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Immersive Virtual Reality typically requires a head-mounted display (HMD) to visualize the environment and hand-held controllers to interact with the virtual objects. Recently, many applications display full-body avatars to represent the user and animate the arms to follow the controllers. Embodiment is higher when the self-avatar movements align correctly with the user. However, having a full-body self-avatar following the user’s movements can be challenging due to the disparities between the virtual body and the user’s body. This can lead to misalignments in the hand position that can be noticeable when interacting with virtual objects. In this work, we propose five different interaction modes to allow the user to interact with virtual objects despite the self-avatar and controller misalignment and study their influence on embodiment, proprioception, preference, and task performance. We modify aspects such as whether the virtual controllers are rendered, whether controllers are rendered in their real physical location or attached to the user’s hand, and whether stretching the avatar arms to always reach the real controllers. We evaluate the interaction modes both quantitatively (performance metrics) and qualitatively (embodiment, proprioception, and user preference questionnaires). Our results show that the stretching arms solution, which provides body continuity and guarantees that the virtual hands or controllers are in the correct location, offers the best results in embodiment, user preference, proprioception, and performance. Also, rendering the controller does not have an effect on either embodiment or user preference., This work has received funding from the European Union’sHorizon 2020 research and innovation programme under HORIZON-CL42022-HUMAN-01 grant agreement No 101093159 (XR4ED), and from MCIN/AEI/10.13039/501100011033/FEDER "A way to make Europe", UE (PID2021-122136OB-C21). Jose Luis Ponton was also funded by the Spanish Ministry of Universities (FPU21/01927)., Peer Reviewed, Postprint (author's final draft)

Este Trabajo de Final de Grado, desarrollado en el marco del grado en Ingeniería Informática en la especialidad de Software en la Facultad de Informática de Barcelona, tiene como propósito investigar acerca de si el uso de una herramienta para tomar fotografías dentro de un entorno de realidad virtual ayuda a mejorar la experiencia o la memoria de la experiencia del usuario o no. Esta investigación está dirigida a proporcionar nueva información acerca de este ámbito en la realidad virtual que ayudará a desarrollar futuras aplicaciones usando estos conocimientos que aportamos. Para llevar a cabo esta investigación, primero se explicarán las diferentes herramientas necesarias que tuvimos que implementar para poder tener un entorno atractivo e inmersivo donde podamos llevar a cabo las pruebas con usuarios. Una vez detallado esto, procederemos a hablar sobre la prueba piloto que hicimos como una primera iteración de la prueba con usuarios. Por último, las conclusiones preliminares que hemos obtenido gracias a este piloto, las cuales indican que esta herramienta, a pesar de ser llamativa para los usuarios en las experiencias de realidad virtual, acaba distrayendo al usuario del escenario que les rodea. Aunque dichas conclusiones no podrán ser definitivas hasta obtener más datos a través de más iteraciones de pruebas con diferentes usuarios., This Final Degree Project, developed within the framework of the Bachelor's Degree in Computer Engineering in the Software speciality at the Barcelona School of Informatics, aims to investigate whether the use of a tool to take photographs within a virtual reality environment helps to improve the experience or memory of the user experience or not. This research is aimed at providing new information on this field in virtual reality that will help develop future applications using the knowledge we provide. To carry out this research, first the different necessary tools that we had to implement in order to have an attractive and immersive environment where we can carry out the tests with users will be explained. Once this is detailed, we will proceed to talk about the pilot test that we did as a first iteration of the test with users. Finally, the preliminary conclusions we have obtained thanks to this pilot, which indicate that this tool, despite being striking for users in virtual reality experiences, ends up distracting the user from the scenario that surrounds them. Although these conclusions may not be definitive until more data is obtained through more testing iterations with different users.

Exposure therapy (ET) for anxiety disorders involves introducing the participant to an anxiety-provoking situation over several treatment sessions. Each time, the participant is exposed to a higher anxiety-provoking stimulus; for example, in the case of fear of heights, the participant would successively experience being at a greater height. ET is effective, and its counterpart, virtual reality (VR) exposure therapy (VRET), where VR substitutes real-world exposure, is equally so. However, ET is time-consuming, requiring several sessions. This study aimed to compare the results of single-session exposure with those of traditional VRET with regard to reducing public speaking anxiety. We introduced a paradigm concerned with public speaking anxiety where the VR exposure occurred in a single session while the participant interacted with a virtual therapist. Over time, the therapist transformed into an entire audience with almost imperceptible changes. We carried out a feasibility study with 45 participants, comparing 3 conditions: single-session exposure (n=16, 36%); conventional multiple-session exposure (n=14, 31%), where the same content was delivered in successive segments over 5 sessions; and a control group (n=15, 33%), who interacted with a single virtual character to talk about everyday matters. A week later, the participants were required to speak on a stage in front of a large audience in VR. Across most of the series of conventional public speaking anxiety measures, the single-session exposure was at least as effective in reducing anxiety as the multiple-session exposure, and both these conditions were better than the control condition. The 12-item Personal Report of Confidence as a Speaker was used to measure public speaking anxiety levels, where higher values indicated more anxiety. Using a Bayesian model, the posterior probabilities of improvement compared to a high baseline were at least 1.7 times greater for single- and multiple-session exposures compared, This research was funded by the European Research Council Advanced Grant MoTIVE, Moments in Time in Immersive Virtual Environments (#742989), and by the Departament de Recerca i Universitats de la Generalitat de Catalunya (AGAUR 2021SGR-01165 - NEUROVIRTUAL), supported by FEDER (Fons Europeu de Desenvolupament Regional). GS was supported by the “la Caixa” Foundation (ID 100010434) with fellowship code LCF/BQ/DR19/11740007., Peer Reviewed, Postprint (published version)

