first object, on the left, is the intersection between a sphere and a cube; the second solid, on the right is the result of the union of three cylinders. Figure 2.26 Immersive solid modeling . . . . . . . . . . . . Figure 2.27 Design reviews on large displays . . . . . . . . Figure 2.28 Design reviews on immersive systems . . . . . Figure 2.29 Collaborative design reviews between distant locations . . . . . . . . . . . . . . . . . . . . . . Figure 3.1 The use of VR during the design process at PSA. The figure is translated into English from the original one [88]. . . . . . . . . . . . . . . . . . Figure 3.2 CAVE system at PSA . . . . . . . . . . . . . . . . Figure 3.3 Collaborative product design meetings at each stage of an industrial design process. CEO: Chief Executive Officer, DIR: Director, STY: Stylist, ARC: Architect, CAD: CAD designer, ERG: Ergonomist. . . . . . . . . . . . . . . . . .

Figure 3 . 4

 34 Figure 3.4Forte is a 2D design tool that takes a userdriven approach of generative design:a user sketches a reading chair inspired by the painting 'The Great Wave off Kanagawa' (a) with specified loading scenario (red arrow forces, blue ground); Forte then generates structures (with real-time feedback) to support the loads while resembling the user's sketch (b), which can then be post-processed to create a 3D fabrication-ready model (cd).[START_REF] Xiang 'anthony' Chen | Forte: User-Driven Generative Design[END_REF] . . . . . . . . . . . Figure3.5 Dreamsketch: the user navigating through the resulting solutions by directly manipulating the bike handle (top). [62] . . . . . . . . . . . . . . Figure 3.6 Shape generator in Autodesk Inventor [19] . . . Figure 3.7 Virtuose 6D, Haption . . . . . . . . . . . . . . . . Figure 3.8 CAVE-like system, EVE. . . . . . . . . . . . . . . Figure 3.9 Wall-sized display, WILDER. . . . . . . . . . . . Figure 4.1 Various VR assembly simulations . . . . . . . . Figure 4.2 Example of VR-CAD systems with OpenCascade. Figure 4.3 Example of VR-CAD systems that store design histories (Constructive History Graph (CHG)). Toma et al.'s VR-CAD system (left) can create digital mockup based on Solidworks, whereas D 3 (right) can add mesh deformations on imported CAD model. Both systems do not support any modifications on design histories of imported CAD models. . . . . . . . . . . . . . . Figure 4.4 cRea-VR, a VR-CAD system that can modify parameters of native CAD part designed with CA-TIA V5 in an immersive environment. . . . . . Figure 4.5 System structure of cRea-VR. cRea-VR can be divided into four main components: Interaction engine, Visualization system, Inference engine and Encapsulation. [88] . . . . . . . . . . . . . . . . . Figure 4.6 Sketch of the Rear-view mirror, an example of industrial CAD part designed using CATIA V5 R . Green line is a guide curve of a sweep operation generating the 3D shape. Constraints and parameter values are highlighted in blue: for example, red constraint defines the distance to the bottom of the Rear-view mirror (60 mm). . . Figure 4.7 Interaction flow of cRea-VR [88] . . . . . . . . .

Figure 6 . 5

 65 Figure 6.4Interaction with ShapeCompare: when a part is selected (Selection), the system generates a set of design alternatives on a row of the wallsized display (Display). All alternatives can be scrolled up and down with a three-finger drag (Slide shapes), rotated in 3D with a widget (Rotation), and displayed on the external screen with a two finger long press (Update 2nd screen). Figure 6.5 Louvet et al.'s In(SITE), 6 Degree of Freedom (DoF) manipulation of a 3D object on a multitouch wall-sized display. The user is performing a xy translation (main picture), z translation (a), roll rotation (b), and pitch & yaw rotation (c). Figure 6.6Brainstorming session with participants. . . . . Figure6.7Usability study setup: the target shape is displayed with a transparent yellow color in a realistic environment on an external screen next to the wall-sized display. . . . . . . . . . . . . . Figure6.8The mirrors modified by each participant during the study. . . . . . . . . . . . . . . . . . . . Figure6.[START_REF] Berg | An Industry Case Study: Investigating Early Design Decision Making in Virtual Reality[END_REF] Igarashi et al's Suggestive Interface[START_REF] Igarashi | A Suggestive Interface for 3D Drawing[END_REF]. . . . . . Figure6.9Selection widget, users can select a thumbnail of the two extreme shapes to generate the corresponding design alternatives. . . . . . . . . . . Figure6.11Two solutions for visualizing the design history: the similar shape appears just above the selected shape (top), or the similar shape always appears in the central column (bottom). . Figure6.12 Interaction flows of two conditions: after shape selection (1), Selection Widget helps users to select a CAD parameter by displaying shapes corresponding to parameter extrema(2). Then users can explore design alternatives using Shape-Compare or ShapeSlide. . . . . . . . . . . . . . . . Figure6.13 Pairs of participants are exploring the design to find the one meeting their design criteria with ShapeCompare (top) and with ShapeSlide (bottom). Figure6.14 (Left) design criteria of Specialist 1 and Specialist 2. (Right) design criteria values displayed next the mirror. . . . . . . . . . . . . . . . . . . . . . Figure 6.15 Mean TCT by Visualization (left) and by Task (right). Error bars show 95% CI. . . . . . . . . . Figure 6.16 Mean Selections by Visualization (left) and by Task. Error bars show 95% CI. . . . . . . . . . . Figure 6.17 Tagged expression proportions by Visualization.

