R Ma

N Yuan

S Sun

P Zhang

L Fang

X.-H Zhang

X Zhao

Preliminary investigation of the microwave pyrolysis mechanism of sludge based on high frequency structure simulator simulation of the electromagnetic field distribution

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

To cite this version:

R. Ma, N. Yuan, S. Sun, P. Zhang, L. Fang, et al.. Preliminary investigation of the microwave pyrolysis mechanism of sludge based on high frequency structure simulator simulation of the electromagnetic field distribution. Bioresource Technology, 2017Technology, , 234, pp.370-379. 10.1016Technology, /j.biortech.2017.02.076. hal-01515158 .02.076. hal-01515158 ÿ ÿ ÿ 2ÿ ÿ 34 56 7 87 94ÿ 95 7 7 9ÿ ÿ 5ÿ 7 4 5ÿ 34 6 7 ÿ 597 8ÿ ÿ 6 5ÿ 5ÿ 9ÿ 7 ÿ4 559ÿ 4 4 5ÿ7 86 4 ÿ7 86 7 9ÿ ÿ 5ÿ6 5 4 895 7 ÿ7 56 ÿ 7 47 ! 7 9ÿ ÿ

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Irene Garcia
email: irene.garcia@uji.es

Luis E Rodríguez

Mauricia Benedito
email: mauri.benedito@uji.es

Sergi Trilles
email: sergi.trilles@uji.es

Arturo Beltrán
email: arturo.beltran@uji.es

Laura Díaz
email: laura.diaz@uji.es

Joaquín Huerta
email: huerta@uji.es

Mobile application for noise pollution monitoring through Gamification techniques

Keywords: Gamification, mobile applications, environmental monitoring, noise pollution, PPGIS, VGI

Full data coverage of urban environments is crucial to monitor the status of the area to detect, for instance, trends and detrimental environmental changes. Collecting observations related to environmental factors such as noise pollution in urban environments through classical approaches implies the deployment of Sensor Networks. The cost of deployment and maintenance of such infrastructure might be relatively high for local and regional governments. On the other hand recent mass-market mobile devices such as smartphones are full of sensors. For instance, it is possible to perform measurements of noise through its microphone. Therefore they become low-cost measuring devices that many citizens have in their pocket. In this paper we present an approach for gathering noise pollution data by using mobile applications. The applications are designed following gamification techniques to encourage users to participate using their personal smartphones. In this way the users are involved in taking and sharing noise pollution measurements in their cities that other stakeholders can use in their analysis and decision making processes.

Introduction

Many people on Earth are living in cities and it is expected that 70% of human population will live in cities by 2050 [START_REF]United Nations: Report about State of the World's Cities 2010/2011: Bridging the urban divide[END_REF]. This fact influences in the growth of activities carried on in industrial parks and urban areas including traffic and other human activities that affect environmental conditions such as noise pollution.

In order to guarantee a sustainable development of our cities, European policies try to regulate the evolution of these environmental conditions. Among others, the European Noise Directive (END) [START_REF]Parliament and of the Council of 25 June 2002 relating to the assessment and management of environmental noise[END_REF], adopted in 2002, establishes a legal framework related to the assessment of environmental noise. In Article 3, it is defined "environmental noise" as "unwanted or harmful outdoor sound created by human activities, including noise emitted by means of transport, road traffic, rail traffic, air traffic, and from sites of industrial activity". In the same article, other concepts like "annoyance" or "harmful effects for health" are defined.

There are authors who state that noise pollution could seriously affect human health: In [START_REF] Goines | Noise Pollution: A modern plague[END_REF][START_REF] Trombetta Zannin | Environmental noise pollution in the city of Curitiba, Brazil[END_REF] it is discussed the set of issues a sustained exposure to noise pollution could trigger, ranging from less-severe sleep disturbances or hearing impairment to much serious cardiovascular disturbances or mental instability.

Daily city activities cannot be stopped, but it is important to continuously pinpoint noise observations to understand if there is any underlying problem that could be a cause of human health issues that should be solved by any government entity. Noise pollution could be measured through sensor networks, but it is a phenomenon that occurs in the entire city with different intensity throughout time and space. Therefore, data acquired with this method could not be enough to depict the city situation.

In this context, it is important to consider a different way for data collection with a high temporal and spatial noise data resolution and with a low deploying cost. The key for this noise pollution monitoring in cities is based in citizenship participation. Involving citizens in monitor noise pollution by using mobile applications is a very cheap method for administrations to acquire real-time data that may help local or regional governments to identify potential problems and therefore, try to solve them.

In this paper we present two mobile application prototypes to collect noise pollution data in urban areas. One of the issues that arise when developing a crowdsourcing monitoring application is the fact that we rely on the measurements taken by the users, but, how to engage users to use this application and provide observations? The main idea is to engage citizens to take noise samples by gamifying the process of acquiring data to obtaining a noise pollution map. One of the problems we identify in the traditional mobile noise measurement taking is that we have to convince the user he or she has to start taking noise samples and keep this practice through time. In this new data acquiring approach, it is crucial the massive and maintained participation over time from general public. This would help creating a huge noise pollution repository to be used for further and more accurate analysis. The difficulty arises from the boredom of doing repetitive tasks without an incentive or amusing elements.

Here is where gamification techniques take major importance, because they provide a mechanism to motivate users to use the application and provide information while they are using a gamified application. In this paper we propose a general approach for noise pollution data collection that implements a crowdsourcing noise pollution monitoring application based on gamification techniques. The main idea applying these techniques to environmental monitoring is to encourage users to participate in data collection process by using their personal smartphone devices. The output of this public participation is a high amount of georeferenced noise pollution dataset that can be later used for further analysis or decision making processes. We demonstrate the application of these gamification techniques by implementing two mobile application prototypes as a proof of concept. Therefore, NoiseBattle and Nois-eQuest mobile applications will be presented as a new participatory way of noise pollution data collection.

The remainder of this paper is organized as follows: In section 2 we discuss the background of this work, including topics such as noise pollution monitoring, general gamification concepts and related work. In section 3 we describe how we applied to this project the gamification concepts. In section 4 we briefly describe the general architecture of this Project and present the two prototype applications in development and finally, in section 5, we present the conclusions and future work ideas.

2

Background & Related work

Environmental Noise Pollution Monitoring

Environmental monitoring is a crucial task to control our planet status and development trends. With the adequate set of technologies and tools it is possible to monitor almost any measurable parameter. In our case, we are interested in controlling the noise levels on cities.

In [START_REF] Bugs | An assessment of Public Participation GIS and Web 2.0 technologies in urban planning practice in Canela, Brazil[END_REF] it is described and applied the concept of creating a GI system with Volunteered Geographic Information (VGI), called Public Participatory GIS. The authors define a PPGIS as the result of using GIS capabilities and techniques by the general public, although it was first described in [START_REF] Nyerges | Public participation geographic information systems[END_REF]. Moreover, in this paper, scientist community is encouraged to break top-down strategies of delivering geographic data, where government entities, institutions or companies provide them at their own interest. The authors' state that is important to create new bottom-up data productions in order to create GI systems that really fits users' needs and availability. An example of PPGIS application it is found in [START_REF] Bugs | An assessment of Public Participation GIS and Web 2.0 technologies in urban planning practice in Canela, Brazil[END_REF], where Canela (Brazil) users can post comments about POIs related to health or education, such as complains for a school menu service or asking for information related to cultural heritage.

In [START_REF] Goodchild | Citizens as Voluntary sensors: spatial data infrastructure in the world of Web 2.0[END_REF] we could find a good description of the concept "Citizens as Voluntary Sensors". The author states that humanity as a collective, possesses a huge amount of knowledge about the Earth surface and its properties, such as place names, topographic areas or status of a transportation network. If we enable this people with electronic devices to digitize this information, we have a massive collection of raw data collected by volunteers that we can use in our analysis, services and geoprocesses.

Following the PPGIS and Citizens as Voluntary Sensors guidelines, we thought that it would be interesting to join both concepts to apply them in environmental noise pollution monitoring. In this field, some attempts already exist:

According to [START_REF] Maisonneuve | Participatory noise pollution monitoring using mobile phones[END_REF] there are three main approaches to assess noise pollution: simulation maps and data collection through sensor networks. First method consists in applying physical noise propagation laws considering well-known noise sources to get noise affection maps, while second method is based on acquiring data using a distributed network of sensor devices. Finally, there is another method they outline, based in the direct participation of citizenship by providing VGI.

In this paper, we are going to extend the idea described in [START_REF] Maisonneuve | Participatory noise pollution monitoring using mobile phones[END_REF] by developing two mobile applications to collect noise pollution data in urban areas by applying to its development Gamification concepts. Therefore, as users will collect their own noise samples, we are using the concept of citizens as sensors [START_REF] Goodchild | Citizens as Voluntary sensors: spatial data infrastructure in the world of Web 2.0[END_REF] and, as we are going to publish our data in a Noise Mapping Platform, we are contributing to the enlargement of a PPGIS.