An increasing number of virtual reality applications require environments that emulate real-world conditions. These environments often involve dynamic virtual humans showing realistic behaviors. Understanding user perception and navigation among these virtual agents is key for designing realistic and effective environments featuring groups of virtual humans. While collision risk significantly influences human locomotion in the real world, this risk is largely absent in virtual settings. This paper studies the impact of the expected collision feedback on user perception and interaction with virtual crowds. We examine the effectiveness of commonly used collision feedback techniques (auditory cues and tactile vibrations) as well as inducing participants to expect that a physical bump with a real person might occur, as if some virtual humans actually correspond to real persons embodied into them and sharing the same physical space. Our results indicate that the expected collision feedback significantly influences both participant behavior—encompassing global navigation and local movements—and subjective perceptions of presence and copresence. Specifically, the introduction of a perceived risk of actual collision was found to significantly impact global navigation strategies and increase the sense of presence. Auditory cues had a similar effect on global navigation and additionally enhanced the sense of copresence. In contrast, vibrotactile feedback was primarily effective in influencing local movements., This work has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 860768 (CLIPE project), and from MCIN/AEI/10.13039/501100011033/FEDER, UE (PID2021- 122136OB-C21), ”A way to make Europe”. Jose Luis Ponton was also funded by the Spanish Ministry of Universities (FPU21/01927)., Peer Reviewed, Postprint (author's final draft)

VR United is a virtual reality application that we have developed to support multiple people simultaneously interacting in the same environment. Each person is represented with a virtual body that looks like themselves. Such immersive shared environments have existed and been the subject of research for the past 30 years. Here, we demonstrate how VR United meets criteria for successful interaction, where a journalist from the Financial Times in London interviewed a professor in New York for two hours. The virtual location of the interview was a restaurant, in line with the series of interviews published as “Lunch with the FT.” We show how the interview was successful, as a substitute for a physically present one. The article based on the interview was published in the Financial Times as normal for the series. We finally consider the future development of such systems, including some implications for immersive journalism., VR United was developed under the European Research Council project “Moments in Time in Immersive Virtual Environments” (MoTIVE) (#742989). The particular application for the interview was funded under the Horizon 2020 programme H2020-FETPROACT-2020-2 (#101017884) GuestXR., Peer Reviewed, Postprint (author's final draft)

La animación de grandes multitudes de personas se ha convertido en un aspecto esencial en el desarrollo de videojuegos debido a su importancia para crear entornos virtuales realistas. Tradicionalmente estas animaciones se realizaban mediante la reproducción de secuencias cortas de animaciones representadas en forma de grafo y diseñadas mediante keyframes. Este método requiere de una gran carga de trabajo y presenta serios problemas a la hora de escalarse a proyectos de mayor tamaño. Además, es fácil que se observen errores en el movimiento de los personajes como cambios bruscos de orientación, patinaje de los pies sobre el suelo, o transiciones entre poses que no son muy naturales. Todo esto se debe a que los grafos se tienen que hacer a mano con lo que es fácil introducir errores, y no siempre hay un buen ajuste entre los parámetros de interpolación entre animaciones y los movimientos que quiere seguir el personaje. Avances significativos en este campo han supuesto la aparición de técnicas como Motion Matching, que prescinde de grafos, para animar a los personajes virtuales mediante la selección de una serie de características de una base de datos de animaciones. Esta selección se hace de forma automática basándose en un mayor número de parámetros que facilitan la búsqueda de transiciones suaves entre poses del personaje. De esta forma es posible tener un mayor número de animaciones que representen una gran variedad de movimientos. En este trabajo integramos este sistema en la simulación de una multitud para animar a sus agentes y presentamos un experimento de realidad virtual que nos permitirá obtener nuevas animaciones capturando los movimientos de personas reales. En concreto, las personas tendrán que andar dentro de diferentes tipos de simulación de multitudes, intentando no colisionar con los personajes virtuales. De este modo, podremos capturar una mayor cantidad de movimientos realistas cuando las personas se eviten entre sí, para después poder integrarlas e