  2.3) [51].

Figure 2 . 2 :

 22 Figure 2.2: Nicolas Joseph Cugnot's Fardier à Vapeur in 1771[START_REF] Joseph | Fardier à Vapeur[END_REF]

Figure 2 . 3 :

 23 Figure 2.3: Karl Benz's motorwagon (Benz patent motor car) in 1885 [9].

Figure 2 . 4 :

 24 Figure 2.4: Ford Model T of 1913 (left). Early mass production of Ford's Highland Park plant in Detroit in 1914: the fuel tank assembly station (right) (Ford Motor Company Ltd.) [51].

Figure 2 . 5 :

 25 Figure 2.5: Application of the V-model to the product development (BMW). Left side of the V-model shows System design phase, and the right side shows System integration phase [119]. The System design phase is divided into Conceptual design and Detailed design.

Figure 2 . 6 :

 26 Figure 2.6: "Over the wall".The designer throws the designs over a wall to the manufacturing engineers who then have to deal with the various manufacturing problems[START_REF] Boothroyd | Product design for manufacture and assembly[END_REF].

2

 2

  .

7

 7

Figure 2 . 7 :

 27 Figure 2.7: Concurrent engineering as expressed by prime European region [106]. Each process is overlapped each other in comparison to traditional sequential process.

  (a) Explicit design process. (b) Collaborative design process.

Figure 2 . 8 :

 28 Figure 2.8: Traditional design process explicitly divided into three different processes (left). Proposed product development process (right) which various teams involve throughout the overall process [17].

Figure 2 .

 2 Figure 2.10: Translation of sketch into tape drawings [119].

Figure 2 .

 2 Figure 2.11: Manufacturing of 1:1 exterior clay models (BMW) [119].

Figure 2 . 12 :

 212 Figure 2.12: Informal selection of concept sketches. This session would involve a number of designers, the section leader and studio manager [115].

Figure 2 . 13 :

 213 Figure 2.13: Detailed virtual car (BMW) [119].

Figure 2 . 14 :

 214 Figure 2.14: During entire PLM, multiple experts work with one unique DMU [74].

Figure 2 . 16 :

 216 Figure 2.16: Example of interior review with a cray model and detailed illustrations [51].

Figure 2 . 15 :

 215 Figure 2.15: Example of various project reviews during product development: SGR (Specification Gate Review)-the requirement review, PGR (Preliminary Gate Review)-the preliminary design review, CGR (Critical Gate Review)-the detailed design review, FEI (First Equipment Inspection)-the prototype review, and IQA (Initial Quality Approval)-the industrialization review [74].

Figure 2 . 18 :

 218 Figure 2.18: Sketchpad [110] (left) and Sword of damocles [112] (right), Ivan Sutherland.

Figure 2 . 19 :

 219 Figure 2.19: Igarashi et al.'s Teddy [56].

Figure 2 . 20 :Figure 2 . 21 :

 220221 Figure 2.20: Example of 3D drawing applications

Figure 2 . 22 :

 222 Figure 2.22: Surface modeling applications

Figure 2 . 23 :

 223 Figure 2.23: Interface of CA-TIA V5.

Figure 2 . 24 :

 224 Figure 2.24: Definition of B-Rep model. On the left (a), the complete solid object; in the middle (b), its representation in terms of topological surfaces; on the right (c), its representation in terms of edge and topological vertices.

Figure 2 . 25 :

 225 Figure 2.25: Example of CSG tree. The final solid object is actually the result of a subtraction between two objects: the first object, on the left, is the intersection between a sphere and a cube; the second solid, on the right is the result of the union of three cylinders.

