Ludovic Hoyet

• PhD
• Researcher at National Institute for Research in Computer Science and Control

ith recent advances in real-time graphics technology, more realistic, believable and appealing virtual characters are needed than ever before. Both player-controlled avatars and non-player characters are now starting to interact with the environment, other virtual humans and crowds. However, simulating physical contacts between characters and match...

Recent advances in rendering and data-driven animation have enabled the creation of compelling characters with impressive levels of realism. While data-driven techniques can produce animations that are extremely faithful to the original motion, many challenging problems remain because of the high complexity of human motion. A better understanding o...

A typical crowd engine pipeline animates numerous moving characters according to a two-step process: global trajectories are generated by a crowd simulator, whereas full body motions are generated by animation engines. Because interactions are only considered at the first stage, animations sometimes lead to residual collisions and/or characters wal...

In Virtual Reality, a number of studies have been conducted to assess the influence of avatar appearance, avatar control and user point of view on the Sense of Embodiment (SoE) towards a virtual avatar. However, such studies tend to explore each factor in isolation. This paper aims to better understand the inter-relations among these three factors...

Avoiding moving obstacles in immersive environments requires adjustments in the walking trajectory and depends on the type of obstacle movement. Previous research studied the impact of speed and direction of motion but not much is known about how predictability of motion impacts human circumvention in terms of distance to the obstacle (proximity)....

We propose a novel contact-aware method to synthesize highly-dense 3D crowds of animated characters. Existing methods animate crowds by, first, computing the 2D global motion approximating subjects as 2D particles and, then, introducing individual character motions without considering their surroundings. This creates the illusion of a 3D crowd, but...

Generating realistic animated virtual humans is a problem that has been extensively studied with many applications in different types of virtual environments. However, the creation process of such realistic animations is challenging, especially because of the number and variety of influencing factors, that should then be identified and evaluated. I...

While data is vital to better understand and model interactions within human crowds, capturing real crowd motions is extremely challenging. Virtual Reality (VR) demonstrated its potential to help, by immersing users into either simulated virtual crowds based on autonomous agents, or within motion-capture-based crowds. In the latter case, users' own...

During mid-air interactions, common approaches (such as the god-object method) typically rely on visually constraining the user's avatar to avoid visual interpenetrations with the virtual environment in the absence of kinesthetic feedback. This paper explores two methods which influence how the position mismatch (positional offset) between users' r...

Stepping strategies following external perturbations from different directions is investigated in this work. We 6 analysed the effect of the perturbation angle as well as the level of awareness of individuals and characterised 7 steps out of the sagittal plane between Loaded Side Steps (LSS), Unloaded Medial Steps (UMS) and Unloaded 8 Crossover Ste...

Motion retargeting is a long-standing problem in character animation, which consists in transferring and adapting the motion of a source character to another target character. A typical application is the creation of motion sequences from off-the-shelf motions by transferring them onto new characters. Motion retargeting is also promising to increas...

Human motion synthesis and editing are essential to many applications like video games, virtual reality, and film post‐production. However, they often introduce artefacts in motion capture data, which can be detrimental to the perceived realism. In particular, footskating is a frequent and disturbing artefact, which requires knowledge of foot conta...

Gaze behavior of virtual characters in video games and virtual reality experiences is a key factor of realism and immersion. Indeed, gaze plays many roles when interacting with the environment; not only does it indicate what characters are looking at, but it also plays an important role in verbal and non-verbal behaviors and in making virtual chara...

In computer animation, the creation of believable and engaging virtual characters has been a longlasting endeavour. While researchers investigated several aspects of character design, not many studies focused on the qualities of biological human motion itself. We approached the perception of motion from the perspective of distinct movement patterns...

Despite the wide availability of large motion databases, and recent advances in exploiting them to create tailored contents, artists still spend tremendous efforts in editing and adapting existing character animations to new contexts. This motion editing problem is a well-addressed research topic. Yet only a few approaches have considered the influ...

Human motion synthesis and editing are essential to many applications like film post-production. However, they often introduce artefacts in motions, which can be detrimental to the perceived realism. In particular, footskating is a frequent and disturbing artefact requiring foot contacts knowledge to be cleaned up. Current approaches to obtain foot...

The real‐time simulation of human crowds has many applications. In a typical crowd simulation, each person ('agent') in the crowd moves towards a goal while adhering to local constraints. Many algorithms exist for specific local ‘steering’ tasks such as collision avoidance or group behavior. However, these do not easily extend to completely new typ...

Simulating crowds requires controlling a very large number of trajectories of characters and is usually performed using crowd steering algorithms. The question of choosing the right algorithm with the right parameter values is of crucial importance given the large impact on the quality of results. In this paper, we study the performance of a number...

Crowd motion data is fundamental for understanding and simulating realistic crowd behaviours. Such data is usually collected through controlled experiments to ensure that both desired individual interactions and collective behaviours can be observed. It is however scarce, due to ethical concerns and logistical difficulties involved in its gathering...