General Gamification Concepts

The 'citizens as sensors' paradigm [START_REF] Goodchild | Citizens as Voluntary sensors: spatial data infrastructure in the world of Web 2.0[END_REF] implements the idea of crowdsourcing the sensor data collection. This is a straightforward way of collecting huge amount of data at a very low cost. Nevertheless, users need an incentive to make volunteers collect those data willingly. At this point here is where the gamification methodology plays its role. In [START_REF] Maisonneuve | Citizen Noise Pollution Monitoring[END_REF] it is questioned how the general public can be motivated to voluntary participation by displaying noise data publicly on a Web GIS platform through maps or allowing tagging the noises measured to enrich this information in a subjective way. However, applications with no incentives will probably attract users highly motivated to collaborate with this platform, just for their satisfaction of contributing to science. Those users will gladly update their observations in the long term, but this set of noise data, although big, will not represent the entire city situation. Gamifying a repetitive or complex problem breaks this gap/wall between a scientific problem and citizenship and allows any citizen to contribute to science unconsciously.

The core concept for gamifying is engagement. As seen in [START_REF] Zichermann | Gamification by Design. Implementing Game Mechanics in Web and Mobile Appls[END_REF], engaging users to do something is crucial to encourage citizenship to collaborate with a project. Engagement could be achieved by motivating people, so it is important to create nice and user-friendly applications that foster people to take the measurements we need.

According to [START_REF] Zichermann | Gamification by Design. Implementing Game Mechanics in Web and Mobile Appls[END_REF] to do a good gamification process it is important to consider four key concepts: user status, access, power & stuff.

Status: Users usually like to compare or share their progress and achievements with other users, to see who is in a better or worse position than others. To do this, it is necessary to split game progress in stages or levels, from easiest to hardest ones.

Access: This concept encourages allowing users to unlock new features depending on their contribution or participation in the game. It is important to make these features exclusive enough to engage the user who achieves them more attached to the application.

Power: With the transference of some power to some users, it is possible to encourage them to keep using the application. The power can be represented by letting them to do actions that are not allowed to users who have used less the application.

Stuff: In addition to all functional concepts stated above, it is important to provide a set of free rewards, badges or gifts for users as an incentive to keep playing. Those items are attractive to users because they can make the difference with others.

Related Work

Nowadays, there are many successful examples of gamified and purpose-oriented applications. It is the case of Phylo1 an application that exploits the natural capacity of human being to recognize visual patterns, an operation with a high computational cost. Phylo presents DNA sequences in the mobile device screen in a gamified context and engages users preparing a race competition among them and providing awards and acknowledgment for winners.

Another example of gamification comes from automobiles' brand Nissan2 . It includes in their new car models an application for monitoring gas emissions and featuring an automatic gaming system to provide real-time information about the gases emitted to the atmosphere. Users are then encouraged to drive responsibly to go up in drivers' rankings.

Regarding the collection of noise using public participation, several projects have been carried on. For example, in [15] is presented a project where the users can contribute to collect noise from the city and publish it in the NoiseTube platform. The platform offers a mobile application that consumes an API for sending the collected data. Later the user can see the maps with the noise data in a website. Other project worth to mention is presented in [START_REF] Bilandzic | Laermometer -A Mobile Noise Mapping Application[END_REF]. In this case the authors describes a mobile application for collecting noise data, and add the possibility of including extra information related with the perception of the noise measured (i.e. annoyance) or the location (i.e. home or work place). In both cases the incentive for collecting data is the mere contribution.

Finally, it is also important to consider the gamification techniques applied to produce FourSquare application, as it is a successful social game oriented to businesspurposes that breaks the wall between the virtual/real world by providing physical rewards to users.

Applying gamification concepts

After explaining the gamification theoretical concepts in section 2.2, we are going to explain how we carried on the gamification process in particular to our prototypes.

Considering the two use cases we have developed, those concepts have been applied as follows:

Status: In our project, we have created this progress based on the number of noise observations: as users collect information, they get more points that will increase general score and therefore, their level.

Access: The access concept is grounded as unlocking quests or owning more city areas, depending on the prototype. Collecting noise observations is the key to progress in both applications. Data acquisition is rewarded: as long as the users collect more noise observations, access to different kind of things is granted.

Power: In one of the prototypes we provide power by giving the capability of sending noises (or sounds) to an enemy in the battle. This kind of actions are important to foster competition among users, so they feel motivated to keep progressing in the game to gain that special power another user has.

Stuff: A set of avatars and rewards have been created for both use cases.

Regarding the target users analysis, we followed the classification found in [START_REF] Richard | Hearts, clubs, diamonds, spades: Players who suits MUDs[END_REF]. In this paper, the author divides users in four different types: killers, achievers, socializers & explorers. In our prototypes, we targeted the following users:

Noise Battle: The user profile we targeted is mainly Achiever. In this application, the idea is providing an environment where the user can win points and conquer areas, with the purpose to make the player feel rewarded just by winning and sending noises to the enemies. The competition factor is very important to make their achievements more satisfying.

Noise Quest: The type of user targeted in this second case is Explorer. Here the competition with other users is not as intense as the previous case. In this application it is more important walking around the city taking measurements than the score achieved by the number of observations taken. The "goodness" of the observation is more valuable than the number of measurements collected.

4

Architecture and prototypes

General architecture

This section describes in detail the conceptual architecture we used. Figure 1 depicts the general architecture of the project. The prototypes in-development for this project follows the same schema. As seen, the modules are divided in three parts: Mobile Client-side application, Middleware Layer and Remote Server-side that are described below these lines.

The Mobile application provides the functionality that allows user to take measurements, send them to the middleware and check the general progress of the battle in course. We suggest that the application should be divided in the following modules: User Interface, Measurement, Mapping and Connection & Encoding. For the User Interface we used Android SDK because it is a free and growing development platform and provides a good integration with Google Maps, the engine we used for our Mapping module. Regarding the Connection & Encoding Module, we decided to implement our own classes in Java to connect and send the data to the Middleware Server. For the Measurement Module we used part of the mobile noise pollution measurement application developed by IFGI (Institute for Geoinformatics, University of Münster) called NoiseDroid. NoiseDroid is an open-source mobile application that allows the user taking noise samples. This application has its own noise quality assessment system which provides information about the usefulness of the noise data collected [START_REF] Foerster | Integrating Human Observations and Sensor Observations -the Example of a Noise Mapping Community[END_REF][START_REF] Everding | In-stream Validation of Measurements with OGC SWE Web Services[END_REF]. Due to the open-source condition of NoiseDroid, we reused source code related to the collection and assessment of the noise samples, and include it in our Measurement Module.

Middleware layer has as main goal to attend all incoming noise observations, store them in a noise database and send the measurements taken to a remote server. This layer, that should lay on an intermediate server, takes care as well of keeping the user's status up-to-date in real-time, writing in the database the new data and sending back the status to the user while notifying other users of the changes on the game they are playing. We have divided the functionality of this server in three different modules: Client Communication, Transactional, Remote Server Connection. For the Client Communication Module we decided to develop our own set of classes in Java. The Transactional Module is programmed in Java as well, but we used Hibernate for the communication with the database. In the case of the Remote Server Connection Module we used the API provided by the server for sending the noise data.

Remote Server-side is the module that will contain all retrieved VGI noise data from users and will allow the analysis by general public by providing some mapping layers. We think about the functionality of this server in these modules: Mapping and Data Management. In order to reuse available resources, we decided to contribute to Open Noise Map Platform (ONMP) by sending our collected data to this noise mapping platform. ONMP was developed by IFGI and provides a Web GIS interface where it is possible to see uploaded noise measurements comfortably, using a map layout.

Noise Battle prototype

Noise Battle is a gamified mobile application developed for Android platform where users have to move around a city taking noise samples. Currently the game is on development and it is not entirely functional or available to download. The final goal of this game from the user's point of view is conquering the city by taking noise measurements.

The city is split into cells of a grid, so the user can conquer the cells by taking more and better measurements than other users in the area. During the game, the users are rewarded by different means: either by measuring in the proximity of one of the rewards placed in the grid or by conquering some cell of it. The rewards might include the possibility of sending noises or sounds to the foes. The sounds that can be sent to the rivals are used to show the power obtained by the sender of the noise. The rivals have the option of re-conquering previously conquered cells by performing better quality measurements or more recent measurements. These mechanisms should encourage the players to provide more accurate (based on a criteria taken from the API used) or updated noise data. Regarding the rewards, we have considered awarding measurements dispersion and data quality (based on NoiseDroid quality assessment) in order to assure a regular number of observations taken in the entire city area. Besides, we also took into account to place rewards (or having higher density of them) in zones where there is more interest about noise pollution conditions. The observations gathered are immediately uploaded to the middleware server, which further submit it to the ONMP platform. The ONMP platform can store it and make it available for visualization or processing.