3 ]Figure 2 . 26 :

 3226 Figure 2.26: Immersive solid modeling

  (a) Buxton et al's Portfolio Wall [18] (b) Khan et al's Spotlight [64]

Figure 2 . 27 :

 227 Figure 2.27: Design reviews on large displays

  (a) Raposo et al's Environ[START_REF] Raposo | Environ: integrating VR and CAD in engineering projects[END_REF] (b) Berta et al's Immersive Workwall[START_REF] Berta | Integrating VR and CAD[END_REF] (c) Schilling et al's MEMPHIS[START_REF] Schilling | CAD-VR geometry and meta data synchronization for design review applications[END_REF]

Figure 2 . 28 :

 228 Figure 2.28: Design reviews on immersive systems

Figure 2 . 29 :

 229 Figure 2.29: Collaborative design reviews between distant locations

Figure 3 . 1 :

 31 Figure 3.1: The use of VR during the design process at PSA. The figure is translated into English from the original one [88].

Figure 3 . 2 :

 32 Figure 3.2: CAVE system at PSA

Figure 3 . 3 :

 33 Figure 3.3: Collaborative product design meetings at each stage of an industrial design process. CEO: Chief Executive Officer, DIR: Director, STY: Stylist, ARC: Architect, CAD: CAD designer, ERG: Ergonomist.

Figure 3 . 4 :Figure 3 . 5 :Figure 3 . 6 :

 343536 Figure 3.4: Forte is a 2D design tool that takes a user-driven approach of generative design:a user sketches a reading chair inspired by the painting 'The Great Wave off Kanagawa' (a) with specified loading scenario (red arrow forces, blue ground); Forte then generates structures (with real-time feedback) to support the loads while resembling the user's sketch (b), which can then be post-processed to create a 3D fabrication-ready model (cd). [19]

  3.8), namely EVE 1 , is composed of four back-projected stereoscopic screens: 4.8x2.7m (front & floor) and 2.7x2.7m (left & right). The resolution of each screen is 1.920x1.080 pixels. Applications run on a server that distributes the environment to four machines connected to each projector. Each machine is powered by a Intel Xeon CPU at 3.7 GHz and a Nvidia Quadro P6000 graphic card.

Figure 3 . 7 :Figure 3 . 8 :

 3738 Figure 3.7: Virtuose 6D, Haption

Figure 3 . 9 :

 39 Figure 3.9: Wall-sized display, WILDER.

  (a) Jayaram et al's VADE [60] (b) Mahdjoub et al's MAS (Multi-agent system) [85]

4. 2 . 2

 22 Parametric designHowever, even if those systems can load native CAD data, they do not support any parameter modifications of CAD part. As introduced in Chapter 2, many studies on 3D modelings in VR allow users to create and modify 3D models in immersive systems. Most of those systems use geometric kernels, such as ACIS 1[START_REF] Chu | Multisensory user interface for a virtual-reality-based computeraided design system[END_REF][START_REF] De Amicis | Parametric Interaction for CAD application in Virtual Reality Environment[END_REF][START_REF] Fiorentino | Spacedesign: a mixed reality workspace for aesthetic industrial design[END_REF][START_REF] Fiorentino | Smart tools for virtual reality based cad[END_REF][START_REF] Stork | Efficient and Precise Solid Modelling Using a 3D Input Device[END_REF] and OpenCascade 2 [45, 57, 120] (Fig.4.2), which do not have a direct link with commercial CAD systems used in industries. As such, users have to convert the model created during the VR session into STEP/IGES formats, which are CAD neutral files, to import it to CAD systems. This data conversion may increase the time for design process, moreover, most of the times this conversion process lose semantic information of CAD part: CHG-also called design history graph[START_REF] Vincent | Resolving Nonuniqueness in Design Feature Histories[END_REF][START_REF] Wu | A face based mechanism for naming, recording and retrieving topological entities[END_REF] or feature dependency graph[START_REF] Hoffmann | Erep: An Editable, High-level Representation for Geometric Design and Analysis[END_REF]-which stores all information about design his-(a) Weidich et al.'s AVALON VR system [120] (b) Foursa et al's TwoView [45]

Figure 4 . 2 :

 42 Figure 4.2: Example of VR-CAD systems with OpenCascade.

  (a) Toma et al.'s VR-CAD system in the CAVE [114] (b) Meyrueis et al's D 3 [91]

Figure 4 . 3 :

 43 Figure 4.3: Example of VR-CAD systems that store design histories (CHG). Toma et al.'s VR-CAD system (left) can create digital mockup based on Solidworks, whereas D 3 (right) can add mesh deformations on imported CAD model. Both systems do not support any modifications on design histories of imported CAD models.

