Volume 06 (1987)

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Extraction and Organization of Form Features into a Structured Boundary Model
(Eurographics Association, 1987) Falcidieno, Bianca; Giannini, Franca
A method is presented for the automatic identification and extraction of feature information from the solid model of an object. The procedure consists of recognizing shape features, extracting those features as solid volumes and arranging them in a hierarchical structure. In this hierarchical model the main shape of the object is represented at the highest levels of abstraction, while form features are described at lower levels of specification. The system is divided into three modules: feature recognition, feature extraction and feature organization. The recognition step works on a face-based representation of solid objects, called Face Adjacency Hypergraph [1] and it takes advantage of the Kyprianou's method [12]. In the extraction phase every recognized form feature is completed with dummy entities to form a feasible object and in the organization step the completed features are arranged in a hierarchical graph, called Structured Face Adjacency Hypergraph, which is a modification of a model defined in a previous work [1].
Visual Simulation of Atmospheric Haze
(Blackwell Publishing Ltd and the Eurographics Association, 1987) Willis, P.J.
For applications such as daylight visual pilot training simulators, the correct representation of aerial haze, mist and fog is of major importance in providing accurate depth cues and training in poor visibility conditions.We present a straightforward derivation of a formula to express this and then show various pictorial examples to illustrate its effectiveness.
An Implementer s View of CGM in GKS Environment
(Blackwell Publishing Ltd and the Eurographics Association, 1987) Moltedo, L.; Noferini, A.
An Editor for Constructing Graphics with TEX
(Blackwell Publishing Ltd and the Eurographics Association, 1987) Waldschmidt, H.
An Algorithm for 3D Scan-Conversion of Polygons
(Eurographics Association, 1987) Kaufman, Arie
A three-dimensional (3D) scan-conversion algorithm, that scanconverts 3D planar polygons into their discrete voxel-map representation within a Cubic Frame Buffer (CFB), is presented. The algorithm, which is a variation of a 2D scan-line filling algorithm, is incremental and uses only simple operations like additions and testy inside the inner loops. The algorithm performs scan-conversion with computational complexity which is linear in the number of voxels written to the CFB. The paper also presents an algorithm that scan-converts polygons clipped to the CFB boundaries with no added time complexity. An all-integer decision mechanism which makes the inner-most loop of the algorithm more efficient is discussed too. All the algorithms guarantee lack of 6-connected "tunnels" in the converted polygons. The algorithms have been implemented as part of the 3D geometry processor of the CUBE Architecture, which is a voxel-based system for 3D graphics. These algorithms allow the' CUBE system to generate the essential primitive polygon within the CFB from a 3D geometric model.
EDITORIAL
(Blackwell Publishing Ltd and the Eurographics Association, 1987) Arnold, David
An Intersection-Sensitive Hidden-Surface Algorithm
(Eurographics Association, 1987) Devai, Ferenc
Given a set of pairwise disjoint planar polygonal faces with altogether N edges in the three-dimensional space. Let k be the number of intersection points of the projections of the edges in a projection plane, 0 < k < N(N-1)/2. An algorithm for the elimination of hidden surfaces in O((N+k)log N) time and O(N+k) space is proposed. If k is O(N), which is often the case in practice, the algorithm has O(N log N) expected time, regardless of the probability distribution of the input data. The constants of proportionality are low enough to make this algorithm of practical use. The method is a three-dimensional generalization of a two-dimensional scan-line algorithm, called the NlogN algorithm. A total order hide of faces is introduced. By determining the intersections of the projected edges, regions are designated within which visibility is unvaried. Then each region is visited, maintaining the total order hide, from which visible surfaces and rendering of partially transparent objects can be inferred.
A Fast Ray Tracing Algorithm Using Space Indexing Techniques
(Eurographics Association, 1987) Qunsheng, Peng; Zhu, Yining; Liang, Youdong
A fast ray tracing algorithm is presented. Spatial coherency is exploited by adopting a linear octree data structure which corresponds to an adaptive partitioning of space. A ray strides over a number of empty regions aligning on its way and intersects the desired objects directly, Efficiency of the algorithm is achieved by decreasing the number of regions that the ray must be checked with, by reducing the computations involved in skipping an empty region and by performing a binary search to find the next region. An efficient algorithm based on linear programming for mapping the whole environment into a sorted linear octree is also described. Only the terminal nodes containing boundary surfaces of objects are explicitly represented, which not only shortens the searching process but also leads to a considerable saving on storage space.
Calendar of Events
(Blackwell Publishing Ltd and the Eurographics Association, 1987)
Executive Committee Nominations -1987
(Blackwell Publishing Ltd and the Eurographics Association, 1987)
A Simple and Efficient Haloed Line Algorithm for Hidden Line Elimination
(Blackwell Publishing Ltd and the Eurographics Association, 1987) Franklin, W.R; Akman, V.
