EG1990 Proceedings (Technical Papers)
Permanent URI for this collection
A PIPELINED-PARALLEL ARCHITECTURE FOR 2.5-D BATCH RASTERIZERS
[meta data] [files:
Birk, Yitzhak
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Mccrossin, lames M .
Relaxed Multi-rate Systolic Array Graphics Engine for High Resolution Real-time Computer Graphics
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Jayasinghe, J.A.K.S.
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Herrmann, O.E.
Some Possible Applications of CORDIC Processors in Computer Graphics
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Kocsis, F.
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Böhme, J.F.
TRIMO A Workstation-Based Interactive System for the Generation, Manipulation, and Display of Surfaces over Arbitrary Topological Meshes
[meta data] [files:
Slusallek, Philipp B.
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Seidel, Hans-Peter
Factoring a Homogeneous Transformation for a more Efficient Graphics Pipeline
[meta data] [files:
Abi-Ezzi, Salim S.
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Wozny, Michael J.
INTERPOLATING CURVE NETWORKS WITH NEW BLENDING PATCHES
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Saitoh, Tsuyoshi
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Hosaka, Mamoru
AN OBJECT ORIENTED APPROACH TO ENSURE PORTABILITY OF CAD STANDARD PARTS LIBRARIES
[meta data] [files:
Pierra, Guy
PRESENTATION OF PRODUCT MODEL DATA -AN INTERFACE BETWEEN GRAPHICS AND CAD-
[meta data] [files:
Klement, Kornel
COLOR IMAGE RECONSTRUCTION FROM NONUNIFORM SPARSE SAMPLES USING A THIN PLATE MODEL
[meta data] [files:
Metaxas, Dimitris
;
Milios, Evangelos
ADAPTIVE POLYGONIZATION OF IMPLICIT SURFACES USING SIMPLICIAL DECOMPOSITION AND BOUNDARY CONSTRAINTS
[meta data] [files:
Velho, Luiz
Joint Editing with DAPHNE A System integrating CGMs into SGML Documents
[meta data] [files:
Scheller, Angela
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Fuhrhop, Christian
DaScript Plus A PostScript Extension supporting 3D Graphics with 2D Functionality
[meta data] [files:
Samara, Veronika
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Schaub, Jutta
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Noll, Stefan
Shading and Shadowing with Linear Light Sources
[meta data] [files:
Poulin, Pierre
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Amanatides, John
END USER PROGRAMMING ENVIRONMENTS : INTERACTIVE PROGRAMMING-ON-EXAMPLE IN CAD PARAMETRIC DESIGN
[meta data] [files:
Girard, P.
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Pierra, G.
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Guittet, L.
3D MODELLING AND MOTION OF DEFORMABLE SOLIDS FROM 2D IMAGES
[meta data] [files:
Neveu, Marc
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Faudot, Dominique
Tightly-Coupled Multiprocessing for a Global Illumination Algorithm
[meta data] [files:
Drettakis, George
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Fiume, Eugene
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Fournier, Alain
EDEN - AN EDITOR ENVIRONMENT FOR OBJECT- ORIENTED GRAPHICS EDITING
[meta data] [files:
Fellner, Dieter W.
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Kappe, F.
A Stochastic Functional Approach for Terrain Modeling
[meta data] [files:
Dong, Jun-Cai
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Peng, Qun-Sheng
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Liang, You-Dong
CHARACTERIZATION OF TOPOGRAPHIC SURFACES
[meta data] [files:
Falcidieno, Bianca
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Spagnuolo, Michela
AUTOMATIC MODELLING OF NATURAL SCENES FOR GENERATING SYNTHETIC MOVIES
[meta data] [files:
Koch, Reinhard
AN APPROACH TO IMPROVE THE RELIABILITY OF BOOLEAN OPERATION ON A PAIR OF POLYHEDRA
[meta data] [files:
Li, Xinyou
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Sun, Jiaguang
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Tang, Zesheng
On Formulation and Display for Visualizing Features and Evaluating Quality of Free-form Surfaces
[meta data] [files:
Higashi, Masatake
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Kushimoto, Takuya
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Hosaka, Mamoru
RECONSTRUCTION OF A BOUNDARY REPRESENTATION MODEL FROM THREE ORTHOGRAPHIC PROJECTIONS: A GEOMETRICAL APPROACH
[meta data] [files:
Müller, A.