4. 3 . 1

 31 System architecture cRea-VR made two main breakthrough in VR-CAD systems:

Figure 4 . 4 :

 44 Figure 4.4: cRea-VR, a VR-CAD system that can modify parameters of native CAD part designed with CATIA V5 in an immersive environment.

Figure 4 . 5 :

 45 Figure 4.5: System structure of cRea-VR. cRea-VR can be divided into four main components: Interaction engine, Visualization system, Inference engine and Encapsulation. [88]

Figure 4 . 6 :

 46 Figure 4.6: Sketch of the Rear-view mirror, an example of industrial CAD part designed using CATIA V5 R . Green line is a guide curve of a sweep operation generating the 3D shape. Constraints and parameter values are highlighted in blue: for example, red constraint defines the distance to the bottom of the Rear-view mirror (60 mm).

  (a) Initial CAD model, Rear-view mirror, designed with CATIA V5. (b) Exploration of CAD model. Users can check information of each part by pointing. Yellow rays is casted from users' handed device. (c) Shape selection and Target selection. Users first select the part to modify, then choose the target constraint (e.g. Distance or Radius.) (d) Parameter modification. Users can modify the selected parameter by horizontal scroll motion in the CAVE. The green dot line is the selected sketch and updated at real time. (e) Validation. Once the modification is validated. 3D shape is generated. (f) Updated CAD model. The original CAD data is updated without any data conversion.

Figure 4 . 7 :

 47 Figure 4.7: Interaction flow of cRea-VR [88]

Figure 4 . 8 :

 48 Figure 4.8: Data flow of the VR-CAD server. The VR-CAD Server generates meshes (.obj) and linkage information (.xml) based on the users' requests and transmit them to front-end applications running on interactive systems.

Figure 4 . 9 :

 49 Figure 4.9: Different types of network architecture[START_REF] Fleury | Architectures and Mechanisms to Maintain efficiently Consistency in Collaborative Virtual Environments[END_REF]

( a )

 a Shared centralized world (b) Homogeneous replicated world (c) Partially replicated world

Figure 4 . 10 :

 410 Figure 4.10: Different types of data distributions [42]. Blue lines: executions of object behaviors; red lines: object modifications; Green line (c): modification of an object through one of its proxies

Figure 4 . 11 :

 411 Figure 4.11: Distributed architecture for collaborative CAD data modifications between remote platforms.

Figure 4 . 12 :

 412 Figure 4.12: Distributed architecture of a proof of concept between WILDER(left) and CAVE (right). Remote users can collaboratively modify the Rear-view mirror without using classical desktop interface.

  (a) Gregory et al's inTouch [49] (b) Liu et al's Virtual DesignWorks [79, 80]

Figure 5 . 1 :

 51 Figure 5.1: Virtual painting (left) and surface deformation (right) using force feedback devices

4 . 6 )

 46 based on a linkage file (Fig. 4.8). Once the user selects the

Figure 5 . 2 :

 52 Figure 5.2: Computation of different shapes of Rear-view mirror: when users select the red distance constraint highlighted in Figure 4.6, full meshes are used to provide visual feedback to the users (only one mesh is visible at a time), and sub-part meshes are used for haptic rendering (the two closest meshes are used for force feedback computation).

Figure 5 . 3 :Algorithm 1

 531 Figure 5.3: Example of computed sub-part meshes of the right side part for 3D interaction. P hand is user's hand position. P i is a nearest point on each surface from P hand . Algorithm 1 Two Closest Sub-parts Selection Input: (MeshSet[], MeshSetSize, P hand ) Initialization 1: D minA ← Nearest3DPointOnMesh(MeshSet[0],P hand ) 2: D minB ← D minA LOOP Process 3: for i = 1 to MeshSetSize do 4:(P i , D i ) ← Nearest3DPointOnMesh(MeshSet[i],P hand ) 5: if (D i ≤ D minB ) then 6:if (D i ≤ D minA ) then 7:(MeshId B , P closestB ) ← (MeshId A , P closestA ) 8:(MeshId A , P closestA ) ← (i,P i ) 9: else 10:(MeshId B , P closestB ) ← (i,P i ) 11:end if 12:end if 13: end for Output: MeshId A , MeshId B , P closestA , P closestB

Figure 5 . 4 :

 54 Figure 5.4: Yamada et al's force feedback grid [125]. Grid points (center) or planes (right) attract user's hand during 3D modeling.

