Volume 11 (1992)

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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.
Modeling with Time and Events in Computer Animation
(Blackwell Science Ltd and the Eurographics Association, 1992) Kalra, Devendra; Barr, Alan H.
In this paper, we present a general, systematic and consistent treatment of time and events for computer animation. We first formalize the concepts of events and create a time primitive called an event unit. We then present a succession of organization schemes to compose event units for generating complex motion sequences. We present a directed graph representation for the organization of time and events that suggests the form of an event-based time programming language. Details of implementation of a general event simulation system are given. Our approach provides a clean partitioning for the problem of motion design, a hierarchical scheme to compose motion behaviors from time primitives and a programming model for organizing animation. Traditional methods of kinematic controls and key frame interpolation are special cases of our general scheme. In addition, our treatment of events can be combined with kinematics, dynamics or constraint-based systems to generate powerful motion modeling systems.
A Statistical Comparison of Two Hidden Surface Techniques: the Scan-line and Z-buffer Algorithms
(Blackwell Science Ltd and the Eurographics Association, 1992) Slater, Mel; Drake, Kieron; Davison, Allan; Kordakis, Emmanouell and Billyard, Adam and Miranda, Eliot
This paper compares two image space hidden surface removal algorithms for polygonal scenes. These are the z-buffer and scan-line algorithms. There is first an overview of each algorithm, followed by a simulation experiment, designed to compare the number of polygons per second which can be rendered by each algorithm. The simulation varies the number of polygons in the scene, and the size and distribution of polygons over the display. The results suggest that the z-buffer is preferred for a large enough number of polygons, however, smaller polygons and uniform distribution of polygons favour the scan-line approach. The analysis does not take into account the complexity of the shading rule, which is likely also to favour the scan-line method.
A Cooperative Architecture for Hypermedia Editing - CoMEdiA
(Blackwell Science Ltd and the Eurographics Association, 1992) Santos, Adelino
CoMEdiA is a cooperative hypermedia editing prototype, which enables co-authors to cooperatively produce hypermedia documents. It allows co-authors to communicate their ideas, drafts, guidelines, constraints, and annotations with other co-authors in order to exchange information (remotely or face-to-face), improvepassages and modify notes until a final document is achieved. We did not concentrate on the depth but on the breadth of the features. Our efforts were on integrating and coordinating concepts from collaboration, multimedia, and hyper organization rather than on making a specialized system in any of them. Our first step was to investigate issues in group editing and cooperation. Then we started by having text in our documents, later static images, and 2D-Graphics. This procedure was adopted because we felt these were the most simple media to integrate and process.
PHIFI: A PHIGS Interactive System for the Visualization of Scalar and Vector Fields
(Blackwell Science Ltd and the Eurographics Association, 1992) Ascani, Fabrizio; Moltedo, Laura
This paper describes the characteristics of PHIFI, an interactive system for the visualization of scalar and vector fields. PHIFI has been developed at the IAC where applications of the system have also been investigated.
Ray Tracing and Graphics Standards
(Blackwell Science Ltd and the Eurographics Association, 1992) Urban, B.; Haberstroh, T.
Existing standards for three-dimensional graphic representations are unable to produce any realistically shaded images (except PHIGS PLUS, which provides discrete shading only). Ray Tracing or Radiosity are not taken into account up to this time.This article is intended to show one way to integrate the Ray Tracing technique into the pipeline of the graphics standards GKS-3D and PHIGS. No modifications of the viewing concepts are required by our implementation.
The Fractal Nature of an Ecological Model
(Blackwell Science Ltd and the Eurographics Association, 1992) Bennan, Wang; Yin, Shi
With the help of computer graphics, the chaotic behaviour of an ecological model in the complex plane has been investigated. Convergence maps that show multi-fractal characteristics (science) and beautiful patterns (art) are presented.
Simulation of Facial Muscle Actions Based on Rational Free Form Deformations
(Blackwell Science Ltd and the Eurographics Association, 1992) Kalra, Prem; Mangili, Angelo; Thalmann, Nadia Magnenat; Thalmann, Daniel
This paper describes interactive facilities for simulating abstract muscle actions using Rational Free Form Deformations (RFFD). The particular muscle action is simulated as the displacement of the control points of the control-unit for an RFFD defined on a region of interest. One or several simulated muscle actions constitute a Minimum Perceptible Action (MPA), which is defined as the atomic action unit, similar to Action Unit (AU) of the Facial Action Coding System (FACS), to build an expression.
Template-Based Volume Viewing
(Blackwell Science Ltd and the Eurographics Association, 1992) Yagel, Roni; Kaufman, Arie
We present an efficient three-phase algorithm for volume viewing that is based on exploiting coherency between rays in parallel projection. The algorithm starts by building a ray-template and determining a special plane for projection - the base-plane. Parallel rays are cast into the volume from within the projected region of the volume on the base-plane, by repeating the sequence of steps specified in the ray-template. We carefully choose the type of line to be employed and the way the template is being placed on the base-plane in order to assure uniform sampling of the volume by the discrete rays. We conclude by describing an optimized software implementation of our algorithm and reporting its performance.
Modelling and Programming Evolutions of Surfaces
(Blackwell Science Ltd and the Eurographics Association, 1992) Chen, X.; Lienhardt, P.
In recent years, a lot of work has been done on modelling natural phenomena and simulating the evolution of natural objects. For instance, procedural methods have been developed for simulating corpuscular phenomena and tree growth. In this paper we present a new procedural method for simulating evolutions of subdivisions of surfaces (i.e. partitions of surfaces into vertices, edges and faces). The representations of topology, embedding and photometry are clearly distinguished in the geometric model used for the representation of such subdivisions and thus, each of these features may be evolved independently (as in natural metamorphoses). Evolutions are achieved by applying topological and embedding operations on the geometric model. Control of these evolutions is based upon the behaviour concept. Behaviours (i.e. sets of operations) are associated with cells of the modelled subdivision. At each step, and for each cell, the corresponding behaviour is applied to the cell. The definition and computation of parameters have been studied, in order to control such evolutions. The method has been implemented and tested with many examples of surface evolutions (mainly evolutions of vegetal surfaces: leaves, flowers). Based on the method, a language has been defined for programming surface evolutions.
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.
Modelling the Texture of Paint
(Blackwell Science Ltd and the Eurographics Association, 1992) Cockshott, Tunde; Patterson, John; England, David
Interactive Shape Control of Interpolating B-splines
(Blackwell Science Ltd and the Eurographics Association, 1992) Krokos, M. A.; Slater, M.
This paper presents a new methodfor providing interactive shape control of interpolating B-splines. The CAD designer can directly interact with geometric entities defined on the B-spline at any interpolated data point- shape adjustments can be performed either globally or locally. Our approach is based on B?-splines of order k (?,k ?1), i.e. ?-reparametrized, classical B-splines. The method presented can be easily generalised to surfaces defined either as tensor products or by using the skinning technique- interactive shape control can be provided in both surface parametric directions.
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.
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.

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