EG1987 Proceedings (Technical Papers)

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A Means to Improve the GKS-3D/PHIGS Output Pipeline Implementation
(Eurographics Association, 1987) Herman, Ivan; Reviczky, Janos
The output pipeline of GKS-3D/PHIGS isexamined to find some possible points where the implementation could be improved to raise efficiency while remaining strictly within the scope of the Standards. Some interesting results are presented in the paper which have led to a 25-30% improvement in speed when compared to a more conservative implementation.
Display of Solid Models with a Multi-Processor System
(Eurographics Association, 1987) Jansen, Frederik W.; Sutherland, Robert J.
There is a growing need for fast high-quality display of solid objects. Recently-developed custom-VLSI hardware offers high-speed display but lacks the flexibility and processing power at the pixel level to sustain the calculations and filter operations needed for realistic reflection models, texture mapping and anti-aliasing. Multi-processor systems built with general-purpose components of relatively high capacity and moderate cost provide an alternative; they also offer higher performance than single processor systems but retain their flexibility. A CSG hidden-surface algorithm based on depth-buffering and image subdivision is presented which is suitable for use with such a multi-processor system.
A New Algorithm of Space Tracing Using a CSG Model
(Eurographics Association, 1987) Bouatouch, Kadi; Madani, M.O.; Priol, Thierry; Arnaldi, Bruno
This paper describes a new algorithm of space tracing. Scenes are modeled by a CSG tree. Space is subdivided regularly into 3D regions called boxes. With each box is associated a subtree which is the restriction of the whole scene CSG tree to primitives belonging to this box. A 3D grid is used to access boxes.
A New Scan Line Algorithm for the Rendering of CGS Trees
(Eurographics Association, 1987) Pueyo, Xavier; Mendoza, Joan Carles
A scan line algorithm is proposed to render CSG modelled solids. Scan planes intersections are obtained by means of a proposed generalisation of Porter’s algorithm. 2-D scan plane primitives are decomposed in a way that provides a more accurate disjointness information then 3-D inclosing boxes and a simple way to class spans. Furtheremore, this scan plane organisation allows the use of most of scan line hidden surface strategies that make use of different types of coherence to speed up the visibility process.
Generative Scene Modelling
(Eurographics Association, 1987) Beyer, Thomas; Friedell, Mark
We describe a new theory of scene modelling that includes generative processes as integral components of scene descriptions. A single, uniform treatment of generative processes replaces the variety of ad hoc mechanisms commonly in use. We discuss the implementation of the theory in an experimental modelling system and show that L-systems, fractals, and particle systems, as well as many specialized generative processes, become comparatively easy to define and use.
Designing a System to Provide Graphical User Interfaces: The THESEUS Approach
(Eurographics Association, 1987) Huebner, W.; Lux-Mulders, G.; Muth, M.
This paper presents the design of THESEUS, a system for programming graphical user interfaces especially targetted at the area of software engineering. Starting with the special needs and requirements that arise in this area, the design alternatives for such a system - abstraction level of the programming interface, division of control and dialogue specification - are discussed. The decisions that resulted in the layer model of THESEUS are substantiated. THESEUS offers an application-oriented programming interface supporting a user interface with multiple windowing, graphics and modem interaction techniques. The dialogue control mechanisms,' event driven input management and the definition of hierarchical object-oriented output are described in detail. Experience with a first implementation is also presented.
A Fast Voxel Traversal Algorithm for Ray Tracing
(Eurographics Association, 1987) Amanatides, John; Woo, Andrew
A fast and simple voxel traversal algorithm through a 3D space partition is introduced. Going from one voxel to its neighbour requires only two floating point comparisons and one floating point addition. Also, multiple ray intersections with objects that are in more than one voxel are eliminated.
The Reconstruction of Neurone Morphology from Thin Optical Sections - Graphical Aspects
(Eurographics Association, 1987) Brown, A. D.; Wheal, H. V.; Stockley, E. W.
The aims of the project are two-fold: firstly, to create an accurate three-dimensional model of a neurone from the mammalian nervous system, which can be used to obtain quantitative geometric and topological data on the neurone, and secondly, to create a software simulation of an active neurone, that accurately mirrors the electrochemical responses of a real, living mammalian neurone to external excitations and to changes in its electrochemical ambient. The focus of this paper is the first of these two goals. Portions of brain tissue are prepared, containing stained neurones. Using an optical sectioning technique, these neurones can be photographed in two-dimensional slices, down to about 10um thick. These photographs are digitised, and input to a computer. The system reconstructs the three-dimensional structure of the neurone, and provides a number of ways of displaying the reconstruction.
