Roland Geraerts

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• PhD
• Professor (Associate) at Utrecht University

Path planning for walking characters in complicated virtual environments is a fundamental task in simulations and games. In this paper, we present an improved definition of the Explicit Corridor Map (ECM), a navigation mesh that allows efficient path planning and crowd simulation for disk-shaped characters of any radius. The ECM is a medial axis (M...

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...

Path planning and crowd simulation are important computational tasks in computer games and applications of high social relevance, such as crowd management and safety training. Virtual characters (agents) need to autonomously find a path from their current position to a designated goal position. This is usually solved by running the A* algorithm on...

We present a novel crowd simulation model that combines the advantages of agent-based and flow-based paradigms while only relying on local information. Our model can handle arbitrary and dynamically changing crowd densities, and it enables agents to gradually interpolate between individual and coordinated behavior. This interpolation is based on a...

We present Social Groups and Navigation (SGN), a method to simulate the walking behavior of small pedestrian groups in virtual environments. SGN is the first method to simulate group behavior on both global and local levels of an underlying planning hierarchy. We define quantitative metrics to measure the coherence and the sociality of a group base...

Building Information Modelling (BIM) has become the de facto standard for the digital representation of buildings. However, from the pedestrian dynamics perspective, BIM Industry Foundation Classes (IFC) schema specification do not fully support data properties required for two-way data sharing with pedestrian modelling tools. An international team...

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...

The quantification of pedestrian safety is an important research topic. If reliable quantification is possible, it can be used to predict and prevent dangerous situations, such as the crowd crush at the 2010 Love Parade. To quantify safety, we can use several metrics like density, velocity, flow and pressure. Unfortunately, there are several method...

This article presents a glossary of terms that are frequently used in research on human crowds. This topic is inherently multidisciplinary as it includes work in and across computer science, engineering, mathematics, physics, psychology and social science, for example. We do not view the glossary presented here as a collection of finalised and form...

Path planning for walking characters in complicated virtual environments is a fundamental task in simulations and games. A navigation mesh is a data structure that allows efficient path planning. The Explicit Corridor Map (ECM) is a navigation mesh based on the medial axis. It enables path planning for disk-shaped characters of any radius. In this...

The k-nearest neighbour (kNN) problem appears in many different fields of computer science, such as computer animation and robotics. In crowd simulation, kNN queries are typically used by a collision-avoidance method to prevent unnecessary computations. Many different methods for finding these neighbours exist, but it is unclear which will work bes...

A multi-layered environment is a representation of the walkable space in a 3D virtual environment that comprises a set of two-dimensional layers together with the locations where the different layers touch, which are called connections. This representation can be used for crowd simulations, e.g. to determine evacuation times in complex buildings. S...

A multi-layered environment (MLE) [van Toll et al. 2011] is a representation of the walkable environment (WE) in a 3D virtual environment that comprises a set of two-dimensional layers together with the locations where the different layers touch, which are called connections. This representation can be used for crowd simulations, e.g. to determine...

With the rise and success of digital games over the past few decades, path planning algorithms have become an important aspect in modern game development for all types of genres. Indirectly-controlled playable characters as well as non-player characters have to find their way through the game's environment to reach their goal destinations. Modern g...

We present a new method, Social Groups and Navigation (SGN), to simulate the walking behavior of small pedestrian groups in virtual environments. SGN is the first method to simulate group behavior on both global and local levels. We define quantitative metrics to measure the coherence and the sociality of a group based on existing empirical data of...

We present a crowd simulation model that combines the advantages of agent-based and flow-based paradigms while only relying on local information. Our model can handle arbitrary and dynamically changing crowd densities, and it enables agents to gradually interpolate between individual and coordinated behavior. Our model can be used with any existing...

Path planning and crowd simulation are important computational tasks in computer games and applications of high social relevance, such as crowd management and safety training. Virtual characters (agents) need to autonomously find a path from their current position to a designated goal position. This is usually solved by running the A* algorithm on...

The Weighted Region Problem is defined as the problem of finding a cost-optimal path in a weighted planar polygonal subdivision. Searching for paths on a grid representation of the scene is fast and easy to implement. However, grid representations do not capture the exact geometry of the scene. Hence, grid paths can be inaccurate or might not even...

The Weighted Region Problem is defined as the problem of finding a cost-optimal path in a weighted planar polygonal subdivision. Searching for paths on a grid representation of the scene is fast and easy to implement. However, grid representations do not capture the exact geometry of the scene. Hence, grid paths can be inaccurate or might not even...

This paper presents a GPU-accelerated approach for improving the approximated construction of Generalized Voronoi Diagrams (GVDs). Previous work has shown how to render a GVD onto the GPU framebuffer, and copy it to the CPU for extraction of a high-quality diagram. We improve upon this technique by performing more computations in parallel on the GP...

A huge challenge is to simulate tens of thousands of virtual characters in real-time where they pro-actively and realistically avoid collisions with each other and with obstacles present in their environment. This environment contains semantic information (e.g. roads and bicycle lanes, dangerous and pleasant areas), is three-dimensional (e.g. conta...

