Implicit Patches: An Optimized and Powerful Ray Intersection Algorithm for Implicit Surfaces

International audienceThis paper describes an new and optimized direct ray tracing algorithm over complex implicit surfaces generated by skeletons. Its main originality is its ability to avoid unwanted blending between parts of the same object, thank to the portioning of the surface into several pieces, so called Implicit Patches. Moreover, these patches enable to exploit the properties of local field functions, and to speed-up considerably the rendering. Extensive statistics of the various optimizations proposed are given and discussed. The implantation into public domain software RayShade is sketched

Displacement constraints for interactive modeling and animation of articulated structures

PublishedInternational audienceThis paper presents an integrated set of methods for the automatic construction and interactive animation of solid systems that satisfy specified geometric constraints. Displacement contraints enable the user to design articulated bodies with various degrees of freedom in rotation or in translation at highes and to restrict the scope of the movement at will. The graph of constrained objects may contain closed loops. The animation is achieved by decoupling the free motion of each solid component from the action of the constraints. We do this with iterative tunings in displacements. The method is currently implemented in a dynamically based animation system and takes the physical parameters into account while reestablishing the constraints. In particular, first-order momenta are preserved during this process. The approach would be easy to extend to modeling systems or animation modules without a physical model just by allowing the user to control more parameters. (source Springer

Reactive Balance Control in Immersive Visual Flows: 2D vs. 3D Virtual Stimuli

Poster at 14th Annual CyberTherapy and CyberPsychology Conference - http://online.liebertpub.com/toc/cpb/12/5International audienceThe aim is to study the effects of 2D vs. 3D visual inputs on balance control. Ten subjects were fully immersed in virtual environment, using 10 different 2D/3D motion flow conditions. Analysis of visual and postural responses shows significant differences of reactivity in 3D versus 2D

Reactive Ocular and Balance Control in Immersive Visual Flows: 2D vs. 3D Virtual Stimuli

Short paper - Section III. Original Research - Also published in Advanced Technologies in the Behavioral Social and Neurosciences (vol. 7): http://fr.scribd.com/doc/17030552)International audienceThe control of gaze and balance strongly depend on the processing of visual cues. The aim of this study is to assess the effects of the dynamic 2D and 3D visual inputs on the oculomotor and balance reactive control. Thirteen subjects were immersed in a virtual environment using 10 different 2D/3D visual flow conditions. Analysis of eye movement and postural adjustments shows that 2D and 3D flows induce specific measurable behavioral responses

Environnement de Réalité Augmentée Collaboratif : Manipulation d'Objets Réels et Virtuels

National audienceLa réalité augmentée est un outil indispensable pour certaines situations collaboratives. Nous proposons un environnement multi-utilisateurs, multi-périphériques dédié aux applications collaboratives. Il repose sur une architecture modulaire et facilement configurable pour une mise en place rapide d'une session de travail. Cette plate-forme est utilisée pour démontrer des techniques d'interactions très intuitives pour la manipulation d'objets réels et virtuels et la visualisation à plusieurs échelles. On introduit également des méthodes pour ajouter de façon dynamique des objets réels et virtuels, qui s'intègrent alors dans le même espace. Basé sur des concepts de vue privée et de droits d'accès aux éléments de la scène, l'environnement gère l'interaction multi-utilisateurs

Soundtracks for Computer Animation : Sound Rendering in Dynamic Environments with Occlusions

