Gigavoxels: ray-guided streaming for efficient and detailed voxel rendering

Figure 1: Images show volume data that consist of billions of voxels rendered with our dynamic sparse octree approach. Our algorithm achieves real-time to interactive rates on volumes exceeding the GPU memory capacities by far, tanks to an efficient streaming based on a ray-casting solution. Basically, the volume is only used at the resolution that is needed to produce the final image. Besides the gain in memory and speed, our rendering is inherently anti-aliased. We propose a new approach to efficiently render large volumetric data sets. The system achieves interactive to real-time rendering performance for several billion voxels. Our solution is based on an adaptive data representation depending on the current view and occlusion information, coupled to an efficient ray-casting rendering algorithm. One key element of our method is to guide data production and streaming directly based on information extracted during rendering. Our data structure exploits the fact that in CG scenes, details are often concentrated on the interface between free space and clusters of density and shows that volumetric models might become a valuable alternative as a rendering primitive for real-time applications. In this spirit, we allow a quality/performance trade-off and exploit temporal coherence. We also introduce a mipmapping-like process that allows for an increased display rate and better quality through high quality filtering. To further enrich the data set, we create additional details through a variety of procedural methods. We demonstrate our approach in several scenarios, like the exploration of a 3D scan (8192 3 resolution), of hypertextured meshes (16384 3 virtual resolution), or of a fractal (theoretically infinite resolution). All examples are rendered on current generation hardware at 20-90 fps and respect the limited GPU memory budget. This is the author’s version of the paper. The ultimate version has been published in the I3D 2009 conference proceedings.

Gestion de la complexité géométrique dans le calcul d'éclairement pour la présentation publique de scènes archéologiques complexes

International audienceFor cultural heritage, more and more 3D objects are acquired using 3D scanners [Levoy 2000]. The resulting objects are very detailed with a large visual richness but their geometric complexity requires specific methods to render them. We first show how to simplify those objects using a low-resolution mesh with its associated normal maps [Boubekeur 2005] which encode details. Using this representation, we show how to add global illumination with a grid-based and vector-based representation [Pacanowski 2005]. This grid captures efficiently low-frequency indirect illumination. We use 3D textures (for large objects) and 2D textures (for quasi-planar objects) for storing a fixed set of irradiance vectors. These grids are built during a preprocessing step by using almost any existing stochastic global illumination approach. During the rendering step, the indirect illumination within a grid cell is interpolated from its associated irradiance vectors, resulting in a smooth everywhere representation. Furthermore, the vector-based representation offers additional robustness against local variations of geometric properties of the scene.Pour l’étude du patrimoine, de plus en plus d’objets 3D sont acquis par le biais de scanners 3D [Levoy 2000]. Les objets ainsi acquis contiennent de nombreux détails et fournissent une très grande richesse visuelle. Mais pour les afficher, leur très grande complexité géométrique nécessite l’utilisation d’algorithmes spécifiques. Nous montrons ici comment simplifier ces objets par un maillage de faible résolution et une collection de cartes de normales [Boubekeur 2005] pour préserver les détails. Avec cette représentation, nous montrons comment il est possible de calculer un éclairement réaliste à l’aide d’une grille et de données vectorielles [Pacanowski 2005]. Cette grille permet de capturer efficacement les basses fréquences d’un éclairement indirect. Nous utilisons des textures 3D (pour des gros objets) et potentiellement des textures 2D (pour les objets quasi-plans) afin de stocker un nombre prédéterminé de vecteurs d’irradiance. Ces grilles sont calculées au cours d’un pré-calcul à l’aide de n’importe quelle méthode stochastique de calcul d’éclairement global. Pour l’affichage, l’éclairement indirect dû à la grille est interpolé au sein de la cellule associée à la position courante, fournissant ainsi une représentation continue. De plus, cette approche vectorielle permet une plus grande robustesse aux variations locales des propriétés géométriques de la scène

TileTrees

International audienceTexture mapping with atlases suffer from several drawbacks: Wasted memory, seams, uniform resolution and no support of implicit surfaces. Texture mapping in a volume solves most of these issues, but unfortunately it induces an important space and time overhead. To address this problem, we introduce the TileTree: A novel data structure for texture mapping surfaces. TileTrees store square texture tiles into the leaves of an octree surrounding the surface. At rendering time the surface is projected onto the tiles, and the color is retrieved by a simple 2D texture fetch into a tile map. This avoids the dif culties of global planar parameterizations while still mapping large pieces of surface to regular 2D textures. Our method is simple to implement, does not require long pre-processing time, nor any modi cation of the textured geometry. It is not limited to triangle meshes. The resulting texture has little distortion and is seamlessly interpolated over smooth surfaces. Our method natively supports adaptive resolution. We show that TileTrees are more compact than other volume approaches, while providing fast access to the data. We also describe an interactive painting application, enabling to create, edit and render objects without having to convert between texture representations

Gestion de la complexité géométrique dans le calcul d'éclairement pour la présentation publique de scènes archéologiques complexes