In Figure 2 (left) it is possible to see a sample of the battlefield where a game is going to start. As seen, the city is divided in a grid where each cell represents an area the user can conquer through taking noise measures. For each measurement performed, it is possible to see the minimum, maximum and mean of noise measured. Then the player can decide to submit it as his move in the game. In this case there are some items placed for each cell that represent locations where the player can take a noise measurement and receive a reward. Figure 2 (centre) represents a more advanced state of the battle for that city, where some users have started using the application and conquered some areas. The areas conquered can be recognized by the colour of the cell. In this scenario there are three players, each of them with a different colour and avatar associated competing each other. Figure 2 (right) provides a higher level of detail of the image in the centre. In the next section we briefly describe the second prototype. Fig. 2. Some images depicting NoiseBattle prototype working.

Noise Quest prototype

Noise Quest is a prototype of mobile application for Android platform that using quests, challenges and missions will guide a user around a city taking noise samples following a storyline. At this point, NoiseQuest application development is in a very early stage, so it is not possible to present any sample screenshot. The quests are focused in conquering different POIs by taking samples, making a competition with the different users playing the game and progressing in the story. The general idea of this application is to obtain noise measurements distributed uniformly around the city throughout time. For this purpose, the application will guide the user over all city area following a storyline where he or she is the main character. This game has different levels of difficulty so quests will be easier at the very beginning of the game and getting harder as long as the player advances in the game. The game starts in the user position and taking this point as a centre it draws three concentric circles with a determined radius whose size depends on the selected level: the higher the level, the bigger the circles are and therefore, the general difficulty of the game increases until covering the entire city area. First quests consist in obtaining measurements in the user's surroundings, located in the most inner circle. As long as the user completes the quests, the missions and challenges will lead the user to positions farther away, in the outer circles.

Conclusion

In this paper we presented an approach for designing environmental noise pollution monitoring applications based on crowdsourcing by means of applying gamification techniques. We presented a conceptual architecture and components to implement this kind of applications. For demonstration purposes two gamified mobile applications for noise pollution monitoring have been developed. The use of these applications by general public could contribute to increase urban society welfare through noise sampling, locating areas with a higher noise pollution to make some research or analysis and try to solve the problem. Gamifying it is an interesting process to convert tiring and repetitive tasks in others lighter and more user-engaging ones that can provide huge amount of data to alllevels government entities and other decision makers. Logically, if a tool capable of spotting noise problems is created, it would be interesting from local authorities to consider this potential source of data to improve liveability of a city.

Developing purpose-oriented and gamified applications for mobile platforms it is very interesting due to its big range of possibilities and topics to create applications. Nevertheless, we think that in parallel, it is recommended to provide a pure GIS application where it would be possible to check and make operations with the set of data and make analysis.

As future work, it would be interesting to implement mechanisms for filtering and correcting VGI data, as per nature, some of them might be false or inaccurate for scientific analysis. On the prototypes functionality, two improvements could be done: at this point, both applications are spatially dividing the city in a grid in NoiseBattle case and in concentric and growing circles in NoiseQuest example. It would be interesting to change these geometric shapes into more real ones that fit a city district or neighborhood, so the user is competing in more natural divisions. The second idea would be implementing a noise measurements expiring policy for observations. A user would lose his/her score progressively in time with the aim of sticking the user to the application: the idea is encouraging them to keep them taking noise samples by slowly removing their conquers and score due to inactivity.

Fig. 1 .

 1 Fig. 1. General architecture of the proposed solution.

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Acknowledgements. This work has been partially supported by the GEOCLOUD project ref. IPT-430000-2010-11, INNPACTO 2010 subprogramme, Ministry of Science and Innova-tion; OSMOSIS: Open Source Mobile Sensor Information System. IMPIVA Institute (Institute of Small and Medium-sized Enterprises from Generalitat Valenciana) and European Regional Development Fund (ERDF), ref. IMPIVA I+D IMIDTA/2009/793 and IMIDTA/2010/24


Paolo Ciancarini

Andrea Gasparro

Priority Level Planning in Kriegspiel

Back in 1950, Shannon introduced planning in board games like Chess as a selective approach, where the main idea is to select specific branches of the game tree that satisfy certain conditions. He contrasted this approach with brute force Minimax-like methods, based on an exhaustive search of the game tree, that aims to select the best path inside a given search horizon. Historically, the brute force approach won hands down against planning in complex games such as Chess, as the strongest Chess programs nowadays all exploit brute force algorithms. However, planning is still interesting and even necessary in some game-playing domains, for instance based on incomplete information, where there is no way to evaluate precisely or even build the game tree. In this paper we describe a technique that produced positive results in Kriegspiel, a variant of Chess played as an incomplete information game. Our main result is the definition of an algorithm for combining MonteCarlo search with planning; we tested the algorithm on a strong Kriegspiel program based on MonteCarlo search, and obtained a clear improvement.

Introduction

Partial information games are a challenging domain to study and test decision making under uncertainty, that is a key concept in game theory and also a widely studied topic in many economical simulations [START_REF] Ciancarini | Decision Making under Uncertainty: A Rational Approach to Kriegspiel[END_REF]. For instance, uncertainty can be introduced in perfect information games by making invisible the opponent moves (as in a war-game referred by an arbiter [START_REF] Perla | The Art of Wargaming[END_REF]). This invisibility usually introduces important changes to any algorithmic playing approach: the search space size and the related game tree branching usually grow dramatically, whereas one of the key results in games theory, namely Zermelo's theorem [START_REF] Zermelo | On an Application of Set Theory to the Theory of the Game of Chess[END_REF], is no more valid because its assumptions do not apply. More important, these changes reflect on the effectiveness of playing algorithms which work well for the standard game [START_REF] Campbell | A comparison of minimax tree search algorithms[END_REF] but must be completely redefined for its variants based on partial information.

Kriegspiel, the board game we are focusing on in this paper, is a practical example of our previous statements: removing most of the information given to a player about his opponent's moves, increases dramatically the average branching factor during middle game from 33, that is the Chess branching factor, to 33!, that is Kriegspiel branching because a player can try its pseudolegal moves in any order. We remind that the branching factor greatly affects the performances of Minimax and its derivative algorithms. Hence, the best Kriegspiel artificial player, as described in [START_REF] Ciancarini | Monte Carlo Tree Search in Kriegspiel[END_REF], is not based on Minimax, but on Monte Carlo Tree search instead.

This paper has the following structure: in section 2 we provide a description of Kriegspiel, introducing its rules and most important features, from the point of view of an artificial player. Section 3 contains a description of the state of the art, with special interest to Darkboard, the current world champion of Kriegspiel. Section 4 presents the main topic of this paper, namely our original planning based approach, that we applied to Darkboard to play Kriegspiel, but that can be applied to other playing domains based on partial information and with a large branching factor. In section 5 we present the results obtained by an experimental player, based on the technique we presented, matched against the current world champion program, Darkboard. Finally, in section 6 we summarize and discuss our results, concluding with the future developments we are considering.

Kriegspiel

Kriegspiel, or Blind Chess, is a chess variant invented by Michael Henry Temple at the end of the XIX century, first played and standardized at the famous London chess club "The Gambit". It can be considered a descendant of an already existent prussian war game, named Kriegspiele, invented at the beginning of XIX century for training Prussian army officers. Kriegspiel rules are the same as chess for what concern the goal of the game and piece movement rules, but differently from Chess, there are three main actors involved: the white player, the black player and an umpire.

Each player can see only its pieces, while from the point of view of the umpire, Kriegspiel is just a normal chess game. Being the only one informed on the real state of the board, the umpire is in charge to inform players if the moves they make are legal or they are not. For instance, a move could be illegal because it exposes the king to a check, or because the trajectory to a square is not completely free. If a move is refused by the referee, a player has to chose a different one, that is again evaluated by the umpire, and so on.

Thus, designing a program to play Kriegspiel is very different from designing a program to play Chess, due to information on the game state only partially available. Partial information grows the branching factor, while the space state remains the same of chess, that Shannon estimated at 10 42 [START_REF] Shannon | Programming a computer for playing Chess[END_REF]. The reason of the larger branching factor resides in the fact that a Kriegspiel player can try its pseudo-legal moves in any order: if a move is legal then it must stay, else the player must try another move. Thus, all possible permutations of pseudo-legal moves should be enumerated to define the branching factor of Kriegspiel.

