EG1987 Proceedings (Technical Papers)

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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].
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.
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.
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.
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.
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.
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.
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.
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.
Splines for Engineers
(Eurographics Association, 1987) Ohlin, S.C.
This paper introduces the concept of interpolation consistency. It is claimed that this property is an essential one for splines that are intended for use in Computer Aided Design. Consistency is defined as the property of an interpolation algorithm that, if the given set of points is extended by any point on the interpolated curve, the algorithm applied to the extended set of points will yield exactly the same curve as before. A clear distinction is made between function interpolation, where y is a function of x, and curve interpolation, where x and y are Cartesian coordinates in the geometric plane. The class of consistent curve interpolating planear splines that corresponds to cubic function interpolation is discussed in some detail and includes the Cornu spiral, the lemniscate, and the tension-free mechanical spline. Next the class that corresponds to pentic function interpolation is considered, and an efficient algorithm is presented for the calculation of one such spline, a planar spline where the curvature is a cubic polynomial in the arclength. This algorithm produces curves where the curvature is, loosely speaking, as constant as possible. Some examples illustrating the desirable properties of this spline are given.
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.
Viz: A Production System Based User Interface Management System
(Eurographics Association, 1987) van Harmelen, Mark; Wilson, Stephanie M.
A production system based User Interface Management System (UIMS) is discussed. The UIMS, called Viz, has been designed and implemented in a windowed workstation environment, and (a) capitalises on the graphical facilities of the workstation while (b) being designed for both textual and graphical applications. The paper considers interaction, the appearance of Viz generated interfaces, and dialogue descriptions which parameterise Viz.
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 Temporal Scripting Language for Object-Oriented Animation
(Eurographics Association, 1987) Fiume, E.; Tsichritzis, D.; Dami, L.
Object orientation and concurrency are inherent to computer animation. Since the pieces of an animation can come from various media such as computer-generated imagery, video, and sound, the case for object orientation is all the stronger. However, languages for expressing the temporal co-ordination of animated objects have been slow in coming. We present such a language in this paper. Since the movements that an animated object can perform are also encapsulated as objects in our system, the scripting language can also be used to specify motion co-ordination. Such \u2018 motion objects\u201d can be applied to any animated object. The syntax, semantics, and implementation of this language will be described, and we shall show how to specify device-independent computer animation.
An Interactive Graphic Simulator for the Teaching of Fibrendoscopic Techniques
(Eurographics Association, 1987) Gillies, Duncan; Williams, Christopher
A simulator has been designed and implemented for teaching the skills required for fibrendoscopic investigation of the colon. The student using the simulator manipulates a dummy endoscope control head in which the rotary and linear movements are converted to voltages and interfaced to the computer via analogue to digital converters. The simulator is based on a three dimensional computer model of the colon and endoscope. The program reads the endoscope controls, determines the position of the tip of the endoscope, and using this as viewpoint draws the appropriate view. In the worst case, the whole cycle takes 0.185 seconds on an ordinary IBM PC, giving a frame rate of just under 6/sec.
Parallel Graphical Output from Dialogue Cells
(Eurographics Association, 1987) Ten Hagen, P.J.W.; Schouten, H.J.
A system that accepts and processes graphical output from parallel processes using a single workstation, and its use in a User Interface Management System called Dialogue Cells, is described. It allows for a programmer to easily, concisely and precisely describe pictures and operations on them in a highly interactive environment. Each parallel process can do output independently, but pictures can also be moved from one process to another. Each process has its own graphical output environment. The description and implementation of the system is based on GKS.
A Metric for Computing Adaptive Detail in Animated Scenes Using Object-Oriented Programming
(Eurographics Association, 1987) Blake, Edwin H.
A spatial metric for adapting the level of detail in a modelled object to achieve a convincing degree of realism on a display is formulated and illustrated with a simple implementation. This spatial metric is designed to be of most benefit to animations of natural environments. The metric can operate with a wide range of different representations: the essential requirement being that an abstract data structure with hierarchical levels of detail is formulated. Such models are most easily implemented with procedural recursive representations, such as fractals. The actor/message passing approach to modelling animation is adopted as being most appropriate and intuitive when simulating the objects and events of the natural environment. This object-oriented programming method also gives a uniform abstract interface to differing data representations. A stick figure, which has a non-uniform hierarchical structure, was chosen for the first implementation. This prototype was implemented in Smalltalk which had to be extended to include a part-whole (assembly-subassembly) hierarchy. The need to extend the metric to include temporal (dynamic) trade-offs is discussed.
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.

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