Volume 09 (1990)
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Item EURASIP Short Course Medical Imaging: Techniques and Trends(Blackwell Publishing Ltd and the Eurographics Association, 1990)Item Project DIGIS: Building Interactive Applications by Direct Manipulation(Blackwell Publishing Ltd and the Eurographics Association, 1990) Bos, Jan van den; Laffra, ChrisAbstractDIGIS is a design and implementation system for developers of general purpose interactive applications (IA). It is itself an interactive system that accomplishes its task by Direct Manipulation techniques, in principle without using a programming language. DIGIS is a generator in the form of a window-based workbench. It has two input sources. One is a toolkit of predetined interaction tools consisting of prototypes and instances. The other is the set of predetined application procedures thai make up the application part of the IA. The application procedures do not handle user input but may handle textual or graphical screen output. The task of the developer is to build the user interface by selecting the appropriate interaction tools. tailor them to the interface, and tie them to application procedures. This includes the visual representations of interaction tools, their prompts, echoes and feedback. In the process he maps user input to parameter lists for the application procedures, and return parameters to interface output. DIGIS will also support the detinition of composite input (interaction patterns such as sequences). Unix and X are the initiat operating environment, adaption of the input sources to PCTE. OSF/Motif, and Open Look is feasible and anticipated.The design of DIGIS is based on a hierarchical interaction model that is the second focus of this paper. The implementation will be done using PROCOL, a locally developed concurrent object-oriented language. which offers protocols that support composite input. The language is a superset of C, and therefore fully compatible with existing C libraries.ACM Categories and Subject Descriptors: D.2.2 [Software Engineering]: Tools and Techniques -user interfaces, programmer workbench-D.3.3 [Programming Language]: Language Constructs -input/output, programming structures-H.1.2 [Models and Principles]: User/Machine Systems -human factors-1.3.6 [Computer Graphics]: Methodology and Techniques - interaction techniques, ergonomics, languages:Item Shading and Shadowing with Linear Light Sources(Eurographics Association, 1990) Poulin, Pierre; Amanatides, JohnIn virtually all rendering systems, linear light sources are modeled with a series of point light sources that require considerable computing resources to produce realistic looking results. A general solution for shading surfaces illuminated by a linear light source is proposed. A formulation allowing for faster computation of the diffuse component of light reflection is derived. By assuming Phong's specular component, simple, inexpensive and convincing results are produced with the use of a Chebyshev approximation. A shadowing algorithm is also presented. As shadowing from linear light sources is expensive, two acceleration schemes, extended from ray tracing, are evaluated.Item Call for Participation: Computer Graphics and Education 91(Blackwell Publishing Ltd and the Eurographics Association, 1990)Item A Browser for Large Directed Graphs(Blackwell Publishing Ltd and the Eurographics Association, 1990) Bovey, J. D.The paper describes an experimental graph browsing tool which provides fast interactive browsing on very large graphs. The particular graph for which the program was developed is based on the distributed tile system of a group of workstations but there is no reason why the same techniques should not be used on graphs from other sources.Item END USER PROGRAMMING ENVIRONMENTS : INTERACTIVE PROGRAMMING-ON-EXAMPLE IN CAD PARAMETRIC DESIGN(Eurographics Association, 1990) Girard, P.; Pierra, G.; Guittet, L.In recent years, the number of computer end-users who do not know programming has increased rapidly. This new phenomenon has spurred a great deal of research about program design using very different approaches from the usual methods, which, as is well known, are very difficult to learn [1]. This research has touched on many programming fields : physical system simulation [2], graphical interface tailoring [3] and "macros" implementation [4] [5], data base access [6], lessons programming in Computer Aided Teaching [1] ... B.A. Myers [7] suggests a useful taxonomy for classifying these different systems. The three orthogonal criteria he uses define eight categories. A system is much more suitable for end-user programming when it is : - interactive, i.e. able to quickly echo the effect of one step of program designing, - graphic, or visual, i.e. allowing program design by commands working (at least) on a bi-dimensional environment, - associated with a running example, i.e. program designing uses values representing a running example of the program. The goal of this paper is twofold. On the one hand, it looks at a domain, rarely quoted in synthetic reviews [6] [7] [4], where