This huge increment in the branching factor reflects the fact that in each state a player does not know what is the current position of the opponent's pieces. Hence, an artificial player should somehow keep trace of all the possible configurations of the board, in each different moment of the game. This leads to the need to abstract away different positions, that are indistinguishable from the agent point of view, into a single representation: this is the key idea behind Metapositions, first applied in Shogi [START_REF] Sakuta | Deterministic Solving of Problems with Uncertainty[END_REF] and successfully reused in Kriegspiel [START_REF] Bolognesi | Searching over Metapositions in Kriegspiel[END_REF].

The reason why we have chosen Kriegspiel as our domain of study is that it is not yet a fully explored game, with significative differences from Phantom Go and other imperfect information games, as that the nature of Kriegspiel's uncertainty is completely dynamic, making it an interesting environment to simulate different kind of real life tasks.

Planning in board games: State of the Art

Recent researches in games like Phantom Go and Kriegspiel contributed to focus on a relatively unexplored category of partial information games, derived by well known perfect information games, introducing a concept of invisible moves. This area proved to be a challenging domain for artificial players based on brute force, leading to the development of strategies to handle meta states, with the aim to reduce the space state and the branching. This happened exploring metapositions in in Kriegspiel, as described in [START_REF] Ciancarini | Representing Kriegspiel States with Metapositions[END_REF].

A strategy similar to the one used to play Go proved to be quite effective in Phantom Go, as described in [START_REF] Cazenave | A Phantom-Go program[END_REF], also because of the monotonous decrease of uncertainty that makes progress somehow simpler to handle, in comparison with Kriegspiel.

Until a few years ago, only a few amount of research had been devoted to Monte Carlo in games with dynamic uncertainty, with the notable exceptions of [START_REF] Chung | Monte Carlo planning in RTS games[END_REF], which first studied planning based on MonteCarlo, and [START_REF] Kocsis | Bandit based Monte Carlo Planning[END_REF], which developed a more efficient approach based on a bandit algorithm called UCT (Upper Confidence bounds applied to Trees). We exploited UCT in the development of Darkboard, that is basically a program combining UCT with a node evaluation function [START_REF] Ciancarini | Monte Carlo Tree Search in Kriegspiel[END_REF].

The contributes to the study of Kriegspiel, brought by the experiments conducted developing the artificial player Darkboard, were the most significant progress in the study of the game, involving for the first time the use of metapositions in Kriegspiel, also introducing a Monte Carlo based approach to handle middle-game. Darkboard represents the state of the art in Kriegspiel playing as it is also the current Kriegspiel world champion.

Priority Level Planning in Kriegspiel

Kriegspiel is a hard game to play for rational agents: due to the huge branching factor mentioned above, in approaches of Shannon's "Type B", that is brute force, the ability to evaluate different states plays a key role in reducing the search space, that directly reflects on the effectiveness of brute force analysis. Unfortunately, even with the help of Metapositions, this is a very hard task for artificial players, as it involves the ability to understand the "meaning" of a position.

An approach based on planning is a more natural choice to provide an agent with a "human like" understanding of a position. However, planning was not successful in chess-playing programs, as it reduces consistently the speed of states evaluation and, consequently, the horizon of the program. This actually cuts off the possibility to base the evaluation of a state on a long range analysis.

Our approach is then based on a planning technique, meant to predict the evolution of game tree branches, basing only on factors that must be present in the present state. This requires the search of "structural factors" included in each state, that can be associated to a predictable evolution in the long run.

This technique seems to apply perfectly with Kriegspiel, because strategical elements are included in each state. Those elements can be used to form a plan, where a plan is just a sequence of transitions which fit the actual configuration of the board. An example of the strategical elements we are speaking about can be the presence of open files, if heavy pieces are still on the board, etc.

In this paper we focus on the middle-game, as it is the game phase where introducing a priority level planner does not cause any sensible change in move generation's speed. We have built a planner which during middle-game (which starts when the opening phase ends, i.e. when the program exits from its opening book, and ends when the position has no more pawns) splits move generation in two phases: first, it tries to elaborate short term plans, aiming to reach "important" goals which are enough "close", if there are not such goals reachable from the current state, it tries a long term evaluation of each interesting candidate transition originated from the current state.

This algorithm requires the definition of two different categories of goals:

priority goals Goals that represent a short term advantage. Examples of short term goals may be piece capture, king safety, etc. long term goals Examples of long term goals may be placing our pieces in favorable positions, regrouping pieces in a way that makes easy for them to cooperate, etc. Each goal has a priority that represent its importance. This category includes what a chess player could call strategic or long-term goals.

The goal sets were defined according to standard chess theory. This highlights an advantage of choosing Kriegspiel as our applicative domain: a Kriegspiel planner can benefit from the well known theory of Chess, to identify key factors in a position, as long as it evaluates those factors in his own way, considering the significant differences introduced by partial information.

Our algorithm for move generation includes the following three steps:

EVALUATION The program evaluates the current board state, searching for priority goals. This task is simplified by Kriegspiel rules, since we identify priority targets thanks to umpire messages informing that a pawn try is available, that a piece has been captured or that one of the player has delivered a check. SELECTION If a priority goal is reachable, the goal set includes only the moves that are supposed to lead to the goal, else the agent analyzes each action within two level of depths searching for long term goals. This description highlights the fundamental importance of long term goals in move generation, as priority goals cover only a small set of possibilities. At the same time, long term goals deal with strategic factors. This technique may be promising in a domain with a clear notion of strategy, as it is the key concept used to predict the quality of a path, without the need to evaluate a large set of states. This also means that this technique can be applied not only to Kriegspiel, but also to any strategic game with partial information and a large branching factor.

Fig 1 summarizes the process we just described.

The above algorithm contains the key idea of our approach. However, if implemented verbatim it would be be highly ineffective in practice. The reason is that an agent whose move generation relies entirely upon its goal set, when no priority goal is available, is forced to define a huge number of goals to deal with each possible situation. This leads to two different problems: first, it turns out to lack flexibility to handle a complex game like Kriegspiel; second, this does not correspond to what we defined as a long term goal set.

Instead, before searching for long term goals, we execute a one step Monte Carlo analysis to filter moves that have an evaluation below some threshold. After doing so, we execute the steps described above. Nothing changes in handling This second approach offers two advantages. First, it does not force the agent to misrepresent the idea behind the concept of long term goals. The second advantage is that filtering the moves that the planner has to analyze reduces the computational cost dramatically, as it cuts the branching factor, while the brute force method may be limited to a very short depth. Thus, both strategies benefit one of each other.

Experimental results

To evaluate the result obtained introducing a priority level planning in Darkboard, we tested our enhanced player in tournaments against other programs. Those programs were:

-World Champion The current world champion version of Darkboard, presented in [START_REF] Ciancarini | Monte Carlo Tree Search in Kriegspiel[END_REF]. -Random Player A pseudo-random player, useful to evaluate the behavior of our program against an unpredictable opponent. -Strategic Darkboard The World Champion program enriched with a priority level planner.

Our experiments consisted in tournaments of 20 games between Strategic Darkboard and another program. This is a well known technique, since the first Belle's experiments by Ken Thompson [START_REF] Thompson | Computer Chess Strenght[END_REF].

The first series of experiments, consisting in 3 tournaments of 20 games each against the Random Player, confirmed that the random player is not an interesting opponent, as the average result is 85% of success for Strategic Darkboard, where all games that were not won were draws for stalemate (if the opponent king is in check and cannot move a game is draw according to chess rules).

The second series of experiments was far more interesting, consisting in 5 tournaments of 20 games each between Strategic Darkboard and the World Champion: it ended with the average success rate of 61% for Strategic Darkboard. Thus, according to the standard Elo scale, Strategic Darkboard gained a class, compared to Darkboard previous's version.

The table summarizes the results obtained in our tests. A second set of experiments against human players is currently taking place on the Internet Computer Club (ICC), which hosts the largest Kriegspiel community. The partial results until now indicate a smaller improvement, but it will take some time to collect enough data to drawn some definitive conclusion.

Conclusions and further developments

One problem when implementing a program for playing an imperfect information game with a high branching factor is the horizon effect. Because of that, planning may be an interesting approach in such a domain, due to the fact that a planner does not analyze the totality of the states, but instead it focusses only on promising branches.

The technique we have proposed is a hybrid between planning and brute force, developed to manage two different aspect: short term game playing, that is based on brute force and somehow does not care about the branching factor, since there is a priority goal reachable inside the horizon of the agent, and long term playing, basing on the notion of strategy.

While experimental results are promising, it is important to remember that this technique relies heavily on the presence of a dense notion of strategy in the application domain, that is a key condition for limiting the depth of the searching algorithm. This limitation however is double edged, since a dense notion of strategy leads to impressing performances as shown by the experiment conducted against the world champion program of Kriegspiel.