User studies are a useful tool for researchers, allowing them to collect data on how users perceive, interact with and process different types of sensory information. If planned in advance, user experiments can be leveraged in every stage of a research project, from early design, prototyping and feature exploration to applied proofs of concept, passing through validation and data collection for model training. User studies can provide the researcher with different types of information depending on the chosen methodology: user performance metrics, surveys and interviews, field studies, physiological data, etc. Considering human perception and other cognitive processes is particularly important in computer graphics, where most research produces outputs whose ultimate purpose is to be seen or perceived by a human. Being able to measure in an objective and systematic way how the information we generate is integrated into the representational space humans create to situate themselves in the world means that researchers will have more information to implement optimal algorithms, tools and techniques. In this tutorial we will give an overview of good practices for user studies in computer graphics with a particular focus on virtual reality use cases. We will cover the basics on how to design, carry out and analyze good user studies, as well as different particularities to be taken into account in immersive environments., Peer Reviewed, Postprint (published version)

Background: Persecutory delusions are a major psychiatric problem that often do not respond sufficiently to standard pharmacological or psychological treatments. We developed a new brief automated virtual reality (VR) cognitive treatment that has the potential to be used easily in clinical services. We aimed to compare VR cognitive therapy with an alternative VR therapy (mental relaxation), with an emphasis on understanding potential mechanisms of action. Methods: THRIVE was a parallel-group, single-blind, randomised controlled trial across four UK National Health Service trusts in England. Participants were included if they were aged 16 years or older, had a persistent (at least 3 months) persecutory delusion held with at least 50% conviction, reported feeling threatened when outside with other people, and had a primary diagnosis from the referring clinical team of a non-affective psychotic disorder. We randomly assigned (1:1) patients to either THRIVE VR cognitive therapy or VR mental relaxation, using a permuted blocks algorithm with randomly varying block size, stratified by severity of delusion. Usual care continued for all participants. Each VR therapy was provided in four sessions over approximately 4 weeks, supported by an assistant psychologist or clinical psychologist. Trial assessors were masked to group allocation. Outcomes were assessed at 0, 2 (therapy mid-point), 4 (primary endpoint, end of treatment), 8, 16, and 24 weeks. The primary outcome was persecutory delusion conviction, assessed by the Psychotic Symptoms Rating Scale (PSYRATS; rated 0–100%). Outcome analyses were done in the intention-to-treat population. We assessed the treatment credibility and expectancy of the interventions and the two mechanisms (defence behaviours and safety beliefs) that the cognitive intervention was designed to target. This trial is prospectively registered with the ISRCTN registry, ISRCTN12497310. Findings: From Sept 21, 2018, to May 13, 2021 (with a pause due to CO, The trial was funded by the Medical Research Council Developmental Pathway Funding Scheme (MR/P02629X/1). It was also supported by the National Institute for Health and Care Research (NIHR) Oxford Health Biomedical Research Centre (BRC-1215-2000). DF is an NIHR Senior Investigator. DMC is an Emeritus NIHR Senior Investigator. This paper presents independent research funded by the NIHR. The views expressed are those of the authors and not necessarily those of the NHS, the NIHR, or the Department of Health and Social Care. FW is funded by a Wellcome Trust Clinical Doctoral Fellowship (102176/B/13/Z). MS is supported by the European Research Council Grant MoTIVE (742989)., Peer Reviewed, Article signat per 23 autors/es: Department of Experimental Psychology (Prof D Freeman DClinPsy, R Lister DClinPsy, F Waite DClinPsych, S Lambe DClinPsy, A Beckley MA, E Bold BSc, L Jenner BA, R Diamond DClinPsych, M Kirkham DClinPsych, E Twivy DClinPsych, C Causier MSc, L Carr BSc, S Saidel MSc, A Rovira PhD, Prof D M Clark DPhil, L Rosebrock PhD), Oxford Primary Care Clinical Trials Unit, Nuffield Department of Primary Care Health Sciences (U Galal MSc, L-M Yu PhD), University of Oxford, Oxford, UK; Oxford Health NHS Foundation Trust, Oxford, UK (Prof D Freeman, F Waite, S Lambe, R Diamond, A Rovira, Prof D M Clark, L Rosebrock); Black Country Healthcare NHS Foundation Trust, Dudley, UK (R Lister); Northamptonshire Healthcare NHS Foundation Trust, Kettering, UK (R Day BSc, A Ivins DClinPsych, R Nah DClinPsy); Event Lab, Faculty of Psychology Spain (A Beacco PhD, Prof M Slater DSc), Institute of Neurosciences (Prof M Slater), University of Barcelona, Barcelona, Spain; Universitat Politècnica de Catalunya, Barcelona, Spain (A Beacco); Central and North West London NHS Foundation Trust, London, UK (R Nah), Postprint (published version)

Developed decades ago, Hierarchical Task Network Planners are now starting to be used in the video game industry as part of their AI systems. Due to its expressiveness and efficiency with complex models, they are a good alternative to the widely used State Machines or Behavior Trees. Despite the great opportunities that this technique offers, there's a lack of examples and optimizations for video games. In this project we will develop an HTN Planning system, including the Planner algorithm, domain language and the entities' domain, to recreate a Virtual Ecosystem with a concrete thematic. Our HTN Planning system will be based on the SHOP2 system from Dana Nau. It will be implemented in C/C++ and executed using the video game engine "Unreal Engine 5", while trying to optimize it for the chosen ecosystem.

