EG1990 Proceedings (Technical Papers)

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3D MODELLING AND MOTION OF DEFORMABLE SOLIDS FROM 2D IMAGES
(Eurographics Association, 1990) Neveu, Marc; Faudot, Dominique
Our 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.
ADAPTIVE POLYGONIZATION OF IMPLICIT SURFACES USING SIMPLICIAL DECOMPOSITION AND BOUNDARY CONSTRAINTS
(Eurographics Association, 1990) Velho, Luiz
This 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.
AN APPROACH TO IMPROVE THE RELIABILITY OF BOOLEAN OPERATION ON A PAIR OF POLYHEDRA
(Eurographics Association, 1990) Li, Xinyou; Sun, Jiaguang; Tang, Zesheng
It 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.
AN APPROACH TO THE FORMAL SPECIFICATION OF THE COMPONENTS OF AN INTERACTION
(Eurographics Association, 1990) Faconti, Giorgio P.; Paterno, Fabio
In 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.
The Architecture of a Prototype System for Drawing Data Structures
(Eurographics Association, 1990) Ding, Chen; Mateti, Prabhaker
Automatic 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.
AUTOMATIC MODELLING OF NATURAL SCENES FOR GENERATING SYNTHETIC MOVIES
(Eurographics Association, 1990) Koch, Reinhard
A 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.
CHARACTERIZATION OF TOPOGRAPHIC SURFACES
(Eurographics Association, 1990) Falcidieno, Bianca; Spagnuolo, Michela
This 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 points
COLOR IMAGE RECONSTRUCTION FROM NONUNIFORM SPARSE SAMPLES USING A THIN PLATE MODEL
(Eurographics Association, 1990) Metaxas, Dimitris; Milios, Evangelos
In 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.
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.
Colour Illustrations
(Eurographics Association, 1990) -
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.
Cross Scanline Algorithm
(Eurographics Association, 1990) Tanaka, Toshimitsu; Talcahashi, Tokiichiro
This 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.
DaScript Plus A PostScript Extension supporting 3D Graphics with 2D Functionality
(Eurographics Association, 1990) Samara, Veronika; Schaub, Jutta; Noll, Stefan
In 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.
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.
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].
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.
Fast Rendering of Arbitrary Distributed Volume Densities
(Eurographics Association, 1990) Sakas, Georgios
In 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.
Hemi-Cube Ray-Tracing: A Method for Generating Soft Shadows
(Eurographics Association, 1990) Meyer, Urs
This 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.
HYPERIMAGES - AN ALTERNATIVE TO THE CONVENTIONAL DIGITAL IMAGES
(Eurographics Association, 1990) Bieri, Hanspeter
Hyperimages 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.
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. 1

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