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Richter, D.
The Architecture of a Prototype System for Drawing Data Structures
[meta data] [files:
Ding, Chen
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Mateti, Prabhaker
HYPERIMAGES - AN ALTERNATIVE TO THE CONVENTIONAL DIGITAL IMAGES
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Bieri, Hanspeter
PRELOG - A SYSTEM FOR PRESENTING AND RENDERING LOGIC SPECIFICATIONS OF INTERACTIVE SYSTEMS
[meta data] [files:
Johnson, C.W.
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Harrison, M.D.
TRIES: DATA STRUCTURES BASED ON BINARY REPRESENTATION FOR RAY TRACING
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Thirion, Jean-Philippe
AN APPROACH TO THE FORMAL SPECIFICATION OF THE COMPONENTS OF AN INTERACTION
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Faconti, Giorgio P.
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Paterno, Fabio
OPTIMIZATION OF THE BINARY SPACE PARTITION ALGORITHM (BSP) FOR THE VISUALIZATION OF DYNAMIC SCENES
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Torres, Enric
INTERACTIVE RAY-TRACING FOR IMAGE PRODUCTION WITH INCREASING REALISM
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Sousa, A. Augusto
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Costa, Antonio M. C.
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Ferreira, Fernando N.
RENDERING MIRAGES AND OTHER ATMOSPHERIC PHENOMENA
[meta data] [files:
Berger, Marc
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Levit, Nancy
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Trout, Terry
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Recent Submissions
Item A PIPELINED-PARALLEL ARCHITECTURE FOR 2.5-D BATCH RASTERIZERS(Eurographics Association, 1990) Birk, Yitzhak; Mccrossin, lames M .The emergence of application programs that take advantage of highly expressive page description languages has sharply increased the amount of computing required for rasterizing an average page, and single-microprocessor rasterizers presently limit the performance of most printers. The pipelined-parallel architecture employs intrapage parallelism to permit the construction of cost-effective multiprocessor rasterizers for computer-driven high-function printers. Initially, blocks of datastream that are independent in terms of datastream environment are identified by a sequential “scanner“. They are then processed in parallel, and each is converted into a multitude of simple, regular objects, which are sorted by “geographical” target on the page into “bins” that correspond to a predetermined partition of the page. Sequencing information is retained. The bins are then processed in parallel (sequentially within each bin) to build the full-page bitmap. The phases are pipelined for increased performance. By breaking rasterization into two main stages and parallelizing along a different dimension in each of them, we are able to attain intrapage parallelism while maintaining correctness, even with non commutative merging modes, such as “overpaint”.Item Relaxed Multi-rate Systolic Array Graphics Engine for High Resolution Real-time Computer Graphics(Eurographics Association, 1990) Jayasinghe, J.A.K.S.; Herrmann, O.E.Generation of realistic images while supporting faster interaction is a topic in computer graphics research which has drawn considerable attention. Conventional frame buffer has been identified as a major bottle-neck for faster interaction [11]. Systolic Array Graphics (SAG) engines have been proposed to meet the above requirements by replacing the conventional frame buffer by a processor array. The speed limitations of the hardware restrict the use of SAG engines to displays resolutions of order 512x512 pixels when they are refreshed at 50Hz frame rate. In this paper we present an architectural solution to reduce the speed limitations of hardware. In the new architecture, a faster video stream is achieved by decoupling the speeds of the video and instruction streams by a multi-rate clocking scheme. We relax some timing constrains of the faster video stream by space domain multiplexing, i.e. using more wires.Item Colour Illustrations(Eurographics Association, 1990) -Item Some Possible Applications of CORDIC Processors in Computer Graphics(Eurographics Association, 1990) Kocsis, F.; Böhme, J.F.Some application possibilities of an ASIC-type processing element, the CORDIC processor, in computer graphics are discussed. CORDIC-based solutions are derived for some basic computer geometry computations: conversion between coordinate systems, rotations, point-line and pointplane distance calculations, ray-patch intersection computations, intensity and scalar product calculations. The main results are the following. Some basic computational tasks of computer graphics can be advantageously implemented using CORDIC arithmetic. The CORDIC processing element can serve as a building block even in high performance parallel graphics systems. A short example compares the possibilities of the CORDIC-based solution to the performance of the well-known polygon rendering with Pixel-planes.