Figure 5 . 5 :

 55 Figure 5.5: Norm of the attractive force during modification of a shape. Red arrows describe user's hand position.

5 . 6 )

 56 manages VR simulation by peerto-peer connection among each process with centralized CAD data distribution. Each process runs on a different computer, communicating through TCP protocol. VR-CAD Server deploys required information to interact with the CAD data (meshes and linkage file) to VH Server and VR Platform using a Shared data server. VH Server, an acronym of a Visuo-Haptic Server, lies on two main parallel threads: physics and VRPN Client/Server. In the physics thread, the distance computation described in section 5.3.2 is managed between user's hand (i.e. haptic arm) position and the computed sub-part meshes loaded from Shared data server at each haptic frame. The physics thread also handles force feedback computation. VRPN Client/Server compounds visual proxy position with motion tracking data gathered from an external VRPN server, and broadcasts it to VR platform for visual rendering. VR Platform manages an immersive visual rendering and handles events during the VR simulation. When the rendering system is composed of a set of clusters, only graphic master node (master of synchronization node) handles communication with VH Server before deploying the meshes to graphic slaves.

Figure 5 . 6 :

 56 Figure 5.6: System architecture of VR-CAD system. Each process is connected through TCP protocol: meshes and linkage information of CAD data are distributed using Shared data server. Selected part information contains: sub-part Id, constraint Id and a set of parameter offsets. Generated mesh information includes: number of generated meshes and parameter values.

Figure 5 . 7 :

 57 Figure 5.7: Experimental set-up: EVE system (Fig. 3.8) and Scale1.

Figure 5 . 8 :

 58 Figure 5.8: Four examples of the experimental task: orange parts had to be modified to reach the yellow targets. (a) LeftBottomCorner, +40mm difference from initial radius. (b) RightBottomCorner, -30mm difference from initial radius. (c) Bottom, -40mm difference from initial length. (d) RightSide, +30mm difference from initial length.

Figure 5 . 9 :

 59 Figure 5.9: Haptic arm handle of Scale1 (left) and its visual proxy (right). 3Drepresentation of the virtual handle is co-located with the actual one in CAVE system.

Figure 5 . 10 :

 510 Figure 5.10: Mean TCT by Technique (left) and Technique×Consistency (right). Error bars show 95% the CI.

Figure 5 . 11 :

 511 Figure 5.11: WDS rates by Technique (left) and Technique×Part (right).

Figure 5 . 12 :

 512 Figure 5.12: Mean Overshoots by Technique (left) and Feedback (right).

Figure 5 . 13 :

 513 Figure 5.13: Mean Overshoots by Technique×Feedback (left) and Tech-nique×Part (right).

Figure 5 . 14 :

 514 Figure 5.14: Participant ratings by Technique×Feedback for not mentally demanding, not physically demanding, not difficult to use, not frustrating, consistent and overall evaluation on a 5-point Likert scale (5 is best, 1 is worst). N: NoForce and F: Force.

Figure 5 . 15 :

 515 Figure 5.15: Native CAD data modification in a user-oriented environment.A user modifies the shape of Rear-view mirror within a realistic virtual environment of a car's cockpit while perceiving modification impact from a first person perspective in real time.

  (a) Ball et al.'s study on effect of physical navigation on user performance [6]. (b) Liu et al.'s study on visual physical navigation vs. virtual navigation [78]. (c) Langner et al.'s multiuser application for multiple coordinated data [68].

Figure 6 . 1 :

 61 Figure 6.1: User studies and applications with wall-sized displays

Figure 6 . 2 :

 62 Figure 6.2: Distributed brain scan images on a wall-sized display and a physical model of the brain to control the orientation of the images [8].

  (a) Forlines et al.'s Hybrid-Pointing [44]. (b) Vogel et al.'s distant freehand interaction [116]. (c) Nancel et al.'s highprecision pointing using a handheld device [92].

Figure 6 . 3 :

 63 Figure 6.3: Study on interaction techniques on wall-sized displays

Figure 6 . 4 :

 64 Figure 6.4: Interaction with ShapeCompare: when a part is selected (Selection), the system generates a set of design alternatives on a row of the wall-sized display (Display). All alternatives can be scrolled up and down with a three-finger drag (Slide shapes), rotated in 3D with a widget (Rotation), and displayed on the external screen with a two finger long press (Update 2nd screen).

Figure 6 . 5 :

 65 Figure 6.5: Louvet et al.'s In(SITE), 6 DoF manipulation of a 3D object on a multi-touch wall-sized display. The user is performing a xy translation (main picture), z translation (a), roll rotation (b), and pitch & yaw rotation (c).

