Fodil Fadli
email: f.fadli@qu.edu.qa

Hichem Barki
email: hbarki@qu.edu.qa

Ahmed Shaat

Lamine Mahdjoubi
email: lamine.mahdjoubi@uwe.ac.uk

Pawel Boguslawski
email: pawel.boguslawski@uwe.ac.uk

Vadim Zverovich
email: vadim.zverovich@uwe.ac.uk

3D Capture Techniques for BIM Enabled LCM

de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

1 Why 3D capture is essential to BIM? 3D capture techniques aim to generate virtual models through the usage of different kinds of sensors in an environment of interest. Thanks to the recent technological progress of computing devices and the rapid drop of their prices, 3D capture gained more popularity and became more accessible for professionals and even amateurs. As a consequence, it is now easy to quickly generate large amounts of very complex virtual models, ranging from unstructured point clouds to meshes and surfaces, encoding the geometry, topology, texture, and other physical properties of the surrounding world.

3D capture finds applications in many domains, including BIM, robot motion planning, life cycle analysis [START_REF] El-Omari | Integrating 3D laser scanning and photogrammetry for progress measurement of construction work[END_REF], and emergency preparedness [START_REF] Barki | BIM models generation from 2D CAD drawings and 3D scans: an analysis of challenges and opportunities for AEC practitioners[END_REF][START_REF] Fadli | 3D scene capture: a comprehensive review of techniques and tools for efficient Life Cycle Analysis (LCA) and Emergency Preparedness (EP) applications[END_REF]. It is essential as it constitutes the first step towards the development of suitable BLM processes employing BIM models that greatly help practitioners by offering better visualization and interaction means. BIM is a recent approach that aims to complement or supersede traditional CAD design. The current state of the art reveals that it is much easier to achieve BIM for new projects than for already completed or in progress projects, complicating by the way the undertaking of life cycle-related tasks on existing projects, e.g., maintenance, renovations, etc. This is a big concern when one considers that many countries have realized the importance of BIM and are initiating BIM reforms and pushing towards its quick adoption. While initial CAD/GIS plans, if they exist for a particular scene, represent a valuable source of information; acquiring knowledge about dynamic scene aspects (human behaviour, construction and as-built differences) is a necessary and relatively difficult task, making 3D capture unavoidable in our BLM context, because it is the only way to deal with dynamic scenes information.

In this paper, we introduce, review, and analyze the usage of 3D capture techniques, ranging from photogrammetry to 3D scanning. Contrary to prior review papers which tend to summarize the literature or avoid discussing some relevant capture aspects, our comprehensive analysis is oriented towards 3D capture practitioners who need to make critical decisions, by examining the relevant aspects of each technology, the different pros and cons, and the potential application domains. We conclude this work by providing a set of recommendations for field practitioners, in order to enhance the use of such techniques in BIM integrated life cycle management. We shall note that even if this work introduces 3D capture techniques in general, the provided review focuses only on the most prominent ones: photogrammetry and laser scanning.

3D scene capture techniques

The current literature shows that 3D capture retained much attention in the past decades. Even capture techniques cannot be strictly categorized, one may broadly distinguish 3D scanning/modeling approaches and image-based techniques. Manual building surveying (manual geometry measurements and drafting boards usage) represents the most basic and oldest capture technique. As a consequence of computing devices emergence and the development of CAD tools, CAD modeling became popular and allowed the generation of 3D models. The aforementioned techniques are characterized by long modeling times, the inability to encode fine architectural details, and the requirement for highly skilled operators.

Based on the employed sensor underlying acquisition principles, one may classify 3D scanning techniques into different categories [START_REF] Scopigno | Tutorial T1 : 3D Data Acquisition[END_REF], such as passive/active, reflective/transmissive, destructive/non-destructive, optical/non-optical, etc. Active probing techniques capture the shape of 3D physical objects using Coordinate Measuring Machines (CMM) composed of mechanical arms that probe objects' surfaces along user-defined profiles (cf. Fig. 1 left) [START_REF]MicroScribe Portable Scanners[END_REF]. Although successfully used for reverse engineering, such a time-consuming and manually operated technique does not provide consistent control on the sampling accuracy, does not allow recording visual properties of objects, and doesn't operate on soft or large-size objects (destructive approach).

Non-contact 3D scanning techniques, whether optical (Lidar) or non-optical (Radar, Sonar, or Computer Tomography (CT)) employ different sensing principles and may also be classified into transmissive and reflective ones, depending on the nature of the interaction of the emitted wave with the target objects. These techniques do not intrinsically interfere with the scanned object and thus reduce the impact of the capture on fragile objects. Lidar or laser scanning is the most relevant in our context and consists in emitting laser beams, of frequencies typically between 500-1500nm [START_REF] Baltsavias | A comparison between photogrammetry and laser scanning[END_REF], and analyzing their reflections, in order to deduce the distance between the device (cf. Fig. 1 right) and the scanned objects. One of the main reasons of the wide adoption of laser scanning is laser's tight focus allowing to capture large scenes, compared to other optical techniques.