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 Cross Scanline Algorithm(Eurographics Association, 1990) Tanaka, Toshimitsu; Talcahashi, TokiichiroThis paper proposes a new hidden surface removal algorithm which is based on the scanline algorithm but scans in two directions, horizontally and vertically. Named the cross scanline algorithm, it can efficiently detect all polygons and calculate their exact projected areas in each pixel even if the polygons are much smaller than the pixel. Comparisons with the regular sub-scanlines algorithm show that high quality anti-aliased images can be generated.Item Factoring a Homogeneous Transformation for a more Efficient Graphics Pipeline(Eurographics Association, 1990) Abi-Ezzi, Salim S.; Wozny, Michael J.We identify an intermediate coordinate system situated between world coordinates and display coordinates, which exhibits unique features for lighting calculations and for clipping in homogeneous coordinates. Our key contribution is an algorithm for extracting such a coordinate system from a homogeneous viewing transformation that relates WC to DC. The algorithm is based on factoring the transformation into a product of a Euclidean factor and a sparse (computationally cheap) but non- Euclidean factor. A particularly strong application of the proposed technique is the graphical processing of curved surface primitives, such as what is needed in the PHIGS PLUS viewing pipeline. Furthermore, in PHIGS PLUS the graphical data is retained by the graphics system, therefore, it is possible to perform the factoring of the viewing transformation at creation time, and to take advantage of this factored form at traversal time.Item INTERPOLATING CURVE NETWORKS WITH NEW BLENDING PATCHES(Eurographics Association, 1990) Saitoh, Tsuyoshi; Hosaka, MamoruThis paper describes methods of c o n s t r u c t i n g s u r f a c e patches which s a t i s f y independently given boundary conditions on a l l i t s four or t h r e e s i d e s . A patch c o n s i s t s of two p a r t s : one i s a patch s a t i s f y i n g a t l e a s t p o s i t i o n a l condition of the boundary curves, and the other gives n u l l position vectors and independent i t s f i r s t and second d e r i v a t i v e vectors on t h e i r boundaries. The l a t t e r i s used for compensating d e r i v a t i v e vectors t o s a t i s f y given boundary conditions. A network o f curves whose meshes are four or t h r e e s i d e s can be i n t e r p o l a t e d smoothly with patches of t h i s type.Item AN INTERACTIVE DEBUGGER FOR PHIGS(Eurographics Association, 1990) Howard, T.L.J.; Hewitt, W.T.; Larkin, S.The Programmer’s Hierarchical Interactive Graphics System (PHIGS) is an International Standard for integrating application modelling and interactive computer graphics. With PHIGS, application models are constructed from hierarchical data structures called structure networks, which may be edited interactively. While structure networks are in principle straightforward to create, organising and managing them correctly is in practice a much more difficult proposition. One of the main difficulties arises from the atomic nature of the traversal process by which structure networks are interpreted for display. This paper draws an analogy between structure network traversal and programming language execution, and presents the PHIGS Debugger, a development tool for PHIGS applications. The PHIGS Debugger supports interactive incremental traversal of structure networks and debugging of the PHIGS Centralised Structure Store, and is a component of the PHIGS Toolkit, an emerging set of portable integrated tools for PHIGS environments. 1Item AN OBJECT ORIENTED APPROACH TO ENSURE PORTABILITY OF CAD STANDARD PARTS LIBRARIES(Eurographics Association, 1990) Pierra, GuyThe integration, in CAD systems, of libraries of standard parts is often considered to be one of the key factors for increasing productivity of Computer Aided Design [1] [2] [3]. These libraries must be able to integrate homogeneously both the standard components external to the firm (standardized items and suppliers' standards) and internal firm-specific standards.Item COLOR SHADING IN 2D SYNTHESIS(Eurographics Association, 1990) Bourdin, J.J.; Braquelaire, J.P.In interactive 2D synthesis applications, features for filling regions are generally elementary (uniform colouring, filling with a regular pattern.. .). Interactive design of 2D colour shadings raises two major problems: the difficulty of specifying a shading precisely, and the rapidity of related filling algorithms. In this paper, we propose a model to specify 2D colour shading of a region by