Issue 1

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https://diglib.eg.org/handle/10.2312/60

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    Classification of Ray-Generators in Uniform Subdivisions and Octrees for Ray Tracing
    (Blackwell Science Ltd and the Eurographics Association, 1994) Endl, Robert; Sommer, Manfred
    Spatial subdivisions cause an enormous acceleration of ray tracing due to the reduction of ray-object intersections. For this purpose it is necessary to generate the sequence of ray-cells (all cells met consecutively by a given ray). A method generating this sequence will be called a ray-generator. First this paper analyses the common properties of ray-generators in order to establish a classification. Then some well-known ray- generators are described and classified, as well as some new ones. In the sequel nine different ray-generators are implemented in one single program allowing direct comparisons with the same scene. Finally, global time measurements for two scenes are given, as well as time measurements for random rays enabling the calculation of mean values for the time of initialization and determination of ray-cells.
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    Computer Generated Copper Plates
    (Blackwell Science Ltd and the Eurographics Association, 1994) Leister, Wolfgang
    Making computer generated copper plates with image generation algorithms is presented. The method uses a kind of volume texturing in connection with image processing algorithms, and is suitable for implementation in a ray tracing algorithm. Experience shows that this method is especially interesting for illustrations in books and for generating icons on user interfaces.
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    Controllable Locality in C2 Interpolating Curves by B2-splines / S-splines
    (Blackwell Science Ltd and the Eurographics Association, 1994) Kuroda, Mitsuru; Furukawa, Susumu; Kimura, Fumihiko
    This paper presents a systematic scheme for controlling the local behaviour of C2 interpolating curves, based on the cubic B2-splines and the quartic S-splines. Both splines have an additional control point obtained by knot- insertion or degree-elevation in each span of the conventional uniform cubic interpolating B-splines. The shape designer can choose the desired range of locality for each span and get the corresponding additional control point as a barycentric combination of interpolation points within the range, without solving any variational problem and simultaneous equations. The scheme is consistent over the entire curve subject to some typical end conditions. The class of the curves derived includes the conventional cubic interpolating B-splines. Examples demonstrate the behaviour of the new interpolating curves and the capability of the scheme.
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    A Data Structure for Artificial Terrain Generation
    (Blackwell Science Ltd and the Eurographics Association, 1994) Dixon, A. R.; Kirby, G. H.; Wills, D. P. M.
    This paper addresses the problems of maintaining the consistency of spatial data under recursive subdivision algorithms for artificial terrain generation. Fractal modelling techniques are outlined, with particular reference to those based on fractional Brownian motion, and included is a brief history of recursive subdivision techniques. Existing polyhedral data structures are reviewed and shown to be inadequate for maintenance of consistency as polygons are subdivided. A new edge-based data structure is presented which provides for the efficient use and consistent storage of spatial data under these conditions. The data structure is applicable to polygons of any order and allows neighbouring polygons of different order to be stored and subdivided. Artificial terrain is demonstrated from subdivision of the hexagon, of the quadrilateral and of a combination of hexagons, quadrilaterals and triangles.
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    Experiments in the Parallel Computation of 3D Convex Hulls
    (Blackwell Science Ltd and the Eurographics Association, 1994) Claret, A.R.; Day, A.M.
    Two parallel implementations of a 3D convex hull algorithm are reported. The paper considers a MIMD distributed memory architecture and the implementations are carried out on the Meiko Computing Surface using T800 transputers and the programming languages Occam and C. The first method uses a simple parallel geometric decomposition strategy and produces encouraging results. With the second approach a parallel generic Divide-and-Conquer kernel is incorporated. This is an example of the algorithmic skeleton approach to parallel programming and involves run-time, dynamic allocation of work to processors. The resulting performances for both methods are measured and compared.
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    Strands, Gravity and Botanical Tree Imagery
    (Blackwell Science Ltd and the Eurographics Association, 1994) Holton, Matthew
    This paper presents a technique for the modelling and rendering of realistic botanical tree images. A strand model is used that is analogous to the internal vascular structure of a tree. The model is"grown" under the simulated influence of gravity and light. The strand densities at each branching point are used to determine branching angles, branch lengths and branch thicknesses, taking into account stored, user definable parameters that characterize the species of tree being modelled. These parameters address such factors as gravimorphism, phototropism, orthotropism, plagiotropism, planartropism and phyllotaxis, and are distributed according to a branch ordering system.Branch segments and joints are modelled by Bezier splines, with an assumed circular cross-section. Leaves are made up from numbers of sample ranges from vector plane equations. The trees are rendered using a surface sampling algorithm with a light Z buffer for shadows and autoregression textures for tree bark and grass.