Bezier Patches with Local Shape Control Parameters
(Eurographics Association, 1987) Schmitt, Francis J. M.; Du, Wen-Hui
In this paper, we introduce three types of shape control parmeters (tension, bias, and continuity) into the modelling of free-form surfaces composed of bicubic Bernstein-Bezier patches. This is an extension to surfaces of the three control parameters introduced in the local interpolatory spline curves by Kochanck and Bartels [12]. We first analyze the general conditions for guaranteeing the G' continuity of the surface at corners where three, four, or five patches meet. The analysis of the continuity constraints reveals the remaining degrees of freedom which can be exploited for the control of the surface shape. The shape control parameters arc then introduced. Experimental results are provided. They show the efficiency of these parameters for an easy and intuitive control of the surface shape.
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.
Dynamic Management of 3D Scenes
(Eurographics Association, 1987) Hegron, Gerard
When simulating a moving observer or sensor in a 3D scene which contains a large number of objects, only the objects lying in the field of view or of interaction, named the local data base, have to be taken into account in order to decrease, at each step, computation time necessary for either image generation or various processings. This paper presents an algorithm which achieves the dynamic management of the local data base, that is to say which manages the set of objects which enter or leave the field of view of an observer (camera, sensor) during its displacement. This method consists, broadly, of the following two steps: a binary space partitioning of the 3D space is performed off-line from the object bounding boxes by means of planes perpendicular to the X, Y and Z axes and a subregion adjacency graph is created; the dynamic management of the local data base is achieved on-line by modelling the bounded bearing volume of the sensor by a cube of R "radius" (half-edge), and by using the adjacency graph, and inclusion and intersection criteria in order to exploit spatial and temporal coherences between each displacement. When the scene data base is very large, the dynamic management of the RAM memory can be done simultaneously by using this method reasoning from the bounding boxes of disjoined sub - scenes.
Unifying Vector and Polygon Algorithms for Scan Conversion and Clipping
(Eurographics Association, 1987) Kilgour, AIistair
In both scan conversion and clipping, algorithm for dealing with polygons are generally presented independently of those for vectors, although many of the operations performed are similar. This paper shows how polygon algorithms for both problems can be developed from the corresponding vector algorithm. As well as yielding a unification at the conceptual level, this approach can lead to reduced code size in graphics system implementation, and produces polygon algorithms which are comparable in both robustness and efficiency with those previously presented.
COLOUR SECTION
(Eurographics Association, 1987) -
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].
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.
Active-Ray Tracing for 3D Medical Imaging
(Eurographics Association, 1987) Trousset, Yves; Schmitt, Francis
Large quantities of three-dimensional (3D) information are produced by 3D medical imaging techniques such as CT and MRI, in the form of digital volumes (DV). We propose a new approach to help a human observer to visualize these volumes. This approach is based on the idea that, in order to achieve true user-interaction, segmentation and visualization should not be treated separately. This is achieved by introducing active ray tracing, a method inspired by ray tracing but working directely on unsegmented digital volumes. Segmentation takes place as the active rays penetrate through the volume.
A Window Managment System on Top of GKS
(Eurographics Association, 1987) Hartelt, Helga I.M.; Magalhaes, Leo Pini; Daltrini, Beatriz Mascia
This paper presents a Window Management System, GAV, which utilizes a GKS Graphics System as a supporting tool. GAV allows the definition, by the users (designers of application programs), of several areas of visualization in the same screen. Each of these areas is a workstation according to the concept of workstation established in GKS. GAV even allows different parts of application programs to be done by different users. These users can use the full set of GKS functions in each part, without worrying about the existence of the other parts, Finally, GAV allows the grouping of workstation in sets called screen configurations. Advantages and disadvantages of the adopted solution to the problem of constructing a Window Management System are discussed.
The Clockworks: An Object-Oriented Computer Animation System
(Eurographics Association, 1987) Breen, David E.; Getto, Phillip H.; Apodaca, Anthony A.; Schmidt, Daniel G.; Sarachan, Brion D.
The Clockworks is an object-oriented computer animation system developed at RPl's Center for Interactive Computer Graphics (CICG). The Clockworks has the ability to model and graphically simulate complex 3-D engineering processes, Its interactive capabilities also allow it be used as a design tool. Object-oriented concepts have been utilized in developing its high level architecture and its low level implementation. The Clockworks is defined as a collection of objects which communicate with the user and each other via messages. The actual implementation involved the creation of an object-oriented programming methodology using C and Unix. The complete system provides a rich research environment for exploring modelling, scripting and rendering. It also provides an interactive environment for design and a simulation environment for visual analysis of complex interacting structures.
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.
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.

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