Volume 23 (2004)

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25th EUROGRAPHICS General Assembly
(The Eurographics Association and Blackwell Publishing Ltd., 2004)
7th International Workshop on Immersive Projection Technology and 9th Eurographics Workshop on Virtual Environments
(The Eurographics Association and Blackwell Publishing Ltd., 2004) Kunz, Dr. Andreas
ACM/EG Symposium on Computer Animation 2004
(The Eurographics Association and Blackwell Publishing Ltd., 2004) Boulic, Ronan; Pai, Dinesh K.; Badler, Norman; Desbrun, Mathieu; Reveret, Lionel
Anisotropic Filtering of Non-Linear Surface Features
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Hildebrandt, Klaus; Polthier, Konrad
A new method for noise removal of arbitrary surfaces meshes is presented which focuses on the preservation and sharpening of non-linear geometric features such as curved surface regions and feature lines. Our method uses a prescribed mean curvature flow (PMC) for simplicial surfaces which is based on three new contributions: 1. the definition and efficient calculation of a discrete shape operator and principal curvature properties on simplicial surfaces that is fully consistent with the well-known discrete mean curvature formula, 2. an anisotropic discrete mean curvature vector that combines the advantages of the mean curvature normal with the special anisotropic behaviour along feature lines of a surface, and 3. an anisotropic prescribed mean curvature flow which converges to surfaces with an estimated mean curvature distribution and with preserved non-linear features. Additionally, the PMC flow prevents boundary shrinkage at constrained and free boundary segments.
Applied Geometry:Discrete Differential Calculus for Graphics
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Desbrun, Mathieu
Geometry has been extensively studied for centuries, almost exclusively from a differential point of view. However, with the advent of the digital age, the interest directed to smooth surfaces has now partially shifted due to the growing importance of discrete geometry. From 3D surfaces in graphics to higher dimensional manifolds in mechanics, computational sciences must deal with sampled geometric data on a daily basis-hence our interest in Applied Geometry.In this talk we cover different aspects of Applied Geometry. First, we discuss the problem of Shape Approximation, where an initial surface is accurately discretized (i.e., remeshed) using anisotropic elements through error minimization. Second, once we have a discrete geometry to work with, we briefly show how to develop a full- blown discrete calculus on such discrete manifolds, allowing us to manipulate functions, vector fields, or even tensors while preserving the fundamental structures and invariants of the differential case. We will emphasize the applicability of our discrete variational approach to geometry by showing results on surface parameterization, smoothing, and remeshing, as well as virtual actors and thin-shell simulation.Joint work with: Pierre Alliez (INRIA) , David Cohen-Steiner (Duke U.), Eitan Grinspun (NYU), Anil Hirani (Caltech), Jerrold E. Marsden (Caltech), Mark Meyer (Pixar), Fred Pighin (USC), Peter Schroeder (Caltech), Yiying Tong (USC).
Approximate Soft Shadows win an Image-Space Flood-Fill Algorithm
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Arvo, Jukka; Hirvikorpi, Mika; Tyystjaervi, Joonas
Most former soft shadow algorithms have either suffered from restricted self-shadowing capabilities, been too slow for interactive applications, or could only be used with a limited types of geometry. In this paper, we propose an efficient image-based approach for computing soft shadows. Our method is based on shadow mapping and provides the associated benefits. We use pixel-based visibility computations for rendering penumbra regions directly into the screen-space. This is accomplished by using a modified flood-fill algorithm which enables us to implement the algorithm using programmable graphics hardware. Even though the resulting images are most often high quality, we do not claim that the proposed method is physically correct. The computation time and memory requirements for soft shadows depend on image resolution and the number of lights, not geometric scene complexity.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Picture/Image Generation I.3.7 [Three-Dimensional Graphics and Realism]: Color, shading, shadowing, and texture
Approximated Centroidal Voronoi Diagrams for Uniform Polygonal Mesh Coarsening
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Valette, Sebastien; Chassery, Jean-Marc
We present a novel clustering algorithm for polygonal meshes which approximates a Centroidal Voronoi Diagram construction. The clustering provides an efficient way to construct uniform tessellations, and therefore leads to uniform coarsening of polygonal meshes, when the output triangulation has many fewer elements than the input mesh. The mesh topology is also simplified by the clustering algorithm. Based on a mathematical framework, our algorithm is easy to implement, and has low memory requirements. We demonstrate the efficiency of the proposed scheme by processing several reference meshes having up to 1 million triangles and very high genus within a few minutes on a low- end computer.
Approximation of Optimal Voxel Size for Collision Detection in Maintainability Simulations within Massive Virtual Environments
(The Eurographics Association and Blackwell Publishing Ltd., 2004) Borro, D.; Garcia-Alonso, A.; Matey, L.