Figure 6 . 6 :

 66 Figure 6.6: Brainstorming session with participants.

Figure 6 . 7 :

 67 Figure 6.7: Usability study setup: the target shape is displayed with a transparent yellow color in a realistic environment on an external screen next to the wall-sized display.

Figure 6 . 8 :

 68 Figure 6.8: The mirrors modified by each participant during the study.

Figure 6 . 10 :

 610 Figure 6.10: Igarashi et al's Suggestive Interface [55].

Figure 6 . 12 :

 612 Figure 6.12: Interaction flows of two conditions: after shape selection (1),Selection Widget helps users to select a CAD parameter by displaying shapes corresponding to parameter extrema (2). Then users can explore design alternatives using ShapeCompare or ShapeSlide.

Figure 6 . 13 :

 613 Figure 6.13: Pairs of participants are exploring the design to find the one meeting their design criteria with ShapeCompare (top) and with ShapeSlide (bottom).

Figure 6 . 14 :

 614 Figure 6.14: (Left) design criteria of Specialist 1 and Specialist 2. (Right) design criteria values displayed next the mirror.

Figure 6 . 15 :Mean selection counts per trialFigure 6 . 16 :

 615616 Figure 6.15: Mean TCT by Visualization (left) and by Task (right). Error bars show 95% CI.

Figure 6 . 17 :

 617 Figure 6.17: Tagged expression proportions by Visualization.

Figure 6 . 18 :

 618 Figure 6.18: Ratings to questionnaires on a 5-point Likert scale (5 is best, 1 is worst). Error bars show 95% CI.

Figure 6 . 19 :

 619 Figure 6.19: Multiple people could discuss, explore and adjust the design using distributed CAD models on a wall-sized display.

Figure 7 . 1 :

 71 Figure 7.1: Collaboration between a wall-sized display with ShapeCompare and HMD.

  https://bitbucket.org/amiede/classicthesis/ Titre :Techniques de Modification de Donn ées CAO pour les Revues de Projet avec des Syst èmes Interactifs H ét érog ènes Mots cl és : R éalit é virtuelle, Surface interactive, Interaction collaborative, Architecture distribu ée, Conception assist ée par ordinateur

  Data Collection . . . . . . . . . . . . . . . . . . . 6.5.7 Data Analysis . . . . . . . . . . . . . . . . . . . . 6.6 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.6.1 TCT . . . . . . . . . . . . . . . . . . . . . . . . . . 6.6.2 Number of Selections . . . . . . . . . . . . . . . 6.6.3 Conversation analysis . . . . . . . . . . . . . . . 6.6.4 Qualitative Feedback . . . . . . . . . . . . . . . . 6.7 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 6.8 Design Recommendations . . . . . . . . . . . . . . . . . 6.9 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 7 conclusion and future perspectives 7.1 Contribution . . . . . . . . . . . . . . . . . . . . . . . . . 7.2 Enhancements and future work . . . . . . . . . . . . . .

	L I S T O F F I G U R E S
	Figure 2.1	Simon Stevin's sailing chariot in 1600 [118] . .
	Figure 2.2	Nicolas Joseph Cugnot's Fardier à Vapeur in
		1771 [28] . . . . . . . . . . . . . . . . . . . . . .
	Figure 2.3	Karl Benz's motorwagon (Benz patent motor
		car) in 1885 [9]. . . . . . . . . . . . . . . . . . .
	Figure 2.4	Ford Model T of 1913 (left). Early mass produc-
		tion of Ford's Highland Park plant in Detroit
		in 1914: the fuel tank assembly station (right)
		(Ford Motor Company Ltd.) [51]. . . . . . . . .
	bibliography Figure 2.5

x contents xiii 6.5.6

  Surface evaluation on virtual surface models (BMW)[START_REF] Weber | Automotive Development Processes[END_REF]. . . . . . . . . . . . . . . . . . . . . Figure2.[START_REF] Bourdot | VR-CAD integration: Multimodal immersive interaction and advanced haptic paradigms for implicit edition of CAD models[END_REF]

. . . . . . . . . . . xiv list of figures xv Figure 2.17

  .7 Virtuose 6D, Haption . . . . . . . . . . . . . . . . Figure 3.8 CAVE-like system, EVE. . . . . . . . . . . . . . . Figure 3.9 Wall-sized display, WILDER. . . . . . . . . . . . Figure 4.1 Various VR assembly simulations . . . . . . . . Figure 4.2 Example of VR-CAD systems with OpenCascade. Data flow of the VR-CAD server. The VR-CAD Server generates meshes (.obj) and linkage information (.xml) based on the users' requests and transmit them to front-end applications running on interactive systems. . . . . . . . . . Experimental set-up: EVE system (Fig. 3.8) and Scale1. . . . . . . . . . . . . . . . . . . . . . . . .

