Nuria Pelechano

• PhD University of Pennsylvania
• Professor (Associate) at Polytechnic University of Catalonia

Simulating believable crowds for applications like movies or games is challenging due to the many components that comprise a realistic outcome. Users typically need to manually tune a large number of simulation parameters until they reach the desired results. We introduce MPACT, a framework that leverages image‐based encoding to convert unlabelled...

High‐quality motion reconstruction that follows the user's movements can be achieved by high‐end mocap systems with many sensors. However, obtaining such animation quality with fewer input devices is gaining popularity as it brings mocap closer to the general public. The main challenges include the loss of end‐effector accuracy in learning‐based ap...

This paper proposes a novel approach to enhance the realism of a rule-based crowd simulation model by incorporating social rules and gaze-driven attention with consistent animations. Current crowd simulation models focus mostly on steering towards a goal while avoiding collision based on the agent’s direction of movement. This leads to robot-like s...

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 c...

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 virtu...

Recent developments in extended reality (XR) are already demonstrating the benefits of this technology in the educational sector. Unfortunately, educators may not be familiar with XR technology and may find it difficult to adopt this technology in their classrooms. This article presents the overall architecture and objectives of an EU-funded projec...

Human and animal presence in natural landscapes is initially revealed by the immediate impact of their locomotion, from footprints to crushed grass. In this work, we present an approach to model the effects of virtual characters on natural terrains, focusing on the impact of human locomotion. We introduce a lightweight solution to compute accurate...

High-quality motion reconstruction that follows the user's movements can be achieved by high-end mocap systems with many sensors. However, obtaining such animation quality with fewer input devices is gaining popularity as it brings mocap closer to the general public. The main challenges include the loss of end-effector accuracy in learning-based ap...

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 virtu...

Current statistical models to simulate pandemics miss the most relevant information about the close atomic interactions between individuals which is the key aspect of virus spread. Thus, they lack a proper visualization of such interactions and their impact on virus spread. In the field of computer graphics, and more specifically in computer animat...

Accurate and reliable human motion reconstruction is crucial for creating natural interactions of full-body avatars in Virtual Reality (VR) and entertainment applications. As the Metaverse and social applications gain popularity, users are seeking cost-effective solutions to create full-body animations that are comparable in quality to those produc...

Simulating crowds with realistic behaviors is a difficult but very important task for a variety of applications. Quantifying how a person balances between different conflicting criteria such as goal seeking, collision avoidance and moving within a group is not intuitive, especially if we consider that behaviors differ largely between people. Inspir...

In the era of the metaverse, self-avatars are gaining popularity, as they can enhance presence and provide embodiment when a user is immersed in Virtual Reality. They are also very important in collaborative Virtual Reality to improve communication through gestures. Whether we are using a complex motion capture solution or a few trackers with inver...

In the era of the metaverse, self-avatars are gaining popularity, as they can enhance presence and provide embodiment when a user is immersed in Virtual Reality. They are also very important in collaborative Virtual Reality to improve communication through gestures. Whether we are using a complex motion capture solution or a few trackers with inver...

The use of self-avatars is gaining popularity thanks to affordable VR headsets. Unfortunately, mainstream VR devices often use a small number of trackers and provide low-accuracy animations. Previous studies have shown that the Sense of Embodiment, and in particular the Sense of Agency, depends on the extent to which the avatar's movements mimic th...

A variety of skills are required to develop realistic virtual characters. The aim of the CLIPE project is to train the next generation of researchers in virtual humans and make more realistic virtual characters that are capable of interacting naturally with humans, as Yiorgos Chrysanthou, Nuria Pelechano, Nefeli Andreou and Rafael Blanco explain.

The use of self-avatars is gaining popularity thanks to affordable VR headsets. Unfortunately, mainstream VR devices often use a small number of trackers and provide low-accuracy animations. Previous studies have shown that the Sense of Embodiment, and in particular the Sense of Agency, depends on the extent to which the avatar's movements mimic th...

