Volume 09 (1990)

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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.
EDITORIAL
(Blackwell Publishing Ltd and the Eurographics Association, 1990) Arnold, David
An Approach to Hierarchical Input Devices
(Blackwell Publishing Ltd and the Eurographics Association, 1990) Duce, D. A.; Liere, R van; Hagen, P.J.W. ten
This paper shows how a formal description of the GKS input model can be extended to include hierarchically structured input devices
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.
IFSs and Interactive Image Synthesis
(Blackwell Publishing Ltd and the Eurographics Association, 1990) Horn, Alastair N.
Deterministic Fractal geometry provides a framework for describing both the geometry of man-made structures and the geometry of nature.Certain deterministic Fractals which exist in the plane may be"partitioned" into a number of"tiles" equivalent to the whole under some geometric mapping. We term such Fractals self-tiling images.We describe a scheme called Iterated Function Systems (IFSs) which an represent self-tiling images. IFSs make explicit the mappings which take a self-tiling image into its tiles.We show how a self-tiling image exists as the limit of both random and deterministic processes based upon its associated IFS, and exploit massive SIMD parallelism in image generation on the AMT DAP.We also attempt to answer the question:"Can one synthesise images by the interactive graphical manipulation of a representation of IFSs?", and present our interactive system for image synthesis (ISIS).
Durer, Gaskets and Barnsley s Chaos Game
(Blackwell Publishing Ltd and the Eurographics Association, 1990) Jones, Huw
Michael Barnsley has generated the Sierpinski triangle or gasket using his"Chaos Game", a technique for generating random points within a fractal object. Extensions of the method are discussed to generate fractal"gaskets" based on other regular polygons. One such figure resembles a tiling pattern based on pentagons known to Albrecht Durer almost 500 years ago.
Report of the Eurographics UK Conference
(Blackwell Publishing Ltd and the Eurographics Association, 1990) Mumford, Anne
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.
Calendar of Events
(Blackwell Publishing Ltd and the Eurographics Association, 1990)
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”.
Eurographics
(Blackwell Publishing Ltd and the Eurographics Association, 1990)
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
Offers to EUROGRAPHICS Members
(Blackwell Publishing Ltd and the Eurographics Association, 1990)
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.

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