Volume 18 (1999)
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Item Active Storytelling(Blackwell Publishers Ltd and the Eurographics Association, 1999) Glassner, AndrewItem Weighted Multipass Methods for Global Illumination(Blackwell Publishers Ltd and the Eurographics Association, 1999) Suykens, Frank; Willems, Yves D.In multipass rendering, care has to be taken to include all light transport only once in the final solution. Therefore the different methods in current multipass configurations handle a perfectly disjunct part of the light transport. In this paper a Monte Carlo variance reduction technique is presented that probabilistically weights overlapping transport between different methods. A good heuristic for the weights is derived so that strengths of the respective methods are retained. The technique is applied to a combination of radiosity and bidirectional path tracing and significant improvement is obtained over the non-weighted combination. This method promises to be a very useful extension to other multipass algorithms as well.Item Fast Lines: a Span by Span Method(Blackwell Publishers Ltd and the Eurographics Association, 1999) Boyer, V.; Bourdin, J.J.Straight line's scan conversion and drawing is a major field in computer graphics. Algorithm's time computation is very important. Nowadays, most of research papers suggest improvements of the DDA method that was first presented by J. Bresenham. But other approaches exist as well like combinatory analysis and linguistic methods. Both of them use multiple string copies that slow down the efficiency of the algorithms. This paper proposes a new algorithm based on a careful analysis of the line segments' properties some of them previously unused. Our algorithm is proved significantly faster than previously published ones.Item Hermitian B-Splines(Blackwell Publishers Ltd and the Eurographics Association, 1999) Grisoni, Laurent; Blanc, Carole; Schlick, ChristopheThis paper proposes to study a spline model, called HB-splines, that is in fact a B-spline representation of Hermite splines, combined with some restriction on the differential values at segment boundaries. Although this model does not appear able to offer something new to the computer graphics community, we think that HB-splines deserve to be considered for themselves because they embed many interesting features. First, they include all the classical properties required in a geometric modeling environment (convex hull, local control, arbitrary orders of parametric or geometric continuity). Second, they have a nice aptitude for direct manipulation (i.e. manipulation without using control points). For this purpose, we propose a new graphic widget, called control sails, that offers the user an intuitive way to specify local properties (position, tangent, curvature) of a curve or a surface. Finally, they provide an elegant formulation of a biorthogonal wavelet family, that permits multiresolution manipulations of the resulting curves or surfaces, in a very efficient way.Item A Free Form Feature Taxonomy(Blackwell Publishers Ltd and the Eurographics Association, 1999) Fontana, M.; Giannini, F.; Meirana, M.In this paper the notion of free form feature for aesthetic design is presented. The design of industrial products constituted by free form surfaces is done by using CAD systems representing curves and surfaces by means of NURBS functions, which are usually defined by low level entities that are not intuitive and require some knowledge of the mathematical language. Similarly to the feature-based approach adopted by CAD systems for classical mechanical design, a set of high level modelling entities which provides commonly performed shape modifications has been identified. Particularly, the paper suggests a classification of the so-called detail features for an aesthetic and/or functional characterization of predefined free form surfaces. Feature types are formally described by means of an analytical definition of the surface modification through deformation and elimination laws. A topological classification is then given according to the application domain of such laws. A further sub-classification of morphological types is then suggested according to geometric properties of weak convexity and concavity for the resulting modified shape, leading to a taxonomy of simple free form features meaningful for aesthetic design.Item Event Reports(Blackwell Publishers Ltd and the Eurographics Association, 1999)Second Eurographics Workshop on Parallel Graphics and Visualization, Rennes, France September 24-25, 1998Item Generalized View-Dependent Simplification(Blackwell Publishers Ltd and the Eurographics Association, 1999) El-Sana, Jihad; Varshney, AmitabhWe propose a technique for performing view-dependent geometry and topology simplifications for level-of-detail-based renderings of large models. The algorithm proceeds by preprocessing the input dataset into a binary tree, the view-dependence tree