these techniques are often used efficiently, and where end-user programming goes beyond the experimental phase : we are referring to parametric-design in Computer Aided Design (CAD). On the other hand, it presents a graphical interactive programming-on-examples system, named LIKE, which removes most of the problems pointed out by recent studies [7] [5].Item 3D MODELLING AND MOTION OF DEFORMABLE SOLIDS FROM 2D IMAGES(Eurographics Association, 1990) Neveu, Marc; Faudot, DominiqueOur work purpose is to elaborate a geometric and motional model for deformable solids, known only by a very small number of general crosssections images. We start from a generic 3D model of the studied solid we distort according to detected boundaries in the above mentioned images. To give the solid motion model, our work uses moving point constraints and inbetweening methods on an image sequence : we select keyframes on which we interpolate characteristic points. Then we use Coons patches to compute the inbetween frames and realize an animation? On an echocardiographic application, we obtained good results in the model precision and detected edges by image processing similar to cardiologists' hand drawn edges. Besides, the model distortion, characteristic points tracking and 2D motion simulation are encouraging, although improvements are necessary.Item TRIMO A Workstation-Based Interactive System for the Generation, Manipulation, and Display of Surfaces over Arbitrary Topological Meshes(Eurographics Association, 1990) Slusallek, Philipp B.; Seidel, Hans-PeterTRIMO has been designed as a workstation-based interactive system for the generation, manipulation, and display of surfaces over arbitrary toplogical meshes. In addition to rational tensor product Bezier and B-spline surfaces, TRIMO also supports piecewise rational triangular Bezier and B-patch surfaces. TRIMO has been implemented in C++ under the X Window System. Special emphasis has been given to a hierarchical data structure and to a menu-and-mouse-driven hierarchical user interface.Item KA?MOE: A Clausal Language for CAD MOdeling Systems with Morphological Constraints(Blackwell Publishing Ltd and the Eurographics Association, 1990) Milanese, VitalianoA declarative language (KA?MOE) for CAD-CAM modeling is presented. The language is designed to protect topological models constraints and guarantee their inheritance in complex entities built up from simpler ones. By itself, KA?MOE behaves as an evolution of Prolog, which is integrated with primitives for modularization and for privatizing modeling structures so as to guarantee interfacing the language with relational or deductive Data Bases.Item Hemi-Cube Ray-Tracing: A Method for Generating Soft Shadows(Eurographics Association, 1990) Meyer, UrsThis paper presents a new ray-tracing technique for generating soft shadows. The technique treats scenes consisting of light sources and opaque objects which are polygons or polyhedra of arbitrary shape and size. To determine the intensity at a point on a surface, the hemisphere is sampled extensively through the use of hemi-cubes. So-called item-buffer boxes, a combination of itembuffers and buffer boxes, are used to calculate ray intersections as well as to suppress image aliasing. Several methods for reducing aliasing caused by hemi-cubes are discussed. The uniform treatment of rays allows for a straightforward extension of the algorithm to produce fuzzy reflections. The success of the new technique depends on a fast implementation of a visible surface algorithm as provided by today’s high-end graphics workstations. The results are images of realistically illuminated synthetic environments.Item EG Call for Participation in the Eurographics Working Group on Relationships betwee image Synthesis and Analysis(Blackwell Publishing Ltd and the Eurographics Association, 1990)Item PRELOG - A SYSTEM FOR PRESENTING AND RENDERING LOGIC SPECIFICATIONS OF INTERACTIVE SYSTEMS(Eurographics Association, 1990) Johnson, C.W.; Harrison, M.D.Formal specifications provide the non-specialist with an extremely poor impression of what it would be like to interact with a computer system. Prototypes provide a far better impression of the ‘look and feel’ of possible implementations but lack the precision of more formal approaches. Unfortunately, specification and prototyping are typically treated as alternatives. If these two activities can be harnessed then the designer has a means of incorporating the user into systems design. Tools can ease the transition from specification to prototype by supporting the visualisation of a design in terms of graphical representations of the proposed system. This paper describes Prelog, a tool for Presenting and REndering LOGic specifications of interactive systems. Prelog supports the structured representation of interaction objects which describe virtual devices. Interaction objects support reasoning about prototypes because they provide a means of abstracting away from device dependent pragmatics which make renderings intractable.Item A Direct Manipulation Technique for Specifying 3D Object Transformations with