This work deals with the automatic 3D reconstruction of objects from frontal RGB images. This aims at a better understanding of the reconstruction of 3D objects from RGB images and their use in immersive virtual environments. We propose a complete workflow that can be easily adapted to almost any other family of rigid objects. To explain and validate our method, we focus on guitars. First, we detect and segment the guitars present in the image using semantic segmentation methods based on convolutional neural networks. In a second step, we perform the final 3D reconstruction of the guitar by warping the rendered depth maps of a fitted 3D template in 2D image space to match the input silhouette. We validated our method by obtaining guitar reconstructions from real input images and renders of all guitar models available in the ShapeNet database. Numerical results for different object families were obtained by computing standard mesh evaluation metrics such as Intersection over Union, Chamfer Distance, and the F-score. The results of this study show that our method can automatically generate high-quality 3D object reconstructions from frontal images using various segmentation and 3D reconstruction techniques., Postprint (published version)

In the last few years the field of Virtual Reality (VR) has experienced significant growth through the introduction of low-cost VR devices to the mass market. However, VR has been used for many years by researchers since it has proven to be a powerful tool across a vast array of research fields and applications. The key aspect of any VR experience is that it is completely immersive, which means that the virtual world totally surrounds the participant. Some game engines such as Unity already support VR out of the box and an application can be configured for VR in a matter of minutes. However, there is still the lack of a standard and easy to use tool in order to embody participants into a virtual human character that responds synchronously to their movements with corresponding virtual body movements. In this paper we introduce QuickVR, a library based on Unity which not only offers embodiment in a virtual character, but also provides a series of high level features that are necessary in any VR application, helping to dramatically reduce the production time. Our tool is easy to use by coding novices, but also easy extensible and customizable by more experienced programmers., Postprint (published version)

We created a virtual reality version of a 1983 performance by Dire Straits, this being a highly complex scenario consisting of both the virtual band performance and the appearance and behaviour of the virtual audience surrounding the participants. Our goal was to understand the responses of participants, and to learn how this type of scenario might be improved for later reconstructions of other concerts. To understand the responses of participants we carried out two studies which used senti- ment analysis of texts written by the participants. Study 1 (n = 25) (Beacco et al. in IEEE Virtual Reality: 538–545, 2021) had the unexpected finding that negative sentiment was caused by the virtual audience, where e.g. some participants were fearful of being harassed by audience members. In Study 2 (n = 26) notwithstanding some changes, the audience again led to negative sentiment—e.g. a feeling of being stared at. For Study 2 we compared sentiment with questionnaire scores, finding that the illusion of being at the concert was associated with positive sentiment for males but negative for females. Overall, we found sentiment was dominated by responses to the audience rather than the band. Participants had been placed in an unusual situation, being alone at a concert, surrounded by strangers, who seemed to pose a social threat for some of them. We relate our findings to the concept of Plausibility, the illusion that events and situations in the VR are really happening. The results indicate high Plausibility, since the negative sentiment, for example in response to being started at, only makes sense if the events are experienced as actually happening. We conclude with the need for co-design of VR scenarios, and the use of sentiment analysis in this process, rather than sole reliance on concepts proposed by researchers, typically expressed through questionnaires, which may not reflect the experiences of participants., Postprint (published version)

© 2009 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works., We present a complete automatic system to obtain a realistic 3D avatar reconstruction of a person using only a frontal RGB image. Our proposed workflow first determines the pose, shape and semantic information from the input image. All this information is processed to create the skeleton and the 3D skinned textured mesh that forms the final avatar. We use a specific head reconstruction method to correctly match our final mesh to a realistic avatar. Our pipeline focuses on three main aspects: automation of the process, identification of the person, and usability of the avatar., Postprint (author's final draft)

We review the concept of presence in virtual reality, normally thought of as the sense of “being there” in the virtual world. We argued in a 2009 paper that presence consists of two orthogonal illusions that we refer to as Place Illusion (PI, the illusion of being in the place depicted by the VR) and Plausibility (Psi, the illusion that the virtual situations and events are really happening). Both are with the proviso that the participant in the virtual reality knows for sure that these are illusions. Presence (PI and Psi) together with the illusion of ownership over the virtual body that self-represents the participant, are the three key illusions of virtual reality. Copresence, togetherness with others in the virtual world, can be a consequence in the context of interaction between remotely located participants in the same shared virtual environments, or between participants and virtual humans. We then review several different methods of measuring presence: questionnaires, physiological and behavioural measures, breaks in presence, and a psychophysics method based on transitions between different system configurations. Presence is not the only way to assess the responses of people to virtual reality experiences, and we present methods that rely solely on participant preferences, including the use of sentiment analysis that allows participants to express their experience in their own words rather than be required to adopt the terminology and concepts of researchers. We discuss several open questions and controversies that exist in this field, providing an update to the 2009 paper, in particular with respect to models of Plausibility. We argue that Plausibility is the most interesting and complex illusion to understand and is worthy of significant more research. Regarding measurement we conclude that the ideal method would be a combination of a psychophysical method and qualitative methods including sentiment analysis., Postprint (published version)