	Figure 4.8 Figure 6.4
		Figure 5.8	Four examples of the experimental task: orange
			parts had to be modified to reach the yellow
			targets. (a) LeftBottomCorner, +40mm differ-
	Figure 4.9	Different types of network architecture [42] . . ence from initial radius. (b) RightBottomCorner,
	Figure 4.10	Different types of data distributions [42]. Blue -30mm difference from initial radius. (c) Bot-
		lines: executions of object behaviors; red lines: tom, -40mm difference from initial length. (d)
		object modifications; Green line (c): modifica-RightSide, +30mm difference from initial length.
		tion of an object through one of its proxies . . Figure 5.9 Haptic arm handle of Scale1 (left) and its visual
	Figure 4.11	Distributed architecture for collaborative CAD proxy (right). 3D representation of the virtual
		data modifications between remote platforms. handle is co-located with the actual one in CAVE
	Figure 4.12	Distributed architecture of a proof of concept system. . . . . . . . . . . . . . . . . . . . . . . .
		between WILDER(left) and CAVE (right). Re-Figure 5.10 Mean Task Completion Time (TCT) by Technique
		mote users can collaboratively modify the Rear-(left) and Technique×Consistency (right). Er-
		view mirror without using classical desktop in-ror bars show 95% the Confidence Interval (CI).
		Figure 5.11	Wrong Direction Starts (WDS) rates by Tech-
		Figure 6.2	Green line is a guide curve of a sweep opera-Distributed brain scan images on a wall-sized
	Figure 5.6	tion generating the 3D shape. Constraints and System architecture of VR-CAD system. Each display and a physical model of the brain to
		parameter values are highlighted in blue: for process is connected through Transmission Con-control the orientation of the images [8]. . . . .
		example, red constraint defines the distance to trol Protocol (TCP) protocol: meshes and link-Figure 6.3 Study on interaction techniques on wall-sized
		the bottom of the Rear-view mirror (60 mm). . . age information of CAD data are distributed displays . . . . . . . . . . . . . . . . . . . . . . .
		Figure 4.7 using Shared data server. Selected part informa-Interaction flow of cRea-VR [88] . . . . . . . . .
		tion contains: sub-part Id, constraint Id and a
		set of parameter offsets. Generated mesh infor-
		mation includes: number of generated meshes

Figure 4.3 Example of VR-CAD systems that store design histories (Constructive History Graph (CHG)). Toma et al.'s VR-CAD system (left) can create digital mockup based on Solidworks, whereas D 3 (right) can add mesh deformations on imported CAD model. Both systems do not support any modifications on design histories of imported CAD models. . . . . . . . . . . . . . . Figure 4.4 cRea-VR, a VR-CAD system that can modify parameters of native CAD part designed with CA-TIA V5 in an immersive environment. . . . . . Figure 4.5 System structure of cRea-VR. cRea-VR can be divided into four main components: Interaction engine, Visualization system, Inference engine and Encapsulation. [88] . . . . . . . . . . . . . . . . . Figure 4.6 Sketch of the Rear-view mirror, an example of industrial CAD part designed using CATIA V5 R . terface. . . . . . . . . . . . . . . . . . . . . . . . Figure 5.1 Virtual painting (left) and surface deformation (right) using force feedback devices . . . . . . Figure 5.2 Computation of different shapes of Rear-view mirror: when users select the red distance constraint highlighted in Figure 4.6, full meshes are used to provide visual feedback to the users (only one mesh is visible at a time), and subpart meshes are used for haptic rendering (the two closest meshes are used for force feedback computation). . . . . . . . . . . . . . . . . . . . Figure 5.3 Example of computed sub-part meshes of the right side part for 3D interaction. P hand is user's hand position. P i is a nearest point on each surface from P hand . . . . . . . . . . . . . . . . . Figure 5.4 Yamada et al's force feedback grid [125]. Grid points (center) or planes (right) attract user's hand during 3D modeling. . . . . . . . . . . . . Figure 5.5 Norm of the attractive force during modification of a shape. Red arrows describe user's hand position. . . . . . . . . . . . . . . . . . . . and parameter values. . . . . . . . . . . . . . . Figure 5.7 nique (left) and Technique×Part (right). . . . Figure 5.12 Mean Overshoots by Technique (left) and Feedback (right). . . . . . . . . . . . . . . . . . . . . Figure 5.13 Mean Overshoots by Technique×Feedback (left) and Technique×Part (right). . . . . . . . . . . Figure 5.14 Participant ratings by Technique×Feedback for not mentally demanding, not physically demanding, not difficult to use, not frustrating, consistent and overall evaluation on a 5-point Likert scale (5 is best, 1 is worst). N: NoForce and F: Force. . . . . . . . . . . . . . . . . . . . . . . . . Figure 5.15 Native CAD data modification in a user-oriented environment. A user modifies the shape of Rear-view mirror within a realistic virtual environment of a car's cockpit while perceiving modification impact from a first person perspective in real time. . . . . . . . . . . . . . . . Figure 6.1 User studies and applications with wall-sized displays . . . . . . . . . . . . . . . . . . . . . . .