International audienceFor cultural heritage, more and more 3D objects are acquired using 3D scanners [Levoy 2000]. The resulting objects are very detailed with a large visual richness but their geometric complexity requires specific methods to render them. We first show how to simplify those objects using a low-resolution mesh with its associated normal maps [Boubekeur 2005] which encode details. Using this representation, we show how to add global illumination with a grid-based and vector-based representation [Pacanowski 2005]. This grid captures efficiently low-frequency indirect illumination. We use 3D textures (for large objects) and 2D textures (for quasi-planar objects) for storing a fixed set of irradiance vectors. These grids are built during a preprocessing step by using almost any existing stochastic global illumination approach. During the rendering step, the indirect illumination within a grid cell is interpolated from its associated irradiance vectors, resulting in a smooth everywhere representation. Furthermore, the vector-based representation offers additional robustness against local variations of geometric properties of the scene.Pour l’étude du patrimoine, de plus en plus d’objets 3D sont acquis par le biais de scanners 3D [Levoy 2000]. Les objets ainsi acquis contiennent de nombreux détails et fournissent une très grande richesse visuelle. Mais pour les afficher, leur très grande complexité géométrique nécessite l’utilisation d’algorithmes spécifiques. Nous montrons ici comment simplifier ces objets par un maillage de faible résolution et une collection de cartes de normales [Boubekeur 2005] pour préserver les détails. Avec cette représentation, nous montrons comment il est possible de calculer un éclairement réaliste à l’aide d’une grille et de données vectorielles [Pacanowski 2005]. Cette grille permet de capturer efficacement les basses fréquences d’un éclairement indirect. Nous utilisons des textures 3D (pour des gros objets) et potentiellement des textures 2D (pour les objets quasi-plans) afin de stocker un nombre prédéterminé de vecteurs d’irradiance. Ces grilles sont calculées au cours d’un pré-calcul à l’aide de n’importe quelle méthode stochastique de calcul d’éclairement global. Pour l’affichage, l’éclairement indirect dû à la grille est interpolé au sein de la cellule associée à la position courante, fournissant ainsi une représentation continue. De plus, cette approche vectorielle permet une plus grande robustesse aux variations locales des propriétés géométriques de la scène

Efficient Many-Light Rendering of Scenes with Participating Media

We present several approaches based on virtual lights that aim at capturing the light transport without compromising quality, and while preserving the elegance and efficiency of many-light rendering. By reformulating the integration scheme, we obtain two numerically efficient techniques; one tailored specifically for interactive, high-quality lighting on surfaces, and one for handling scenes with participating media

Accurate geometry reconstruction of vascular structures using implicit splines

3-D visualization of blood vessel from standard medical datasets (e.g. CT or MRI) play an important role in many clinical situations, including the diagnosis of vessel stenosis, virtual angioscopy, vascular surgery planning and computer aided vascular surgery. However, unlike other human organs, the vasculature system is a very complex network of vessel, which makes it a very challenging task to perform its 3-D visualization. Conventional techniques of medical volume data visualization are in general not well-suited for the above-mentioned tasks. This problem can be solved by reconstructing vascular geometry. Although various methods have been proposed for reconstructing vascular structures, most of these approaches are model-based, and are usually too ideal to correctly represent the actual variation presented by the cross-sections of a vascular structure. In addition, the underlying shape is usually expressed as polygonal meshes or in parametric forms, which is very inconvenient for implementing ramification of branching. As a result, the reconstructed geometries are not suitable for computer aided diagnosis and computer guided minimally invasive vascular surgery. In this research, we develop a set of techniques associated with the geometry reconstruction of vasculatures, including segmentation, modelling, reconstruction, exploration and rendering of vascular structures. The reconstructed geometry can not only help to greatly enhance the visual quality of 3-D vascular structures, but also provide an actual geometric representation of vasculatures, which can provide various benefits. The key findings of this research are as follows: 1. A localized hybrid level-set method of segmentation has been developed to extract the vascular structures from 3-D medical datasets. 2. A skeleton-based implicit modelling technique has been proposed and applied to the reconstruction of vasculatures, which can achieve an accurate geometric reconstruction of the vascular structures as implicit surfaces in an analytical form. 3. An accelerating technique using modern GPU (Graphics Processing Unit) is devised and applied to rendering the implicitly represented vasculatures. 4. The implicitly modelled vasculature is investigated for the application of virtual angioscopy

Animation faciale basée données : un état de l'art

National audienceCet article dresse un panorama des différentes problématiques liées à l'animation faciale basée données et présente les dernières avancées et solutions proposées par l'état de l'art. Le but de l'animation basée données est d'animer des personnages virtuels reproduisant les actions effectuées par des acteurs humains. Dans ce contexte, le visage joue un rôle prépondérant puisqu'il est l'un des principaux vecteurs de l'émotion et de la communication chez l'humain. Par ailleurs, contrairement au reste du corps dont les mouvements sont contraints par des articulations et des os, les déformations du visage suivent une autre forme de dynamique ce qui en fait un cas d'étude à part. Les applications sont diverses, par exemple, la création d'avatars virtuels ou l'animation de personnages présentant un comportement naturel. Dans ce papier, nous aborderons la question depuis la capture des données faciales (les différents dispositifs et méthodes de capture) jusqu'aux méthodes de synthèse exploitant ces données

Efficient Point-Cloud Processing with Primitive Shapes

This thesis presents methods for efficient processing of point-clouds based on primitive shapes. The set of considered simple parametric shapes consists of planes, spheres, cylinders, cones and tori. The algorithms developed in this work are targeted at scenarios in which the occurring surfaces can be well represented by this set of shape primitives which is the case in many man-made environments such as e.g. industrial compounds, cities or building interiors. A primitive subsumes a set of corresponding points in the point-cloud and serves as a proxy for them. Therefore primitives are well suited to directly address the unavoidable oversampling of large point-clouds and lay the foundation for efficient point-cloud processing algorithms. The first contribution of this thesis is a novel shape primitive detection method that is efficient even on very large and noisy point-clouds. Several applications for the detected primitives are subsequently explored, resulting in a set of novel algorithms for primitive-based point-cloud processing in the areas of compression, recognition and completion. Each of these application directly exploits and benefits from one or more of the detected primitives' properties such as approximation, abstraction, segmentation and continuability