Volume 10 (1991)

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An Algorithm of hidden Surface Removal based on Frame-To- Frame Coherence
(Eurographics Association, 1991) Tost, Daniele
Frame-to-frame coherence capitalizes on the continuity existing between successive frames in order to predict the visibility of the scene at a given instant on the basis of its visibility at the previous instant. It is shown that all the algorithms based on frame-to-frame coherence share a common model and involve similar data structures. This model is used as a framework for a discussion of possible frame-to-frame coherence algorithms. A specific solution based on a partition of the image space into several 2-D regions is then presented. A temporal graph of the depth priority relationship of the objects is first computed in a pre-process along with a temporal BSP tree of each object. In the first frame a total traversal of both data structures is required in order to establish the priority list of the faces of the scenes. In successive frames, the priority list is easily updated with partial traversals and with no geometrical computations. The complexity of the proposed algorithm is discussed. Some examples are presented with comments on the results of their implementation.
Animation of Landscapes Using Satellite Imagery
(Eurographics Association, 1991) Geymayer, Barbara; Prantl, Manfred; Müller-Seelich, Heimo; Tabatabai, Behnam
The paper presents methods to animate synthetic landscapes. The modeling of the landscape, the interactive specification of the flight path and the simulation of an explosion are described. The landscape is visualized by superimposing texture information computed from different satellite data onto a digital elevation model. A pyramid data structure is used to store the texture and digital elevation model data in different resolutions. This approach allows the generation of pictures with constant data density in an efficient way. The flight path is modeled interactively using a wireframe representation of the landscape. An explosion is simulated using physically modeled trajectories of the exploding parts. The approach is explained in the context of the “ERZBERG” animation in which an impressive flight through a valley towards the exploding Erzberg mountain has been generated.
At Last an ISO C Binding of GKS
(Blackwell Science Ltd and the Eurographics Association, 1991) Bakker, Miente
The C4 bindings of GKS1 and other semantic computer graphics standards like GKS-3D2 and PHIGS3 are long overdue. While GKS was completed in 1985 and GKS-3D2 (and PHIGS3) became an international standard in 1988, none of their C bindings could be standardized, for the simple reason that the C language itself was not a standard. Instead, a host of de facto GKS/C bindings9 appeared.This paper will give the flavour of the ISO C binding5,6 of GKS- the main features will be outlined.1983 CR Categories: D.3.0,I.3.0,I.3.4.
Block Iterations in the Complex Plane
(Blackwell Science Ltd and the Eurographics Association, 1991) Szyszkowicz, Mieczyslaw
In this note we propose a new technique for execution of the feedback process z ? z2+ c. The presented method is used to discover a family of sets in the complex plane.
C 2 Gregory patch
(Eurographics Association, 1991) Miuraa, Kenjiro Takai; Wangb, Kuo-King
G² continuity of free-form surfaces is sometimes very important in engineering applications. The conditions for G2 continuity between two Bezier patches has been studied and methods developed to ensure such continuity. However, certain restrictions on the shapes of such patches arise within the Bezier-patch formulation. The Gregory patch is a kind of free-form surface patch which is an extension of the Bezier patch such that cross-boundary first derivatives can be specified without restrictions on the compatibility condition. In this paper, we extend the idea of the Gregory patch and develop a formulation for the C² Gregory patch. The properties of the C² Gregory patch are discussed as well as its connection with a Bezier patch and a G² continuous interpolation method based upon such patches.
Cartographic Algorithms: Problems of Implementation and Evaluation and the Impact of Digitising Errors
(Blackwell Science Ltd and the Eurographics Association, 1991) Visvalingam, M.; Whyatt, J.D.
Cartographic generalisation remains one of the outstanding challenges in digital cartography and Geographical Information Systems (GIS). It is generally assumed that computerisation will lead to the removal of spurious variability introduced by the subjective decisions of individual cartographers. This paper demonstrates through an in-depth study of a line simplification algorithm that computerisation introduces its own sources of variability. The algorithm, referred to as the Douglas-Peucker algorithm in cartographic literature, has been widely used in image processing, pattern recognition and GIS for some 20 years. An analysis of this algorithm and study of some implementations in wide use identify the presence of variability resulting from the subjective decisions of software implementors. Spurious variability in software complicates the processes of evaluation and comparison of alternative algorithms for cartographic tasks. No doubt, variability in implementation could be removed by rigorous study and specification of algorithms. Such future work must address the presence of digitising error in cartographic data. Our analysis suggests that it would be difficult to adapt the Douglas-Peucker algorithm to cope with digitising error without altering the method.