The animation of user avatars plays a crucial role in conveying their pose, gestures, and relative distances to virtual objects or other users. Self‐avatar animation in immersive VR helps improve the user experience and provides a Sense of Embodiment. However, consumer‐grade VR devices typically include at most three trackers, one at the Head Mount...

The articles in this special section focus on methodologies that have been or could be used to help fight pandemics with computer graphics (CG). The development of new algorithms and computational solutions to simulate, visualize, and predict scenarios in the pandemic world has been a reality in recent years. Many researchers at universities and co...

The animation of user avatars plays a crucial role in conveying their pose, gestures, and relative distances to virtual objects or other users. Self-avatar animation in immersive VR helps improve the user experience and provides a Sense of Embodiment. However, consumer-grade VR devices typically include at most three trackers, one at the Head Mount...

The use of self-avatars in a VR application can enhance presence and embodiment which leads to a better user experience. In collaborative VR it also facilitates non-verbal communication. Currently it is possible to track a few body parts with cheap trackers and then apply IK methods to animate a character. However, the correspondence between tracke...

Recent advancements in crowd simulation unravel a wide range of functionalities for virtual agents, delivering highly‐realistic, natural virtual crowds. Such systems are of particular importance to a variety of applications in fields such as: entertainment (e.g., movies, computer games); architectural and urban planning; and simulations for sports...

The use of self-avatars in a VR application can enhance presence and embodiment which leads to a better user experience. In collaborative VR it also facilitates non-verbal communication. Currently it is possible to track a few body parts with cheap trackers and then apply IK methods to animate a character. However, the correspondence between tracke...

Simulating virtual crowds is an important challenge in many areas such as games and virtual reality applications. A lot of effort has been dedicated to improving pathfinding, collision avoidance, or decision making, to achieve more realistic human-like behavior. However, crowd simulation will be far from appearing realistic as long as virtual human...

Simulating virtual crowds is an important challenge in many areas such as games and virtual reality applications. A lot of effort has been dedicated to improving pathfinding, collision avoidance, or decision making, to achieve more realistic human-like behavior. However, crowd simulation will be far from appearing realistic as long as virtual human...

Path finding for autonomous agents has been traditionally driven by finding optimal paths, typically by using A* search or any of its variants. When it comes to simulating virtual humanoids, traditional approaches rarely consider aspects of human memory or orientation. In this work, we propose a new path finding algorithm, inspired by current resea...

Authoring meaningful crowds to populate a virtual city can be a cumbersome, time-consuming and an error-prone task. In this work, we present a new framework for authoring populated environments in an easier and faster way, by relying on the use of procedural techniques. Our framework consists of the procedural generation of semantically-augmented v...

Immersive virtual environments have proven to be a plausible platform to be used by multiple disciplines to simulate different types of scenarios and situations at a low cost. When participants are immersed in a virtual environment experience presence, they are more likely to behave as if they were in the real world. Improving the level of realism...

Understanding human decision making is a key requirement to improve crowd simulation models so that they can better mimic real human behavior. It is often difficult to study human decision making during dangerous situations because of the complexity of the scenarios and situations to be simulated. Immersive virtual reality offers the possibility to...

As part of the open sourcing of the Microsoft Rocketbox avatar library for research and academic purposes, here we discuss the importance of rigged avatars for the Virtual and Augmented Reality (VR, AR) research community. Avatars, virtual representations of humans, are widely used in VR applications. Furthermore many research areas ranging from cr...

A navigation mesh is a representation of a 2D or 3D virtual environment that enables path planning and crowd simulation for walking characters. Various state-of-the-art navigation meshes exist, but there is no standardized way of evaluating or comparing them. Each implementation is in a different state of maturity, has been tested on different hard...