Table 6 .

 6 Ratings to questionnaires on a 5-point Likert scale (5 is best, 1 is worst). Error bars show 95% CI. . . . . . . . . . . . . . . . . . . . . . . . . . . Figure6.[START_REF] Xiang 'anthony' Chen | Forte: User-Driven Generative Design[END_REF] Multiple people could discuss, explore and adjust the design using distributed CAD models on a wall-sized display. . . . . . . . . . . . . . .

	Figure 6.15	Mean TCT by Visualization (left) and by Task
		(right). Error bars show 95% CI. . . . . . . . . .
	Figure 6.16	Mean Selections by Visualization (left) and by
		Task. Error bars show 95% CI. . . . . . . . . . .
	Figure 6.17	Tagged expression proportions by Visualization.

.14 (Left) design criteria of Specialist 1 and Specialist 2. (Right) design criteria values displayed next the mirror. . . . . . . . . . . . . . . . . . . . . . 1

Tagged data from conversation analysis. . . . .

,

  Detailed design involves the highest number of actors in review meetings and need to interact with the PLM database without any conversions of data format. During Design review meetings of the Detailed design stage, DMUs based on CAD data are presented in the virtual environment to verify or compare different versions. For example, project members compare several design alternatives of A-pillars (i.e. vertical supports of a car's front window) in the CAVE system to assess driver's field of view from a physical driver's seat installed in the CAVE. They successively compare pillars designs by visualizing them one by one in a virtual cockpit to test and compare these possible designs. But as highlighted in Section 2.2.2.3, Design review meetings require data preparations before the review session because existing systems for design reviews do not support direct modifications of CAD part parameters. Consequently, CAD engineers need to create several versions from the initial CAD model and apply modifications afterward based on remarks from several experts which are usually logged as handwritten notes with screen-shots of the scene. This back-and-forth between the virtual environment and the workstation is time-consuming and could induce misannotations or misinterpretations in the logged remarks. Updating the initial CAD model after the meeting usually takes a few days.

  TCT, as recommended by Robertson & Kaptein[START_REF] Robertson | Modern Statistical Methods for HCI[END_REF] (p. 316). I did not find any significant learning effects due to technique presentation order.A repeated measures ANOVA on TCT with the model Visualiza-tion×Task revealed significant effects on Visualization (F 1,47 = 4.83,

Table 6 .

 6 6.1). I did not find difference in the total number of sentences between ShapeCompare (1343, 51.83% of total) and ShapeSlide (1248, 48.17% of total) (Table.6.17). The participants used more Deictic instructions with

	Category	ShapeCompare ShapeSlide Total
	Deictic-Specific	158	105	263
	Deictic-Range	41	1	42
	Expression-Verbal	133	156	289
	Expression-Gesture	24	38	62
	Direction	45	65	110
	Others	70	84	154
	None	872	799 1671
	Sum	1343	1248 2591

1: Tagged data from conversation analysis.

http://www.digiscope.fr/en/platforms/eve

http://www.middlevr.com/middlevr-for-unity/

https://ar-tracking.com

https://www.haption.com/fr/products-fr/scale-one-fr.html

http://business.panasonic.com/AW-UE70.html

http://www.digiscope.fr/en/platforms/wilder

https://www.vicon.com

http://www.pqlabs.com

http://business.panasonic.com/AW-UE70.html

http://vcg.isti.cnr.it/vcglib/

https://webrtc.org/

https://www.kurento.org

All analyses except Friedman tests were performed with the SAS JMP statistical platform. Friedman tests were performed with R.

I used a significance level of α = 0.05 for all statistical tests.

In all barplots, error bars show the 95% confidence intervals (CI).

https://figshare.com/articles/Video _ 1 _ ShapeGuide _ Shape-Based _ 3D _ Interaction _ for _ Parameter _ Modification _ of _ Native _ CAD _ Data _ mp4/7296020

https://www.autodesk.com/products/autocad

All analyses were performed with R and we used a significance level of α = 0.05 for all statistical tests.