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Item Interactive Rendering of Volumetric Data Sets(The Eurographics Association, 1994) Juskiw, "Scott; Durdle, Nelson G.; W. StrasserThe bela architecture for interactive rendering of regularly structured volumetric data sets is presented. The proposed architecture is scalable and uses custom processors to achieve high-speed shading, projection. and composition of voxel primitives. A general purpose image composition network supports the accumulation of both volumetric and geometric elements into the final rendered scene. Data access contentions between processors are eliminated via the use of an enhanced dual object space and image space partitioning scheme that does not require replication or redistribution of rendered data. The bela architecture is intended for rendering large data sets and meets the performance requirements of a full frame interactive image generation system.Item Cross Scan Buffer and its Applications(Blackwell Science Ltd and the Eurographics Association, 1994) Tanaka, Toshimitsu; Takahashi, TokiichiroWe propose the Cross Scanline Buffer which preserves the result of hidden surface removal as performed by the Cross Scanline Algorithm. The Cross Scan Buffer reduces image re-generation time and eliminates aliasing artifacts even if the image is arbitrarily scaled. Perfect anti-aliasing is achieved because the Cross Scanline Algorithm analytically determines visible polygonal surfaces and divides them into sets of triangles and trapezia. The Cross Scan Buffer supports the various applications that currently use the conventional buffering methods for anti-aliasing. This paper introduces and tests three applications: image scaling, shadow creation, and texture mapping. Experimental results verify that the Cross Scan Buffer is very powerful yet efficient.Item A Constraint-Based Reasoning Framework for Behavioural Animation(Blackwell Science Ltd and the Eurographics Association, 1994) Mah, Sang; Calvert, Thomas W.; Havens, WilliamBehaviour is a reflection of a reasoning process that must deal with constraints imposed by an external environment, internal knowledge and physical structure. This paper proposes a framework for behavioural animation that is based on the next generation of object-oriented, constraint-based expert systems technology, and applies a control structure of knowledge agents and knowledge units to determine the behaviour of objects to be animated. Knowledge agents are responsible for planning, plan implementation and information extraction from the environment. The activity of an agent is dependent on the knowledge units ascribed to them by the animator. The interaction between agents and knowledge units is resolved by the reasoning engine, and thus, influences the eventual motion displayed. An example given is NSAIL, a pilot implementation using the model-based ECHIDNA constraint logic programming shell. With this approach, the motion for a sailing scenario and other behavioural domains can be specified at a high level through the characterization of the knowledge agents.Item Real Time Fitting of Hand-Sketched Pressure Brushstrokes(Blackwell Science Ltd and the Eurographics Association, 1994) Pudet, ThierryA method is described for fitting the outline of hand-sketched pressure brushstrokes with Bezier curves. It combines the brush-trajectory model, in which a stroke is generated by dragging a brush along a given trajectory, with a fast curve fitting algorithm.The method has been implemented for a vector-based drawing program in which the user draws with a cordless pressure-sensitive stylus on a digitizing tablet. From the trajectory followed by the stylus, its associated pressure data, and a specified brush, a stroke of variable width is computed and displayed in real time.First, the digitized trajectory is fitted, thus removing noise. Then, from polygonal approximations of the fitted trajectory and the brush outline, a polygonal approximation of the stroke outline is computed. Working with polygonal approximations reduces computations to simple geometric operations and greatly simplifies the treatment of dynamic, pressure-controlled brushes. Last, the polygonal approximation of the stroke outline is fitted. The result is a closed piecewise Bezier curve approximating the brushstroke outline to within an arbitrary error tolerance.Several examples of hand-sketched drawings realized with this method are presented.Item Computation of Offset Curves by the Huygens Principle(Blackwell Science Ltd and the Eurographics Association, 1994) Mikheev, A.; Nozik, M.; Rubinstein, J.A new algorithm for computing offset curves is proposed. The algorithm is based on the Huygens principle for propagating wave-fronts. It automatically avoids the topological singularities that appear in conventional methods. The algorithm is simple to implement and it does not require any multiplication or other floating number operations.Item Experience with a Difference Engine for Graphics(The Eurographics Association, 1994) Kuijk, A.A.M.; Blake, E.H.; Steffens, E.H.; W. Strasser"The prototype of a novel raster graphics architecture has now become operational. The display hardware can be regarded as a very fast difference engine that works in two-dimensions. The speed is partly achieved by the use of custom VLSI components for the lowest level primitive operations and this permits the video rate reconstruction of images and other signals com pressed by encoding them on various polynomial bases. A novel feature of the architecture is that it avoids the use of a frame buffer. The paper describes our experience with the new hardware in terms of positive and negative performance aspects. We discuss the architecture and its operating parameters. Another part of the paper evaluates our ex perience of hardware development in an academic set ting. We believe there are significant lessons here for graphics researchers who might want to develop their own systems."Item Multiresolution Tiling(Blackwell Science Ltd and the Eurographics Association, 1994) Meyers, DavidThis paper describes an efficient method for constructing a tiling between a pair of planar contours. The problem is of interest in a number of domains, including medical imaging, biological research and geological reconstructions. Our method, based on ideas from multiresolution analysis and wavelets, requires O(n) space and appears to require O(n log n) time for average inputs, compared to the O(n2) space and O(n2 log n) time required by the optimizing algorithm of Fuchs, Kedem and Uselton1. The results computed by our algorithm are in many cases nearly the same as those of the optimizing algorithm, but at a small fraction of the computational cost. The performance improvement makes the algorithm usable for large contours in an interactive system. The use of multiresolution analysis provides an efficient mechanism for data compression by discarding wavelet coefficients smaller than a threshold value during reconstruction. The amount of detail lost can be controlled by appropriate choice of the threshold value. The use of lower resolution approximations to the original contours yields significant savings in the time required to display a reconstructed object, and in the space required to store it.Item Deriving Spectral, Reflectance Functions of Computer-Simulated Object Colours(Blackwell Science Ltd and the Eurographics Association, 1994) Schettini, R.A method is presented which, given the RGB values of a colour stimulus displayed on a given cathode ray tube (to which a CIE XYZ triple corresponds), makes it possible to find a spectral reflectance function characterizing an object colour. Such an object when"illuminated" by a given illuminant produces a metameric spectral power distribution, that is, one with the same XYZ tristimulus values. The method is useful in the colorimetric matching of colours on different media or supports.Item A New Approach to the Construction of Surfaces from Contour Data(Blackwell Science Ltd and the Eurographics Association, 1994) Jones, Mark W.; Chen, MinThis paper presents a new approach to the construction of a surface from a stack of contour slices. Unlike most existing methods, this new approach handles ambiguous conditions consistently without employing an algorithm to establish a correspondence between vertices on one contour and those on the next. It is easy to implement and fast to compute, requiring only basic geometric properties, namely closedness and simplicity, to be available with contour data. The advantages of this new approach have also been demonstrated with solutions to a few classical problems from the literature and some practical problems in medical imaging. It can also be applied to geographical surveying and keyframe animations.Item A Robust and Consistent Algorithm for Intersecting Convex Polyhedra(Blackwell Science Ltd and the Eurographics Association, 1994) Sugihara, KokichiThis paper presents a numerically robust and topologically consistent algorithm for intersecting convex polyhedra. This algorithm is new in the sense that the consistency issue is completely separated from the numerical error issue. The intersection operation is combinatorially abstracted as the operation of changing the vertex-edge graphs associated with the input polyhedra, and numerical computation is employed only for choosing the branch of processing which is most likely to lead to the correct solution of the problem. Hence, the resultant algorithm is completely free from topological inconsistency.