One of the main challenges in video games is to compute paths as efficiently as possible for groups of agents. As both the size of the environments and the number of autonomous agents increase, it becomes harder to obtain results in real time under the constraints of memory and computing resources. Hierarchical approaches, such as HNA* (Hierarchica...

Achieving realistic virtual humans is crucial in virtual reality applications and video games. Nowadays there are software and game development tools, that are of great help to generate and simulate characters. They offer easy to use GUIs to create characters by dragging and drooping features, and making small modifications. Similarly, there are to...

Virtual navigation should be as similar as possible to how we move in the real world, however the limitations of hardware and physical space make this a challenging problem. Tracking natural walk is only feasible when the dimensions of the virtual environment match those of the real world. The problem of most navigation techniques is that they prod...

Authoring realistic behaviors to populate a large virtual city can be a cumbersome, time-consuming and error-prone task. Believable crowds require the effort of storytellers and programming experts working together for long periods of time. In this work, we present a new framework to allow users to generate populated environments in an easier and f...

This paper presents a virtual reality experiment in which two participants share both the virtual and the physical space while performing a collaborative task. We are interested in studying what are the differences in human locomotor behavior between the real world and the VR scenario. For that purpose, participants performed the experiment in both...

Crowd simulation models typically combine low level and high level behavior. The low level deals with reactive behavior and collision avoidance, while the high level deals with path finding and decision making. There has been a large amount of work studying collision avoidance maneuvres for humans in both virtual reality and from real data. When it...

The challenge of path-finding in video games is to compute optimal or near optimal paths as efficiently as possible. As both the size of the environments and the number of autonomous agents increase, this computation has to be done under hard constraints of memory and CPU resources. Hierarchical approaches, such as HNA* can compute paths more effic...

A navigation mesh is a representation of a 2D or 3D virtual environment that enables path planning and crowd simulation for walking characters. Various state-of-the-art navigation meshes exist, but there is no standardized way of evaluating or comparing them. Each implementation is in a different state of maturity, has been tested on different hard...

This book provides a deep understanding of state-of-art methods for simulation of heterogeneous crowds in computer graphics. It will cover different aspects that are necessary to achieve plausible crowd behaviors. The book will be a review of the most recent literature in this field that can help professionals and graduate students interested in th...

Path-finding can become an important bottleneck as both the size of the virtual environments and the number of agents navigating them increase. It is important to develop techniques that can be efficiently applied to any environment independently of its abstract representation. In this paper we present a hierarchical NavMesh representation to speed...

With advances in virtual reality technology and its multiple applications, the need for believable, immersive virtual environments is increasing. Even though current computer graphics methods allow us to develop highly realistic virtual worlds, the main element failing to enhance presence is autonomous groups of human inhabitants. A great number of...

Following seminal work [225] on flocking behaviors using particle systems, the field of crowd simulation has grown into a well-developed, multi-faceted area of study [50, 271]. Steering, or goal-directed collision avoidance, is the layer of intelligence that interfaces with navigation to move an agent along its planned path by performing a series o...

Crowd simulations can better depict real populations if they include agent traits that introduce character heterogeneity. The memory model presented is one avenue for differentiating indi– viduals. Agents are capable of remembering objects and their locations they encounter in the environment. These memories can be strengthened through repeated enc...

There exists a wealth of research [118, 208, 272] that separately addresses the problems of charac– ter animation, steering, navigation, and behavior authoring, with many open challenges [125] that need to be addressed in an effort to arrive at a common framework for simulating autonomous virtual humans for the next generation of narrative-driven i...

ADAPT is a modular, flexible platform which provides a comprehensive feature set for anima– tion, navigation, and behavior tools needed for end-to-end simulation development. By allowing a user to independently incorporate a new animation choreographer or steering system, and make those components immediately accessible to the behavior level withou...

Character navigation in complex scenes is commonly performed by having a Navigation Mesh (NavMesh), which encodes a convex decomposition of the scene. The NavMesh is represented with a Cell-and-Portal Graph (CPG), where cells are convex regions and portals are the edges shared by convex regions that a character can traverse. Path finding algorithms...