This paper describes a Collision Method for massive virtual environments composed of millions of triangles. It has been applied in the aeronautics industry for maintainability simulations using virtual aircraft engine mock-ups. The method performs well and has a good interactive frame rate even when it is used for computing force feedback with haptic devices. Space sorting problems chiefly related to voxel techniques, such as memory requirements and optimal voxel size, have been solved. We use advanced memory structures and hashing techniques. To find the optimal voxel size, several analytical solutions have been proposed and compared. These solutions are based on the performance cost function of the algorithm used. Experiments have been undertaken to verify these analytical solutions.
Author Index Volume 23 (2004)
(The Eurographics Association and Blackwell Publishing Ltd., 2004)
Balancing Considered Harmful - Faster Photon Mapping using the Voxel Volume Heuristic -
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Wald, Ingo; Guenther, Johannes; Slusallek, Philipp
Photon mapping is one of the most important algorithms for computing global illumination. Especially for efficiently producing convincing caustics, there are no real alternatives to photon mapping. On the other hand, photon mapping is also quite costly: Each radiance lookup requires to find the k nearest neighbors in a kd-tree, which can be more costly than shooting several rays. Therefore, the nearest-neighbor queries often dominate the rendering time of a photon map based renderer.In this paper, we present a method that reorganizes - i.e. un balances - the kd-tree for storing the photons in a way that allows for finding the k-nearest neighbors much more efficiently, thereby accelerating the radiance estimates by a factor of 1.2-3.4. Most importantly, our method still finds exactly the same k-nearest-neighbors as the original method, without introducing any approximations or loss of accuracy. The impact of our method is demonstrated with several practical examples.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Global Illumination I.3.7 [Computer Graphics]: Raytracing
A Biophysically-Based Spectral Model of Light Interaction with Human Skin
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Krishnaswamy, Aravind; Baranoski, Gladimir V.G.
Despite the notable progress in physically-based rendering, there is still a long way to go before we can automatically generate predictable images of biological materials. In this paper, we address an open problem in this area, namely the spectral simulation of light interaction with human skin. We propose a novel biophysically based model that accounts for all components of light propagation in skin tissues, namely surface reflectance, subsurface reflectance and transmittance, and the biological mechanisms of light absorption by pigments in these tissues. The model is controlled by biologically meaningful parameters, and its formulation, based on standard Monte Carlo techniques, enables its straightforward incorporation into realistic image synthesis frameworks. Besides its biophysically-based nature, the key difference between the proposed model and the existing skin models is its comprehensiveness, i.e., it computes both spectral (reflectance and transmittance) and scattering (bidirectional surface-scattering distribution function) quantities for skin specimens. In order to assess the predictability of our simulations, we evaluate their accuracy by comparing results from the model with actual skin measured data. We also present computer generated images to illustrate the flexibility of the proposed model with respect to variations in the biological input data, and its applicability not only in the predictive image synthesis of different skin tones, but also in the spectral simulation of medical conditions.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism
CGForum 2004 Cover Image
(The Eurographics Association and Blackwell Publishing Ltd., 2004)
Coherent Hierarchical Culling: Hardware Occlusion Queries Made Useful
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Bittner, Jiri; Wimmer, Michael; Piringer, Harald; Purgathofer, Werner
We present a simple but powerful algorithm for optimizing the usage of hardware occlusion queries in arbitrary complex scenes. Our method minimizes the number of issued queries and reduces the delays due to the latency of query results. We reuse the results of occlusion queries from the last frame in order to initiate and schedule the queries in the next frame. This is done by processing nodes of a spatial hierarchy in a front-to-back order and interleaving occlusion queries with rendering of certain previously visible nodes. The proposed scheduling of the queries makes use of spatial and temporal coherence of visibility. Despite its simplicity, the algorithm achieves good culling efficiency for scenes of various types. The implementation of the algorithm is straightforward and it can be easily integrated in existing real-time rendering packages based on common hierarchical data structures.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism
Combined Correlated and Importance Sampling in Direct Light Source Computation and Environment Mapping
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Szecsi, Laszlo; Sbert, Mateu; Szirmay-Kalos, Laszlo
This paper presents a general variance reduction method that is a quasi-optimal combination of correlated and importance sampling. The weights of the combination are selected automatically in order to keep the merits of both importance and correlated sampling. The proposed sampling method is used for efficient direct light source computation of large area sources and for the calculation of the reflected illumination of environment maps. Importance sampling would be good in these cases if the sources are hidden, while correlated sampling is efficient if the sources are fully visible. The proposed method automatically detects the particular case and provides results that inherit the advantages of both techniques.