A further development will focus on refining the long term goal set; in our experience human players, that currently outperform our Kriegspiel program, orient their game playing according to repetitive strategies: analyzing an already available collection of Kriegspiel games with a pattern recognition algorithm,may lead to identify new goals or even just to update the already existing one ratings, hopefully improving the long term view of the agent, that's the most interesting feature of this technique.

Finally, even if we obtained some interesting results, Strategic Darkboard played with a handicap: in fact, the goal set used by the program is quite limited. Future development will focus on additional strategies to populate the goal set with efficient targets, thus we expect an improvement of the playing strength.

Fig. 1 .

 1 Fig. 1. Activity Diagram representing the move generation process

Fig. 2 .

 2 Fig. 2. Activity Diagram representing the move generation in Strategic Darkboard

Table 1 .

 1 Results of playing experiments

	Opponent	Strategic DB Opponent
	World Champion	61%	39%
	Random Player	85%	15%


Aljosha Demeulemeester

Katriina Kilpi

Shirley A Elprama

Sammy Lievens

Charles-Frederik Hollemeersch

An Jacobs

Peter Lambert

Rik Van De Walle

The ICOCOON Virtual Meeting Room: a Virtual Environment as a Support Tool for Multipoint Teleconference Systems

Globalization and increasing collaboration between remote teams drive the need for teleconference systems. However, currently no videoconferencing system matches the face-to-face experience for a business meeting with many participants in a flexible and affordable manner. In search for a better solution, we created a Virtual Meeting Room (VMR) application that visualizes key events detected using computer vision (e.g., participant entering the meeting room, talking, presenting) in a 3D virtual environment. The goal was to provide a good sense of overview to users when many meeting participants -represented by 3D avatars -from remote locations join a teleconference. In this paper, a technical overview of the working prototype -built using 3D game technology -is presented. Also, feedback from multiple user tests performed during the development of the prototype is discussed and presented as a set of recommendations. From the technical perspective, we found that existing 3D game technology is mature, affordable and contains the features needed to build the VMR application. From the users' and experts' feedback, we conclude that the VMR has merits as a teleconferencing support tool accompanying a video stream that conveys more detailed non-verbal communication of the active speaker.

Introduction

Teleconferencing systems are omnipresent in modern business environments. They range from basic phone conferencing systems, which allow many persons to join a phone conversation, to more elaborate setups using high-definition video streams displayed on large screens. Teleconferencing allows remote teams to collaborate without loss of time in traveling, which leads to cost and energy savings [START_REF] Lab | How Meeting In Second Life Transformed IBM's Technolgy Elite Into Virtual World Believers[END_REF]. However, current-generation systems are lacking as users still report the need for face-to-face meetings, particularly when many participants are involved. Some of the central complaints about the current teleconferencing tools, on top of the complicated setups, are the lack of a clear overview of the entire meeting situation and the lack of the co-presence experience due to the way in which the audiovisual data is presented. The multidisciplinary ICOCOON project 4 aimed to tackle these issues by extracting knowledge by means of computer vision from audiovisual streams captured by a visual sensor network from multiple locations involved in a teleconference. This knowledge is then used to automatically select the most relevant video stream (e.g., someone presenting or asking a question) among all video streams from all locations to present to the user. Additionally, the project investigated the possibility of visualizing the captured knowledge in a virtual environment (VE) 5 resulting in our Virtual Meeting Room (VMR) application, which is the focus of this paper. Our approach aimed to visualize the high-level interpretation of captured knowledge in the context of a business meeting (see Section 3). The main goal of the VMR is to provide the same sense of overview (and more) one has during a conventional face-to-face meeting where all parties are present in the same location. The basic premise was that this could be valuable, especially in business meetings with many participants where only one participant is shown in a video feed to remote participants. Using a virtual environment, 3D humanoid avatars can convey actions of meeting participants in a way that can be interpreted intuitively by a user. Also, this approach offers a lot of flexibility on the way knowledge is visualized. This allows for an abstract representation of what is happening in the real world which facilitates the feeling of overview.

In this paper, we present a technical overview of our working teleconferencing prototype. Additionally, we present recommendations on the use of the VMR and the way knowledge should be visualized. The recommendations are derived from user evaluations and expert reviews, performed at different stages in the development of the prototype. The paper is structured as follows. After the overview of related work in Section 2, Section 3 discusses the semantics of captured knowledge and its representation in the VE. In Section 4, a high-level technical overview of the complete system is given. Section 5 describes the visualization module that renders and animates the virtual environment and the 3D avatars that represent the meeting participants. Section 6 describes the user research methods used and the set up of the proxy meeting technology. In Section 7, we formulate recommendations based on the feedback of the users and experts which we discuss further in Section 8.

Related Work

The next generation of teleconferencing goes beyond merely displaying a captured video stream of one or multiple meeting participants. The immersive 3D videoconferencing system of Kauff and Schreer [START_REF] Kauff | An immersive 3D video-conferencing system using shared virtual team user environments[END_REF] uses a shared virtual table environment. Participant video streams are modified using image-based rendering to enable natural representation of gestures, eye contact and gaze. As a downside, the amount of participants is limited and they require a specialized setup for the purpose of teleconferencing.

Teleconferencing using a large amount of participants has been explored by IBM [START_REF] Lab | How Meeting In Second Life Transformed IBM's Technolgy Elite Into Virtual World Believers[END_REF] using Second Life (SL), the massively multi-user online game-like 3D virtual world for social interaction. Users in SL are represented by a customizable 3D avatar in the virtual world and can interact with each other through spatial voice chat, text chat and avatar animation. The avatar is explicitly controlled by the user. The authors report positive feedback from the participants of a conference held using SL with over 200 participants. Kantonen et al. [START_REF] Kantonen | Mixed reality in virtual world teleconferencing[END_REF] enabled two types of participant: the first (virtual) participant uses a SL viewer and explicitly controls his avatar in the VE, the second uses augmented reality to visualize virtual participants in the physical meeting room. Hand tracking is performed to allow interaction with the augmented virtual world and to allow gesturing with their avatar. Regenbrecht et al. [START_REF] Regenbrecht | An augmented virtuality approach to 3D videoconferencing[END_REF] present an augmented virtuality system for teleconferencing with video streams of participants being visualized inside the VE. Recent work by Lou et al. [START_REF] Lou | PresenceScape: Virtual World Mediated Rich Communication[END_REF] focuses on informal communication in work settings. Their system called PresenceScape provides an immersive and interactive virtual office environment for the informal communication in the office space.

Using 3D avatars for communication has been extensively studied, both from the technical point of view as from the user perspective. A self-animated avatar in an augmented virtuality setup directly reflects the movement of a human in the real world. This allows using gestures and body language to convey a message [START_REF] Dodds | Talk to the Virtual Hands: Self-Animated Avatars Improve Communication in Head-Mounted Display Virtual Environments[END_REF]. The appearance (i.e., surface texture and geometry) of the avatar is usually predefined and the animation is done by manipulating the virtual bones of the character. A real-time motion capture system can track the position of all human limbs. However, to decrease the required network bandwidth, and to increase the amount of expressiveness in the avatar visualization, Arita et al. [START_REF] Arita | Real-time Human Proxy: An Avatar-based Communication System[END_REF] symbolizes the raw motion capture data using knowledge on the communication context (e.g., teleconferencing, tele-teaching). The captured symbols, which represent intentions of communication, are sent over the network and transformed into high resolution motion data suitable to animate different avatars. This is comparable to our approach of detecting meeting participant actions that are relevant, sending this knowledge to all visualization clients and visualizing this in the most appropriate way in the VE. However, our system currently does not use detailed human motion capturing. This technology is not mature enough to capture human limb movement of many participants in one room full of obstructions (e.g., chairs, tables) without imposing many restrictions. Detailed non-verbal communication of participants is conveyed through the video stream that accompanies the VMR. As an alternative to motion capturing, the surface geometry of humans can be continuously captured using real-time 3D reconstruction from video streams [START_REF] Lien | Skeleton-Based Compression of 3-D Tele-Immersion Data[END_REF]. These geometry sequences are implicitly animated and can be directly visualized in a VE. However, due to the lack of a control structure such as an animation skeleton, the geometry cannot easily be modified automatically to adapt the participant's virtual representation to the VE and other avatars (e.g., pointing or looking in the right direction). Also, 3D reconstruction requires more network bandwidth than streaming (symbolized) motion data.

While little research has focused on avatars in formal settings, Inkpen and Sedlin [START_REF] Inkpen | Me and my avatar: exploring users' comfort with avatars for workplace communication[END_REF] investigated the use of 2D avatars for workplace videoconferencing. Their findings suggest that users are concerned how they are represented as avatars, but not about the representation of the ones they interact with. Focusing more on showing behavior than the design of avatars, Reidsma et al. [START_REF] Reidsma | Virtual meeting rooms: from observation to simulation[END_REF] developed a virtual meeting room that can translate observations (such as gestures and gaze) from audio and video to animations in an avatar based virtual meeting room.

