Volume 18 (1999)

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    Eurographics
    (Blackwell Publishers Ltd and the Eurographics Association, 1999)
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    Partitioning and Handling Massive Models for Interactive Collision Detection
    (Blackwell Publishers Ltd and the Eurographics Association, 1999) Wilson, A.; Larsen, E.; Manocha, D.; Lin, M. C.
    We describe an approach for interactive collision detection and proximity computations on massive models composed of millions of geometric primitives. We address issues related to interactive data access and processing in a large geometric database, which may not fit into main memory of typical desktop workstations or computers. We present a new algorithm using overlap graphs for localizing the "regions of interest" within a massive model, thereby reducing runtime memory requirements. The overlap graph is computed off-line, pre-processed using graph partitioning algorithms, and modified on the fly as needed. At run time, we traverse localized sub-graphs to check the corresponding geometry for proximity and pre-fetch geometry and auxiliary data structures. To perform interactive proximity queries, we use bounding-volume hierarchies and take advantage of spatial and temporal coherence. Based on the proposed algorithms, we have developed a system called IMMPACT and used it for interaction with a CAD model of a power plant consisting of over 15 million triangles. We are able to perform a number of proximity queries in real-time on such a model. In terms of model complexity and application to large models, we have improved the performance of interactive collision detection and proximity computation algorithms by an order of magnitude.
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    Active Storytelling
    (Blackwell Publishers Ltd and the Eurographics Association, 1999) Glassner, Andrew
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    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.
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    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.
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    Editorial
    (Blackwell Publishers Ltd and the Eurographics Association, 1999) Coquillart, Sabine; Seidel, Hans-Peter
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    Event Reports
    (Blackwell Publishers Ltd and the Eurographics Association, 1999)
    VisSym '99: Joint EUROGRAPHICS - IEEE TCVG Symposium on Visualization6th Eurographics Workshop on Design, Specification, and Verification of Interactive Systems â 99
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    The Hybrid World of Virtual Environments
    (Blackwell Publishers Ltd and the Eurographics Association, 1999) Smith, Shamus; Duke, David; Massink, Mieke
    Much of the work concerned with virtual environments has addressed the development of new rendering technologies or interaction techniques. As the technology matures and becomes adopted in a wider range of applications, there is, however, a need to better understand how this technology can be accommodated in software engineering practice. A particular challenge presented by virtual environments is the complexity of the interaction that is supported, and sometimes necessary, for a particular task. Methods such as finite-state automata which are used to represent and design dialogue components for more conventional interfaces, e.g. using direct manipulation within a desktop model, do not seem to capture adequately the style of interaction that is afforded by richer input devices and graphical models. In this paper, we suggest that virtual environments are, fundamentally, what are known as hybrid systems. Building on this insight, we demonstrate how techniques developed for modelling hybrid systems can be used to represent and understand virtual interaction in a way that can be used in the specification and design phases of software development, and which have the potential to support prototyping and analysis of virtual interfaces.
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    Announcements
    (Blackwell Publishers Ltd and the Eurographics Association, 1999)
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    An Efficient 2? D rendering and Compositing System
    (Blackwell Publishers Ltd and the Eurographics Association, 1999) Froumentin, M.; Willis, P.
    We describe a method for doing image compositing using either 2D geometric shapes or raster images as input primitives. The resolution of the final image is virtually unlimited but, as no frame buffer is used, performance is much less dependant on resolution than with standard painting programs, allowing rendering very large images in reasonable time. Many standard features found in compositing programs have been implemented, like hierarchical data structures for input primitives, lighting control for each layer and filter operations (for antialiasing or defocus).
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    Image Morphing with Feature Preserving Texture
    (Blackwell Publishers Ltd and the Eurographics Association, 1999) Tal, Ayellet; Elber, Gershon
    Image metamorphosis as an animation tool has mostly been employed in the context of the entire image. This work explores the use of isolated and focused image based metamorphosis between two-dimensional objects, while capturing the features, colors, and textures of the objects. This pinpointed approach allows one to independently overlay several such dynamic shapes, without any bleeding of one shape into another. Hence, shape blending and metamorphosis of two-dimensional objects can be exploited as animated sequences of clip arts.
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    Approximate Line Scan-Conversion and Antialiasing
    (Blackwell Publishers Ltd and the Eurographics Association, 1999) Chen, Jim X.; Wang, Xusheng
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    Extending the CSG Tree. Warping, Blending and Boolean Operations in an Implicit Surface Modeling System
    (Blackwell Publishers Ltd and the Eurographics Association, 1999) Wyvill, Brian; Guy, Andrew; Galin, Eric
    Automatic blending has characterized the major advantage of implicit surface modeling systems. Recently, the introduction of deformations based on space warping and Boolean operations between primitives has increased the usefulness of such systems. We propose a further enhancement which will extend the range of models that can be easily and intuitively defined with a skeletal implicit surface system. We describe a hierarchical method which allows arbitrary compositions of models that make use of blending, warping and Boolean operations. We call this structure the BlobTree. Blending and space warping are treated in the same way as union, difference and intersection, i.e. as nodes in the BlobTree. The traversal of the BlobTree is described along with two rendering algorithms; a polygonizer and a ray tracer. We present some examples of interesting models which can be made easily using our approach that would be very difficult to represent with conventional systems.
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    Hermitian B-Splines
    (Blackwell Publishers Ltd and the Eurographics Association, 1999) Grisoni, Laurent; Blanc, Carole; Schlick, Christophe
    This 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.
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    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.
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    Event Reports
    (Blackwell Publishers Ltd and the Eurographics Association, 1999)
    Second Eurographics Workshop on Parallel Graphics and Visualization, Rennes, France September 24-25, 1998
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    Generalized View-Dependent Simplification
    (Blackwell Publishers Ltd and the Eurographics Association, 1999) El-Sana, Jihad; Varshney, Amitabh
    We 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.
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    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.
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    Event Reports
    (Blackwell Publishers Ltd and the Eurographics Association, 1999)
    Eurographics '99Eurographics '99 Awards10th Eurographics Workshop on RenderingSiggraph '992000 Cover Competition
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    Interactive Mechanical Design Variation for Haptics and CAD
    (Blackwell Publishers Ltd and the Eurographics Association, 1999) Nelson, Donald D.; Cohen, Elaine
    A 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.