As an image-based capture technique, photogrammetry has a long history [START_REF] Masson | Paul Debevec and the Art of Photogrammetry[END_REF] but it is only recently that it has been used to model 3D scenes, thanks to the recent popularization of high quality cameras (cf. Fig. 1 right). The principle consists in deducing the 3D structure of a scene by examining a set of overlapping images, generated by positioning targets with known coordinates on the scene objects to be captured, and then taking several image captures from different positions and angles.

By using such a priori information about the position/orientation of the camera and the target points coordinates, the captured images can be combined by using some principles of projective geometry, in order to construct a 3D scene model [START_REF] Debevec | Modeling and rendering architecture from photographs[END_REF]. Photogrammetry excels in extracting scene colour and texture information under reasonable conditions.

Analysis and usage of capture technologies

In the sequel and based on several criteria of interest, we will compare photogrammetry and laser scanning, which are the most prominent capture techniques among the two aforementioned broad categories. Variations of such techniques qre discussed whenever relevant.

Resolution, precision, and range. The quality of a capture device is usually assessed through a set of objective measures defined as range, resolution, precision, and accuracy parameters. Compared to photogrammetry, whose accuracy is unpredictable because of many parameters (e.g., the 2D image to 3D model conversion errors), the accuracy of laser scanning may be easily estimated in advance. Even if some previous work claims that recent photogrammetric devices are able to achieve similar or even higher resolution/accuracy than laser scanners, there is an agreement that laser scanning performs better in general and can go below the millimetre accuracy. For complex geometry scenes and objects, photogrammetric techniques are still unable to reproduce accurate details [START_REF] Scopigno | Tutorial T1 : 3D Data Acquisition[END_REF]. Furthermore, the fact that laser beams have tight focus implies that they are more precise in capturing scenes at higher ranges, and even at very short ranges at the level of molecules [START_REF] Cracknell | Introduction to Remote Sensing[END_REF].

Environmental conditions represent an important factor that determines the usability of capture techniques, as some of the latter are guaranteed to perform correctly only under some environmental conditions. Because of its emissive nature, laser scanning is less affected by ambient light fluctuations and the resulting acquisition data is relatively invariant with respect to climate conditions, except that it is unable to operate on very shiny materials like water surfaces. in contrast, photogrammetry is highly influenced by weather/lighting conditions and the outcome deteriorates for large dark scenes. This concern represents one of the main cons of photogrammetric techniques.

Data and operation complexity. As laser scanning is the most advanced data capture, it is predictable that it is the most efficient in data capture, while millions of points can be captured per second and this rate is even increasing with the progress of laser technology. In fact, laser scanners provide an automated way of scanning large 3D areas in 360 horizontal direction, allowing for more capture density. In contrast, photogrammetry relies on several 2D image captures followed by a heavy post-processing for 3D point cloud generation, making it less efficient and constrained by the single image capture resolution. Laser scanning operates in near real-time while photogrammetry is employed in an offline fashion because of the aforementioned reasons. In the literature, laser scanning has been reported to be slower than photogrammetry for high resolution captures. However, this is an unfair conclusion as photogrammetry is unable to reproduce the higher resolution captures of laser scanning and even if it does, it becomes terribly slow.

A natural consequence of the high capture speed of laser scanners is the large size of the captured data. According to the laser capture resolution, the more laser beams are emitted, the more points are collected. For complex and large scenes, typical point clouds may easily contain billions of points coming from hundreds of individual scans. Even if large point clouds provide very detailed information about a scene, such huge data amounts make the processing and knowledge extraction tasks more involved and time consuming. On the other hand, photogrammetric results are smaller, but the continuous progress of imaging devices and image processing algorithms gave rise to applications involving tens of thousands of images and thus yielding to very large point clouds.

The most critical issue of photogrammetric approaches concerns the processing or combination of the individual image captures into a unique model. Due to the manual placement of targets for image registration and the manual choice of camera positions/rotations, such a process becomes very time consuming and tedious. The most time consuming sub-step in a photogrammetric process is the combination of the individual 2D images into a unique 3D point cloud. For laser scanning techniques, 2D-to-3D conversion is eliminated as the capture is already three-dimensional and the registration of the individual 3D point clouds is relatively easier. For more details about 3D capture complexity and processing cost precise measures, the reader is referred to [START_REF] Jaselskis | Improving Transportation Projects Using Laser Scanning[END_REF]2].

Safety and autonomy. Photogrammetric techniques are safer than laser techniques as the former require the use of conventional still cameras, while the latter are harmful for the operator's eyes. The recent trend going towards the usage of LED light as a replacement of laser is an alternative that addresses the safety concern of laser scanning, while presenting the advantage that LED light is as accurate as laser for close range captures only. Regarding the capture autonomy and hence mobility, photogrammetry outperforms laser scanning as the latter makes usage of powerconsuming built-in amplifiers. It is worth noting that recently, some hardware manufacturers successfully introduced handheld and flexible laser scanners for small size objects capture, and that attempts have been made to use them for large scenes capture.

