Volume 19 (2000)

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    Event Reports
    (Blackwell Publishers Ltd and the Eurographics Association, 2000)
    1999 Siggraph / Eurographics Workshop on Graphics HardwareGVE '99: 1999 Eurographics/ SIGGRAPH Workshop on Graphics and Visualization5th Eurographics Workshop on Multimedia
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    Augmented Reality with Back-Projection Systems using Transflective Surfaces
    (Blackwell Publishers Ltd and the Eurographics Association, 2000) Bimber, Oliver; Encarnacao, L. Miguel; Schmalstieg, Dieter
    In this paper, we introduce the concept of Extended VR (extending viewing space and interaction space of back-projection VR systems), by describing the use of a hand-held semi-transparent mirror to support augmented reality tasks with back-projection systems. This setup overcomes the problem of occlusion of virtual objects by real ones linked with such display systems. The presented approach allows an intuitive and effective application of immersive or semi-immersive virtual reality tasks and interaction techniques to an augmented surrounding space. Thereby, we use the tracked mirror as an interactive image-plane that merges the reflected graphics, which are displayed on the projection plane, with the transmitted image of the real environment. In our implementation, we also address traditional augmented reality problems, such as real-object registration and virtual-object occlusion. The presentation is complemented by a hypothesis of conceivable further setups that apply transflective surfaces to support an Extended VR environment.
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    A Multiresolution Model for Soft Objects Supporting Interactive Cuts and Lacerations
    (Blackwell Publishers Ltd and the Eurographics Association, 2000) Ganovelli, Fabio; Cignoni, Paolo; Montani, Claudio; Scopigno, Roberto
    Performing a really interactive and physically-based simulation of complex soft objects is still an open problem in computer animation/simulation. Given the application domain of virtual surgery training, a complete model should be quite realistic, interactive and should enable the user to modify the topology of the objects. Recent papers propose the adoption of multiresolution techniques to optimize time performance by representing at high resolution only the object parts considered more important or critical. The speed up obtainable at simulation time are counterbalanced by the need of a preprocessing phase strongly dependent on the topology of the object, with the drawback that performing dynamic topology modification becomes a prohibitive issue. In this paper we present an approach that couples multiresolution and topological modifications, based on the adoption of a particle systems approach to the physical simulation. Our approach is based on a tetrahedral decomposition of the space, chosen both for its suitability to support a particle system and for the ready availability of many techniques recently proposed for the simplification and multiresolution management of 3D simplicial decompositions. The multiresolution simulation system is designed to ensure the required speedup and to support dynamic changes of the topology, e.g. due to cuts or lacerations of the represented tissue.
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    An Adaptive Spectral Rendering with a Perceptual Control
    (Blackwell Publishers Ltd and the Eurographics Association, 2000) Claude Iehl, Jean; Peroche, Bernard
    In this paper, we present a spectral rendering method based on a ray tracing algorithm and guided by a perceptual control of the error made. An adaptive representation of spectral data for light sources and materials is used and induces, for each pixel, the evaluation of an algebraic expression. For each visible wavelength, the computations of complex spread in refractive and dispersive materials, based on several photon maps, are locally restricted by an adaptive evaluation of the expression. This method allows to simulate high quality physically-based pictures and, in particular, some specific phenomena like dispersion in transparent objects, scattered caustics,. . .
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    Editorial
    (Blackwell Publishers Ltd and the Eurographics Association, 2000) Coquillart, Sabine; Duke, David
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    LCTS: Ray Shooting using Longest Common Traversal Sequences
    (Blackwell Publishers Ltd and the Eurographics Association, 2000) Havran, V.; Bittner, J.