of general vertex-pair collapses. A subset of the Delaunay edges is used to limit the number of vertex pairs considered for topology simplification. Dependencies to avoid mesh foldovers in manifold regions of the input object are stored in the view-dependence tree in an implicit fashion. We have observed that this not only reduces the space requirements by a factor of two, it also highly localizes the memory accesses at run time. The view-dependence tree is used at run time to generate the triangles for display. We also propose a cubic-spline-based distance metric that can be used to unify the geometry and topology simplifications by considering the vertex positions and normals in an integrated manner.Item Multiresolution Curve and Surface Representation: Reversing Subdivision Rules by Least-Squares Data Fitting(Blackwell Publishers Ltd and the Eurographics Association, 1999) Samavati, Faramarz F.; Bartels, Richard H.This work explores how three techniques for defining and representing curves and surfaces can be related efficiently. The techniques are subdivision, least-squares data fitting, and wavelets. We show how least-squares data fitting can be used to "reverse" a subdivision rule, how this reversal is related to wavelets, how this relationship can provide a multilevel representation, and how the decomposition/reconstruction process can be carried out in linear time and space through the use of a matrix factorization.Some insights that this work brings forth are that the inner product used in a multiresolution analysis in uences the support of a wavelet, that wavelets can be constructed by straightforward matrix observations, and that matrix partitioning and factorization can provide alternatives to inverses or duals for building efficient decomposition and reconstruction processes. We illustrate our findings using an example curve, grey-scale image, and tensor-product surface.Item Event Reports(Blackwell Publishers Ltd and the Eurographics Association, 1999)Eurographics '99Eurographics '99 Awards10th Eurographics Workshop on RenderingSiggraph '992000 Cover CompetitionItem Interactive Mechanical Design Variation for Haptics and CAD(Blackwell Publishers Ltd and the Eurographics Association, 1999) Nelson, Donald D.; Cohen, ElaineA fast design variation technique for mechanical systems is presented. It is used to interactively optimize mechanical characteristics while "self-assembling" or satisfying large systems of mechanical constraints. The high speed method is central to providing inverse dynamics force feedback in haptics and control applications. Performance advantages with the use of augmented coordinates for inverse dynamics of closed loop topologies are also noted. The interaction framework allows manipulation of complex assemblies while maintaining kinematically admissible configurations though linkage and joint limit constraints. Furthermore, design variables such as link length can be treated as free variables and optimized to meet design criteria such as assembly dexterity. Assemblies with flexible bodies fit naturally within this framework. Thus, the contribution of this paper is the advancement of techniques in augmented coordinates for the kinematic and force feedback interaction with virtual mechanical assembly design optimization at force control rates.Item Editorial(Blackwell Publishers Ltd and the Eurographics Association, 1999) Coquillart, Sabine; Seidel, Hans-PeterItem Multi-layered impostors for accelerated rendering(Blackwell Publishers Ltd and the Eurographics Association, 1999) Decoret, Xavier; Sillion, Francois; Schaufler, Gernot; Dorsey, JulieThis 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.Item Improved Laplacian Smoothing of Noisy Surface Meshes(Blackwell Publishers Ltd and the Eurographics Association, 1999) Vollmer, J.; Mencl, R.; Muller, H.This paper presents a technique for smoothing polygonal surface meshes that avoids the well-known problem of deformation and shrinkage caused by many smoothing methods, like e.g. the Laplacian algorithm. The basic idea is to push the vertices of the smoothed mesh back towards their previous locations. This technique can be also used in order to smooth unstructured point sets, by reconstructing a surface mesh to which the smoothing technique is applied. The key observation is that a surface mesh which is not necessarily topologically correct, but which can efficiently be reconstructed, is sufficient for that purpose.Item Texturing 3D Models of Real World Objects from Multiple Unregistered Photographic Views(Blackwell Publishers Ltd and the Eurographics Association, 1999) Neugebauer, Peter J.; Klein, KonradAs the efficiency of computer graphic rendering methods is increasing, generating realistic models is now becoming a limiting factor. In this paper we present a new technique to enhance already existing geometry models of real world objects with textures reconstructed from a sparse set of unregistered still photographs. The aim