Volume 11 (1992)

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Rendering NURB Regions For 2D Animation
(Blackwell Science Ltd and the Eurographics Association, 1992) Willis, Philip; Oddy, Robert
We describe an accurate method of rendering by scan-conversion of closed regions bounded by NURBs, with particular comments on its application to computer-based 2D animation. It is shown that the method is fast, analytically accurate, and can be readily extended to include anti-aliasing and clipping.
Realistic Generation and Real Time Animation of Images of the Human Colon
(Blackwell Science Ltd and the Eurographics Association, 1992) Haritsis, Angelo; Gillies, Duncan; Williams, Christopher
A simulator has been built to teach doctors the skill of handling a flexible endoscope for gastrointestinal investigations. Trainees use a dummy endoscope in which the control actions are transduced into voltages and sensed by the computer. The simulator computes the position and viewing direction of the endoscope within an internal model of the human colon. Then a renderer draws the view, reproducing as far as possible what would be seen during a real colonoscopy. Since the system must generate at least ten frames per second for realistic animation, standard rendering techniques, such as ray tracing, could not be used. Consequently a new method was devised, based on identifying coherent regions along each scan line which can be rendered by table lookup. The method allows shaded Lambertian surfaces to be drawn at a frame rate of 15 per second, using modest computing resources. Although several approximations were required in the analysis, the computer images of the internal surfaces of the human colon present a high degree of visual realism.
A Computer Model For Pinscreen Simulation: A New Animation Paradigm
(Blackwell Science Ltd and the Eurographics Association, 1992) Lopes, Pedro Faria; Gomes, Mario Rui
Actual computer image and motion synthesis paradigms are presented in order to introduce a new computer animation paradigm that simulates the traditional pinscreen animation technique. Pinscreen is a very particular and difficult device that enables a"chiaroscuro" approach to image synthesis. The paper describes the traditional pinscreen technique, the way it is operated, results and related difficulties. An extended computer model, including colour and time extensions, to simulate the pinscreen is presented. Results achieved with vector and raster approaches are discussed. Advantages and possibilities of the method when compared with the traditional method and the problems that arise from this technique will also be explained. Finally current and future work is referenced.
X: Why Z?
(Blackwell Science Ltd and the Eurographics Association, 1992) Bowen, Jonathan P.
Window management systems are now used extensively for user interfaces to computer systems. In particular, X11 has come to dominate the workstation market as a widely accepted industry standard on many different hardware platforms. However, no formal standard currently exists for this window system, both in terms of an international standards body (although this is being addressed), and in terms of a precise (mathematical) specification of what the interface is intended to do. This paper advocates the use of a formal notation to describe such an important system to avoid ambiguity and undesired or unintended variations between different implementations of the same system.Theformal notation used for demonstration purposes, Z, is based on set theory, and has been developed at the Programming Research Group in Oxford.
Composing Hierarchically Structured Images
(Blackwell Science Ltd and the Eurographics Association, 1992) Patterson, John W.; Cockton, Gilbert
This paper begins by examining the classical raster-based composition model, establishing its weakness, and developing a new composition algebra based on line drawing. It then examines the role of composition in the Hierarchical Display Model, demonstrates that the forms of composition assumed in this model are inadequate to deal correctly with the interactions of two-dimensional representations of three-dimensional objects, and shows that our composition algebra resolves this difficulty. The composition steps required can be packaged with the use of a single attribute which constrains the apparent order of composition. This attribute is associated with the object which is to be taken out of order , obviating any needsfor layers.
Combined Direct and Inverse Kinematic Control for Articulated Figure Motion Editing
(Blackwell Science Ltd and the Eurographics Association, 1992) Boulic, Ronan; Thalmann, Daniel
A new approach for the animation of articulated figures is presented. We propose a system of articulated motion design which offers a full combination of both direct and inverse kinematic control of the joint parameters. Such an approach allows an animator to specify interactively goal-directed changes to existing sampled joint motions, resulting in a more general and expressive class of possible joint motions. The fundamental idea is to consider any desired-joint space motion as a reference model inserted into the secondary task of an inverse kinematic control scheme. This approach profits from the use of half-space Cartesian main tasks in conjunction with a parallel control of the articulated figure called the coach-trainee metaphor. In addition, a transition function is introduced so as to guarantee the continuity of the control. The resulting combined kinematic control scheme leads to a new methodology of joint-motion editing which is demonstrated through the improvement of a functional model of human walking.
A Simple Description of Complex Curves
(Blackwell Science Ltd and the Eurographics Association, 1992) Bouras, A.; Shariat, B.; Vandorpe, D.
In this paper, we propose a method of complex curves description, based on the use of standard primitives (curve arcs), inscribed in including boxes. This method simplifies the creation steps (curves are not defined with the help of control points), and the manipulation steps (using including boxes).This study constitutes an extension to our descriptive universal language, named"G", which is used in a general desig n environment, permitting the integration of various models (solids1, polyhedrons2, surfaces3 and fractals), in order to offer the adequate tools adapted to the problems to be solved, in a unique modeller.