Equipment and operation cost. Evaluating the capture budget is a crucial factor from the a financial point of view. Photogrammetric techniques are the most accessible ones as they employ still cameras whose prices are rapidly decreasing and whose performance and specifications are continuously increasing. In contrast, despite their commercialization since three decades, laser scanners prices are still high. According to [START_REF] Scopigno | Tutorial T1 : 3D Data Acquisition[END_REF], laser scanners prices range from tens of thousands of dollars to hundreds of thousands of dollars, depending on the sophistication of the scanner, the included accessories/software, and the specifications. In consequence, laser scanning is still restricted to companies or educational institutions with consequent budgets. Recently, scanner rental services have emerged [START_REF]Laser scanning Europe. Rent a laser scanner at little cost[END_REF] as an alternative for institutions with lower budges. Another factor influencing the cost of a capture process consists in the lifetime of the capture device. While photogrammetric devices may be used for decades, laser scanners have a much smaller lifetime (thousands of hours) because they are quickly deteriorated by the operational temperature of the built-in amplifier [START_REF] Baltsavias | A comparison between photogrammetry and laser scanning[END_REF]. When it comes to the operational cost of a capture process which is correlated to the learning curve of that process, since still cameras can be found on almost any private office, it is natural that they are the easiest to use, compared to the non-public-friendly laser scanners which require specific trainings and thus an an additional operational cost.

Applications. Whenever some geometric or physical information about a scene is required or needs to be reconstructed, data capture enters into action. Photogrammetry and 3D scanning have been interchangeably and successfully used in many applications. On the one hand, Terrestrial Laser Scanning (TLS) has been applied for interior building modeling, navigation, and exploration [START_REF] Xiao | 3D Data Acquisition by Terrestrial Laser Scanning for Protection of Historical Buildings[END_REF], while Airborne Laser Scanning (ALS) has been used for 3D city/terrain modelling and landslide volume computation in geology, in order to capture the geometry of cities and terrains [START_REF] Tse | 3D City Modelling from LIDAR Data[END_REF].

In transportation projects, it has been used for acquiring design and construction data [START_REF] Jaselskis | Improving Transportation Projects Using Laser Scanning[END_REF]. Cultural heritage and historical buildings digitization is probably the most explored domain where laser capture has been used for heritage documentation and preservation [START_REF] Xiao | 3D Data Acquisition by Terrestrial Laser Scanning for Protection of Historical Buildings[END_REF]. On the other hand, photogrammetry touched similar application domains like for example in bridge engineering [START_REF] Jiang | Close-range photogrammetry applications in bridge measurement: Literature review[END_REF], but the application domain that deserved most of the researchers attention was cultural heritage preservation, where it has been used for the digitization and reconstruction of photorealistic 3D models for many historical sites [START_REF] Debevec | Modeling and rendering architecture from photographs[END_REF], [START_REF] Al-Kheder | Developing a documentation system for desert palaces in Jordan using 3D laser scanning and digital photogrammetry[END_REF], thanks to the ability of photogrammetry to better capture visual aspects of scenes.

Life Cycle Management (LCM) connection to Sustainability

Assessment (SA) in the built environment (BE)

In order to understand and adapt LCM usage in the BE and hence interoperability to BIM, sustainability and its assessment must be well understood and scrutinized.

In fact LCM goes in accordance with SA to determine its integration into any BIM model. In this respect, we elaborate on the most adequate definition of sustainability and its rigorous assessment. There are as many definitions of sustainability and sustainable development as there are individuals and interest groups trying to define the term. All the definitions however, share a common concern for: (i) living within the limits, (ii) understanding the interconnections between economy, society, and environment, and (iii) equitable distribution of resources and opportunities [START_REF] Fadli | Measuring Sustainability Levels of Tourist Resorts: STAM and the Use of Radar Diagrams[END_REF].

In 1981, Malcolm Wells suggested a matrix, which appears to be the first attempt to use indicators to help achieve sustainability [START_REF] Wells | Gentle Architecture[END_REF]. Although, Wells' matrix was invaluable, it was still far from comprehensive. It did not either elaborate real complexity or recognize value shifts and differences in the sustainable design process. In 1990, Kroner has further developed the matrix with categories and sub-categories, while Salem enlarged it by adding a priority tab [START_REF] Bell | Sustainability Indicators: Measuring the Immeasurable?[END_REF]. It was further refined during the last decade but remained limited to environmental factors mainly [START_REF] Fadli | Measuring Sustainability Levels of Tourist Resorts: STAM and the Use of Radar Diagrams[END_REF]. Assessments of sustainability can help inform the societal discussion and influence the environmental governance towards the main objectives of sustainability. The effectiveness of an assessment system in this regards requires that it matches up well against a number of requirements, in such a way that it can be seen to be: (i) hopeful, (ii) holistic, (iii) protective, (iv) Harmonious, (v) Participatory, and (vi) habit forming [START_REF] Pintér | Bellagio stamp: Principles for sustainability assessment and measurement[END_REF].