A central problem of applications dealing with virtual environments is planning a collision-free path for a character. Since environments and their characters are growing more realistic, a character's path needs to be visually convincing, meaning that the path is smooth, short, has some clearance to the obstacles in the environment, and avoids othe...

This paper presents our path planning method MIRAN (Modified Indicative Routes and Navigation) that takes a character's region preferences into account. Given an indicative route as a rough estimation of a character's preferred route, MIRAN efficiently computes a visually convincing path that is smooth, keeps clearance from obstacles, avoids unnece...

Path planning is one of the classical computational tasks in video games. Virtual characters need to au-tonomously find a path from their current position to a designated goal position. This is usually solved by run-ning the A* algorithm on a grid or a navigation mesh. However, in many modern games, strictly following the resulting path is not suff...

Modern virtual environments can contain a variety of characters and traversable regions. Each character may have differ-ent preferences for the traversable region types. Pedestrians may prefer to walk on sidewalks, but they may occasionally need to traverse roads and dirt paths. By contrast, wild animals might try to stay in forest areas, but they...

The addition of a crowd in a virtual environment, such as a game world, can make the environment more realistic. While researchers focused on the visual modeling and simulation of a crowd, its sound production has received less attention. We propose the generation of the sound of a crowd by retrieving a very small set of speech snippets from a user...

We present a novel approach for planning and directing heterogeneous groups of virtual agents based on techniques from linear programming. Our method efficiently identifies the most promising paths in both time and space and provides an optimal distribution of the groups’ members over these paths such that their average traveling time is minimized....

Games and simulations frequently model scenarios where obstacles move, appear, and disappear in an environment. A city environment changes as new buildings and roads are constructed, and routes can become partially blocked by small obstacles many times in a typical day. This paper studies the effect of using local updates to repair only the affecte...

We present a novel approach for planning and directing heterogeneous groups of virtual agents based on techniques from linear programming. Our method efficiently identifies the most promising paths in both time and space and provides an optimal distribution of the groups' members over these paths such that their av-erage traveling time is minimized...

Virtual characters in games and simulations often need to plan visually convincing paths through a crowded environment. This paper describes how crowd density information can be used to guide a large number of characters through a crowded environment. Crowd density information helps characters avoid congested routes that could lead to traffic jams....

Texas, USA. The JVWR is an academic journal. As such, it is dedicated to the open exchange of information. For this reason, JVWR is freely available to individuals and institutions. Copies of this journal or articles in this journal may be distributed for research or educational purposes only free of charge and without permission. However, the JVWR...

Virtual characters often need to plan visually convincing paths through a complicated environment. For example, a traveler may need to walk from an airport entrance to a staircase, descend the staircase, walk to a shuttle, ride the shuttle to a destination, ride an elevator back to the ground floor, and finally move on the ground floor again to rea...

Natural locomotion of virtual characters is very important in games and simulations. The naturalness of the total motion strongly depends on both the path the character chooses and the animation of the walking character. Therefore, much work has been done on path planning and generating walking animations. However, the combination of both fields ha...

Virtual characters often need to plan visually convincing paths through a complicated environment. For example, a traveler may need to walk from an airport entrance to a staircase, descend the staircase, walk to a shuttle, ride the shuttle to a destination, ride an elevator back to the ground floor, and finally move on the ground floor again to rea...

In computer games, one or more groups of units need to move from one location to another as quickly as possible. If there is only one group, then it can be solved efficiently as a dynamic flow problem. If there are several groups with different origins and destinations, then the problem becomes NP-hard. In current games, these problems are solved b...

A central problem of applications dealing with virtual environments is planning a collision-free path for a character. Since environments and their characters are growing more realistic, a character's path needs to be visually convincing, meaning that the path is smooth, short, has some clearance to the obstacles in the environment, and avoids othe...

A relatively new area within the field of path planning deals with computing a stealthy path for a character moving in a virtual environment. Besides efficiently obtaining a path that is collision-free, short and smooth, the added difficulty is that the path must have little or no exposure to observers. We propose a new algorithm for computing such...

In computer games, one or more groups of units need to move from one location to another as quickly as possible. If there is only one group, then it can be solved efficiently as a dynamic flow problem. If there are several groups with different origins and destinations, then the problem becomes NP-hard. In current games, these problems are solved b...

Planning high-quality camera motions is a challenging problem for applications dealing with interactive virtual environments. This challenge is caused by conflicting requirements. On the one hand we need good motions, formed by trajectories that are collision-free and keep the character that is being followed in clear view. On the other hand, we ne...

An important challenge in virtual environment applications is to steer virtual characters through complex and dynamic worlds. The characters should be able to plan their paths and move toward their desired locations, avoiding at the same time collisions with the environment and with other moving entities. In this paper we propose a general method f...

This book constitutes the proceedings of the Second International Workshop on Motion in Games, held in Zeist, The Netherlands, in November 2009. The 23 papers presented in this volume were carefully reviewed and selected. The topics covered are avoidance behaviour, behaviour and affect, crowd simulation, motion analysis and synthesis, navigation an...