Virtual reality applications depend on multiple factors, for example, quality of rendering, responsiveness, and interfaces. In order to evaluate the relative contributions of different factors to quality of experience, post-exposure questionnaires are typically used. Questionnaires are problematic as the questions can frame how participants think about their experience and cannot easily take account of non-additivity among the various factors. Traditional experimental design can incorporate non-additivity but with a large factorial design table beyond two factors. Here, we extend a previous method by introducing a reinforcement learning (RL) agent that proposes possible changes to factor levels during the exposure and requires the participant to either accept these or not. Eventually, the RL converges on a policy where no further proposed changes are accepted. An experiment was carried out with 20 participants where four binary factors were considered. A consistent configuration of factors emerged where participants preferred to use a teleportation technique for navigation (compared to walking-in-place), a full-body representation (rather than hands only), the responsiveness of virtual human characters (compared to being ignored) and realistic compared to cartoon rendering. We propose this new method to evaluate participant choices and discuss various extensions., This research is supported by the European Research Council Advanced grant Moments in Time in Immersive Virtual Environments (MoTIVE) grant no. 742989 and all authors were funded by this grant except for G.S. who is supported by ‘la Caixa’ Foundation (ID 100010434) with Fellowship code no. LCF/BQ/DR19/11740007., Peer Reviewed, Postprint (published version)

We present methods used to produce and study a first version of an attempt to reconstruct a 1983 live rock concert in virtual reality. An approximately 10 minute performance by the rock band Dire Straits was rendered in virtual reality, based on the use of computer vision techniques to extract the appearance and movements of the band, and crowd simulation for the audience. An online pilot study was conducted where participants experienced the scenario and freely wrote about their experience. The documents produced were analyzed using sentiment analysis, and groups of responses with similar sentiment scores were found and compared. The results showed that some participants were disturbed not by the band performance but by the accompanying virtual audience that surrounded them. The results point to a profound level of plausibility of the experience, though not in the way that the authors expected. The findings add to our understanding of plausibility of virtual environments., This work is funded by the European Research Council (ERC) Advanced Grant Moments in Time in Immersive Virtual Environments (MoTIVE) #742989., Peer Reviewed, Postprint (author's final draft)

The proportion of the population who experience persecutory thoughts is 10–15%. People then engage in safety-seeking behaviours, typically avoiding social interactions, which prevents disconfirmatory experiences and hence paranoia persists. Here we show that persecutory thoughts can be reduced if prior to engaging in social interaction in VR participants first see their virtual body-double doing so. Thirty non-clinical participants were recruited to take part in a study, where they were embodied in a virtual body that closely resembled themselves, and asked to interact with members of a crowd. In the Random condition (n=15) they observed their body-double wandering around but not engaging with the crowd. In the Targeted condition the body-double correctly interacted with members of the crowd. The Green Paranoid Thoughts Scale was measured 1 week before and 1 week after the exposure and decreased only for those in the Targeted condition. The results suggest that the observation of the body-double correctly carrying out a social interaction task in VR may lead to anxiety-reducing mental rehearsal for interaction thus overcoming safety behaviours. The results also extend knowledge of the effects of vicarious agency, suggesting that identification with the actions of body-double can influence subsequent psychological state., Postprint (published version)

Group pressure can often result in people carrying out harmful actions towards others that they would not normally carry out by themselves. However, few studies have manipulated factors that might overcome this. Here male participants (n=60) were in a virtual reality (VR) scenario of sexual harassment (SH) of a lone woman by a group of males in a bar. Participants were either only embodied as one of the males (Group, n=20), or also as the woman (Woman, n=20). A control group (n=20) only experienced the empty bar, not the SH. One week later they were the Teacher in a VR version of Milgram’s Obedience experiment where they were encouraged to give shocks to a female Learner by a group of 3 virtual males. Those who had been in the Woman condition gave about half the number of shocks of those in the Group condition, with the controls between these two. We explain the results through embodiment promoting identification with the woman or the group, and delegitimization of the group for those in the Woman condition. The experiment raised important ethical issues, showing that a VR study with positive ethical intentions can sometimes produce unexpected and non-beneficent results., Tis research was funded by the US Ofce of Naval Research, Award Number N62909-14-1-N119 ‘Exploring Moral Action Using Immersive Virtual Reality’, Peer Reviewed, Postprint (published version)