Compression of Large-Scale Terrain Data for Real-Time Visualization Using a Tiled Quad Tree
(The Eurographics Association and Blackwell Publishing Ltd., 2004) Platings, M.; Day, A. M.
The aim of the rapid world modeling project is to implement a system to visualize the topography of the entire world on consumer-level hardware. This presents a significant problem in terms of both storage requirements and rendering speed. This paper presents the a??Tiled Quad Treea??, a technique and format for the storage of digital terrain models, to work as part of an integrated system for the visualization of global terrain data. We show how this format efficiently stores and compresses elevation data, in a way that allows the data to be read very rapidly from hard disk or similar storage medium, to facilitate real-time rendering. The results of compressing several distinct data sets are presented.
Computer Graphics forum
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Duke, David; Scopigno, Roberto
Computing Maximal Tiles and Application to Impostor-Based Simplification
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Andujar, C.; Brunet, P.; Chica, A.; Navazo, I.; Rossignac, J.; Vinacua, A.
The computation of the largest planar region approximating a 3D object is an important problem with wide applications in modeling and rendering. Given a voxelization of the 3D object, we propose an efficient algorithm to solve a discrete version of this problem. The input of the algorithm is the set of grid edges connecting the interior and the exterior of the object (called sticks). Using a voting-based approach, we compute the plane that slices the largest number of sticks and is orientation-compatible with these sticks. The robustness and efficiency of our approach rests on the use of two different parameterizations of the planes with suitable properties. The first of these is exact and is used to retrieve precomputed local solutions of the problem. The second one is discrete and is used in a hierarchical voting scheme to compute the global maximum. This problem has diverse applications that range from finding object signatures to generating simplified models. Here we demonstrate the merits of the algorithm for efficiently computing an optimized set of textured impostors for a given polygonal model.Categories and Subject Descriptors (according to ACM CCS): I.3.5 [Computer Graphics]: Computational Geometry and Object Modeling
Crowd of Virtual Humans: a New Approach for Real Time Navigation in Complex and Structured Environments
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Lamarche, Fabrice; Donikian, Stephane
The navigation activity is an every day practice for any human being capable of locomotion. Our objective in this work is to reproduce this crucial human activity inside virtual environments. Putting together the high complexity of a realistic environment such as a city, a big amount of virtual humans and the real-time constraint requires to optimize each aspect of the animation process. In this paper, we present a suitable topological structuring of the geometric environment to allow fast path finding as well as an efficient reactive navigation algorithm for virtual humans evolving inside a crowd.
Cultural Heritage Preservation Using Constructive Shape Modeling
(The Eurographics Association and Blackwell Publishing Ltd., 2004) Vilbrandt, C.; Pasko, G.; Pasko, A.; Fayolle, P.-A.; Vilbrandt, T.; Goodwin, J. R.; Goodwin, J. M.; Kunii, T. L.
Issues of digital preservation of shapes and internal structures of historical cultural objects are discussed. An overview of existing approaches to digital preservation related to shape modeling is presented and corresponding problems are considered. We propose a new digital preservation paradigm based on both constructive modeling reflecting the logical structure of the objects and open standards and procedures. Constructive Solid Geometry (CSG) and Function Representation (FRep) are examined and practically applied as mathematical representations producing compressed yet precise data structures, thus providing inter-operability between current and future computer platforms crucial to archiving. Examples of CSG reconstruction of historical temples and FRep modeling of traditional lacquer ware are given. We examine the application of fitting of a parameterized FRep model to a cloud of data points as a step towards automation of the modeling process. Virtual venues for public access to cultural heritage objects including real time interactive simulation of cultural heritage sites over the Web are discussed and illustrated.
Deferred Splatting
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Guennebaud, Gael; Barthe, Loic; Paulin, Mathias
In recent years it has been shown that, above a certain complexity, points become the most efficient rendering primitives. Although the programmability of the lastest graphics hardware allows efficient implementation of high quality surface splatting algorithms, their performance remains below those obtained with simpler point based rendering algorithms when they are used for scenes of high complexity. In this paper, our goal is to apply high quality point based rendering algorithms on complex scenes. For this purpose, we show how to take advantage of temporal coherency in a very accurate hardware accelerated point selection algorithm allowing the expensive computations to be peformed only on visible points. Our algorithm is based on a multi-pass hardware accelerated EWA splatting. It is also suitable for any rendering application since no pre-process is needed and no assumption is made on the data structure. In addition, we briefly discuss the association of our method with other existing culling techniques and optimization for particular applications.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Viewing algorithms

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