Path planning is a central problem in virtual environments and games. When computer-controlled characters move around in virtual worlds they have to plan their paths to desired locations. These paths must avoid collisions with the environment and with other moving characters. Also a chosen path must be natural, meaning that it is the kind of path a...

A central problem in games is planning high-quality paths for characters avoiding obstacles in the environment. Current games require a path planner that is fast (to ensure real-time interaction) and flexible (to avoid local hazards). In addition, a path needs to be natural, meaning that the path is smooth, short, keeps some clearance to obstacles,...

A central problem in interactive virtual environments is planning high-quality paths for characters avoiding obstacles in the environment. Current applications require a path planner that is fast (to ensure real-time interaction with the environment) and flexible (to avoid local hazards). In addition, paths need to be natural, i.e. smooth and short...

In the last fifteen years, sampling-based planners like the Probabilistic Roadmap Method (PRM) have proved to be successful in solving complex motion planning problems. While theoretically, the complexity of the motion planning problem is exponential in the number of degrees of freedom, sampling-based planners can successfully handle this curse of...

Many algorithms have been proposed that create a path for a robot in an environment with obstacles. Most methods are aimed at finding a solution. However, for many applications, the path must be of a good quality as well. That is, a path should be short and should keep some amount of minimum clearance to the obstacles. Traveling along such a path r...

A central problem in robotics is planning a collision-free path for a moving object in an environment with obstacles. Contemporary applications require a path planner that is fast (to ensure real-time interaction with the environment) and flexible (to avoid local hazards). In addition, paths need to be smooth and short. We propose a new framework,...

In many virtual environment applications, paths have to be planned for characters to traverse from a start to a goal position in the virtual world while avoiding obstacles. Contemporary applications require a path planner that is fast (to ensure real‐time interaction with the environment) and flexible (to avoid local hazards such as small and dynam...

Our goal is to create road maps that are particularly suited for motion planning in virtual environments. We use our reachability roadmap method to compute an initial, resolution complete roadmap. This roadmap is small which keeps query times and memory consumption low. However, for use in virtual environments, there are additional criteria that mu...

The probabilistic roadmap approach is one of the leading motion planning techniques. Over the past decade the technique has been studied by many different researchers. This has led to a large number of variants of the approach, each with its own merits. It is difficult to compare the different techniques because they were tested on different types...

In robotics research, it is often difficult to compare and evaluate techniques experimentally. This paper identifies these difficulties and provides solutions based on our work during the last four years in the field of sampling-based motion planning.

In robot motion planning, many algorithms have been proposed that create a path for a robot in an environment with obstacles. Since it can be hard to create such paths, most algorithms are aimed at finding a solution. However, for most applications the paths must be of a good quality as well. That is, paths should preferably be short, be smooth, an...

The last decade, sampling based planners like the Probabilistic Roadmap Method have proved to be successful in solving complex motion planning problems. We give a reachability based analysis for these planners which leads to a better understanding of the success of the approach and enhancements of the techniques suggested. This also enables us to s...

Many motion planning techniques, like the probabilistic roadmap method (PRM), generate low quality paths. In this paper, we will study a number of different quality criteria on paths in particular length and clearance. We will describe a number of techniques to improve the quality of paths. These are based on a new approach to increase the path cle...

The probabilistic roadmap approach is a commonly used motion planning technique. A crucial ingredient of the approach is a sampling algorithm that samples the conguration space of the moving object for free congurations. Over the past decade many sampling techniques have been proposed. It is dicult to compare the dierent techniques because they wer...

Many motion planning techniques, like the probabilistic roadmap method (PRM), generate low quality paths. In this paper, we study a number of different quality criteria on paths in particular length and clearance. We describe a number of techniques to improve the quality of paths. These are based on a new approach to increase the path clearance. Ex...

The probabilistic roadmap approach is one of the leading motion planning techniques. Over the past eight years the technique has been studied by many different researchers. This has led to a large number of variants of the approach, each with its own merits. It is difficult to compare the different techniques because they were tested on different t...

The probabilistic roadmap approach is one of the leading motion plan- ning techniques. Over the past eight years the technique has been studied by many different researchers. This has led to a large number of variants of the approach, each with its own merits. It is difficult to compare the different techniques because they were tested on different...

The probabilistic roadmap approach is one of the leading motion planning techniques. Over the past eight years the technique has been studied by many different researchers. This has led to a large number of variants of the approach, each with its own merits. It is difficult to compare the different techniques because they were tested on different t...

One of the fundamental tasks robots have to perform is planning their motions while avoiding collisions with obstacles in the environment. This is the central topic of the thesis. We restrict ourselves to motion planning for two- and three-dimensional rigid bodies and articulated robots moving in static and known virtual environments. This thesis h...

In robot motion planning, many algorithms have been proposed that create a roadmap from which a path for a moving object can be extracted. These algorithms generally do not give guarantees on the quality of the roadmap, i.e. they do not promise that a path will always be found in the roadmap if one exists in the world. Furthermore, such roadmaps of...

The last decade, sampling based planners like the Probabilistic Roadmap Method have proved to be successful in solving complex motion planning problems. We give a reachability based analysis for these planners which leads to a better understanding of the success of the approach and enhancements of the techniques suggested. This also enables us to s...