decomposing it into two components: a support describing the “shape” of the shading, and a colouring function defined on this shape. We then present an incremental algorithm for support generation.Item PRESENTATION OF PRODUCT MODEL DATA -AN INTERFACE BETWEEN GRAPHICS AND CAD-(Eurographics Association, 1990) Klement, KornelThe associative visualization of revisable product model data is of great importance for the usefulness and the acceptance of standards in the field of CAD data exchange. The outlines of a separate Presentation module which meets the resulting requirements are developed in this paper. Thereby Presentation is defined as the sum of interfacing areas between Graphics and CAD with regard to product model data visualization. The basic concepts of Presentation are introduced in a top-down approach starting with a global view on Graphics, CAD and standardization efforts in these domains. In a last refinement the linkages of product model data and graphical data primitives and attributes are examined especially those for representing product shape and annot ation information.Item A shadow algorithm for CSG(Eurographics Association, 1990) Jansen, Frederik W.; van der Zalm, Arno N. T.An algorithm is presented for constructing shadow volumes for CSG objects. For each primitive solid, the algorithm calculates a tree of shadow volumes to model the shadows generated by the shadow-generating parts of the boundary of the primitive. The shadow of the complete CSG object is the union of these shadow trees. An implementation of the algorithm is described for a scan-line display algorithm for CSG objects with polygonal primitives.Item COLOR IMAGE RECONSTRUCTION FROM NONUNIFORM SPARSE SAMPLES USING A THIN PLATE MODEL(Eurographics Association, 1990) Metaxas, Dimitris; Milios, EvangelosIn this paper we solve the problem of reconstructing a color image from sparse, noisy, and nonuniformly distributed color measurements. We apply a method for reconstructing a surface from sparse depth measurements to each of the R, G and B components of the color data, by treating each as a surface, with depth measurements being the R, G and B values. We apply this method to the reconstruction of nonuniformly distributed sparse color data from even 12.5% of the pixels, if no discontinuities are given and from 6.25% of the pixels, if the discontinuities are given. Also we present results of reconstructing a corrupted version of the original image with Gaussian noise of zero-mean and standard deviation 30 from 25% of the data, for color levels between 0 and 255. The applicability of the method is independent of the choice of the color space used.Item ADAPTIVE POLYGONIZATION OF IMPLICIT SURFACES USING SIMPLICIAL DECOMPOSITION AND BOUNDARY CONSTRAINTS(Eurographics Association, 1990) Velho, LuizThis paper presents a method to generate a polygonal approximation of implicit surfaces. Space partitioning by simplicial decomposition is used to sample the surface, which provides an unambiguous framework for polygon creation. Simplices are adaptively subdivided in order to faithfully represent the surface with a minimum number of elements. The space subdivision is done recursively, without the need of additional data structures to keep track of the process, which usually results in large memory requirements. Furthermore, boundary constraints are imposed on the surface tesselation to overcome the problem of discontinuities usually associated with adaptive methods.Item Joint Editing with DAPHNE A System integrating CGMs into SGML Documents(Eurographics Association, 1990) Scheller, Angela; Fuhrhop, ChristianThis paper presents DAPHNE, a document processing system for joint editing within the German Research Network DFN. DAPHNE is based on two international standards in the area of document and graphics processing, the Standard Generalized Markup Language SGML and the Computer Graphics Metafile CGM. The functionality of DAPHNE is described with special emphasis on integrating graphics in documents, as well as the experience with the system in a pilot phase and future plans for extensions.Item DaScript Plus A PostScript Extension supporting 3D Graphics with 2D Functionality(Eurographics Association, 1990) Samara, Veronika; Schaub, Jutta; Noll, StefanIn the world of electronic publishing page description languages describe a very powerful interface between document creation software and raster output devices. 