Classification of Quad-encoding Techniques
(Blackwell Science Ltd and the Eurographics Association, 1991) Hunter, Andrew; Willis, Philip
Many quad encoding technique have been published previously, using a variety of approaches to the different facets of quad storage, representation and manipulation. We review the major classes and identify three parameters which distinguish them. These are then used explicitly to classify a large number of published methods, with short discussion on each. In doing this we are also able to highlight some new approaches, to identify rare examples which escape the classification, and to suggest approaches to choosing a method to suit a given application.
Colour Illustrations
(Eurographics Association, 1991) -
Combining Volume Rendering with Line and Surface Rendering
(Eurographics Association, 1991) Frühauf, Martin
Volume data is discrete sampled data in the three-dimensional space. Volume rendering is defined as volume visualization directly from volume primitives and not via surface primitives. Geometric objects are represented as a list of vertices and connecting lines or surface patches. Independent algorithms for rendering the two different categories of data are used. The system, proposed here, combines the results of the different algorithms in one image. A set of common parameters influencing both rendering algorithms and ensuring the consistency of the resulting merged image is identified. A volume rendering algorithm capable to produce the information to be merged is described in detail. The system is able to handle opaque and translucent objects by merging lists of image space elements. The independence of the both rendering modules allows to employ a wide range of algorithms for rendering of geometric objects, even rendering in hardware.
Computational Physics : A Modeler - Simulator for animated physical Objects
(Eurographics Association, 1991) Luciani, Annie; Jimenez, Stephane; Florens, Jean Loup; Cadoz, Claude; Raoult, Olivier
Physical modeling for animation is now firmly established. The present aim is to design and build a structured and well-defined tool rather than merely specific algorithms to simulate physical knowledge. We will first define the basic functions of a modeler - simulator for physical modeling which enables operator gestural control, and where the simulation processes are real time oriented. These constraints cannot be achieved by any kind of models and algorithms. Concerning the theoretical elements, the choice of the underlying Physics and the categorization of interactions will be presented. We will then introduce the Cordis-Anima system, its constructive langage, its real time simulator and its force feedback gestural transducers. Finally, we will describe, with some examples, how we model, simulate and manipulate a large variety of physical objects and scenes with our system.
Computer Art from Numerical Methods
(Blackwell Science Ltd and the Eurographics Association, 1991) Szyszkowicz, Mieczyslaw
Zero-finding methods, Euler s method and the numerical algorithms elaborated as package subroutines are studied by using a computer graphics technique. The patterns obtained show chaotic behaviour (science) and beauty of numerical algorithms (art).
Configurable Representations in Feature-based Modelling
(Eurographics Association, 1991) Falcidieno, B.; Giannini, F.; Porzia, C.; Spagnuolo, M.
A double description is proposed for the representation of a feature-based model which supports the distinction between form and functionality. This description consists of a primary representation in terms of geometric features ( geometric feature graph) and a set of feature-based representations which are created by transformations that are viewpoint specific and apply to the geometric feature graph.
A constraint-based UIMS using graph unification
(Eurographics Association, 1991) Samuel, J. F.
This paper describes an experimental UIMS developed to investigate methods of combining and reusing objects within a constraint-based system. A novel approach based on graph-unification facilitated the definition of composite objects and allowed behaviours to be transferred easily from one object to another. A very simple form of local propagation was used as the constraint satisfaction mechanism, which, as well as being fast, could also cope with cyclic dependencies. This method used a time-stamping method which made it possible to express time-dependency in the constraints. The system has features from both class-based and prototype-based object-oriented languages. Dynamic modification of objects can be performed rapidly enough for interactive control. Interfaces built with the system include a variety of 'standard' user interface objects such as sliders as well as a number of physical simulations utilising time-dependent constraints.
Construction Techniques of Graphic, Direct-Manipulation User Interfaces
(Eurographics Association, 1991) Preea, Wolfgang; Pornberger, Gustav; Sikora, Hermann
This paper deals with human-computer interaction in several ways. On the one hand it presents the roots of interactive, graphic user interfaces and how such interfaces are implemented on the abstraction level of programming languages: The construction of graphic, direct-manipulation interfaces with conventional programming techniques is compared with an object-oriented approach based on powerful class libraries (called user interface application frameworks). Although application frameworks substantially ease the building of highly interactive applications the abstraction level is considered to be too low to support prototyping such interfaces in a comfortable way. Hence we portray DICE1 (Dynamic Interface Creation Environment), a tool for prototyping graphic user interfaces implemented itself in an object-oriented manner. In particular this paper discusses the question of how dynamic behavior can be added to a user interface prototype. It also presents a useful and powerful way to combine conventionally developed and object-oriented software systems.