International audienceWith the development of virtual reality systems and multi-modal simulations, soundtrack generation is becoming an important issue in computer graphics. In the context of computer generated animation, many more parameters than the sole object geometry as well as specific events can be used to generate, control and render a soundtrack that fits the object motions. Producing a convincing soundtrack involves the rendering of the interactions of sound with the dynamic environment : in particular sound reflections and sound absorption due to partial occlusions, usually implying an unacceptable computational cost. We present an integrated approach to sound and image rendering in a computer animation context, which allows the animator to recreate the process of sound recording, while ``physical effects" are automatically computed. Moreover, our sound rendering process efficiently combines a sound reflection model and an attenuation model due to scattering/diffraction by partial occluders, through the use of graphics hardware allowing interactive computation rates.Avec le développement des systèmes de réalité virtuelle et des simulations multi-modales, générer une bande son devient un problème qui touche de plus en plus le milieu de l'informatique graphique. Dans le contexte d'une animation de synthèse, de nombreux paramètres et évènements peuvent être utilisés pour générer, contrôler et effectuer le rendu d'une bande son accompagnant l'action. Produire une bande son convaincante implique toutefois le rendu des interactions du son avec l'environnement dynamique, en particulier ses multiples réflections et l'absorption due aux occlusions partielles, nécessitant habituellement des calculs couteux. Nous présentons une approche pour le rendu simultané du son et de l'image dans un contexte d'animation de synthèse permettant à l'animateur de recréer un processus de prise de son virtuelle, les calculs d'effets étant réalisés automatiquement. Notre processus de rendu permet de prendre en compte, en temps interactif, les réflections du son ainsi qu'un modèle de dispersion/diffraction due aux occlusions partielles en utilisant le hardware spécialisé des stations grahiques

Réalité Augmentée et Environnement Collaboratif : Un Tour d'Horizon

National audienceLa Réalité Augmentée (RA) est généralement définie comme une branche dérivée de la Réalité Virtuelle. D'une façon plus générale, le concept de réalité augmentée regroupe une approche multidisciplinaire visant un mélange entre réel et virtuel. La forte potentialité induite par cette connexion promet un cadre adéquat pour l'interaction 3D ou les applications collaboratives. On présente dans cet article un tour d'horizon des principaux travaux menés à ce jour dans le cadre de l'image et de la RA et plus particulièrement le cadre collaboratif

ECHO & NarSYS - An accoustic modeler and sound renderer

International audienceComputer graphics simulations are now widely used in the field of environmental modelling, for example to evaluate the visual impact of an architectural project on its environment and interactively change its design. Realistic sound simulation is equally important for environmental modelling. At iMAGIS, a joint project of INRIA, CNRS, Joseph Fourier University and the Institut National Polytechnique of Grenoble, we are currently developing an integrated interactive acoustic modelling and sound rendering system for virtual environments. The aim of the system is to provide an interactive simulation of global sound propagation in a given environment and an integrated sound/computer graphics rendering to obtain computer simulated movies of the environment with realistic and coherent soundtracks

Fast Non-Linear Projections using Graphics Hardware

http://artis.imag.fr/Publications/2008/GHFP08/International audienceLinear perspective projections are used extensively in graphics. They provide a non-distorted view, with simple computations that map easily to hardware. Non-linear projections, such as the view given by a fish-eye lens are also used, either for artistic reasons or in order to provide a larger field of view, e.g. to approximate environment reflections or omnidirectional shadow maps. As the computations related to non-linear projections are more involved, they are harder to implement, especially in hardware, and have found little use so far in practical applications. In this paper, we apply existing methods for non-linear projections [Lloyd et al. 2006; Hou et al. 2006; Fournier 2005] to a specific class: non-linear projections with a single center of projection, radial symmetry and convexity. This class includes, but is not limited to, paraboloid projections, hemispherical projections and fish-eye lenses. We show that, for this class, the projection of a 3D triangle is a single curved triangle, and we give a mathematical analysis of the curved edges of the triangle; this analysis allows us to reduce the computations involved, and to provide a faster implementation. The overhead for non-linearity is bearable and can be balanced with the fact that a single nonlinear projection can replaces as many as five linear projections (in a hemicube), with less discontinuities and a smaller memory cost, thus making non-linear projections a practical alternative. More at http://artis.imag.fr/Publications/2008/GHFP0

Visual-vestibular compensation in balance recovery: A transfer function model-based analysis

International audienc