3D graphics systems offer the possibility to give a more or less realistic description of the 3D world. The current page description languages support 2D graphics only. However, documents also need graphics descriptions that contain 3D information. DaScript Plus provides a sufficient mapping of the PHIGS PLUS functionality. It allows the device independent incorporation of realistic 3D pictures within documents, and their high quality output on laser printers and type setters.Item A PROPOSAL FOR A POSTSCRIPT 3D EXTENSION(Eurographics Association, 1990) Cesar, Christian L.A 3D graphics extension to the PostScript language is proposed. The extension maintains the same graphic programming style that characterizes the language's 2D environment. The extensions proposed cover 3D graphics state, 3D coordinate system and transformations, and 3D path, surface and solid volume construction operators. The proposed extensions cover mostly 3D object modelling issues. Rendering extensions are not covered. Consideration is given to how the semantics of 2D graphic operators may be extended into 3D.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 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 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 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 EDEN - AN EDITOR ENVIRONMENT FOR OBJECT- ORIENTED GRAPHICS EDITING(Eurographics Association, 1990) Fellner, Dieter W.; Kappe, F.Systems allowing the creation and manipulation of graphical information (so-called Graphic Editors) have become essential in various fields of applications. At the same time the typical user of such a system has changed. Not computer experts, but designers, secretaries, technicians, teachers etc. are today's typical users of computer graphics, mostly on microcomputers. Obviously it would be desirable to have a common concept of graphics editing covering many applications. The purpose of this paper is a brief survey of the EDEN project started at the IIGb in 1987: the motivation for the project, the major steps, results, current status and future work is presented here. EDEN (short for EDitor ENvironnient) is a generic concept for object-oriented graphics editing, providing device independence at the workstation and graphics output level as well as an application independent file-format for the storage and exchange between different graphics applications.Item AN INTERPOLATION METHOD FOR STOCHASTIC MODELS(Eurographics Association, 1990) Ramstein, G.This paper presents a method using stochastic models for the simulation and interpolation of natural phenomena. These models are based on the general concept of random functions with stationary increments, to which the fbm belongs. The consideration of this family of stochastic processes, instead of just considering the fractal one, leads to greater diversity and realism. Another way to enhance realism is to combine analysis and interpolation. We suggest calculating the stochastic parameters from the analysis of existing natural surfaces and to use them as input data for the interpolation algorithm. We propose an interpolation algorithm which respects the stochastic behavior of this class of processes. This method provides a better understanding of the interpolation mechanisms. One can thus study the influence of the stochastic parameters and the data points localization on the interpolated valued. A final advantage of this algorithm is to interpolate surfaces defined by irregular data points. This type of representation is actually often encountered in cartography (contour lines, spot elevations, ...). This possibility is also very interesting for image synthesis applications, since it allows specifying with ease the rough shape of a given image.Item A Stochastic Functional Approach for Terrain Modeling(Eurographics Association, 1990) Dong, Jun-Cai; Peng, Qun-Sheng; Liang, You-DongA new functional modeling approach - -functional modeling, is presented to depict various classes of natural terrain. While this approach possesses the functions of several previous methods, it does not suffer the drawbacks of creases or periodity. By choosing the control parameters properly, our approach can easily generate different terrains related to various smoothness, such as cliffs,fractal mountains and smooth terrains. It can also simulate the natural weathering processes as from the cliff to the fractal mountain and to the smooth terrain not only in the appearance but also in quantity. And it is capable of modeling the terrain whose "rock bed” and "rock quilt" are associated with different smoothness.Item Mathematical Models for Semi-globalized Spectral Synthesis(Eurographics Association, 1990) Anjyo, Ken-ichiSemi-globalized spectral synthesis is proposed as a new tool for three-dimensional scene description consisting of many natural objects, such as terrain, sea waves, and clouds. The method is based on the mathematical theory of spectral representation of stochastic processes. In this paper, mathematical models in the method are presented under rigorous formulation and then their stochastic properties are shown. Some simple techniques for practical improvements of the original models in depicting scenes are also explained along with the examples obtained.Item A Constraint-Based Figure-Maker(Eurographics