LCM-SA interoperability into BIM models. The recent decades have witnessed a maturing of concern and interest in building performance that is increasingly evidenced in building design. Sustainable or green design is not simply about attaining higher environmental performance standards or investing in new values; it is also about rethinking "design intelligence" and how it is placed in buildings. The distinction between the notions "Green", "Intelligent", "smart" and "Sustainable" is critical in what underlies valid sustainable buildings. Sustainability assessment is a procedure used to evaluate whether environmental, economic and societal changes arising from man's activities and use of resources are decreasing or increasing our ability to maintain long-run sustainability.

During the last two decades, the science of "assessing sustainability in the built environment" has flourished and the number of assessment tools exploded dramatically to reach over 100 tools worldwide [START_REF] Fadli | Environmental impact assessment of new district developments[END_REF]. Local assessment systems have developed in different countries and regions; responding to perceptions of what is needed in their local conditions. These assessment systems and tools share much in common but also evidence differences of scope, approach, reporting and mitigation measures.

This study opened the door to new horizons in BIM integration of LCM/SA and the use of capture techniques, in fact this would allow the tools stated previously to include life cycle assessment and costing, energy systems design and performance evaluation, productivity analysis, indoor environmental quality assessment, operations and maintenance optimization, whole building design and operations tools [START_REF] Fowler | Sustainable Building Rating Systems Summary[END_REF], and enable their apps into BIM oriented platforms. Commonly-used tools worldwide are performance and/or predicted performance based systems. Each features a suite of tools developed for different buildings and projects such as residential, commercial, industrial, retail and educational and health buildings. Therefore this study will develop further recommendations to enable the use by field practitioners.

Recommendations to enhance qualities of the built environment

The conducted comparative study reveals that laser scanning technology represents the future of 3D capture. It is the most promising technique as it is the most accurate one. Photogrammetric techniques provide less garbage than laser techniques do, but photogrammetric data requires costly post-processing in addition to being limited by the image accuracy and the precision of the registration process. As predicted in [START_REF] Masson | Paul Debevec and the Art of Photogrammetry[END_REF], it is more interesting to combine different capture technologies, as each one comes with its own set of pros and cons. It is natural to think that combining laser scanning and photogrammetry improves the accuracy of photogrammetry and reduces or ideally eliminates the manual steps required for generating 3D models. This observation is consolidated by the recent trends of the combined usage of capture techniques. For instance, a progress reporting application has been proposed in [START_REF] El-Omari | Integrating 3D laser scanning and photogrammetry for progress measurement of construction work[END_REF], where both photogrammetry and laser scanning have been combined to improve the accuracy and speed of collecting data from a construction site. In cultural heritage digitization, laser scanning and photogrammetry have been conjointly used in many works [START_REF] Al-Kheder | Developing a documentation system for desert palaces in Jordan using 3D laser scanning and digital photogrammetry[END_REF][START_REF] Agnello | Integrated surveying techniques in cultural heritage documentation[END_REF][START_REF] Yastikli | Documentation of cultural heritage using digital photogrammetry and laser scanning[END_REF]. In robot motion planning, laser and vision sensors were combined for the development of a robot navigation system in indoor environment [START_REF] Zender | Conceptual spatial representations for indoor mobile robots[END_REF].

As a synthesis, an ideal and universal 3D capture technique doesn't exist. Our discussion shows that when the need arises for data capture in a particular context, a good practice would be to start by carefully identifying the application requirements, and then transposing these needs to each technique, in order to find the most adequate capture technique for that context. As an advice, one might consider using other techniques, in conjunction or complementation of the primarily chosen one, in order to improve the capture process. In cultural heritage, it appears that combining laser scanning (more precision) and photogrammetry (better visualization) gives the best results, while in the emergency preparedness context, laser scanning combined with other techniques (e.g., RFID) represents a good candidate.

Conclusion

In this work, we have conducted a comparative study of the most prominent 3D capture techniques as the capture process is unavoidable for developing a smart BLM impementation through BIM. We have introduced 3D capture techniques and compared them by exposing their weaknesses and strengths, according to many relevant criteria for field practitioners like equipment/operation costs, mobility, accuracy, precision and range, data complexities, etc. As 3D scene capture is involved in a plenty of application domains, our study targets a wide audience of professionals. It provides a set of recommendations and advice that help data capture actors for the correct and critical choice of adequate technologies that best suit the targeted application. Our study shows that an ideal capture technology may not exist for a particular application domain, but the usage of more than one technology is highly recommended for getting better results.

Fig. 1

 1 Fig. 1 3D scanning devices. Left: A contact-based MicroScribe device (photo taken from [3]). Right: The Riegl VZ-400 terrestrial laser scanner.

