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Item Using temporal and spatial coherence for accelerating the calculation of animation sequences(Eurographics Association, 1991) Gröller, Eduard; Purgathofer, WernerRay tracing is a well known technique for generating realistic images. One of the major drawbacks of this approach are the extensive computational requirements for image calculation. When generating animation sequences frame by frame the computational cost might easily become intolerable. In the last years several methods have been devised for accelerating the computational speed by using spatial and temporal coherence. While these techniques work only under certain restrictions, a new approach is presented in this paper which leads to a considerable speed-up of the calculation process without putting any limitations on camera or object movement. In principle, the method is an extension of /ArKi87/, where rays are considered points in 5D space, by the time dimension. CSG is used for object description and has been modified correspondingly to allow easy use of coherence properties. The paper describes the theoretical background and the main concepts of a practical implementation.Item A Median Cut Algorithm for Efficient Sampling of Radiosity Functions(Blackwell Science Ltd and the Eurographics Association, 1994) Feda, Martin; Purgathofer, WernerThis paper presents an efficient method for sampling the illumination functions in higher order radiosity algorithms. In such algorithms, the illumination function is not assumed to be constant across each patch, but it is approximated by a function which is at least C1 continuous. Our median cut sampling algorithm is inspired by the observation that many form factors are computed at higher precision than is necessary. While a high sampling rate is necessary in regions of high illumination, dark areas can be sampled at a much lower rate to compute the received radiosity within a given precision. We adaptively subdivide the emitter into regions of approximately equal influence on the result. Form factors are evaluated by the disk approximation and a ray tracing based test for occlusion detection. The implementation of a higher order radiosity system using B-splines as radiosity function is described. The median cut algorithm can also be used for radiosity algorithms based on the constant radiosity assumption.Item Radiosity for Large Vegetation Scenes(Eurographics Association, 1999) Mastal, Helmut; Tobler, Robert F.; Purgathofer, WernerCalculating radiosity solutions for large scenes containing multiple plants is all but impossible using the radiosity method in its original form. With the introduction of sophisticated hierarchical and clustering algorithms radiosity for vegetation scenes becomes a solvable challenge. The precomputation of the diffuse light distribution in leaf canopies of forests and other plants can be used to calculate realistic images, but also for agricultural planning purposes. This state of the art report gives an overview of the methods that can, and have been, used to calculate global illumination in vegetation scenes, including hierarchical methods, statistical methods based on simplifications, and specialized methods that have been optimized to handle scenes with a dense, non-isotropic distribution of objects such as canopies.