A CAD System for Color Design of a Car
(Blackwell Science Ltd and the Eurographics Association, 1992) Oshima, Tetsuya; Yuasa, Shinji; Sakanoshita, Ken-ichi; Ogata, Yoshinori
We have developed a color CAD system which enables a color designer to evaluate and create body colors of a car on a graphic display and put this system into practical use. The system has three features- generating realistic images comparable to photography to satisfy the car designer s needs, through close analysis of the physical phenomena taking place in the real environment, reproducing the desired colors very accurately on a CRT monitor, through analysis of the CRT colorimetric characteristics of reproducing the specified colors in response to the input signals, and utilizing a parallel computer to generate realistic images at a high speed and to control colors through interactive operation. Application of the CAD system reported here to the field of color design made it possible to fully evaluate and create body colors by means of computer graphics, replacing the conventional method which requires the painting of clay models or prototype cars.
Affine Texture Mapping and Antialiasing Using Integer Arithmetic
(Blackwell Science Ltd and the Eurographics Association, 1992) Nehlig, P.; Ghazanfarpour, D.
Texture mapping techniques are very useful for generating more realistic images. However, texture compression, generally induced by geometric transformations, is at the origin of aliasing artifacts especially the well-known"moire" patterns. Two discrete affine texture mapping methods based exclusively on integer arithmetic are presented here. This original approach of discrete affine mapping is adequate for antialiasing in the case of compressed textures.
The Input Model of Standard Graphics Systems Revisited by Formal Specification
(Blackwell Science Ltd and the Eurographics Association, 1992) Faconti, Giorgio P.; Zani, Nicola; Paterno , Fabio
This paper describes the specification of an input model for graphics systems. The initial aim of the work reported in this paper was to revise the input model adopted by graphics standards by means of formal specification techniques in order to acquire a deep knowledge of its capabilities, to eventually discover errors and to develop improvements. Taking into account similar works done in this area by others and considering a number of major issues related to input recently discussed within the graphics community, a new model is being proposed that addresses the very key concepts of parallelism, extensibility and reconfigurability. The model is based upon composition operations defined over basic components specified as a set of concurrent processes. Composition operations and process definitions have been formally specified by using the LOTOS notation and investigated by means of the LOTOS Interactive Tools Environment. In the first part of the paper, the input model of graphics standards is shortly examined in the light of the results so far achieved by related works on formal specification of computer graphics systems. Subsequently, an improved model is presented. Finally, its capability of simulating the traditional operating modes of logical input devices and a methodology for defining new operating modes is demonstrated.
A line clipping algorithm and its analysis
(Blackwell Science Ltd and the Eurographics Association, 1992) Krammer, Gergely
One of the classical problems of Computer Graphics: line clipping against a rectangle is revisited. Coordinate raster refinement and some unusual forms of the parametric equation of the line are used to develop formulae for a line clipping algorithm. The algorithm is first presented in a form, where clarity of presentation is the prime concern. It is then transformed into one big nested branch, which after optimisation is assumed to be the most efficient form with a heavy cost on size. It is assumed that any mathematical consideration of the clipping problem would after a similar optimisation lead to a branching structure of equal complexity and speed. Line clipping thus belongs to the class of problems for which after a proper mathematical and logical analysis automatic program transformations may do the rest.This work has been supported by a grant from the Hungarian Academy of Sciences, Project No. OTKA 2572/1991
Stochastic Motion-Motion Under the Influence of Wind
(Blackwell Science Ltd and the Eurographics Association, 1992) Shinya, Mikio; Fournier, Alain
Stochastic approaches are very effective for modelling natural phenomena. This paper presents a motion model based on a stochastic process as well as physics, and proposes motion synthesis techniques for stochastic motion-motion under the influence of wind.The motion synthesis process is modelled by a cascade system of three components: wind model, dynamic model, and deformation model. Wind models produce spatio-temporal wind velocity fields using the power spectrum and auto-correlation of wind, just like fractal geometry. Dynamic models describe the dynamic response of the systems, using equation systems or response functions. Deformation models produce deformed shapes of objects according to the geometric models of the objects and the results of the dynamic systems.The biggest advantage of the model is its generality and consistency. The model is applicable to most of the existing trees and grass models, including structural models, particle systems, impressionist models, and 3D texture. It is demonstrated that the coupling of stochastic approaches and physically-based approaches can synthesize realistic motion of trees, grass and snow with modest computational cost.
Two-manifold cell-decomposition of r-sets.