Meeting Observations in the VMR

A typical teleconference has participants from two or more locations. To enhance the feeling of co-presence, the avatars are represented in a single virtual (meeting) room which is the background for the visualization of captured knowledge. Similar to Reidsma et al. [START_REF] Reidsma | Virtual meeting rooms: from observation to simulation[END_REF], we recognize that the observed knowledge from the physical world can be interpreted on progressively more complicated levels. For example, the exact position of the hand of a user can be detected. Depending on the position, this can be interpreted as hands being held up, which in itself can be interpreted as voting behavior or asking to speak. What we define as a meeting observation in our system are the high-level interpretations of the observed knowledge. These need to be visualized in the most recognizable way. Thus, the avatars in the VMR (see Figure 1) do not necessarily reflect participant actions directly. For example, the exact position of a meeting participant is not relevant so the result of the people tracking (see Section 4) does not need to be visualized exactly. Incidentally, it is not straightforward to map coordinates of multiple locations into one virtual location. However, proximity to certain objects (e.g., presenting board, other participant, etc.) is meaningful and is thus categorized as meeting observation. Using 3D humanoid avatars is an intuitive presentation form of meeting observations as opposed to text. This has the additional advantage that, when no high level interpretation of the collected knowledge can be made, the knowledge can be visualized directly to be interpreted by the user. For our earlier hand tracking example, this means that the avatar's hand position directly reflects the participant's hand position while leaving the user to decide on the meaning of the hand gesture.

In a teleconference scenario, knowing who is present is essential. This has to be interpreted as being part of the meeting in some way. Derived from presence are a number of meeting observations that we identified: participant enters the meeting, participant leaves the meeting temporarily (e.g., to restroom), participant exits the meeting permanently, participant re-enters after temporary leaving and participant joins unexpectedly. Additionally, it is visualized which participant is speaking, who is presenting and where each participant is looking (e.g., is s/he paying attention). As a form of metadata about the physical world, detailed information of each participant (e.g., name, company, meeting role, etc.) is also shown in the VE.

Overview of the Teleconference System

The entire system can be subdivided in three main parts. First, information about each location is captured using a visual sensor network comprising of multiple spatially distributed cameras per location (smart rooms). This information is processed by a multitude of computer vision algorithms to attain knowledge about each location. The high-level vision algorithms each monitor a single property of one or multiple objects at a location (e.g., position of participants, are hands up/down, etc.) with high accuracy. The gathered knowledge is sent over the network to the central aggregator using JSON formatted messages. Second, the aggregator enriches and corrects the received knowledge and sends the consistent knowledge to the last subsystem, namely the visualization component (i.e., the VMR application). The latter consists of the visualization server and a visualization client per participant. The server is responsible for adapting the virtual world state to reflect what is happening in the physical world based on the received knowledge. Also, it distributes the virtual world state to the visualization clients that each render their own unique view on the virtual world.

The architecture of the overall detection system consists of multiple smart rooms and the network infrastructure (see Figure 2). Each installed smart room comprises a calibrated smart camera network and one video aggregator. The smart cameras capture, resize, compress and send the video streams towards the video aggregator. The video aggregator extracts knowledge out of the captured video streams and sends this to the knowledge aggregator located in the network. In our smart room prototype, four overview cameras are mounted high and have a full view of the meeting room while three front-view cameras are mounted at eye height for capturing an optimal frontal view. Current extracted knowledge per location consists of a person's position and identification, gaze direction and activity status (e.g., sitting, walking, presenting, hands up/down). Four computer vision algorithms are used: face recognition by use of parabolic edge maps [START_REF] Deboeverie | Face analysis using curve edge maps[END_REF], people tracking [START_REF] Grünwedel | Decentralized tracking of humans using a camera network[END_REF], gaze detection [START_REF] Marin-Jimenez | heres looking at you, kid. detecting people looking at each other in videos[END_REF] and hand detection and tracking. In our prototype, knowledge on people's position is used for extracting the behavior (e.g., entering, sitting, presenting) of the persons involved, based on the location of the person in the physical world (e.g., at the presenter board), the walking direction and speed and the size of each person. The people tracking module is also tightly coupled with the face recognition module that processes all people entering the meeting room and sitting at the table so that each moment in time the correct activity can be linked to the correct person. The person's gaze is extracted using a combination of face recognition and the upper-body detector module. In addition to the smart rooms, participants can also join from other locations. In this case, only the web cam of their personal computing device is used with a video aggregator running locally on that device (see Figure 2). The only difference for this kind of participant is that the types of meeting observation that can be made are reduced.

The VMR Visualization Client

In business meetings, it is common for participants to bring their own computing device (e.g., laptop, tablet, etc.). The VMR client is intended to run on these devices. This approach eliminates the need for dedicated hardware. Also, this allows participants to observe the meeting using the VMR even if they are not in one of the smart rooms. Therefore, the VMR client should run on the widest possible array of devices and require the minimum amount of memory and computing power possible. Because each client renders its own view on the virtual world, real-time 3D rendering, accelerated by common graphics hardware, is the preferred option to visualize the VE. As many avatars can be present in the VE, the avatar animation system should be highly optimized for speed. From these requirements, it was clear that modern 3D game middleware technology (i.e., game engine) is a good fit as it enables state-of-the art simulation and rendering while staying within the limits of commodity hardware. The Second Life system also offers many features relevant for our application but was not chosen because it is less flexible.

To manage and visualize the VE, the Unity 3D game engine6 was selected as the foundation of the VMR application because of its range of features, its ease of use and its limited cost. The features critical to our application are a rendering engine for 3D graphics, scripting of object behavior and appearance, data driven animation and networking support. Equally important, Unity 3D deploys on most platforms, including iOS or Android mobile devices. The ingame Unity Editor enables the placement and configuration of objects in the virtual world. C# scripts are used to animate rigid objects. Unity 3D can load most popular mesh and animations formats and provides a system to play, blend, and cross-fade prerecorded (avatar) animation clips. No free open source engines were found that provide this combination of features. However, advanced path planning and Inverse Kinematics (IK) support is currently not present. The latter is used for automatically calculating joint rotations when directly animating hand and foot positions of a human avatar. Our VMR application requires only basic path planning and IK so this was not seen as a problem. Custom IK can be performed by overwriting the output of the Unity animation system for parts of the bone hierarchy.

To animate the VE and specifically the avatars, a set of controllers were designed that each modifies a (limited) set of virtual object properties. The navigation controller uses a graph based search algorithm to guide an avatar to an object or place (e.g., presenting board, chair) in the VE without collisions with other virtual objects. The animation controller manages a set of artist created animation clips. The clips are scheduled and cross-faded depending on the current desired end state (e.g., sitting, walking). The animation system needs at least one animation clip for each of the (currently six) states. All the avatars used have the same bone structure, avoiding the need for animation retargeting. Currently, avatar customization is limited to dynamically setting surface proper-ties (e.g., shirt color) or replacing the avatar's head. Render assets (i.e., geometry and textures, e.g., head scans) are loaded from a web server when needed. The procedural animation controllers use IK to directly control the head gaze and the avatar's hands. New controllers are easily added to the system. To ensure a consistent virtual world state, the visualization server calls the controllers running on the visualization clients. This uses less bandwidth than frequently sending the result of the controllers to the clients. Also, this allows for more customization of the visualizations at the client by the participant.

User Evaluation of the VMR

To improve and to evaluate our design of the next generation teleconferencing tool we used a multimethod approach. For this we introduced the Virtual Meeting Room to both users and experts with experience in teleconferencing. We conducted six group interviews with users after showing a video demonstration of the proposed system. Secondly, we conducted two expert reviews using heuristic evaluation with a working prototype of the system. Due to time limitations of the project, an evaluation of the prototype with users was not possible. This section describes our findings.

Video Demonstration and Group Interviews

The goal of the demonstration was to provide the users with the possibility to experience a close-to-realistic next generation teleconferencing system and create the feeling of immersion (see Figure 3). The demonstration was followed by group interviews. The setup of the meeting consisted of a table in a meeting room around which the users and two researchers (one leading the discussion, the other one observing) were sitting. The demonstration consisted of three screens: the first screen showing the video stream presenting the remote participants in the meeting (a video clip shot and edited beforehand), with next to it the VMR application demo film. In addition, one meeting participant (played by someone on the video stream) presented slides shown on a third screen. To create a connection between the participants in the VMR and the ones on the mocked up video stream, one of the researchers had a speaking role (i.e., asking a question). The videoconferencing system was reviewed by using variations of VMR visualizations as a starting point for discussion. The six group interviews had 3 -5 participants each (mean group size = 3.8), which resulted in a total of 23 participants. The users' ages ranged between 22 and 50 years old (average = 33 years). The users came from different organizations and had different professional backgrounds such as a researcher, a manager and a historian. All users except for two had experience with both teleconferences and videoconferences. About 44% (n = 10) of the users had experience with virtual world applications.