Constructive Cubes: CSG Evaluation For Display Using Discrete 3-D Scalar Data Sets
(Eurographics Association, 1991) Breen, David E.
The algorithm presented in this paper converts a CSG model into a representation for interactive display on an engineering workstation. Called Constructive Cubes, the algorithm extends the standard CSG-point classification algorithm and then employs a popular isosurface generation algorithm, Marching Cubes, to generate a list of polygons that approximates the surface of a CSG model. The polygons may then be interactively displayed, shaded and inspected on a workstation. The algorithm has many advantages over other CSG algorithms. It is straightforward to implement, requiring no complex surface intersection calculations. The algorithm provides an inherent flexibility that allows a user to balance the time/quality trade-off. It is designed to take advantage of current and future advances in both visualization and engineering workstation design.
Constructive Page Description Opening Up the Prepress World
(Eurographics Association, 1991) Samara, Veronika; Wiedling, Hans-Peter
Constructive Page Description (CPD) is an overall approach allowing different kinds of data to be exchanged between a variety of systems and manipulated in arbitrary system environments. Fully changeable pages, which keep information for modification as long as necessary, as well as fully assembled pages, ready for the printing process, can be constructed by the use of CPD. Moreover, descriptions of data as well as operations can be distributed, and so allow the use of networking facilities. CPD is thereby very flexible in handling, combining, and exchanging data and operations used in the construction of pages. In sum, CPD helps bridge the gap between the printing and the computer graphics world; it is an approach to lead prepress towards an open system architecture.
Continuation Methods for Approximating Isovalued Complex Surfaces
(Eurographics Association, 1991) Zahlten, Cornelia; Jürgens, Hartmut
Basically there are two different approaches for rendering isovalued surfaces in 3D space: projection methods and surface reconstruction. We are discussing two algorithms of the second kind. Both use continuation methods for efficiently scanning an isovalued surface. A simplicial pivoting algorithm by Ralf Widmann which continues earlier work of E. L. Allgower et al., is compared to an approach which is based on subdividing space into cubes. The algorithms determine all simplices or cubes intersecting the surface and then generate an oriented polygonal approximation. For demonstration and comparison we use several fractal and some smooth surfaces. These surfaces are implicitely defined by a function, but it is also possible to apply both methods to 3D volume data.
Control Points for Multivariate B-Spline Surfaces over Arbitrary Triangulations
(Blackwell Science Ltd and the Eurographics Association, 1991) Fong, Philip; Seidel, Hans-Peter
This paper describes first results of a test implementation that implements the new multivariate B-splines as recently developed by Dahmen et al. 10for quadratics and cubics. The surface scheme is based on blending functions and control points and allows the modelling of Ck? 1 -continuous piecewise polynomial surfaces of degree k over arbitrary triangulations of the parameter plane. The surface scheme exhibits both affine invariance and the convex hull property, and the control points can be used to manipulate the shape of the surface locally. Additional degrees of freedom in the underlying knot net allow for the modelling of discontinuities. Explicit formulas are given for the representation of polynomials and piecewise polynomials as linear combinations of B-splines.
A DDA Octree Traversal Algorithm for Ray Tracing
(Eurographics Association, 1991) Sung, Kelvin
A spatial traversal algorithm for ray tracing that combines the memory efficiency of an octree and the traversal speed of a uniform voxel space is described. A new octree representation is proposed and an implementation of the algorithm based on that representation is presented. Performance of the implementation and other spatial structure traversal algorithms are examined.
Declarative Graphics And Dynamic Interaction
(Eurographics Association, 1991) Johnson, C.W.; Harrison, M.D.
First order logic provides a means of integrating the specification and prototyping of interactive systems. It can describe graphical images in a declarative and order independent manner. It supports the definition of abstract devices which avoid the complexity of representing ‘raw’ input from a variety of physical devices. The following pages show how such techniques must be extended in order to prototype and reason about dynamic interaction with graphical interfaces. The incorporation of a temporal ordering into logical specifications provides a means of describing changes in the structure of graphical images. It can also identify the sequencing which may be implicit within specifications of interactive dialogues. This paper describes how PRELOG, a tool for Presenting and REndering LOGic specifications of interactive systems, has been extended to include a temporal logic interpreter.

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