EG1990 Proceedings (Technical Papers)

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A Stochastic Functional Approach for Terrain Modeling
(Eurographics Association, 1990) Dong, Jun-Cai; Peng, Qun-Sheng; Liang, You-Dong
A 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.
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.
OPTIMIZATION OF THE BINARY SPACE PARTITION ALGORITHM (BSP) FOR THE VISUALIZATION OF DYNAMIC SCENES
(Eurographics Association, 1990) Torres, Enric
This 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.
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.
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.
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”.
WSE: An Environment for Exploring Window Strategies
(Eurographics Association, 1990) Koivunen, Marja-Riitta
This 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. Introduction
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.
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.
Mathematical Models for Semi-globalized Spectral Synthesis
(Eurographics Association, 1990) Anjyo, Ken-ichi
Semi-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.
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.
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.
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.
Tightly-Coupled Multiprocessing for a Global Illumination Algorithm
(Eurographics Association, 1990) Drettakis, George; Fiume, Eugene; Fournier, Alain
A 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.
TRIES: DATA STRUCTURES BASED ON BINARY REPRESENTATION FOR RAY TRACING
(Eurographics Association, 1990) Thirion, Jean-Philippe
Tries 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.
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.
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].
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.
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-Peter
TRIMO 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.
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.

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