Association, 1990) Kalra, Devendra; Barr, Alan H.In this paper, we describe a new kind of constraint-based figure-maker for parametrically defined curves. Figures are made by defining objects and imposing constraints on their geometric behavior. We present a formulation of constraints as three ways in which two scalar real valued functions may be compared. This lets us specify equality, optimality and inequality constraints. We also introduce the mechanism of connectors. Connectors are used to connect various geometric entities through constraints. Behavior of connectors depends only on the local properties of curves. Connectors remove the need for an object to know about the kinds of constraints or the kinds of other objects it is connected to in order to act to satisfy a constraint. This makes for a very manageable and scalable program as the number of objects and constraints grows. An objects is modified in response to deviation of its state from the desired state specified through constraints. We have implemented some general low-level methods of specifying and satisfying constraints. These basic mechanisms can be used as an assembly language and combined hierarchically to define very general constraints.Item CHARACTERIZATION OF TOPOGRAPHIC SURFACES(Eurographics Association, 1990) Falcidieno, Bianca; Spagnuolo, MichelaThis paper presents a method for extracting and representang features of a topographic surface approximated by triangular tales An algorithm as given which computes characteristic regions (a. e. regions having concave, convex or planar shape), characteristic lanes (ridges, ravines, generic creases) and characteristic points (maxima, minima, saddle points) The result as a new surface description an terms of an attributed hypergraph representation called Characteristic Region Configuration Graph, an which characteristic regions are considered the basic describers of the surface shape and correspond to the nodes of the graph, whale the arcs and hyperarcs represent the relationships between regions derived from characteristic lanes and pointsItem AUTOMATIC MODELLING OF NATURAL SCENES FOR GENERATING SYNTHETIC MOVIES(Eurographics Association, 1990) Koch, ReinhardA model based analysis by synthesis algorithm is presented. It combines image analysis and synthesis techniques to obtain a three dimensional scene description and to generate synthetic movies out of that scene description. A 3D model world is generated automatically out of TV image sequences containing 3D objects with naturally textured surfaces. The objects are projected into the 2D image domain and compared with subsequent images of the sequence to be analyzed. Differences between input and synthesized images serve to extract shape, motion and surface texture parameters and to adapt the 3D model scene. The model data base can be manipulated to generate synthetic movies with highly realistic, natural looking images.Item AN APPROACH TO IMPROVE THE RELIABILITY OF BOOLEAN OPERATION ON A PAIR OF POLYHEDRA(Eurographics Association, 1990) Li, Xinyou; Sun, Jiaguang; Tang, ZeshengIt is essential and pressing to improve reliability of Boolean operations in geometric modelling systems. The Boolean operations in commercial systems now available are not reliable enough because of numerical calculation errors. Numerical calculation errors hinder us from determining set membership classifications exactly. Some classifications are ambiguous because they are dependent on adopted computing tolerance. Thereby interrelated classifications may conflict with each other and it is very difficult to get correct results of Boolean operations In many cases. We introduce a reliable Boolean operation algorithm which solves the conflicts among interrelated classifications before implementation of Boolean operation by use of reasoning technique. The algorithm has replaced the modelling module of the geometric modelling system GENS 2.0 to form a new system GENS 2.1 on Apollo and Sun workstations. According to tests and compared with Geomod 3.9 and I/ENS, GENS 2.1 is much more reliable.Item On Formulation and Display for Visualizing Features and Evaluating Quality of Free-form Surfaces(Eurographics Association, 1990) Higashi, Masatake; Kushimoto, Takuya; Hosaka, MamoruFor evaluating quality of free-form surfaces and visualizing their features, various curves on a surface, which characterize its properties, are defined and their equations are deduced. Newly introduced curves include those of equi-gradient, silhouette, highlight and a locus of points of extremum gradient on contour curves, loci of points of extremum principal curvature on lines of curvature. The objectives of these curves and their uses are described. Other curves such as contour curves, its orthogonal ones, loci of points of zero curvatures, and lines of curvature as well as umbilics are also treated. Displays