    We describe two new techniques of ray shooting acceleration that exploit the traversal coherence of a spatial hierarchy. The first technique determines a sequence of adjacent leaf-cells of the hierarchy that is pierced by all rays contained within a certain convex shaft. This sequence is used to accelerate ray shooting for all remaining rays within the shaft. The second technique establishes a cut of the hierarchy that contains nodes where the hierarchy traversal can no longer be predetermined for all rays contained within a given shaft. This cut is used to initiate the traversal for all remaining rays contained in the shaft. The description of the methods is followed by results evaluated by their practical implementation.
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    Computation of Irradiance from Triangles by Adaptive Sampling
    (Blackwell Publishers Ltd and the Eurographics Association, 2000) Urena, C.
    We introduce an algorithm for sample positioning in a planar triangle, which can be used to make numerical integration of an arbitrary function defined on it. This algorithm has some interesting properties which make it suitable for applications in the context of realistic rendering. We use an adaptive triangle partitioning procedure, driven by an appropriate measure of the error. The underlying variance is shown to be bounded, and in fact it can be controlled, so that it approaches the minimum possible value. We show results obtained when applying the method to irradiance computation, in the context of final-gather algorithms. We also describe a C++ class which offers all required functionality, and we made available its source code.
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    Towards Blind Detection of Robust Watermarks in Polygonal Models
    (Blackwell Publishers Ltd and the Eurographics Association, 2000) Benedens, Oliver; Busch, Christoph
    We describe a Digital Watermarking system dedicated for embedding watermarks into 3D polygonal models. The system consists of three watermarking algorithms, one named Vertex Flood Algorithm (VFA) suitable for embedding fragile public readable watermarks with high capacity and offering a way of model authentication, one realizing affine invariant watermarks, named Affine Invariant Embedding (AIE) and a third one, named Normal Bin Encoding (NBE) algorithm, realizing watermarks with robustness against more complex operations, most noticeably polygon reduction. The watermarks generated by these algorithms are stackable. We shortly discuss the implementation of the system, which is realized as a 3D Studio MAX plugin.
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    Subdivision Surface Tesselation on the Fly using a versatile Mesh Data Structure
    (Blackwell Publishers Ltd and the Eurographics Association, 2000) Muller, Kerstin; Havemann, Sven
    Subdivision surfaces have become a standard technique for freeform shape modeling. They are intuitive to use and permit designers to flexibly add detail. But with larger control meshes, efficient adaptive rendering techniques are indispensable for interactive visualization and shape modeling. In this paper, we present a realization of tesselation-on-the-fly for Loop subdivision surfaces as part of a framework for interactive visualization.
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    Automatic Creation of Object Hierarchies for Radiosity Clustering
    (Blackwell Publishers Ltd and the Eurographics Association, 2000) Muller, Gordon; Schafer, Stephan; Fellner, Dieter W.
    Using object clusters for hierarchical radiosity greatly improves the efficiency and thus usability of radiosity computations. By eliminating the quadratic starting phase very large scenes containing about 100k polygons can be handled efficiently. Although the main algorithm extends rather easily to using object clusters, the creation of 'good' object hierarchies is a difficult task both in terms of construction time and in the way how surfaces or objects are grouped to clusters. The quality of an object hierarchy for clustering depends on its ability to accurately simulate the hierarchy of the energy flow in a given scene. Additionally it should support visibility computations by providing efficient ray acceleration techniques.In this paper we will present a new approach of building hierarchies of object clusters. Our hybrid structuring algorithm provides accuracy and speed by combining a highly optimized bounding volume hierarchy together with uniform spatial subdivisions for nodes with regular object densities. The algorithm works without user intervention and is well suited for a wide variety of scenes. First results of using these hierarchies in a radiosity clustering environment are very promising and will be presented here.The combination of very deep hierarchies (we use a binary tree) together with an efficient ray acceleration structure shifts the computational effort away from form factor and visibility calculation towards accurately propagating the energy through the hierarchy. We will show how an efficient single pass gathering can be used to minimize traversal costs.