Acknowledgements This research/publication was made possible by a National Priority Research Program NPRP award [NPRP-06-1208-2-492] from the Qatar National Research Fund (a member of The Qatar Foundation). The statements made herein are solely the responsibility of the author(s).


Samuel André
email: samuel.andre@ju.se

Roland Stolt
email: roland.stolt@ju.se

Fredrik Elgh
email: fredrik.elgh@ju.se

Introducing Design Descriptions on Different Levels of Concretisation in a Platform Definition

Keywords: Product platform, quotation, engineering design, reuse, design rationale

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Systematic investments in technology development (TD) has been pointed out as a strategy for companies in industry to gain competitive advantage. This is a paramount challenge for suppliers since their products are to be integrated into different systems introducing several complex interfaces, markets, product uses and individual preferences. In past research a large emphasis has been put on splitting TD from product development (PD) since they differ in prerequisites, technical maturity, time horizon, need for competence, process repeatability, completion point and deliverables [START_REF] Nobelius | Managing R&D Processes -Focusing on Technology Development, Product Development and their Interplay[END_REF]. It follows that by separating TD from PD one can reduce risk in PD projects [START_REF] Lakemond | Interface between technology development, product development and production -Critical factors and a conceptual model[END_REF].

For a sub-supplier developing and manufacturing engineer-to-order (ETO) products, this becomes even more challenging due to the uncertainty regarding future customer requirements and needs. The challenge lies in conducting long term TD, developing the "right" technology for a future market that is ready to be introduced in a product when the time comes. At the same time a sub-supplier must fulfil the customer individual preferences, introducing a demand for customisation which often has, compared to TD, a much shorter timeframe. This stresses for strategies covering both long term and short term perspectives. Product platforms has been suggested as an enabler for efficient customisation. However, the platform definition that builds upon pre-defined modules and components has been shown to not be applicable to all companies working with an ETO business approach [START_REF] Högman | Exploring the potential of applying a platform formulation at supplier level-The case of Volvo Aero Corporation[END_REF]. This article elaborates how such a company can describe the outcome of TD and PD by introducing descriptions on different levels of concretisation. This is discussed in connection to a platform approach as a means to increase reuse of design knowledge. In order to support the presented concept a novel computer tool has been developed. The research question can be stated as: How can a platform be described in order to support customisation in a company working with an ETO business model?

The work presented in this paper has been conducted in close collaboration with an industrial company. The information about the presented case has been gathered from meetings, demonstration of applications, reviews of documents and in-depth interviews. A systematic literature review was made. The frame of reference presented in this paper is a condensed version of the complete literature review made for this work. The overall research approach used is the one proposed by Blessing [4]. This paper can be positioned in between descriptive study 1 and the prescriptive study.

Frame of Reference

Customisation refers to the ability and strategy that aims towards designing and manufacturing tailored products for an individual customer. Simpson [START_REF] Simpson | Product platform design and customization: status and promise[END_REF] proposes product families as a main enabler and describes two basic approaches for the design of product families in order to achieve efficient customisation, top down and bottom up. Hansen [START_REF] Hansen | Development of industrial variant specification systems[END_REF] divides specification processes into four levels in the following way: (1) Engineerto-order, (2) Modify-to-order, (3) Configure-to-order and (4) Select variant.

Platforms in engineering design. Several definitions of product platform can be found in literature and depending on which definition is used, a product platform can be many things. The existing definitions ranges from a platform consisting of components and modules [START_REF] Meyer | The power of product platforms -Building value and cost leadership[END_REF], a group of related products [START_REF] Simpson | Product platform and product family design -Methods and application[END_REF], a technology applied to several products [START_REF] Mcgrath | Product strategy for high-technology companies[END_REF], to a platform consisting of assets such as knowledge and relationships [START_REF] Robertson | Planning for product platform[END_REF]. This is also reflected among sub suppliers, as shown in [START_REF] André | Managing Fluctuating Requirements by Platforms Defined in the Interface Between Technology and Product Development[END_REF], where the company platform description is categorised on four levels of abstraction and compared to their customisation strategy. A risk emphasised in literature is the trade-off between commonality and distinctiveness [START_REF] Robertson | Planning for product platform[END_REF]. Another trade-off is the one between increased development efforts for the initial platform and the uncertainty whether the right platform is chosen in order to develop a sufficient number of derivatives to gain back the extra expenses [START_REF] Halman | Platform-driven development of product families -Linking theory with practice[END_REF]. Platforms are generally described to be of one of either two kinds: Module based (discrete) or scale based (parametric) [START_REF] Simpson | Product platform design and customization: status and promise[END_REF]. Cooper [START_REF] Cooper | Managing technology development projects[END_REF] suggests that one deliverable from TD can be a technology platform, this is further investigated by Högman [START_REF] Högman | Processes and Platforms Aligned with Technology Development -The perspective of a supplier in the Aerospace Industry[END_REF]. Johannesson [START_REF] Johannesson | Emphasizing reuse of generic assets through integrated product and production system development platforms[END_REF] questions if companies have a choice regarding implementing a platform or not since platforms can exist on several levels.