of these curves are shown.Item RECONSTRUCTION OF A BOUNDARY REPRESENTATION MODEL FROM THREE ORTHOGRAPHIC PROJECTIONS: A GEOMETRICAL APPROACH(Eurographics Association, 1990) Müller, A.; Richter, D.A method is presented for creating a boundary representation model from engineering projections. Although the topic of this reconstruction method has been studied for a few years the fundamentals of reconstruction are rather scanty. In this paper we provide a combined geometrical and topological approach to reconstruction. All considerations are restricted to polyhedral objects that consist of only one shell and edges belonging to exactly two faces. The reconstruction problem is mathematically described by introducing dome definitions, and criteria are derived that allow to solve the reconstruction problem for the restricted class of objects provided that the three given projections define a three-dimensional object unambiguously.Item The Architecture of a Prototype System for Drawing Data Structures(Eurographics Association, 1990) Ding, Chen; Mateti, PrabhakerAutomatic drawing of aesthetically pleasing data structure diagrams is a challenging problem which has attracted much research attention. In building such a system, we are confronted with four basic problems: (1) proper user involvement, (2) good user customization facilities, (3) aesthetics, and (4) efficiency. Each of the above problems has been attacked separately in the past. In this paper, we describe a prototype which brings the above four issues together and builds a powerful, usable, and natural automatic diagram drawing system.Item A RASTER GRAPHICS APPROACH TO FLOW VISUALIZATION(Eurographics Association, 1990) van Wijk, Jarke J.Most techniques for the visualization of fluid dynamics are based on vector graphics. Streamlines or arrows are calculated as vectors, which are converted to pixels for display on raster devices. The techniques described here show that it can be advantageous to use a raster graphics approach to the visualization of fluid dynamics. The properties of raster devices can be exploited better, while also anti-aliasing can be realized in a simple way. Three techniques for visualization of two-dimensional flow are described: for the calculation and display of streamlines; an alternative technique based on particle systems for capturing flow in a still image; and for the creation of animations using particles.Item HYPERIMAGES - AN ALTERNATIVE TO THE CONVENTIONAL DIGITAL IMAGES(Eurographics Association, 1990) Bieri, HanspeterHyperimages represent a variation of the conventional digital images which implies pixels of different dimensions within the same image. The extent of a hyperimage is the disjoint union of all pixel extents it contains, which are relatively open unit cubes with respect to the euclidean topology of the underlying space. This approach is independent of any specific dimension of image and space, respectively, and allows strict partitioning of images into subimages, not just subdividing. The applicability of hyperimages is illustrated by a number of algorithms useful in image analysis.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 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 TRIES: DATA STRUCTURES BASED ON BINARY REPRESENTATION FOR RAY TRACING(Eurographics Association, 1990) Thirion, Jean-PhilippeTries are data structures used for multidimensional searching. We introduce an original method to build Tries for a set of convex polyhedra, weshow how Tries can be used for Ray tracing and we compare them with other data structures. Their advantages are mainly compactness of memory representation and fast building of the structure due to simple binary operations. Tries also accelerate the Ray tracing process compared to other octree-like structures. Furthermore, they are easy to implement because they are a unified approach to multidimensional problems. Finally we show experimental results to compare them with other data structures used for image synthesis.Item WSE: An Environment for Exploring Window Strategies(Eurographics Association, 1990) Koivunen, Marja-RiittaThis paper describes Window Strategies Environment (WSE), which is an environment for exploring different window strategies. It is a tool for developers who want to implement and explore different window strategies easily. WSE uses object oriented methodology offering four hierarchical levels for customizing predefined window strategies. The highest level is a simple modifiable language for describing a few essential commands for each strategy. This kind of tool helps the developers to implement and test several approaches to window strategies before selecting one. Also it encourages the developer to direct some of the power to the user so that she can customize the user interface by selecting a preferred strategy from a predefined set of strategies. The environment is implemented under NeWS 1.1 [Sun87] window system for SUN 4/110. It uses Smalltalk style object oriented class mechanisms [Goldberg83, Densmore] offered by NeWS but none of the original NeWS toolkits. 