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    Tone Reproduction for Interactive Walkthroughs
    (Blackwell Publishers Ltd and the Eurographics Association, 2000) Scheel, A.; Stamminger, M.; Seidel, H.-P.
    When a rendering algorithm has created a pixel array of radiance values the task of producing an image is not yet completed. In fact, to visualize the result the radiance values still have to be mapped to luminances, which can be reproduced by the used display. This step is performed with the help of tone reproduction operators. These tools have mainly been applied to still images, but of course they are just as necessary for walkthrough applications, in which several images are created per second. In this paper we illuminate the physiological aspects of tone reproduction for interactive applications. It is shown how tone reproduction can also be introduced into interactive radiosity viewers, where the tone reproduction continuously adjusts to the current view of the user. The overall performance is decreased only moderately, still allowing walkthroughs of large scenes.
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    Floating Points: A Method for Computing Stipple Drawings
    (Blackwell Publishers Ltd and the Eurographics Association, 2000) Deussen, Oliver; Hiller, Stefan; Van Overveld, Cornelius; Strothotte, Thomas
    We present a method for computer generated pen-and-ink illustrations by the simulation of stippling. In a stipple drawing, dots are used to represent tone and also material of surfaces. We create such drawings by generating an initial dot set which is then processed by a relaxation method based on Voronoi diagrams. The point patterns generated are approximations of Poisson disc distributions and can also be used for integrating functions or the positioning of objects. We provide an editor similar to paint systems for interactively creating stipple drawings. This makes it possible to create such drawings within a matter of hours, instead of days or even weeks when the drawing is done manually.
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    Modelling virtual cities dedicated to behavioural animation
    (Blackwell Publishers Ltd and the Eurographics Association, 2000) Thomas, Gwenola; Donikian, Stephane
    In order to populate virtual cities, it is necessary to specify the behaviour of dynamic entities such as pedestrians or car drivers. Since a complete mental model based on vision and image processing cannot be constructed in real time using purely geometrical information, higher levels of information are needed in a model of the virtual environment. For example, the autonomous actors of a virtual world would exploit the knowledge of the environment topology to navigate through it. In this article, we present a model of virtual urban environments using structures and information suitable for behavioural animations. Thanks to this knowledge, autonomous virtual actors can behave like pedestrians or car drivers in a complex city environment. A city modeler has been designed, using this model of urban environment, and enables complex urban environments for behavioural animation to be automatically produced.
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    Real Time Local Approximation of Deformations using Rotations
    (Blackwell Publishers Ltd and the Eurographics Association, 2000) Maillot, Jerome
    Additional realism can be achieved in computer generated images using smooth and increasingly complex deformations. Though significant effort has been spent on improving these deformations, no general method has been proposed yet to deal with rigid pieces connected to soft objects. This paper proposes a general framework to solve this problem. We will present several types of applications, such as flowing small objects in a deformation field, animating rigid features connected to some deformed object, or smoothly attached limbs to a deforming body. All the calculations presented here can be applied to any type of deformation, provided that the deformation at each point only depends on the point itself. Even though we can directly compute the result for some analytical deformation fields, we will show that a good sampling of the deformation in the area of interest is generally enough. One intermediate result consists of a practical method to find the best rotation that approximates a linear transformation. The proposed method is a superset of the Gram-Schmidt orthonormalization process, and is much easier to compute than global methods based on Taylor series.