In virtual reality, several manipulation techniques distort users' motions, for example to reach remote objects or increase precision. These techniques can become problematic when used with avatars, as they create a mismatch between the real performed action and the corresponding displayed action, which can negatively impact the sense of embodiment...

Facial caricature is the art of drawing faces in an exaggerated way to convey emotions such as humor or sarcasm. Automatic caricaturization has been explored both in the 2D and 3D domain. In this paper, we propose two novel approaches to automatically caricaturize input facial scans, filling gaps in the literature in terms of user-control, caricatu...

Human character animation is often critical in entertainment content production, including video games, virtual reality or fiction films. To this end, deep neural networks drive most recent advances through deep learning (DL) and deep reinforcement learning (DRL). In this article, we propose a comprehensive survey on the state‐of‐the‐art approaches...

Human character animation is often critical in entertainment content production, including video games, virtual reality or fiction films. To this end, deep neural networks drive most recent advances through deep learning and deep reinforcement learning. In this article, we propose a comprehensive survey on the state-of-the-art approaches based on e...

Simulating crowds requires controlling a very large number of trajectories and is usually performed using crowd motion algorithms for which appropriate parameter values need to be found. The study of the relation between parametric values for simulation techniques and the quality of the resulting trajectories has been studied either through percept...

Simulating crowds requires controlling a very large number of trajectories and is usually performed using crowd motion algorithms for which appropriate parameter values need to be found. The study of the relation between parametric values for simulation techniques and the quality of the resulting trajectories has been studied either through percept...

This paper is an extended version of a previous paper [1] published at ICAT-EGVE 2020. We explored the potential impact of threat occurrence and repeatability on users’ Sense of Embodiment (SoE) and threat response. To that aim, we conducted an experiment in which participants were embodied in a virtual avatar, and performed a task in which a threa...

Gait patterns provide a rich source of person-specific information such as age, sex, identity, and vulnerability. However, it is unknown to what extent person-specific gait information can affect collision avoidance behaviours with an approaching “person”. We sought to determine whether young adults’ spatiotemporal avoidance behaviours were affecte...

Virtual reality (VR) is a valuable experimental tool for studying human movement, including the analysis of interactions during locomotion tasks for developing crowd simulation algorithms. However, these studies are generally limited to distant interactions in crowds, due to the difficulty of rendering realistic sensations of collisions in VR. In t...

In human interaction, people will keep different distances from each other depending on their gender. For example, males will stand further away from males and closer to females. Previous studies in virtual reality (VR), where people were interacting with virtual humans, showed a similar result. However, many other variables influence proximity, su...

Virtual Reality (VR) offers unlimited possibilities to create virtual populated environments in which a user can be immersed and experience social interactions with virtual humans. A better understanding of these interactions is required to improve the realism of the interactions as well as user’s experience. Using an approach based on Interactioni...

In this paper, we introduce a concept called "virtual co-embodiment", which enables a user to share their virtual avatar with another entity (e.g., another user, robot, or autonomous agent). We describe a proof-of-concept in which two users can be immersed from a first-person perspective in a virtual environment and can have complementary levels of...

Figure 1: Our objective is to analyze eye-gaze activity within a crowd to better understand walkers' interaction neighborhood and simulate crowd behaviour. We designed 2 experiments where participants physically walked both in a real and virtual street populated with other walkers, while we measured their eye-gaze activity (red circle). We evaluate...

The dynamical distance geometry problem (dynDGP) is the problem of finding a realization in a Euclidean space of a weighted undirected graph G representing an animation by relative distances, so that the distances between realized vertices are as close as possible to the edge weights. In the dynDGP, the vertex set of the graph G is the set product...

In this paper, we introduce a concept called "virtual co-embodiment", which enables a user to share their virtual avatar with another entity (e.g., another user, robot, or autonomous agent). We describe a proof-of-concept in which two users can be immersed from a first-person perspective in a virtual environment and can have complementary levels of...

With the increasing use of avatars (i.e. the virtual representation of the user in a virtual environment) in virtual reality, it is important to identify the factors eliciting the sense of embodiment or the factors that can disrupt this feeling. This paper reports an exploratory study aiming at identifying internal factors (personality traits and b...

Retargeting motion from one character to another is a key process in computer animation. It enables to reuse animations designed for a character to animate another one, or to make performance-driven be faithful to what has been performed by the user. Previous work mainly focused on retargeting skeleton animations whereas the contextual meaning of t...

Our work is a perceptual study into the effects of training poses on the Example-Based Facial Rigging (EBFR) method. We analyse the output of EBFR given a set of training poses to see how well the results reproduced our ground truth actor scans compared to a Deformation Transfer approach. While EBFR produced better results overall, there were cases...

In character animation, it is often the case that motions created or captured on a specific morphology need to be reused on characters having a different morphology while maintaining specific relationships such as body contacts or spatial relationships between body parts. This process, called motion retargeting, requires determining which body part...

https://interstices.info/jcms/p_93189/la-simulation-de-foule-au-service-du-divertissement

With the increasing demand in virtual reality applications and games, the need to understand how users perceive their virtual representation (avatar) is becoming more and more important. In particular, with the potential of virtual reality to alter and control avatars in different ways, the user representation in the virtual world does not always n...

