Volume 09 (1990)
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Item Modelling Clip: Some More Results(Blackwell Publishing Ltd and the Eurographics Association, 1990) Hubl, Josef; Herman, IvanThe modedling clip of the PHIGS ISO Standard is mathematically analysed. The most important result of this analysis is the fact that the projective image of a modding clip body (that is a not necessarily bounded convex body in space) is simply the union of two convex bodies. Furthermore, it will also be proved that in some cases one of these two bodies is empty. This fact makes the implementation of the modelling clip fairly straightforward and makes it also possible to use all already existing results on clipping against general convex bodies without change.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 Computer Graphics and Computer-Aided Design Literature: A Keyword-Indexed Bibliography for the Year 1989(Blackwell Publishing Ltd and the Eurographics Association, 1990) Owen, JonItem 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 GosiP: A GKS3D Shell for PHIGS(Blackwell Publishing Ltd and the Eurographics Association, 1990) French, MichaelGosip is an implementation of a GKS-3D level 2c interface to PHIGS. It allows GKS applications to run on PHIGS platforms, offering performance and portability across a wide range of high-performance 3D workstations. Compatibility of the standards is reviewed. A selection of design solutions is given for the problems of error processing, non-retained primitives and attribute management. The concepts of Workstation Display Session and atmbute state are introduced. Some comments are made on implementation dependencies, performance and portability.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 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 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 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).Item Durer, Gaskets and Barnsley s Chaos Game(Blackwell Publishing Ltd and the Eurographics Association, 1990) Jones, HuwMichael 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.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 Eurographics(Blackwell Publishing Ltd and the Eurographics Association, 1990)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 Offers to EUROGRAPHICS Members(Blackwell Publishing Ltd and the Eurographics Association, 1990)Item 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 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 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.Item EDITORIAL(Blackwell Publishing Ltd and the Eurographics Association, 1990) Arnold, DavidItem 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 Calendar of Events(Blackwell Publishing Ltd and the Eurographics Association, 1990)