Volume 18 (1999)

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    Eurographics
    (Blackwell Publishers Ltd and the Eurographics Association, 1999)
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    Creating Architectural Models from Images
    (Blackwell Publishers Ltd and the Eurographics Association, 1999) Liebowitz, David; Criminisi, Antonio; Zisserman, Andrew
    We present methods for creating 3D graphical models of scenes from a limited numbers of images, i.e. one or two, in situations where no scene co-ordinate measurements are available. The methods employ constraints available from geometric relationships that are common in architectural scenes - such as parallelism and orthogonality - together with constraints available from the camera. In particular, by using the circular points of a plane simple, linear algorithms are given for computing plane rectification, plane orientation and camera calibration from a single image. Examples of image based 3D modelling are given for both single images and image pairs.
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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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    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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    Tetrahedra Based Adaptive Polygonization of Implicit Surface Patches
    (Blackwell Publishers Ltd and the Eurographics Association, 1999) Hui, K. C.; Jiang, Z. H.
    This paper presents a tetrahedra based adaptive polygonization technique for tessellating implicit surface patches. An implicit surface patch is defined as an implicit surface bounded by its intersections with a set of clipping surfaces and which lies within an enclosing tetrahedron. To obtain the polygonization of an implicit surface patch, the tetrahedron containing the patch is adaptively subdivided into smaller tetrahedra according to the criteria introduced in the paper. The result is a set of tetrahedra each containing a facet approximating the surface. The intersections between the facets and the clipping surfaces are used to locate the surface patch boundary. Ambiguous results in generating the facets for highly curved surfaces or surfaces with singular points are also addressed. The result of the polygonization is a set of triangular facets that can be used for visualization and numerical analysis. The proposed method is also suitable for locating the intersection of two implicit surfaces.
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    An Interactive Designing System with Virtual Sculpting and Virtual Woodcut Printing
    (Blackwell Publishers Ltd and the Eurographics Association, 1999) Mizunoy, S.; Okadayy, M.; Toriwakiy, J.
    In this paper, we propose an interactive designing method and a system based on it to create 3D objects and 2D images. This system consists of two subsystems for virtual sculpting to create a 3D shape and virtual printing to produce a picture with a printing block. In the virtual sculpting subsystem, a user can form solid objects with curved surfaces as if sculpting them. The user operates virtual chisels, and can remove or attach arbitrary shapes of ellipsoids or cubes from or to the workpiece. A 3D object generated by virtual sculpting looks like a real wooden sculpture. If using a board as a workpiece, a user can generate a virtual printing block. In the virtual printing subsystem, a user can synthesize a woodcut printing image from the virtual printing block mentioned above, a virtual paper sheet, and a printing brush. The user can synthesize a realistic woodcut print with a procedure similar to the actual woodcut printing.
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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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    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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    Approximate Line Scan-Conversion and Antialiasing
    (Blackwell Publishers Ltd and the Eurographics Association, 1999) Chen, Jim X.; Wang, Xusheng
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    Editorial
    (Blackwell Publishers Ltd and the Eurographics Association, 1999) Coquillart, Sabine; Seidel, Hans-Peter
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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.
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    Editorial
    (Blackwell Publishers Ltd and the Eurographics Association, 1999) Coquillart, Sabine; Seidel, Hans-Peter
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    Comprehensive Halftoning of 3D Scenes
    (Blackwell Publishers Ltd and the Eurographics Association, 1999) Veryovka, O.; Buchanan, J.
    The display of images on binary output hardware requires a halftoning step. Conventional halftoning algorithms approximate image values independently from the image content and often introduce artificial texture that obscures fine details. The objective of this research is to adapt a halftoning technique to 3D scene information and thus to enhance the display of computer generated 3D scenes. Our approach is based on the control of halftoning texture by the combination of ordered dithering and error diffusion techniques. We extend our previous work and enable a user to specify the shape, scale, direction, and contrast of the halftoning texture using an external buffer. We control texture shape by constructing a dither matrix from an arbitrary image or a procedural texture. Texture direction and scale are adapted to the external information by the mapping function. Texture contrast and the accuracy of tone reproduction are varied across the image using the error diffusion process. We halftone images of 3D scenes by using the geometry, position, and illumination information to control the halftoning texture. Thus, the texture provides visual cues and can be used to enhance the viewer's comprehension of the display.
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    Eurographics
    (Blackwell Publishers Ltd and the Eurographics Association, 1999)
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    Interactive Cuts through 3-Dimensional Soft Tissue
    (Blackwell Publishers Ltd and the Eurographics Association, 1999) Bielser, Daniel; Maiwald, Volker A.; Gross, Markus H.
    We describe a physically based framework for interactive modeling and cutting of 3-dimensional soft tissue that can be used for surgery simulation. Unlike existing approaches which are mostly designed for tensorproduct grids our methods operate on tetrahedral decompositions giving more topological and geometric flexibility for the efficient modeling of complex anatomical structures. We start from an initial tetrahedralization such as being provided by any conventional meshing method. In order to track topological changes tetrahedra intersected by the virtual scalpel are split into substructures whose connectivity follows the trajectory of the cut, which can be arbitrary. For the efficient computation of collisions between the scalpel and individual tetrahedra we devised a local collision detection algorithm. The underlying physics is approximated through masses and springs attached to each tetrahedral vertex and edge. A hierarchical Runge-Kutta iteration computes the relaxation of the system by traversing the designed data structures in a breadth-first order. The framework includes a force-feedback interface and uses real-time texture mapping to enhance the visual realism.
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    Adaptive Acquisition of Lumigraphs from Synthetic Scenes
    (Blackwell Publishers Ltd and the Eurographics Association, 1999) Schirmacher, Hartmut; Heidrich, Wolfgang; Seidel, Hans-Peter
    Light fields and Lumigraphs are capable of rendering scenes of arbitrary geometrical or illumination complexity in real time. They are thus interesting ways of interacting with both recorded real-world and high-quality synthetic scenes.Unfortunately, both light fields and Lumigraph rely on a dense sampling of the illumination to provide a good rendering quality. This induces high costs both in terms of storage requirements and computational resources for the image acquisition. Techniques for acquiring adaptive light field and Lumigraph representations are thus mandatory for practical applications.In this paper we present a method for the adaptive acquisition of images for Lumigraphs from synthetic scenes. Using image warping to predict the potential improvement in image quality when adding a certain view, we decide which new views of the scene should be rendered and added to the light field. This a-priori error estimator accounts for both visibility problems and illumination effects such as specular highlights.