(Blackwell Science Ltd and the Eurographics Association, 1992) Falcidieno, Bianca; Ratto, Ornella
This paper discusses the relationships studied between manifold solids and r-sets by defining an r-set as a decomposition in two-manifold cells. This decomposition is represented as a graph (Two-manifold Cell Decomposition graph TCD) in which each node corresponds to a 2 manifold component of the regular set, while each arc or hyperarc defines a non-manifold adjacency between components. The TCD model and data structure encoding it were designed in order to be compatible with a traditional boundary architecture.
Formal Specification in the Revision of GKS: An Illustrative Example
(Blackwell Science Ltd and the Eurographics Association, 1992) Duce, D.A.; Damnjanovic, L.B.
The first ISO/IEC standard for computer graphics, the Graphical Kernel System (GKS) was published in August 1985. In accordance with ISO/IEC procedures, GKS is now being reviewed and revised. This paper describes how formal specification techniques are being used by the authors to analyse key parts of proposals being made for changes to the framework of GKS to bring the standard into line with the requirements of applications and the operating environment likely to be found in the mid-1990 s.
The Graphical Translation of English Text into Signed English in the Hand Sign Translator System
(Blackwell Science Ltd and the Eurographics Association, 1992) Holden, E.J.; Roy, G.G.
Signed English is a manual interpretation of English using fingerspelling and signs. A prototype of the Hand Sign Translator (HST) system was developed to graphically translate English into Signed English, using two-handed animation. The HST consists of a practical interface that aims to help users learn Signed English, and the translation process where English text is transformed into a series of images that represent corresponding signs. This paper describes the translation process which involves two stages- the input environment and the animation process. The input environment consists of text analysis in order to extract corresponding kinematic data from the database, named English-Sign Dictionary (ESD). The data is then used as an input to the animation process, Firstly, the skeleton models of keyframe images and their in-between poses are calculated. Secondly, appropriate volume models are applied in order to surround the surface of skin. Then the shapes that are suitable for painting are generated, and finally images are drawn and rendered using a smooth animation technique.
A Run-Length Slice Line Drawing Algorithm without Division Operations
(Blackwell Science Ltd and the Eurographics Association, 1992) Fung, Khun Yee; Nicholl, Tina M.; Dewdney, A. K.
Equidistant Smoothing of Polyhedra with Arbitrary Topologies
(Blackwell Science Ltd and the Eurographics Association, 1992) Ma, Lizhuang; Liang, Youdong; Peng, Qunsheng
Smoothing of polyhedron with arbitrary topology is an important issue in CAGD and CAD/CAM, but so far it is deemed to be difficult to smooth the complex corners of a polyhedron. In this paper, the concept of distance surfaces of a surface and a solid is introduced, and the incisive properties of such surfaces are addressed which provide a theoretical foundation for modifying a general corner. The method is based on making constricted volume and the maximum distance the volume can be constricted is given too. It is shown that by the proposed method in this paper any polyhedron can be G1 smoothed with quadraic and, sometimes toroidal surfaces. The new approach is suitable for engineering design and NC machining. The associated algorithm based on the classification theorem of corners is simple, fast and robust.
Geometric and Group-theoretic Methods for Computer Graphic Studies of Islamic Symmetric Patterns
(Blackwell Science Ltd and the Eurographics Association, 1992) Abas, S. J.; Salman, A.
Over the last several years the authors have used computer graphics to generate, study and analyze more than 300 Islamic geometrical repeat patterns. These patterns offer a rich source for exploitation by artists and are also of interest to mathematicians, crystallographers, architects, archaeologists and others. They can serve as elegant test beds for research into hierarchical programming and texture mapping. The paper discusses the evolution of classical geometric methods for Islamic patterns and goes on to develop algorithms based on group theory for efficient generation of all crystallographic repeat patterns using modern computer graphics.
An Open Model for Hypermedia and Its Application to Geographical Information Systems
(Blackwell Science Ltd and the Eurographics Association, 1992) Hall, W.; Simmons, D.
This paper describes the design and implementation of a multimedia information management environment that is based on an open model for hypermedia. The model, known as Microcosm, is currently implemented in Microsoft Windows and supports many different media types. The open nature of the model and the separation of the links from the data, allows links to be applied across any application running under Windows or the OS/2 version 2 desktop, thus creating a truly integrated environment. One example, which is, discussed in the paper, is the integration of a hypermedia database with a geographical information system. The paper also discusses the application of novel interfaces to dynamic media within a hypermedia system, including the use of moving icons (micons).
Area Sampling Buffer: Tracing Rays with Z-Buffer Hardware
(Blackwell Science Ltd and the Eurographics Association, 1992) Sung, Kelvin
An algorithm that allows the use of z-buffer hardware in assisting area sampling for a ray tracing style renderer is described. The implementation issues involved in discretizing the sampling area and light source area are discussed and solutions are proposed. The effects of the hardware-assisted ray tracing approach on frame-buffer systems and image synthesis processes are considered.

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