An efficient algorithm, HALO, is given to compute haloed line drawings of wire frame objects. Haloed line drawings are described by Appel et al.1HALO has two parts: CUT and DRAW. CUT uses an adaptive grid to find all edge intersections. It overlays a square grid, whose fineness is a function of the number and length of the edges, on the Scene. It determines the cells that each edge passes through, sorts these by cell to obtain the edges in each cell, and then, in each cell, tests each pair of edges in that cell for intersection. For broad classes of input this takes time linear in the number of edges plus the number of intersections. CUT writes a file containing all the locations where each edge is crossed in front by another. Given a halo width, DRAW reads this file edge by edge. For each edge, it subtracts and adds the halo width to each intersection to get the locations where the edge becomes invisible and visible. It sorts these along the edge, and then traverses the edge, plotting those portions where the number of"Visible" transitions is equal to the number of"invisible" transitions. DRAW takes time hear in the number of edge segments. Dividing HALO into two parts means that redrawing a plot with a different halo width is fast, since only DRAW need to be rerun.CR Categories and Subject Descriptions: I.3.5 [Computer Graphics]: Computational Geometry and Object Modeling - geometric algorithm, languages, and systems- F.2.2 [Analysis of Algorithms and Problem Complexity]: Nonnumerid Algorithms and Problems -geometrical problem and computationsGeneral Terms: Algorithms, design.
Calendar of Events
(Blackwell Publishing Ltd and the Eurographics Association, 1987)
Parallel Polygon Rendering with Precomputed Surface Patches
(Eurographics Association, 1987) Theoharis, Theoharis; Page, Ian
We describe an algorithm for rendering a restricted class of trapeziums, and hence arbitrary polygons, in parallel on an NxN SIMD array processor. The algorithm achieves good performance by precomputing “surface patches” (finite portions of half -planes), thus trading storage for increased speed. The number of surface patches that are precomputed grows only linearly with the size of the array processor but as the square of the subpixel accuracy desired. NxN texture patterns can be added at very little extra cost additional to filling a trapezium with a particular colour.
A Scanline Method for Solid Model Display
(Blackwell Publishing Ltd and the Eurographics Association, 1987) Patel, Manjula; Hubbold, Roger J.
The modelling of solid objects is becoming increasingly important in the application of computer graphics to a wide variety of problems, such as CAD/CAM, simulation, and molecular modelling. A variety of methods for rendering solid objects exists, including 2-Buffer, Scanline and Ray Tracing. This paper is concerned with a scanline method for the production of still images of complex objects. The implementation of a scanline algorithm is discussed, in conjunction with a consideration of its performance in relation to the z-buffer method.Many scanline methods cater only for a restricted class of primitives, such as polygons or spheres, whereas this implementation is a general purpose scanline algorithm capable of being extended to handle a variety of primitives. The primitives currently available are polygons, spheres, spheres swept along straight-line trajectories, and cylinders. Polygonal models of cubes, cones and cylinders are also available.The approach is capable of dealing with"positive" and"negative" volumes, allowing objects with holes to be modelled and displayed. It has further been extended to cater for the inclusion of transparent objects into a scene, and consequently allows the modelling of coloured"glass" objects.
Scan Converting Extruded Lines at Ultra High Definition
(Blackwell Publishing Ltd and the Eurographics Association, 1987) Willis, Philip; Watters, Geoff
We consider the problem of generating freehand raster graphics pictures at ultra high definition (typically one gigapixel per picture) by scan converting extruded lines. We describe a fast scan conversion algorithm which is linear in final resolution and which incorporates a number of features to ensure high efficiency. Sample pictures and corresponding performance figures are included.
GOCS - The GKS-oriented Communication System
(Eurographics Association, 1987) Egelhaaf, Chr.; Schuermann, G.
We present a system which offers a distributed GKS in an open network. The GKS kernel and the workstations are located on different hosts. There is no restriction to the full level 2b functionality of GKS due to the distribution. The workstation interface WSI and the communication modules, which are based on the transport protocol T.70, are discussed.
EUROGRAPHICS Membership Application Forms
(Blackwell Publishing Ltd and the Eurographics Association, 1987)
Offers to EUROGRAPHICS Members
(Blackwell Publishing Ltd and the Eurographics Association, 1987)
COLOUR SECTION
(Eurographics Association, 1987) -
Real-Time Scan-Line In-Fill
(Eurographics Association, 1987) Allerton, D. J.; Evemy, J. D.; Zaluska, E. J.
A novel algorithm is described to perform in-fill of wire-frame polygons, typically for application in visual systems for flight simulation. Post-processing is performed on an image formed in a conventional raster-scan framestore using edge-detection in scan-line order. A prototype real-time implementation of this algorithm is operational and is also presented.

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