Product models can serve as a way to describe some parts of a platform. The Product Variant Master (PVM) is a method that have been described in several scientific articles and books, and can be used to model some aspects a product platform [START_REF] Hvam | Product customization[END_REF]. The "Part-of" structure specifies the generic product architecture and the "Kind-of" structure describes the different kind of variants. CRC (Class Responsibility Collaboration) cards are then used to map all variants. Another methodology that has been used to model platforms is the "Configurable Component" (CC) concept. Here the connection from functional requirement to design solution is mapped. Levandowski et al. [START_REF] Levandowski | Set-Based Concurrent Engineering for Early Phases in Platform Development[END_REF] proposes a methodology to model a platform in early phases of development using the CC concept and set-based concurrent engineering.

Reuse of design knowledge. The reuse of design knowledge has been studied by many researchers throughout the years. Haug et al. [START_REF] Haug | Definition and evaluation of product configurator development strategies[END_REF] emphasises knowledge acquisition where the knowledge of the domain experts is gathered and formalised. Stokes [START_REF] Stokes | Managing engineering knowledge: MOKA: methodology for knowledge based engineering applications[END_REF] presents a complete framework and in detailed described methodology, called MOKA, aiming to collect and formalise knowledge in order to create knowledge based systems. Huang et al. [START_REF] Huang | Building a knowledge map model situated in product design[END_REF] describes the methodology for developing a knowledge map and also the implementation in a case in the automotive interior business. Baxter [START_REF] Baxter | An engineering design knowledge reuse methodology using process modelling[END_REF] considers knowledge as actionable information and problematizes that many previous design knowledge reuse systems exclusively focus on geometrical data which is often not applicable in early stages. The author also emphasises that in order to reuse design knowledge, several factors must be met: reusability, availability and relevance. Regli et al. [START_REF] Regli | A survey of design rationale systems: approaches, representation, capture and retrieval[END_REF] defines design rationale as the explanation of why an artefact or some part of an artefact is designed the way it is. According to [START_REF] Elgh | Supporting traceability of design rationale in an automated engineer-to-order business model[END_REF] the access to design rationale can support the development of new products, modification of existing ones or reuse of an existing one in a new context. When it comes to computer support, research has pointed out that three important factors are crucial for system success: Visualisation [START_REF] Huang | Building a knowledge map model situated in product design[END_REF], usability [START_REF] De Pinel | Proposition of ergonomic guidelines to improve usability of PLM systems interfaces[END_REF] and a concurrent working approach [START_REF] Preston | Knowledge acquisition for knowledge-based engineering systems[END_REF].

Summarisation and research opportunities.

A platform approach has been shown to be an enabler for efficient customisation, reuse and production standardization. There is however a lack of research investigating how a platform definition can be described in order to support sub-suppliers working with an engineer-to-order customisation strategy. There is not many examples of supporting tools that aid the work of design engineers in combination with such a platform definition. This stresses for methods based on a real industrial needs. An important step in design knowledge reuse is the knowledge acquisition process consisting of collection and formalisation. There is not much mentioned however of what design knowledge descriptions actually supports a platform definition of this kind and how these descriptions can be structured in order to improve reuse.

An intermediate Design Platform description

As stated, earlier research has shown that it is beneficial to separate TD from PD. TD has a fuzzy timeframe and no direct targeted customer and is triggered by the future market opportunities, possibilities, trends and needs (Fig. 1). This is where the company takes the risk that needs to be taken in order to spur innovation developing new technologies, products and processes. The separation of TD and PD introduces an interface between the two that needs to be managed. The main concept that is presented in this paper is to use a platform approach to handle some aspects of this interface (Fig. 1). The paper also argues that this platform definition, as will be presented, is an enabler for customisation for companies working in an ETO business model. The aim of the platform approach is to enhance the reuse of the technologies and designs developed in a company. Reuse goes hand in hand with platform thinking as a way to keep the design effort efficient and at a manageable level. What often is lacking is a platform description to support the development in order to draw the benefits from platform thinking to a higher degree. However, it is not seldom that sub suppliers does not focus the development towards a platform, but rather develop single instances every new project. This is especially true for companies developing and manufacturing ETO products and where a module-or component based product platform is not possible. This challenge of using a module-or component based product platform can have several reasons such as unknown and ever changing interfaces to the system the product is to be integrated into, different markets, different product uses, individual preferences and a relatively low number of developed and manufactured products. To manage the interface between TD and PD, the Design Platform approach is introduced. As opposed to the top down and bottom up approaches described by Simpson [START_REF] Simpson | Product platform design and customization: status and promise[END_REF] where the platform is the focus of the development, the focus in the Design Platform approach is on the instances with the Design Platform as a support for reuse. The descriptions of the instances is what creates the platform definition which means that the platform evolves as the instances are successively created. When a number of instances has been created it can be seen as a discrete set that spans a design space, i.e. what designs are feasible. The description of this design space is what builds up the Design Platform.

