Issue 5

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https://diglib.eg.org/handle/10.2312/52

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    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.
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    Hidden Surface Elimination on Parallel Processors
    (Blackwell Science Ltd and the Eurographics Association, 1992) Highfield, Julian C.; Bez, Helmut E.
    With the wide availability of general purpose parallel computers, there is a need to reconsider hidden surface elimination (HSE) algorithms with respect to parallel implementation. This paper considers MIMD parallel implementations off our common image space HSE algorithms - recursive subdivision, scan line, painter s, and z-buffer. Their suitability for parallel implementation is investigated and their relative performance in multiprocessor systems is measured using polygonal scene descriptions of between 200 and 2500 polygons. Dependence on the size of scene description is measured and results are extrapolated to larger scene descriptions. It is shown that HSE algorithms may be efficiently parallelised. A distributed z-buffer is shown to be a fast and efficient method of solving HSE problems using parallel computers.
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    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.
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    Representing Conics using NURBS of Degree Two*
    (Blackwell Science Ltd and the Eurographics Association, 1992) Qin, Kaihuai; Sun, Jiaguang; Wang, Xuefu
    In this paper, a new method is presented for representing conics precisely using NURBS of degree two. The method requires only four control vertices to represent a full circle using the full circumscribing square-based representation, which is less than the number required with the other methods using the square control vertex configuration.9, 10, 13 The paper also derives a new condition for NURBS to represent conics precisely and shows the sufficient and necessary conditions for representation of a circular arc, and gives the definition and the knot vector formulae of a periodic NURBS curve.