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End date: 1999 × Author: Sillion, Francois ×

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    A Practical Analysis of Clustering Strategies for Hierarchical Radiosity
    (Blackwell Publishers Ltd and the Eurographics Association, 1999) Hasenfratz, Jean-Marc; Damez, Cyrille; Sillion, Francois; Drettakis, George
    The calculation of radiant energy balance in complex scenes has been made possible by hierarchical radiosity methods based on clustering mechanisms. Although clustering offers an elegant theoretical solution by reducing the asymptotic complexity of the algorithm, its practical use raises many difficulties, and may result in image artifacts or unexpected behavior. This paper proposes a detailed analysis of the expectations placed on clustering and compares the relative merits of existing, as well as newly introduced, clustering algorithms. This comparison starts from the precise definition of various clustering strategies based on a taxonomy of data structures and construction algorithms, and proceeds to an experimental study of the clustering behavior for real-world scenes. Interestingly, we observe that for some scenes light is difficult to simulate even with clustering. Our results lead to a series of observations characterizing the adequacy of clustering methods for meeting such diverse goals as progressive solution improvement, efficient ray casting acceleration, and faithful representation of object density for approximate visibility calculations.
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    Multi-layered impostors for accelerated rendering
    (Blackwell Publishers Ltd and the Eurographics Association, 1999) Decoret, Xavier; Sillion, Francois; Schaufler, Gernot; Dorsey, Julie
    This paper describes the successful combination of pre-generated and dynamically updated image-based representations to accelerate the visualization of complex virtual environments. We introduce a new type of impostor, which has the desirable property of limiting de-occlusion errors to a user-specified amount. This impostor, composed of multiple layers of textured meshes, replaces the distant geometry and is much faster to draw. It captures the relevant depth complexity in the model without resorting to a complete sampling of the scene. We show that layers can be dynamically updated during visualization. This guarantees bounded scene complexity in each frame and also exploits temporal coherence to improve image quality when possible. We demonstrate the strengths of this approach in the context of city walkthroughs.
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    An Exhaustive Error-Bounding Algorithm for Hierarchical Radiosity
    (Blackwell Publishers Ltd and the Eurographics Association, 1998) Holzschuch, Nicolas; Sillion, Francois
    This paper presents a complete algorithm for the evaluation and control of error in radiosity calculations. Providing such control is both extremely important for industrial applications andd one of the most challenging issues remaining in global illumination research. In order to control the error, we need to estimate the accuracy of the calculation while computing the energy exchanged between two objects. Having this information for each radiosity interaction allows to allocate more resources to refine interactions with greater potential error, and to avoid spending more time to refine interactions already represented with sufficient accuracy. Until now, the accuracy of the computed energy exchange could only be approximated using heuristic algorithms. This paper presents the first exhaustive algorithm to compute fully reliable upper and lower bounds on the energy being exchanged in each interaction. This is accomplished by computing first and second derivatives of the radiosity function where appropriate, and making use of two concavity conjectures. These bounds are then used in a refinement criterion for hierarchical radiosity, resulting in a global illumination algorithm with complete control of the error incurred. Results are presented, demonstrating the possibility to create radiosity solutions with guaranteed precision. We then extend our algorithm to consider linear bounding functions instead of constant functions, thus creating simpler meshes in regions where the function is concave, without loss of precision. Our experiments show that the computation of radiosity derivatives along with the radiosity values only requires a modest extra cost, with the advantage of a much greater precision.
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    A Practical Analysis of Clustering Strategies for Hierarchical Radiosity (Supplementary material)
    (Blackwell Publishers Ltd and the Eurographics Association, 1999) Hasenfratz, Jean-Marc; Damez, Cyrille; Sillion, Francois; Drettakis, George
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    Space-Time Hierarchical Radiosity
    (The Eurographics Association, 1999) Damez, Cyrille; Sillion, Francois; Dani Lischinski and Greg Ward Larson
    This paper presents a new hierarchical simulation algorithm allowing the calculation of radiosity solutions for time-dependent scenes where all motion is known a priori. Such solutions could, for instance, be computed to simulate subtle lighting effects (indirect lighting) in animation systems, or to obtain highquality synthetic image sequences to blend with live action video and film. We base our approach on a Space-Time hierarchy, adding a life span to hierarchical surface elements, and present an integrated formulation of Hierarchical Radiosity with this extended hierarchy. We discuss the expected benefits of the technique, review the challenges posed by the approach, and propose first solutions for these issues, most notably for the space-time refinement strategy. We show that a short animation sequence can be computed rapidly at the price of a sizeable memory cost. These results confirm the potential of the approach while helping to identify areas of promising future work.
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    Efficient Impostor Manipulation for Real-Time Visualization of Urban Scenery
    (Blackwell Publishers Ltd and the Eurographics Association, 1997) Sillion, Francois; Drettakis, George; Bodelet, Benoit
    Urban environments present unique challenges to interactive visualization systems, because of the huge complexity of the geometrical data and the widely varying visibility conditions. This paper introduces a new framework for real-time visualisation of such urban scenes. The central concept is that of a dynamic segmentation of the dataset, into a local three-dimensional model and a set of impostors used to represent distant scenery. A segmentation model is presented, based on inherent urban structure. A new impostor structure is introduced, derived from the level-of-detail approach. Impostors combine three-dimensional geometry to correctly model large depth discontinuities and parallax, and textures to rapidly display visual detail. We present the algorithms necessary for the creation of accurate and efficient three-dimensional impostors. The implementation of our algorithms allows interactive navigation in complex urban databases, as required by many applications.