The ultimate goal of PD is not the product as such but a product description. The final product description is what is considered most important and is of course the focus of PD. These descriptions (e.g. CAD drawings) are concretised to a high level which also usually means a narrowing of the design space. Due to the narrowed design space the product instance will have limited possibilities to adapt to a new situation when the prerequisites or requirements change, i.e. the possibilities to reuse the instance will be restricted. If design knowledge is captured, structured, saved and can be retrieved, it can be reused in future development projects as a natural part of the platform definition. By being proactive and exploring a design during TD and PD, this knowledge could be saved and reused by the addition of descriptions on different levels of concretisation. It is here investigated and presented how this can be achieved by saving and structuring blocks of knowledge, here referred to as Design Elements (DEs). These are more elaborated in a subsequent section. These descriptions that now are a part of constituting the platform realises something other than the component and module based product platform (i.e. the highly concretised product description). The platform is now not just composed by the physical elements that is the product but also the elements that supports the designing and constructing of the product. Therefore the name "design platform" is more suitable than "product platform" since it refers the activity as well as the thing, design.

The proposed concept

The proposed concept is based on an object oriented way of thinking. The idea is to see the generic product description as a class, when instantiated becomes an instance (object). There are different levels of classes in the concept whereas the top level is called "Design description class" and is composed by a product architecture class with subclasses, metadata model classes and DE classes. The generic product architecture is based on the theory of PVM [START_REF] Hvam | Product customization[END_REF] but is here tweaked to better fit the purpose. The main concepts of the PVM will be kept but will now also host DEs that also describe parts of the design process. The "part of" structure describes the class hierarchy of subsystems and components whereas the "kind of" structure describes the types of instances. Every class in the "part of" structure is described by a metadata model. Every object corresponding to a certain class is then coupled to this metadata model. Each type of DE is a class of its own. The generic set of DEs is inspired by the ICARE forms [START_REF] Stokes | Managing engineering knowledge: MOKA: methodology for knowledge based engineering applications[END_REF]. An explanation follows: (1) Entity is a description of a specific component or subsystem and includes e.g. function and behaviour. (2) Activity is a task or process and basically describes how something is done including inputs and outputs. (3) Rule describes a valid relation for the designer to use, usually described by a mathematical formula. (4) Constraint describes a limitation usually based on some boundary condition e.g. manufacturing equipment.

The design description is a living document during PD and TD and is continuously filled in with the knowledge and relational descriptions as the product is developed.

Fig. 2. Design description class

The case company is a sub supplier within the automotive business. The company site in focus develops e.g. subsystems for the interior of the car where comfort is essential. Information about the case company was gathered by meetings, demonstration of applications, reviews of documents and in-depth interviews. The focus of the case study is to investigate how the quotation process can be supported by a platform description that contains both product and design process knowledge on different levels of concretisation.

As of today the case company sees possibilities of improvement when it comes to speed, accuracy and level of reuse in the quotation process. However, today there is no existing support for this.

The product

The product in focus is a system to provide a dynamic seat support for a car by the use of pneumatics. The system enables a highly customised pressure distribution on the body which can increase the comfort and the ergonomy eccentially. The system consists of a number of components and subsystems. The carrier plate, seen in Fig. 3, is mounted to the car seat and is the base for the rest of the pneumatic seat support system. The product architecture can be configured to feature from simple lumbar supports to highly dynamic full back massage systems including lumbar, side and cuchion supports. The system consits of pump, valves, hoses and inflatable elements that interfaces the human body and provides the varying pressure distribution. The valves and the pumps are connected to a PCB with hosting software that controlls the pressure, air flow and valve opening and closing sequences.

In order to receive a common generic view of the product the PVM method was used. Through a set of interviews and studying of the product documentation the common structure could be identified and validated. The following activities consisted of identification of metadata to describe and judge the applicability of the bottom most elements of the PVM. The metadata consisted of attributes that was a mix between: (1) given parameters that was customer quantifiable requirements or derivatives of requirements, (2) limitations of the component or subsystem, (3) geometrical dimensions, (4) characteristic features and (5) general information.

The quotation process

The process was mapped from a designer point of view and focus was put upon identifying crucial given parameters (e.g. requirements) going in to the process, what design Fig. 3. The carrier plate with the system mounted on it variables (variables set by the designer) they affected, and in turn what components and subsystems (items) that affected.

The quotation process of the company is similar to the standard case. It starts with an inquiry from customer or by a demo performed by the case company. An inquiry can be received either as a subjective question or with quantifiable requirements. The process is specified from a manager's point of view but does not support the designers to a large extent. The process might differ based on if the customer is experienced with the type of pneumatic system or not. It was discovered that the overall the quotation process can be divided into two parts. The first part is the configuration stage where already designed pneumatic systems are used as a first try in order to make an early judgment of the quotation feasibility. If the quotation continues, it moves into the design stage. This is where the components that are engineered to order is designed. Often a number of systems is offered, ranging from simple to high end, in order for the OEM to be able to offer products to a large customer segment. The first step in the subsequent PD is therefore to identify if commonality can be achieved between the different systems offered.