We have integrated sound propagation and human-like perception into virtual human simulations. While sound propagation and synthesis have been explored in computer graphics, and there exist extensive studies on auditory perception in psychology, ours is the first work to enable virtual humans to plausibly hear, listen, and react to auditory trigger...

The agent control methods discussed so far have a common feature: movement directives come from essentially omniscient navigation algorithms. Footstep steering uses a local context model based on explicit knowledge of surrounding obstacles and agents, while navigation proceeds with search algorithms exploiting multiple-level spatial abstractions. W...

We have covered two key aspects of navigation planning for autonomous agents: the importance of having well-defined abstract representations of the environment and planning in multiple do– mains to achieve paths of high quality with good performance.

Real human crowds and populations are not uniform. Not everyone performs the same behaviors and even similar behaviors are not performed in the same ways [126], and subtle movement differences denote widely different personalities [196]. Physical human populations are heterogeneous, so virtual populations should reflect that. Individual differences...

Autonomous agents navigating virtual environments need a robust abstract representation of the walkable or “free” space. Deciding the most adequate representation—the navigation mesh (NavMesh) [258]—can be a challenge with strong dependencies on the application and the size of the crowd. Ideally the navigation mesh should be formed by cells with a...

This volume presents novel computational models for representing digital humans and their interactions with other virtual characters and meaningful environments. In this context, we describe efficient algorithms to animate, control, and author human-like agents having their own set of unique capabilities, personalities, and desires. We begin with t...

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...

Simulation of crowd behavior has been approached through many different methodologies, but the problem of mimicking human decisions and reactions remains a challenge for all. We propose an alternative model for simulation of pedestrian movements using Reinforcement Learning. Taking the approach of microscopic models, we train an agent to move towar...

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 c...

Our objective with this paper is to show how we can couple a group of real people and a simulated crowd of virtual humans. We attach group behaviors to the simulated humans to get a plausible reaction to real people. We use a two stage system: in the first stage, a group of people are segmented from a live video, then a human detector algorithm ext...

Our objective with this paper is to show how we can couple a group of real people and a simulated crowd of virtual humans. We attach group behaviors to the simulated humans to get a plausible reaction to real people. We use a two stage system: in the first stage, a group of people are segmented from a live video, then a human detector algorithm ext...

Our objective with this paper is to show how we can couple a group of real people and a simulated crowd of virtual humans. We attach group behaviors to the simulated humans to get a plausible reaction to real people. We use a two stage system: in the first stage, a group of people are segmented from a live video, then a human detector algorithm ext...

There are two frequent artifacts in crowd simulation, the first one appears when all agents attempt to traverse the navigation mesh sharing the same way point over portals, increasing the probability of collision against other agents and lining up towards portals; the second one is caused by way points being assigned at locations where clearance is...

Navigation in virtual environments for autonomous characters is tipically handled by the combination of a path planning algorithm which decides the cells to walk through in the navigation mesh, and a local movement algorithm that carries out the frame to frame trajectory within each cell. Local movement is driven by intermediate goals (attractors)...

Character navigation in virtual environments is mostly handled by a combination of path planning with local movement algorithms. Clearance should be taken into consideration when choosing a path, but also when deciding the location of way points within portals. Previous work has considered clearance for path planning, but it is ignored when assigni...

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 dis-tributed across planning...

This paper presents a real-time planning framework for multicharacter 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 ta...

In this paper we present a novel, robust and efficient GPU based technique to automatically generate a Navigation Mesh for complex 3D scenes. Our method consists of two steps: firstly, starting with a 3D scene representing a complex environment of one floor with slopes, steps, and other obstacles, it automatically generates a 2D representation base...

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...