When people hold implicit biases against a group they typically engage in discriminatory behaviour against group members. In the context of the implicit racial bias of ‘White' against ‘Black' people, it has been shown several times that implicit bias is reduced after a short exposure of embodiment in a dark-skinned body in virtual reality. Embodiment usually leads to the illusion of ownership over the virtual body, irrespective of its skin colour. Previous studies have been carried out in virtual scenarios that are affectively neutral or positive. Here, we show that when the scenario is affectively negative the illusion of body ownership of White participants over a White body is lessened, and implicit bias is higher for White participants in a Black virtual body. The study was carried out with 92 White female participants, in a between-groups design with two factors: BodyType (their virtual body was White or Black) and a surrounding Crowd was Negative, Neutral or Positive towards the participant. We argue that negative affect prevents the formation of new positive associations with Black and distress leads to disownership of the virtual body. Although virtual reality is often thought of as an ‘empathy machine' our results suggest caution, that this may not be universally the case., This research was funded under the European Research Council (ERC) Advanced Grant, Moments in Time inImmersive Virtual Environments (MoTIVE) (no. 742989), Peer Reviewed, Postprint (published version)

We present an automatic animatable 3D character reconstruction method from frontal and lateral RGB pictures of the person to reconstruct. We propose a method where, after obtaining a 3D reconstruction from a frontal view, we adapt the template of the Skinned Multi-Person Linear Model (SMPL) to it. This frontal modified SMPL is then used in a second step as an input to reconstruct the character from the lateral view, thus obtaining a correct person reconstruction in all dimensions. Our method enables the creation of 3D animatable characters focusing on two main aspects: shape and texture. The obtained results show that the proposed method achieves an accurate automatic 3D character reconstruction from only two views that enhances current methods while offering a reproducible work-flow., This work is funded by the European Research Council (ERC) Advanced Grant Moments in Time in Immersive Virtual Environments (MoTIVE) number 742989., Peer Reviewed, Postprint (author's final draft)

In this survey we review, classify and compare existing approaches for real-time crowd rendering. We first overview character animation techniques, as they are highly tied to crowd rendering performance, and then we analyze the state of the art in crowd rendering. We discuss different representations for level-of-detail (LoD) rendering of animated characters, including polygon-based, point-based, and image-based techniques, and review different criteria for runtime LoD selection. Besides LoD approaches, we review classic acceleration schemes, such as frustum culling and occlusion culling, and describe how they can be adapted to handle crowds of animated characters. We also discuss specific acceleration techniques for crowd rendering, such as primitive pseudo-instancing, palette skinning, and dynamic key-pose caching, which benefit from current graphics hardware. We also address other factors affecting performance and realism of crowds such as lighting, shadowing, clothing and variability. Finally we provide an exhaustive comparison of the most relevant approaches in the field., Peer Reviewed, Postprint (author's final draft)

Real-time rendering of detailed animated characters in crowd simulations is still a challenging problem in computer graphics. State-of-the-art approaches can render up to several thousand agents by consuming most of the graphics processing unit (GPU) resources, leav- ing little room for other GPU uses such as driving the crowd simulation. Polygonal meshes deformed through skinning in real time are suitable for simulations involving a relatively small number of agents, since the rendering cost of each animated character is proportional to the complexity of its polygonal representation. A number of techniques have been proposed to accelerate the rendering of animated characters. Besides view frustum and occlusion culling techniques, related work has focused mainly on providing level-of-detail (LoD) representations. Unfortunately, most surface simplification methods do not work well with dynamic articulated meshes. As a consequence, the simplified versions of each character are often created manually and they still suffer from a substantial loss of detail. Image-based precomputed impostors for the whole character provide substantial speed improvements by rendering distant characters as a textured polygon, but suffer from two major limitations: all animation cycles have to be known in advance (and thus animation blending is not supported) and resulting textures are huge (as for each view angle and animation frame, an image has to be stored). In this chapter, we overview different approaches to crowd rendering, focusing on impostor-based techniques. We summarize and compare two recent approaches [1,2] based on rigidly animated impostors per body limb. Compared to having impostors representing an entire character, having animated per-joint impostors provides a more memory-efficient approach., Peer Reviewed, Postprint (published version)

This paper presents a real-time animation system for fully embodied virtual humans that satisfies accurate foot placement constraints for different human walking and running styles. Our method offers a fine balance between motion fidelity and character control, and can efficiently animate over sixty agents in real time (25 FPS) and over a hundred characters at 13 FPS. Given a point cloud of reachable support foot configurations extracted from the set of available animation clips, we compute the Delaunay triangulation. At runtime, the triangulation is queried to obtain the simplex containing the next footstep, which is used to compute the barycentric blending weights of the animation clips. Our method synthesizes animations to accurately follow footsteps, and a simple IK solver adjusts small offsets, foot orientation, and handles uneven terrain. To incorporate root velocity fidelity, the method is further extended to include the parametric space of root movement and combine it with footstep based interpolation. The presented method is evaluated on a variety of test cases and error measurements are calculated to offer a quantitative analysis of the results achieved., Peer Reviewed, Postprint (author’s final draft)

Per-joint impostors have been used to achieve high performance when rendering thousands of agents, while still allowing us to blend animation. This provides interactively animated crowds and reduces the memory footprint compared to classic impostors. In this poster we exploit the potential of per joint impostors to further increase both visual quality and performance. The CAVAST framework for crowd simulation and rendering has been used to quantitatively evaluate our improvements with the profiling tools that it provides. Since different applications will have different requirements in terms of performance vs. visual quality, we have extended CAVAST with a new user interface to ease this process., Peer Reviewed, Postprint (published version)