Expert Reviews with Working Prototype

The prototype was reviewed by having a videoconferencing meeting between two locations (see Figure 3). The experts, each with a laptop, sat around a table. Each laptop displayed the VMR, a live video stream of the remote location and a feedback image of their own location. Both expert reviews were conducted with 3 -4 people who all had a background in user experience, two of them especially in virtual world applications.

Results and Recommendations

After the group interviews on the mocked up technology, recommendations were formulated and applied to the prototype. The experts thus evaluated a system that had fundamentally been shaped by the user feedback from the group interviews. Similarly, after the expert reviews, the prototype was adjusted based on the findings of the experts. Although the mockup provided users with too much information, the expert reviews with the working prototype showed that this was no longer the case. This was most likely due to the reduction from three to two screens. Rather, the experts found the VMR to be a useful awareness tool during big meetings (i.e., more than 5 persons) where maintaining a good overview of the situation is harder. For instance, the VMR can provide support by showing what is going on in the real meeting room (e.g. who is speaking at the moment). Also, it gives a useful overview of who is present in the meeting, a feature, which was suspected to become more useful in bigger meetings with more remote participants. However, the findings suggest that the VMR might be of little use in a small videoconferencing meeting where a video stream covers all participants at once. Other changes after the user reviews include the implementation of a feedback image and the possibility to use a working interactive system (as opposed to the static mockup). In addition, the animations in the VMR that the users preferred were used during the expert reviews. In the next paragraphs, we list the recommendations pertaining to the VMR and highlight each recommendation with examples from our research.

VMR should provide an overview. Users and experts viewed the VMR application as an awareness tool that supports the users' knowledge on who is present in the room. Especially in a meeting with many locations and participants, users reported difficulties in keeping track of people's activities as they move in and out of the room. In addition, getting back on track after a moment of distraction was also viewed as being hard. Visualizations on presence status and meeting observations could support the user in having a more efficient meeting experience.

Design for immersion, though it is not always needed. The experts reported feeling immersed when using the prototype because of the interactivity between participants across rooms that the video stream facilitated. This had mostly to do with the video stream. However, depending on various aspects of the meeting such as relevance, commitment and interest, the users argued that immersion is not always needed. According to our users, it is common practice that when a user is not expected to actively contribute to a meeting, this passive follower might choose to multitask during the meeting. Although multitasking can be detrimental to some aspects of meetings, it is not always negative and can even positively impact meeting effectiveness and efficiency (cf. Lyons, Kim and Nevo [START_REF] Lyons | Paying Attention in Meetings: Multitasking in Virtual Worlds[END_REF]). The VMR can help the multitasking participant to get back on track.

Provide background information about users. In teleconferencing meetings, especially with unknown participants, people sometimes miss someone's name, job title or other relevant information. Stemming from this need, the users suggested displaying basic useful information (i.e., name, job title and company) about other meeting participants. We chose to display a person's name close to each avatar, and allow the retrieval of additional information in a pop up when hovering over a specific avatar with the mouse cursor (see Figure 4).

Visualization should be instantly clear and leave no room for misinterpretation. To allow the participant to focus on the meeting itself, all functionalities of the VMR should be instantly clear. Although some users found the size of the pie chart (see Figure 4) intimidating, most users appreciated the pie chart because it provided an overview of the location each participant belongs to. However, the functionality of the prototype, in which one could request additional information about avatars was not clear enough for the experts. Therefore, we suggest using visual cues (for instance a button) to make the functionality more explicit.

Visualizations should not distract. The users found the moving and the blinking of the animations distracting. Some users however pointed out that in certain situations a blinking animation could help to draw the attention of the participant who is otherwise preoccupied. To achieve a balance, we decided to show animations at certain events, such as the event of entering by showing a walking avatar. Some users considered this animation interesting to watch when participants were waiting for the meeting to start. However, when a participant joined a meeting at a later point in time, this animation had to be subtle and non-distracting, which was visualized by the avatar instantly appearing into an empty chair.

Allow users a degree of control. The users indicated that they should be given more control over the information presented in the VMR. For instance, some users argued that some information should be made optional, since it is not always needed. By giving users the possibility to customize which types of information they want to view, their feeling of control is increased. Users should also be allowed to control the appearance of the avatar representing them. While some users reported being satisfied with the minimum adjustments of the default avatar (i.e., avatar's shirt color matches shirt of meeting participant), others wanted more control over the avatar's looks to feel comfortable with their representations. Therefore, allowing customization of avatars based on user needs is recommended.

Connect with reality. To help users understand the VMR and to enhance immersion, observations visualized in the VMR should correspond to reality. This means that any gesturing or actions tied to a direction should translate realistically to the VMR. For example, when a person A is facing person B, the two avatars should also face each other in a similar way. In addition, the seating arrangements of the avatars should correspond to the same sitting order of the participants in same physical locations. During the group interviews, the importance of this connection was not a central topic to be investigated. At the expert reviews, however, this lack of connection turned out to be of importance, when dealing with own feedback image, on the VMR and on the video stream.

Discussion

The VMR was primarily viewed by both users and experts as a possible support tool for bigger meetings with multiple locations and more than six participants. For instance, the VMR can be used to convey information about any meeting participant, but also to provide an overview of the other locations. In addition, the VMR can offer a viable solution in situations where video stream is not possible to certain parties of the meeting (e.g. due to low bandwidth).

We have contributed by exploring the kinds of support people would benefit from in meetings held in VMRs, as proposed by Hasler, Buecheler and Pfeifer Fig. 4. Top down view in the VMR showing the pie chart table overlay that indicates the location of each participant. Also, the user information of Renaldo is shown. [START_REF] Hasler | Collaborative Work in 3D Virtual Environments : A Research Agenda and Operational Framework[END_REF]. Although experts reported feeling immersed, they, like the users, found that full immersion is not always needed (cf. Bowman and McMahan [START_REF] Bowman | Virtual Reality: How Much Immersion Is Enough?[END_REF]), depending on the type of meeting. The design of a VMR should be clear and not contain elements that are distracting to the meeting participants. Also, the information presented in the VMR should be coherent with reality. Finally, we recommend to allow users more control, both regarding the amount of information presented and the customization of avatars.

Moreover, we recommend using a proxy technology tool to allow users the possibility to simulate the future technology. Although only a simulation, the proxy works as a starting point for discussion. It also allows the user researchers to contribute to the development of the technology with user insights, while the developers can continue working on the VMR. Through the iterative process, the prototype could be adapted incrementally, leaving enough time for the changes to be made and allowing the implemented recommendations to be investigated.

Because the prototype of the VMR used for the expert reviews only allowed testing with small meetings (e.g. up to five people), our findings are limited to smaller meetings. Future research could include testing the prototype with a larger group of people in more than one remote locations. This would allow us to investigate whether the usefulness of the VMR increases with more people as we hypothesize. Also, since meeting dynamics might differ in large meetings, the amount or type of information needed could change. For instance, we could investigate the added value of providing additional information, such as the agenda points still to be covered.

Another important aspect of the ICOCOON system is immersion. Even though some research participants reported that it is not always necessary to be immersed during meetings, it would be interesting to study how different camera views and perspectives, specifically first person view, would affect the level of immersion. Further research should be conducted to investigate these research questions.

Conclusion

Game technology provides a good foundation for an experimental VMR application. Our choice of game engine was a good fit for prototyping, incremental design and implementation. Unity 3D strikes a good balance between ease of use and the amount and the complexity of the provided features, which results in a limited amount of software development knowledge needed. From our discussions with users and experts, we conclude that our VMR approach has merits as a teleconferencing support tool without the need for an immersive experience. We strongly feel that the benefit of the VMR rises with increasing amount of participants and locations. However, we could not confirm this due to the limited amount of test users in one session. Essential to our application are avatars that are immediately recognizable as their corresponding participant. Our future research focuses on pre-meeting scanned, photo-realistic avatars. In our current prototype, most non-verbal communication is conveyed through the video stream because our users stressed the fact the redundant information is confusing. Additional research could identify how much of the physical world needs to be brought into the virtual world to make the video redundant. This would change the VMR from a support tool to a communication tool.

Fig. 1 .

 1 Fig.1. The VMR application showing participant Erwin as presenting using a speech bubble with powerpoint logo; participant Victoria as speaking using a spotlight; participant Lucy with raised hand.

Fig. 2 .

 2 Fig. 2. High-level overview of the VMR teleconferencing system.

Fig. 3 .