Virtual reality experiments with virtual crowds are necessary to study human behavior under panic or stressful situations that cannot be evaluated in the real world (i.e., building evacuation due to fire). In order to carry out those experiments it is necessary to use a crowd simulation model in which a real person is seamlessly immersed and experi...

Rendering detailed animated characters is a major limiting factor in crowd simulation. In this paper we present a new representation for 3D animated characters which supports output‐sensitive rendering. Our approach is flexible in the sense that it does not require us to pre‐define the animation sequences beforehand, nor to pre‐compute a dense set...

Most current games perform navigation in virtual environments through A* for path finding combined with a local movement algorithm. Navigation Meshes are the most popular approach to combine path finding with local movement. This paper presents a new Automatic Navigation Mesh Generator (ANavMG) that subdivides any polygon representing the environme...

A personality model named High-Density Autonomous Crowds (HiDAC) simulation system provides individual differences by assigning each person different psychological and physiological traits. Users normally set these parameters to model a crowd's nonuniformity and diversity. The approach creates plausible variations in the crowd and enables novice us...

This paper presents an Animation Planning Mediator (APM) designed to synthesize anima-tions 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 r...

Virtual environments can be used as a test bed for validation of human behavior simulation techniques since they place people within a simulated situation from an egocentric perspective. We propose level of presence achieved by a human in a virtual environment (VE) as a metric for virtual crowd behavior. Using experimental evidence from the presenc...

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) modul...

Crowd simulation models are currently lacking a commonly accepted validation method. In this paper, we propose level of presence achieved by a human in a virtual environment (VE) as a metric for virtual crowd behavior. Using experimental evidence from the presence literature and the results of a pilot experiment that we ran, we explore the egocentr...

Building evacuation simulation provides designers with an efficient way of testing the safety of a building before construction. A significant number of models have been developed in a variety of disciplines (computer graphics, robotics, evacuation dynamics, etc.). This paper presents a review of crowd simulation models and selected commercial soft...

There are many applications of computer animation and simulation where it is necessary to model virtual crowds of autonomous agents. Some of these applications include site planning, education, entertainment, training, and human factors analysis for building evacuation. Other applications include simulations of scenarios where masses of people gath...

Most current crowd simulators animate homogeneous crowds, but include underlying parameters that can be tuned to create variations within the crowd. These parameters, however, are specific to the crowd models and may be difficult for an animator or naive user to use. We propose mapping these parameters to personality traits. In this paper, we exten...

There exist many relevant crowd simulation methodologies. Here we present several systems that have been developed for animation or evacuation dynamics purposes. They all share the requirement for pedestrian movement models, but differ in techniques for generating motion paths. First we shall examine microscopic methods, then macroscopic methods, a...

Local agent motion is based on a combination of geometric information and psychological rules with a forces model to enable a wide variety of behaviors resembling those of real people. HiDAC uses psychological attributes (panic, impatience) and geometric rules (distance, areas of influence, relative angles) to eliminate unrealistic artifacts and al...

We have developed a framework for high-density multiagent simulation with a bottom-up approach. On the low-level agents move within a room driven by a social forces model with psychological and geometric rules affecting several parameters that will allow for a wide variety of emergent and high-density behaviors. Above the motion level, we need a wa...

One of the most difficult aspects of doing research in crowd simulation is evaluation. The real world and its real characters are very complex, making it difficult to compare a simulation to events that might happen in reality. Another option for evaluation is performing user studies to try to determine if the desired qualities for the simulation h...

Creating a new simulation requires numerous elements. Buildings and spaces need to be created and laid out with objects such as furniture or vehicles. Character profiles also need to be defined for the population. This includes roles, relationships, and possible other individual differences such as personality profiles. These character profiles the...

Real populations and crowds are not homogeneous: they are composed of individuals who differ in a variety of ways. Naturally, their external appearances vary, which can be accomplished by using different graphical models and materials. Members of real crowds also differ in their behaviors. These behavioral variations stem from a range of factors, f...