a 2D Input Device(Blackwell Publishing Ltd and the Eurographics Association, 1990) Van Emmerik, Maarten J.G.M.A mechanism is presented for direct manipulation of 3D objects with a conventional 2D input device, such as a mouse. The user can define and modify a model by graphical interaction on a 3D perspective or parallel projection. A gestural interface technique enables the specification of 3D transformations (translation, rotation and scaling) by 2D pick and drag operations. Interaction is not restricted to single objects but can be applied to compound objects as well. The method described in this paper is an easy-to-understand 3D input technique which does not require any special hardware and is compatible with the designer s mental model of object manipulation.Item Report on the First Eurographics Workshop on Object-Oriented Graphics(Blackwell Publishing Ltd and the Eurographics Association, 1990) Otten, DaanItem Yugraph 90(Blackwell Publishing Ltd and the Eurographics Association, 1990) Duce, D.A.Item Fast Rendering of Arbitrary Distributed Volume Densities(Eurographics Association, 1990) Sakas, GeorgiosIn recent years a number of techniques have been developed for rendering volume effects (haze, fog, smoke, clouds, etc.). These techniques are either time consuming (ray-tracing, radiosity) or do not account for arbitrary density distributions. In this paper we briefly analyze the physics of illuminations of volumes and we propose several simplifications suitable. for computer graphics practice. In particular, we present a method for rendering arbitrary distributions by means of projective polygonal rendering and solid texturing techniques in approximately the time needed for a usual polygonal object. The proposed method provides good results in a fraction of the computing time required for approaches like ray-tracing or radiosity. Solid texturing is used to define the density distribution and a point-sampling Monte-Carlo method with user-adjustable accuracy to evaluate the illumination model along the path through the volume. Thus, a trade-off between computing time and picture quality exists. With this technique one can move through or around the volume and to place objects and/or light sources in the volume. By means of rendering methods like shadowing polyhedra, objects can cast shadows on the volume and/or the volume can shadow the ground.Item The Implementation of a 2D Convex Hull Algorithm Using Perturbation(Blackwell Publishing Ltd and the Eurographics Association, 1990) Day, A.M.This paper discusses the problem of geometric degeneracies and outlines possible solutions when converting geometric algorithms into practice. It concentrates on the application of one of the suggested solutions, a perturbation technique, to a 2D convex hull program. An outline of the relevant theory and its conversion into practice is given. Experimental results are presented and discussed.Item COMPUTER GRAPHICS PROFESSIONALS(Blackwell Publishing Ltd and the Eurographics Association, 1990)Item Tightly-Coupled Multiprocessing for a Global Illumination Algorithm(Eurographics Association, 1990) Drettakis, George; Fiume, Eugene; Fournier, AlainA prevailing trend in computer graphics is the demand for increasingly realistic global illumination models and algorithms. Despite the fact that the computational power of uniprocessors is increasing, it is clear that much greater computational power is required to achieve satisfactory throughput. The obvious next step is to employ parallel processing. The advent of affordable, tightly-coupled multiprocessors makes such an approach widely available for the first time. We propose a tightly-coupled parallel decomposition of FIAT, a global illumination algorithm, based on space subdivision and power balancing, that we have recently developed. This algorithm is somewhat ambitious, and severely strains existing uniprocessor environments. We discuss techniques for reducing memory contention and maximising parallelism. We also present empirical data on the actual performance of our parallel solution. Since the model of parallel computation that we have employed is likely to persist for quite some time, our techniques are applicable to other algorithms based on space subdivision.Item A Prolog Rule-Based System for cartographic Name Placement(Blackwell Publishing Ltd and the Eurographics Association, 1990) Cook, Anthony C.; Jones, Christopher B.Manual name placement is an extremely time consuming task and has been one of the most difficult aspects of the map production process to automate. It is complicated by the large number of rules required for the selection and placement of names. A hybrid Prolog/Fortrau rule-based system is described for placing names on a variety of map types. It uses a set of Prolog primitives for spatial search and name placement operations. The Ordnance Surveyâ s 1:625000 scale digital dataset has been used to illustrate the application of rules for the selection of labels as well as for controlling their size and orientation. The application to other types of maps and diagrams is also briefly described.