 3 Fig. 3. Left: Setup during group interviews with three screens: video stream, VMR and presentation slides. Right: Setup during expert reviews: the VMR, the video stream from remote locations and a feedback image of themselves.

Immersive COmmunication by means of COmputer visiON [2]

Bringing in physical elements into a predominantly virtual space is sometimes referred to as Augmented Virtuality.

Unity 3D: http://unity3d.com

Acknowledgements

We would like to thank the following people for their contribution: Erwin Six, Kris Naessens, Donny Tytgat, Vinay Namboodiri, Maarten Aerts, Lizzy Bleumers, Koen Willaert, Bram Lievens, Ralf De Wolf and Chris Poppe. Also, we thank the interviewed participants. The research activities in this paper have been performed in the context of the ICOCOON project[2] and were funded by Ghent University, the Interdisciplinary Institute for Broadband Technology (IBBT), the Institute for the Promotion of Innovation by Science and Technology in Flanders (IWT), the Fund for Scientic Research-Flanders (FWOFlanders), the Belgian Federal Science Policy Office (BFSPO), and the European Union.


Charley Gielkens
email: charley.gielkens@gmail.com

Richard Wetzel

A Framework for Usability Evaluation of Mobile Mixed Reality Games

Keywords: mixed reality, augmented reality, games, usability evaluation

This research presents a framework that supports usability experts in determining which method to use when evaluating Mobile Mixed Reality Games (MMRGs). These are games that combine the real and virtual world by means of e.g. a smartphone and require the player to change their geographical location. As some different styles of MMRGs exist, e.g. running versus cunning or multiplayer versus single player, not every method is suitable for each style. The results of the methods are benchmarked against a heuristic evaluation and it is shown that using Instant Data Analysis (IDA), Diary, interaction logs combined with audio diary and retrospective think aloud combined with IDA perform statistically comparable, but that the latter is not favorable based on qualitative merits.

Introduction

A game that mixes the real and virtual world to some degree is called a Mixed Reality Game [START_REF] Milgram | A taxonomy of mixed reality visual displays[END_REF]. If this is done using a mobile device such a game is called a Mobile Mixed Reality Game (MMRG). If the player has to change their location, the game is considered a truly mobile MMRG [START_REF] Wetzel | Designing mobile augmented reality games[END_REF]. Mixed reality is interpreted rather freely, so that it does not only include Augmented Reality by means of a magic lens [START_REF] Bier | Toolglass and magic lenses[END_REF] but also by means of a map. Such games are also known as location based games.

As MMRGs are migrating from research projects [START_REF] Mccall | Using presence to evaluate an augmented reality location aware game[END_REF][START_REF] Thomas | First Person Indoor/Outdoor Augmented Reality Application: ARQuake[END_REF] to consumer products, they are also migrating from specialized hardware to common hardware like smartphones, i.e. phones with advanced sensors. As the input and output capabilities on these devices is limited compared to a static desktop computer, a high degree of usability is of even greater importance. In current literature little is known about how to measure usability of MMRGs. For both games in general [START_REF] Desurvire | Using heuristics to evaluate the playability of games[END_REF][START_REF] Pinelle | Heuristic evaluation for games[END_REF][START_REF] Pinelle | Usability heuristics for networked multiplayer games[END_REF] and MMRGs [START_REF] Gielkens | A Framework for Usability Evaluation of Mobile Mixed Reality Games[END_REF] heuristic evaluation is a tried and tested method. In [START_REF] Gielkens | A Framework for Usability Evaluation of Mobile Mixed Reality Games[END_REF] a definition for the usability of MMRGs is given, which will also be used here: "usability for MMRGs is the degree to which a player is able to learn, control, understand and safely play a game in the environment it was designed for."

After studying both the Android Marketplace [START_REF] Gielkens | A Framework for Usability Evaluation of Mobile Mixed Reality Games[END_REF] for games and literature on usability evaluation methods [START_REF] Gielkens | A Framework for Usability Evaluation of Mobile Mixed Reality Games[END_REF], it was surmised that different styles of games exist and postulated that each had usability evaluation methods that were better suited to their needs. Four methods were identified that merited testing for certain styles of games which are described using questions. Their relation is visualized in figure 1. As the focus of this study are MMRGs in a context sensitive manner, the evaluation of mock ups (question 1) is not further investigated.

Question 2: game length If a game is played over a longer period of time, the interface is most likely also complicated. In such a case it is advantageous if the player can also actually play it over a longer period of time. Therefore, using a diary is suggested. [START_REF] Sharp | Interaction Design: Beyond Human-Computer Interaction[END_REF] Question 3: amount of players If more players are needed to play the game than there are experts available to observe them, direct observation becomes impossible. In this case it is suggested to use interaction logs (IL) and a spoken diary. The latter means that the participants vocalize their likes and dislikes, but not every single thought like in a think aloud (TA) [START_REF] Ericsson | Protocol analysis : verbal reports as data. 1st paperb edn[END_REF] session.

Question 4: session length When enough experts are available to observe players, but a play session takes a long time, e.g. over an hour, one may want to consider not having the experts present all the time as this is expensive. In order to make evaluating such a session easier, it is suggested to use IL and a spoken diary again.

Question 5: physical activity If you have enough experts and the game doesn't last too long, e.g. less than an hour, the last thing to take into account is the amount of physical activity required to play the game. If one needs to run a lot, performing a concurrent TA becomes very difficult both for the participant as for the expert. It was therefore suggested to use retrospective TA and IDA [START_REF] Kjeldskov | New techniques for usability evaluation of mobile systems[END_REF] when a lot physical activity is involved and just IDA when it isn't.

To validate the suggested methods they are applied to relevant games which are also evaluated using heuristics for MMRGs [START_REF] Gielkens | A Framework for Usability Evaluation of Mobile Mixed Reality Games[END_REF]. For each list all issues will be rated on severity using he five-point scale introduced in [START_REF] Nielsen | Severity Ratings for Usability Problems[END_REF]. The median severity ratings were compared between methods, within games using a Mann-Whitney test and the amount of issues were compared within games, between methods using a χ 2 -test.

For the diary study Parallel Kingdom (http://www.parallelkingdom.com/) was used, for the slow paced game Tidy City [START_REF] Wetzel | Tidy City: A Location-based Game for City Exploration Based on User-created Content[END_REF] was chosen and for the other options Portal Hunt (http://www.totem-games.org/?q=portalhunt) was selected.

Results

In table 1 the amount of issues that have been identified using each method is shown per game, method and severity rating. For IDA (M dn = 1) the median severity was significantly different from the heuristic evaluation (M dn = 2, U =

Discussion

the lack of significant differences, the extra effort that's required for RTA combined with IDA makes a strong case for replacing this method by interaction logs combined with audio diary as that methods resulted in more issues being identified with similar effort. The final version of the framework is visualized in figure 1. Some limitations should be taken into account when reading this. E.g. the limited amount of participants, the use of the same usability expert in multiple evaluations and the fact that the results presented here are all based on a single observation. This means that further validation is required to make sure the results presented here are completely reliable.

Table 1 :

 1 Issues per severity rating, per game, per method

	Severity Heuristics Diary	Severity Heuristics RTA/IDA IL/AD	Severity Heuristics IDA
	0		0	0		0	0	1	0	0	0 10
	1		6	7		1	0	5	3	1	4 17
	2	11	15		2	19	13	11	2	17 12
	3	17	16		3	18	11	32	3	9	4
	4		2	3		4	13	9	10	4	1	0
	Total:	36	41	Total:	50	39	56	Total:	31 43
	Median:		3	2	Median:	3	3	3	Median:	2	1
	(a) Parallel Kingdom		(b) Portal Hunt		(c) Tidy City
				Start		Q3	> number of evaluators
	Use HEA,	Mockup		What are you	Q1	Yes	Amount of players needed for 1 game
	evaluating? Working protoype(/finished product) TA, IDA	Q2	How long does one Q4 < number of evaluators >1 hour	Use IL+spoken
	Use Diary or	No	Is 1 session equal to the		session last?			diary or HEA
	HEA			whole game?			<1 hour
				Use IDA or HEA	No	physical activity? Does the game involve a lot of Q5	Yes
	Fig. 1: ARGUEMENT -Augmented Reality Usability Evaluation Method Elec-
	tioN Tool
	286.00, z = -4.372, p < .01), but not for the other methods. The amount of
	issues did not differ significantly in any case.

Acknowledgements The authors would like to thank Herre van Oostendorp, Christof van Nimwegen, their colleagues of the Mixed and Augmented Reality Solutions department of Fraunhofer FIT and TOTEM, the German-French project on Theories and Tools for Distributed Authoring of Mobile Mixed Reality Games under the Programme Inter Carnot Fraunhofer from BMBF (Grant 01SF0804) and ANR (http://www.totem-games.org).