1. IntroductionItem AN APPROACH TO THE FORMAL SPECIFICATION OF THE COMPONENTS OF AN INTERACTION(Eurographics Association, 1990) Faconti, Giorgio P.; Paterno, FabioIn this paper we present the preliminary results from a work aiming to the formal specification af a model suitable for the description of interactive graphics program within the framework defined by the Reference Model for Computer Graphics Systems, actually under development within the International Organization for Standardization. The architecture defined by the Computer Graphics Reference Model, at its actual state of development, is shortly presented with particular attention paid to the concepts used in the paper. Following, the components of a basic interaction are identified and described as a set of independent communicating processes, referred to as an interactor. The relationships between interactors are described in terms of the communication between their component processes by using ECSP-like constructs.Item OPTIMIZATION OF THE BINARY SPACE PARTITION ALGORITHM (BSP) FOR THE VISUALIZATION OF DYNAMIC SCENES(Eurographics Association, 1990) Torres, EnricThis paper describes an improvement of the generation of BSP trees and its utilization in the visualization of dynamic polyhedral scenes. Dynamic BSP trees, a new six-level structure, are presented. Dynamic BSP trees are based on the inclusion of five different kinds of auxiliary planes in the generation of BSP trees. These planes are included in the structure before the polygons of the scene. In most cases the inclusion of polygons is performed in zero time by making use of precomputed BSP trees of the single objects of the scene. Dynamic BSP trees lead to a very significant reduction in the computation time of the BSP tree building and the posibility of its utilization at interactive speeds for complex scenes where both viewpoint and objects are dynamic. Description and pseudocode of the generation and dynamic modification management algorithms are included, along with a set of examples from a real implementation.Item THREE-DIMENSIONAL TEXTURING USING LATTICES(Eurographics Association, 1990) Lewis, Robert R.This paper describes a way to perform realistic three-dimensional texturing of ray-traced objects with irregular surfaces. Such texturing has teen done in the past with texture mapping, particle systems, or volumetric methods. We propose an alternative to these called a lattice. Lattices work as fast but inexact ray tracers. As long as lattices are used for small objects, though, the inexactness doesn't show on the scale of the display, and the result is acceptable. The paper shows how lattices can be integrated with a more traditional ray tracer, with several examples. Time and memory space considerations are major constraints on lattices, preventing widespread practical application at the present time. The paper discusses these limitations and how they might be reduced.Item INTERACTIVE RAY-TRACING FOR IMAGE PRODUCTION WITH INCREASING REALISM(Eurographics Association, 1990) Sousa, A. Augusto; Costa, Antonio M. C.; Ferreira, Fernando N.The generation of highly realistic images using the conventional Ray-Tracing algorithm, in CAD environments, is totally out of the question if we consider the interactive requirements of most CAD systems. In this paper, some ideas are presented that can lead to an interactive environment, based on images produced by Ray-Tracing. The new concepts of Increasing Realism and Interactive Ray-Tracing are introduced, new problems related to them are detailed and some solutions suggested. In short, we present a new version of Ray-Tracing that is considerably different from conventional ones, because it is interactively controlled by the user, who can at any time modify the evolution of the image realism.Item RENDERING MIRAGES AND OTHER ATMOSPHERIC PHENOMENA(Eurographics Association, 1990) Berger, Marc; Levit, Nancy; Trout, TerryThe past few years have seen some very impressive results in rendering natural phenomena. This paper addresses the problem of how to model and render optical illusions brought about by atmospheric refraction. Refraction of light in non-homogeneous media causes light rays to bend continuously, producing curved ray paths. Tracing these rays and determining their intersections with complex objects creates several difficulties. Our approach is to send rays through a virtual atmospheric object consisting of multiple air layers arranged in horizontal strata, with each layer having its own refractive index. This technique allows the use of line segments to trace curved paths. We give examples of applications to mirage effects.