Simulation, animation and rendering of crowds has become an important part of real-time applications such as videogames. Virtual environments achieve higher realism when being populated by virtual crowds as opposed to appearing uninhabited. There has been a large amount of research on simulation, animation and rendering of crowds, but in most cases they seem to be treated separately as if the limitations in one area did not affect the others. At the end of the day the goal is to populate environments with as many characters as possible in real time, and it is of little use if one can for instance render thousands of characters in real time, but you cannot move more than a hundred due to a simulation bottleneck. The goal of our work is to provide a framework that lets the researcher focus on each of these topics at a time (simulation, animation, or rendering) and be able to explore and push the boundaries on one topic without being strongly limited by the other related issues. This paper presents therefore a new prototyping testbed for crowds that lets the researcher focus on one of these areas of research at a time without loosing sight of the others. We offer default representations, animation and simulation controllers for real time crowd simulation, that can easily be replaced or extended. Fully configurable level-of-detail for both rendering and simulation is also available, Peer Reviewed, Postprint (published version)

Nowadays crowd simulation is becoming more important in computer applications such as building evacuation planning, training, videogames, etc., presenting hundreds or thousands of agents navigating in virtual environments. Some of these applications need to run in real time in order to offer complete interaction with the user. Simulated crowds should seem natural and give a good looking impression to the user. The goal should be to produce both the best motion and animation, while minimizing the awkwardness of movements and eliminating or hiding visual artifacts. Achieving simulation, animation and rendering of crowds in real-time becomes thus a major challenge. Although each of these areas has been studied individually and improvements have been made in the literature, its integration in one real-time system is not straight forward. In the process of integrating animation, simulation and rendering of real time crowds, we need to assume some trade-offs between accuracy and quality of results. The main goal of this thesis is to work on those three aspects of a real-time crowd visualization (simulation, animation and rendering) seeking for possible speed-ups and optimizations allowing us to further increase the number of agents in the simulation, to then integrate them in a real-time system, with the maximum number possible of high quality and natural looking animated agents. In order to accomplish our goal we present new techniques to achieve improvements in each one of these areas: In crowd simulation we work on a multi-domain planning approach and on planning using footsteps instead of just root velocities and positions; in animation we focus on a framework to eliminate foot sliding artifacts and on synthesizing motions of characters to follow footsteps; in rendering we provide novel techniques based on per joint impostors. Finally we present a novel framework to progressively integrate different methods for crowd simulation, animation and rendering. The framework, Avui dia la simulació de multituds està agafant importància en aplicacions per computador, com la planificació d'evacuacions d'edificis, entrenament, videojocs, etc., presentant centenars o milers d'agents navegant en entorns virtuals. Algunes d'aquestes aplicacions necessiten ser executades en temps real per poder oferir una interacció completa amb l'usuari. Les multituds simulades han de resultar naturals i fer una bona impressió a l'usuari. L'objectiu ha de ser produir a la vegada tant els millors moviments com la millor animació, mentre es minimitzen els moviments estranys i s'eliminen o amaguen defectes visuals. Aconseguir la simulació, animació i visualització de multituds en temps real esdevé llavors un repte major. Encara que cadascuna d'aquestes àrees ha estat estudiada individualment i que s'han fet millores en la literatura, la seva integració en un sistema en temps real no és directa. En el procés d'integrar l'animació, la simulació i la visualització de multituds en temps real, necessitem assumir alguns equilibris entre la precisió i la qualitat dels resultats. El principal objectiu d'aquesta tesi és treballar en aquests tres aspectes de les multituds en temps real (simulació, animació i visualització) buscant possibles acceleracions i optimitzacions que ens permetin augmentar encara més el nombre d'agents simulats, per després integrar-los en un sistema en temps real, amb el màxim nombre possible de personatges d'alta qualitat i d'aspecte natural. Per aconseguir el nostre objectiu presentem noves tècniques per obtenir millores en cadascuna d'aquestes àrees: En la simulació de multituds treballem en una aproximació on es planifica en múltiples dominis, i en una planificació fent servir petjades en comptes de només velocitats i posicions dels personatges; en animació ens centrem en una arquitectura per a eliminar els problemes de lliscament dels peus i en sintetitzar els moviments d'un personatge perquè segueixi petjades; en visualització aportem noves t, Postprint (published version)

This paper presents a real-time planning framework for multi-character navigation that enables the use of multiple heterogeneous problem domains of differing complexities for navigation in large, complex, dynamic virtual environments. The original navigation problem is decomposed into a set of smaller problems that are distributed across planning tasks working in these different domains. An anytime dynamic planner is used to efficiently compute and repair plans for each of these tasks, while using plans in one domain to focus and accelerate searches in more complex domains. We demonstrate the benefits of our framework by solving many challenging multi-agent scenarios in complex dynamic environments requiring space-time precision and explicit coordination between interacting agents, by accounting for dynamic information at all stages of the decision-making process., Peer Reviewed, Postprint (published version)