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    Integrating Occlusion Culling and Levels of Detail through Hardly-Visible Sets
    (Blackwell Publishers Ltd and the Eurographics Association, 2000) Andujar, Carlos; Saona-Vazquez, Carlos; Navazo, Isabel; Brunet, Pere
    Occlusion culling and level-of-detail rendering have become two powerful tools for accelerating the handling of very large models in real-time visualization applications. We present a framework that combines both techniques to improve rendering times. Classical occlusion culling algorithms compute potentially visible sets (PVS), which are supersets of the sets of visible polygons. The novelty of our approach is to estimate the degree of visibility of each object of the PVS using synthesized coarse occluders. This allows to arrange the objects of each PVS into several Hardly-Visible Sets (HVS) with similar occlusion degree. According to image accuracy and frame rate requirements, HVS provide a way to avoid sending to the graphics pipeline those objects whose pixel contribution is low due to partial occlusion. The image error can be bounded by the user at navigation time. On the other hand, as HVS offer a tighter estimation of the pixel contribution for each scene object, it can be used for a more convenient selection of the level-of-detail at which objects are rendered. In this paper, we describe the new framework technique, provide details of its implementation using a visibility octree as the chosen occlusion culling data structure and show some experimental results on the image quality.
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    Observational Models of Graphite Pencil Materials
    (Blackwell Publishers Ltd and the Eurographics Association, 2000) Sousa, Mario Costa; Buchanan, John W.
    This paper presents models for graphite pencil, drawing paper, blenders, and kneaded eraser that produce realistic looking pencil marks, textures, and tones. Our models are based on an observation of how lead pencils interact with drawing paper, and on the absorptive and dispersive properties of blenders and erasers interacting with lead material deposited over drawing paper. The models consider parameters such as the particle composition of the lead, the texture of the paper, the position and shape of the pencil materials, and the pressure applied to them. We demonstrate the capabilities of our approach with a variety of images and compare them to digitized pencil drawings. We also present image-based rendering results implementing traditional graphite pencil tone rendering methods.
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    Announcements
    (Blackwell Publishers Ltd and the Eurographics Association, 2000)
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    Book Reviews
    (Blackwell Publishers Ltd and the Eurographics Association, 2000)
    Books reviewed:Salomon, David. Computer Graphics and Geometric ModelingGovil-Pai, Shalini and Pai, Rajesh. Learning Computer GraphicsRoelofs, Greg. PNG: The Definitive GuideMarsh, Duncan. Applied Geometry for Computer Graphics and CADMarchand, Patrick. Graphics and GUIs with MATLAB (2nd edition)Ammerall, Leen. Computer Graphics for Java Programmers
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    Interactive High-Quality Maximum Intensity Projection
    (Blackwell Publishers Ltd and the Eurographics Association, 2000) Mroz, Lukas; Hauser, Helwig; Groller, Eduard
    Maximum Intensity Projection (MIP) is a volume rendering technique which is used to visualize high-intensity structures within volumetric data. At each pixel the highest data value, which is encountered along a corresponding viewing ray is depicted. MIP is, for example, commonly used to extract vascular structures from medical data sets (angiography). Due to lack of depth information in MIP images, animation or interactive variation of viewing parameters is frequently used for investigation. Up to now no MIP algorithms exist which are of both interactive speed and high quality. In this paper we present a high-quality MIP algorithm (trilinear interpolation within cells), which is up to 50 times faster than brute-force MIP and at least 20 times faster than comparable optimized techniques. This speed-up is accomplished by using an alternative storage scheme for volume cells (sorted by value) and by removing cells which do not contribute to any MIP projection (regardless of the viewing direction) in a preprocessing step. Also, a fast maximum estimation within cells is used to further speed up the algorithm.
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    Color Distribution - A New Approach to Texture Compression
    (Blackwell Publishers Ltd and the Eurographics Association, 2000) Ivanov, Denis V.; Kuzmin, Yevgeniy P.
    Texture compression is recently one of the most important topics of 3D scene rendering techniques, because it allows rendering more complicated high-resolution scenes. However, because of some special requirements for these type of techniques, the commonly used block decomposition approach may introduce visual degradation of image details due to lack of colors. We present here a new approach to texture compression, which allows sharing of one color by several blocks providing a larger number of unique colors in each particular block and the best compression ratio. We also present an iterative algorithm for obtaining distributed colors on a texture, and discuss some advantages of our approach. The paper concludes with comparison of our technique with S3TC and other block decomposition methods.