Issue 2

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https://diglib.eg.org/handle/10.2312/67

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    3D Interaction with the Desktop Bat
    (Blackwell Science Ltd and the Eurographics Association, 1995) Steed, Anthony; Slater, Mel
    Many applications now demand interaction with visualizations of 3D scenes and data sets. Current flat 2D displays are limited in their capacity to provide this not only by the display technology but the interaction metaphors and devices used. The Desktop Bat is a device that has 5 degrees of freedom whilst retaining the simplicity of use o fa mouse. To use it for general 3D interaction several metaphors were created for the tasks of navigation and cursor manipulation and a set of experiments were conducted to determine which metaphors were the most efficient in use. Of these metaphors, a velocity control metaphor was the best for navigation and a metaphor that applied rotations and translations relative to the eyepoint coordinate system was best for object control.
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    Collision Detection for Animation using Sphere-Trees
    (Blackwell Science Ltd and the Eurographics Association, 1995) Palmer, I. J.; Grimsdale, R. L.
    The detection of collisions between moving polyhedral objects is one of the most computationally intensive tasks in the computer animation process. The use of object-oriented techniques to encapsulate data within the objects structures compounds this problem through the requirement for inter-object message passing in order to obtain geometric information for collision detection. The REALISM system decreases the time for collision detection by using a three stage process. The first stage identifies objects in the same locality using a global bounding volume table. The second stage locates regions of possible collision using a sphere-tree data structure (a hierarchical tree of spheres based on octree-type spatial subdivision). The final stage finds intersections between polygonal faces of the objects that are contained within the intersecting pairs of leaf nodes. Hence the algorithm uses a spherical geometry approximation rapidly to locate regions of potential collisions and then uses a local intersection test with actual object geometry information. The system is therefore fast and accurate. Tests for various geometric objects support this and show performance improvements of jive times over traditional polyhedral intersection tests.
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    Colouration Issues in Computer Generated Facial Animation
    (Blackwell Science Ltd and the Eurographics Association, 1995) Patel, M.
    In everyday interactions with one another we use the face for recognising people and for communicating with them. Despite the considerable amount of research into computer generated facial animation, one particular aspect, that of the colouration of the face appears to have been neglected. In this paper we address issues pertinent to the use of colour for both modelling the appearance of the face and for enhancing communication during facial expression and animation. Colouration is an integral part of the face, which helps in the recognition of faces as well as in the interpretation of the often subtle signals emitted by the human face.
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    Fast Generation of Leakproof Surfaces from Well-Defined Objects by a Modified Marching Cubes Algorithm
    (Blackwell Science Ltd and the Eurographics Association, 1995) Roll, Stefan; Haase, Axel; von Kienlin, Markus
    Local surface reconstruction by the Marching Cubes algorithm and its derivatives has a well known ambiguity, which prevents constructed surfaces from being closed and simple. We investigate this ambiguity assuming that a 3D image samples well-defined objects. In this case it is justified to aim at tiling of extracted object voxels rather than at reconstructing iso surfaces. Compared to iso surface reconstruction, our algorithm provides essentially the same level of confidence with respect to surface location at a lower computational cost. We present a leak detection and mending scheme which resolves the Marching Cubes ambiguity and guarantees a well-defined behaviour with respect to which objects are covered by which surface. We detail how to implement our leak mending method within a completely tabulated Marching Cubes algorithm. We finally give an example of how the adapted algorithm is of benefit to a recently developed 3D MR spectroscopy technique.
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    Fractals and Quasi-Affine Transformations
    (Blackwell Science Ltd and the Eurographics Association, 1995) Nehlig, P. W.; Reveilles, J.-P.
    In the continuum , contracting affine transformations have a unique fixed point. It is well known that this property is not preserved by dicretization and that the dynamics of discretized functions are very complicated. Discrete geometry allows us to start a theory for these dynamics and to illustrate some of their features by pictures. These pictures, rendered by a simple algorithm, reveal a very large spectrum of fractal structures, from the simplest to the intricatest.
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    Optimised CSG Tree Evaluation for Space Subdivision
    (Blackwell Science Ltd and the Eurographics Association, 1995) Zemcik, Pavel; Chalmers, Alan
    Ray tracing is a well known technique for producing realistic computer images. The computational requirements of this method are such that optimisation techniques, for example space subdivision, must be used if complex scenes are to be rendered in reasonable times. Constructive solid geometry (CSG) is a method for describing the geometry of complex scenes by applying set operations to primitive objects. The status tree approach has been used successfully within ray tracing to evaluate CSG structures. This paper proposes a combination of the status tree and space subdivision techniques as a means to improve further the efficiency of ray tracing.