of the proposed technique is the generation of nearly photo-realistic models of arbitrarily shaped objects with minimal effort. In our approach, we require neither a prior calibration of the camera nor a high precision of the user's interaction. Two main problems have to be addressed of which the first is the recovery of the unknown positions and parameters of the camera. An initial estimate of the orientation is calculated from interactively selected point correspondences. Subsequently, the unknown parameters are accurately calculated by minimising a blend of objective functions in a 3D-2D projective registration approach. The key point of the proposed method of registration is a novel filtering approach which utilises the spatial information provided by the geometry model. Second, the individual images have to be combined yielding a set of consistent texture maps. We present a robust method to recover the texture from the photographs thereby preserving high spatial frequencies and eliminating artifacts, particularly specular highlights. Parts of the object not seen in any of the photographs are interpolated in the textured model. Results are shown for three complex example objects with different materials and numerous self-occlusions.Item 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, GeorgeItem Fast Polyhedral Cell Sorting for Interactive Rendering of Unstructured Grids(Blackwell Publishers Ltd and the Eurographics Association, 1999) Comba, Joao; Klosowsk, James T.; Max, Nelson; Mitchell, Joseph S. B.; Silva, Claudio T.; Williams, Peter L.Direct volume rendering based on projective methods works by projecting, in visibility order, the polyhedral cells of a mesh onto the image plane, and incrementally compositing the cell's color and opacity into the final image. Crucial to this method is the computation of a visibility ordering of the cells. If the mesh is "well-behaved" (acyclic and convex), then the MPVO method of Williams provides a very fast sorting algorithm; however, this method only computes an approximate ordering in general datasets, resulting in visual artifacts when rendered. A recent method of Silva et al. removed the assumption that the mesh is convex, by means of a sweep algorithm used in conjunction with the MPVO method; their algorithm is substantially faster than previous exact methods for general meshes.In this paper we propose a new technique, which we call BSP-XMPVO, which is based on a fast and simple way of using binary space partitions on the boundary elements of the mesh to augment the ordering produced by MPVO. Our results are shown to be orders of magnitude better than previous exact methods of sorting cells.Item Book Reviews(Blackwell Publishers Ltd and the Eurographics Association, 1999)Books reviewed:Arlov, Laura. GUI Design for DummiesLeopoldseder, Hannes and Schopf, Christine (Editors). Cyberarts98Lorentz, H. A. On the Theory of the Reflection and Refraction of LightVince, John. Essential Virtual Reality FastJolion, J.-M. and Kropatsch, W. G. Graph-Based Representations in Pattern RecognitionKokaram, Anil C. Motion Picture Restoration: Digital Algorithms for Artefact Suppression in Degraded Motion Picture Film and VideoItem 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, GeorgeThe 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.Item A Progressive Algorithm for Three Point Transport(Blackwell Publishers Ltd and the Eurographics Association, 1999) Dumont, Reynald; Bouatouch, Kadi; Gosselin, PhilippeWhen computing global illumination in environments made up of surfaces with general Bidirectional Reflection Distribution Functions, a three point formulation of the rendering equation can be used. Brute-force algorithms can lead to a linear system of equations whose matrix is cubic, which is expensive in time and space. The hierarchical approach is more efficient. Aupperle et al. proposed a hierarchical three point algorithm to compute global illumination in the presence of glossy reflection. We present in this paper some improvements we brought to this method: shooting, "lazy" push-pull, photometric subdivision criterion, etc. Then we will show how our new method takes into account non-planar surfaces in the hierarchical resolution process.Item Modelling and Rendering Graphics Scenes Composed of Multiple Volumetric Datasets(Blackwell Publishers Ltd and the Eurographics Association, 1999) Leu, Adrian; Chen, MinThis paper presents a method for modelling graphics scenes consisting of multiple volumetric objects. A two-level hierarchical representation is employed, which enables the reduction of the overall storage consumption as well as rendering time. With this approach, different objects can be derived from the same volumetric dataset, and 2D images can be trivially integrated into a scene. The paper also describes an efficient algorithm for rendering such scenes on ordinary workstations, and addresses issues concerning memory requirements and disk swapping.