When mapping the quotation process it was identified that the company combines two different specification processes [START_REF] Hvam | Product customization[END_REF] when customising the system. Complex sub systems that have predictable interfaces or interfaces towards the own system is developed in the TD projects (Fig. 1). The subsystems and components developed within these projects are then configured upon customer (configure-to-order). The other types of components and subsystems are the ones with complex or unpredictable interfaces towards the customer product that the system should be integrated into. These components and subsystems are designed upon customer order making them engineer-to-order. A figure describing the principal relationships between specification processes and interfaces is shown in Fig. 4.

The identification of Design Elements

The Dependency Structure Matrix (DSM) tool was used to identify connections between parameters, design variables and items. Item refers either to a component or a subsystem. By combining the DSMs, mapping matrices was created to not only see the connections inside one matrix (e.g. parameters) but also between the matrices (parameters, items and design variables). This was done in order to ultimately map the given parameters to items and in that way cluster what parameters that will be the input to designing an item or configuring a system. All three DSMs play a part in defining DEs. Since both parameters (input to the DE) and design variables (output from the DE) are coupled to a generic item class, they will partly define the DE. Some parameters and design variables will be isolated to a specific item, some will span several items and some will only be on the architectural level. When evaluating the result of the DSM Fig. 4. Specification processes and interfaces one could see that the parameters mapped to one specific type of item as well as the type of system architecture. It could be concluded that these two were the parts of the product that were customised upon customer order.

A novel computer support system. A computer application called "Design Platform Manager" (DPM) was created to aid working with the presented concept. The application manages DEs and is created using the scripting language Visual Basic. The object structure is created as the above explanation. The DEs are created on templates using MS Excel for user simplicity. A controlled nomenclature is used to guarantee DE consistency. When a DE has been created by filling in an Excel template, the DPM indexes the Excel file and puts it into a file vault. At start up DPM reads a selection of contents from each DE and presents it in order for the user to search among DEs. When a DE is selected it is opened up in MS Excel to be edited or read. Fig. 5 shows a screenshot of the computer support system user interface as well as four Design Element templates. Upon quotation a class can be searched and the user is presented with the saved design elements that is valid for that specific class. This way the user will have a better foundation for making decisions and judge what labour that has to go in to the subsequent PD and in turn approximate the cost of a product. This enables the designer to have access to some of the design rationale in the beginning of PD that can support the development.

Discussion

To reuse knowledge created in the design process is an ever challenging task in industry. Past research has not been successful in covering the whole issue, rather small pieces have been covered to aid in specific situations, artefacts, processes and types of knowledge. This paper tries to add a piece in the unfinished puzzle by the use of a platform approach in order to support companies working in the ETO business. The presented concept uses Design Elements that are pieces of knowledge about the design Fig. 5. Screen shot of the "Design Platform Manager" user interface and Design Element templates process or the product. The definition assumes that the design knowledge can be discretised and formalised. By introducing DEs in the platform definition one introduces knowledge descriptions that can be on different levels of concretisation which also can constitute parts of the design rationale. This way, relevant design knowledge descriptions for each instance is captured, structured and coupled to a generic architecture to be browsed in the future. In the case of the development of a component where there are no finished designs, these DEs will create a base-line for the designer to start from, describing what entities, activities, rules and constraints that are valid for a specific class of component or subsystem. With the use of the DEs the development can start at a higher degree of concretisation due to the bandwidth of descriptions introduced.

The validation of the concept and proposed computer support system has been done as far as early testing at the case company. The design engineers are positive about the level of support it introduces for knowledge reuse, especially in the quotation process.

Conclusions and future work

The approach presented here addresses an area in platform based development where not much has been explored. The bodies of knowledge in the areas of component and module based product platforms as well as knowledge reuse is vast, but the combination of the two with a focus on sub-suppliers in the ETO business is lacking.

The paper describes how companies in industry can use a platform definition, consisting of both process and product knowledge, as a means to practice reuse to a higher degree. The approach is realized in the novel computer support tool called Design Platform Manager and applied in a case with a company active in the automotive industry.

The future work will consist of continuing the development of the Design Platform Manager in order to fully support the presented concept in terms of modelling design instances, searchability, visualisation of connections between DEs and between DEs and design instances. An ontology is also planned to be developed to better guarantee DE consistency. Evaluation of the concept and computer tool will continue as well.

Fig. 1 .

 1 Fig. 1. The Design Platform is fed with descriptions created in both TD and PD. These descriptions can then be used in future development project.

Acknowledgments. The authors would like to thank the case company for their invaluable information and resources. Also the Swedish Agency for Innovation Systems (VINNOVA) for partly financing this research.