In this paper, we present a new impostor-based representation for 3D animated characters supporting real-time rendering of thousands of agents. We maximize rendering performance by using a collection of pre-computed impostors sampled from a discrete set of view directions. Our approach differs from previous work on view-dependent impostors in that we use per-joint rather than per-character impostors. Our characters are animated by applying the joint rotations directly to the impostors, instead of choosing a single impostor for the whole character from a set of pre-defined poses. This offers more flexibility in terms of animation clips, as our representation supports any arbitrary pose, and thus, the agent behavior is not constrained to a small collection of pre-defined clips. Because our impostors are intended to be valid for any pose, a key issue is to define a proper boundary for each impostor to minimize image artifacts while animating the agents. We pose this problem as a variational optimization problem and provide an efficient algorithm for computing a discrete solution as a pre-process. To the best of our knowledge, this is the first time a crowd rendering algorithm encompassing image-based performance, small graphics processing unit footprint, and animation independence is proposed., Peer Reviewed, Postprint (published version)

This paper presents an Animation Planning Mediator (APM) designed to synthesize animations efficiently for virtual characters in real time crowd simulation. From a set of animation clips, the APM selects the most appropriate and modifies the skeletal configuration of each character to satisfy desired constraints (e.g. eliminating foot-sliding or restricting upper body torsion), while still providing natural looking animations. We use a hardware accelerated character animation library to blend animations increasing the number of possible locomotion types. The APM allows the crowd simulation module to maintain control of path planning, collision avoidance and response. A key advantage of our approach is that the APM can be integrated with any crowd simulator working in continuous space. We show visual results achieved in real time for several hundreds of agents, as well as the quantitative ac-curacy., Postprint (published version)

This poster presents an efficient Animation Planning Mediator (APM) designed to animate virtual characters in real time for crowd simulation. The APM selects the most appropriate animation clip available for each character and modifies the skeletal configuration to satisfy constraints given by the virtual environment and crowd simulation (CS) module, such as eliminating foot-sliding. Using a reduced number of animation clips, we blend within and between animation clips to increase the number of possible locomotion types and to adjust the animations to the velocity of each agent as indicated by the CS module. A key advantage of our approach is that it can be easily integrated with any existing real-time crowd simulation module working in continuous space., Postprint (published version)

High-quality, detailed animated characters are often represented as textured polygonal meshes. The problem with this technique is the high cost that involves rendering and animating each one of these characters. This problem has become a major limiting factor in crowd simulation. Since we want to render a huge number of characters in real-time, the purpose of this thesis is therefore to study the current existing approaches in crowd rendering to derive a novel approach. The main limitations we have found when using impostors are (1) the big amount of memory needed to store them, which also has to be sent to the graphics card, (2) the lack of visual quality in close-up views, and (3) some visibility problems. As we wanted to overcome these limitations, and improve performance results, the found conclusions lead us to present a new representation for 3D animated characters using relief mapping, thus supporting an output-sensitive rendering. The basic idea of our approach is to encode each character through a small collection of textured boxes storing color and depth values. At runtime, each box is animated according to the rigid transformation of its associated bone in the animated skeleton. A fragment shader is used to recover the original geometry using an adapted version of relief mapping. Unlike competing output-sensitive approaches, our compact representation is able to recover high-frequency surface details and reproduces view-motion parallax e ects. Furthermore, the proposed approach ensures correct visibility among di erent animated parts, and it does not require us to prede ne the animation sequences nor to select a subset of discrete views. Finally, a user study demonstrates that our approach allows for a large number of simulated agents with negligible visual artifacts.

La realidad virtual ofrece la posibilidad de interactuar de manera inmersiva en mundos virtuales 3D. Estos mundos virtuales pueden ser representaciones de otros momentos históricos que permiten al usuario explorar los modelos virtuales como si de una visita turística al pasado se tratase. En este proyecto se ha realizado una reconstrucción virtual de la antigua ciudad romana de Tarragona (Tarraco) para ofrecer un entorno interactivo en el que los visitantes a la exposición puedan navegar por diferentes partes de la ciudad así como interactuar con humanoides virtuales representando romanos que ayudarán al usuario a recopilar información histórica y aprender mediante un sencillo juego interactivo., Peer Reviewed, Postprint (author’s final draft)

Real-time crowd simulation for virtual environment applications requires not only navigation and locomotion in large environments while avoiding obstacles and agents, but also rendering high quality 3D fully articulated figures to enhance realism. In this paper, we present a framework for real-time simulation of crowds. The framework is composed of a Hardware Accelerated Character Animation Library (HALCA), a crowd simulation system that can handle large crowds with high densities (HiDAC), and an Animation Planning Mediator (APM) that bridges the gap between the global position of the agents given by HiDAC and the correct skeletal state so that each agent is rendered with natural locomotion in real-time. The main goal of this framework is to allow high quality visualization and animation of several hundred realistic looking characters (about 5000 polygons each) navigating virtual environments on a single display PC, a HMD (Head Mounted Display), or a CAVE system. Results of several applications on a number of platforms are presented., Peer Reviewed, Postprint (published version)