How do people appropriate their virtual hand representation when interacting in virtual environments? In order to answer this question, we conducted an experiment studying the sense of embodiment when interacting with three different virtual hand representations, each one providing a different degree of visual realism but keeping the same control m...

A better understanding of how intentions and traits are perceived from body movements is required for the design of more effective virtual characters that behave in a socially realistic manner. For this purpose, realistic body motion, captured from human movements, is being used more frequently for creating characters with natural animations in gam...

In this article, we investigate the perception of gender from the motion of virtual humans under different emotional conditions and explore the effect of emotional bias on gender perception (e.g., anger being attributed to males more than females). As motion types can present different levels of physiological cues, we also explore how two types of...

Virtual humans are often endowed with human-like characteristics to make them more appealing and engaging. Motion capture is a reliable way to represent natural motion on such characters, thereby allowing a wide range of animations to be automatically created and replicated. However, interpersonal differences in actors' performances can be subtle a...

Humans adjust their movements in advance to prepare for the forthcoming action, resulting in efficient and smooth transitions. However, traditional computer animation approaches such as motion graphs simply concatenate a series of actions without taking into account the following one. In this paper, we propose a new method to produce preparation be...

Animation budget constraints during the development of a game often call for the use of a limited set of generic motions. Editing operations are thus generally required to animate virtual characters with a sufficient level of variety. Evaluating the perceptual plausibility of edited animations can therefore contribute greatly towards producing visu...

It has been shown that humans are sensitive to the portrayal of emotions for virtual characters. However, previous work in this area has often examined this sensitivity using extreme examples of facial or body animation. Less is known about how attuned people are at recognizing emotions as they are expressed during conversational communication. In...

Although body and facial features affect social judgements about others [Allison et al, 2000, Trends in Cognitive Sciences, 4(7), 267-278], it is unclear how static and dynamic visual features are related to the perceived traits of others. Using images of both familiar and unfamiliar characters, we examined how visual information from faces and bod...

In this paper, we investigate the ability of humans to determine the gender of conversing characters, based on facial and body cues for emotion. We used a corpus of simultaneously captured facial and body motions from four male and four female actors. In our Gender Rating task, participants were asked to rate how male or female they considered the...

Better understanding of how social traits and intentions are conveyed through human body motion is central in creating believable, life-like virtual characters. Body motion conveys socially relevant information on which people make judgments, such as other people's personality or gender. [e.g. Koppensteiner and Grammer 2011, Thoresen et al. 2012]....

Variations in the timing and speed of movements in human interactions carry important social information. For example, seeing one player push another player at a football game, we can deduce whether the player being pushed resisted or anticipated the oncoming push based on subtle differences in the timing and velocity of movements of both players....

Although humans can infer other people’s intentions from their visual actions (Blakemore, & Decety, 2001), it is not well understood how auditory information can influence this process. We investigated whether auditory emotional information can influence the perceived intention of another from their visual body motion. Participants viewed a set of...

When humans perform a series of motions, they prepare for the next motion in advance so as to enhance the response time of their movements. This kind of preparation behaviour results in a natural and smooth transition of the overall movement. In this paper, we propose a new method to synthesize the behaviour using reinforcement learning. To create...

Timing of events conveys important information about causality [Michotte, 1963, The perception of causality, New York, Basic Books]. We examined whether the sensitivity to timing in human motion changes with ageing. Stimuli consisted of computer animations of one character (pusher) approaching and pushing another character (target) on the back, cau...

Understanding whether observers are sensitive to physical distortions in dynamic events is important in order to develop plausible simulations while saving time on details that observers cannot perceive [Barzel et al. 1996]. In this experiment, we evaluated observers' sensitivity to physical distortions in virtual throwing animations. As previous r...

Animation budget constraints during the development of a game often call for the use of a limited set of generic motions. Editing operations are thus generally required to animate virtual characters with a sufficient level of variety. Evaluating the perceptual plausibility of edited animations can therefore contribute greatly towards pro-ducing vis...

Subtle animation details such as finger or facial movements help to bring virtual characters to life and increase their appeal. However, it is not always possible to capture finger animations simultaneously with full-body motion, due to limitations of the setup or tight production schedules. Therefore, hand motions are often either omitted, manuall...

In everyday life, videogames, and movies, motions of human characters and inanimate objects are often in close spatiotemporal relation (e.g., a throwing action of a baseball player). These events have not received much attention in human motion research. Using motion capture, we recorded an actor throwing a tennis ball with an over-arm or under-arm...

In biological motion perception, it is often necessary to normalize certain factors, such as body shape or walking speed, in order to vary them methodically. For example, in order to create an average motion, or to compute and compare quantitative metrics, it is necessary that sets of motions be aligned in time. For computer animation, a character'...