Volume 07 (1988)
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Item Generation of High-Quality Curve and Surface with Smoothly Varying Curvature(Eurographics Association, 1988) Higashi, Masatake; Kaneko, Kohji; Hosaka, MamoruA method for generating curves and surfaces which satisfy constraints of tangent directions and curvature at arbitrary points and which have smoothly varying curvature is introduced. The method is geometrical determination of a Bezier polygon, and quite different from conventional methods such as minimizing the integral of the square of curvature value or the second derivative. This method enables following things : generation of smooth curves by explicitly indicating the characteristic properties of the curves generation of smooth surfaces having not only smooth boundaries but also cross tangent and curvature which change smoothly along the boundary curve, high accurate approximation of intersection curves of surfaces, by satisfying a tangent direction, an osculating plane. and curvature constrained by the surface equations.Item Book Reviews(Blackwell Publishing Ltd and the Eurographics Association, 1988) Owen, J.Title: CGM and CGI: Metafile and Interface Standards for Computer GraphicsTitle: Computer Graphics: Systems and ConceptsTitle: Computer Graphics and Geometric Modeling Using Beta-splinesItem 7th EUROGRAPHICS UK Conference(Blackwell Publishing Ltd and the Eurographics Association, 1988)Item Offers to EUROGRAPHICS Members(Blackwell Publishing Ltd and the Eurographics Association, 1988)Item Application Profiles for Computer Graphics Standards - A Touch of Realism(Eurographics Association, 1988) Mumford, Anne M.Computer graphics standards have become widely used and are now a fact of life. We have reached the stage of reviewing and extending the current standards. There is an important move within the user community which needs to be taken into consideration in these processes. This is the development of application profiles within user groups to make their use of the graphics standards easier and to ensure portability. This paper suggests that this move is important and cannot be ignored by users of standards or those involved with the current standards work.Item Fellows of the Eurographics Association(Blackwell Publishing Ltd and the Eurographics Association, 1988) Prior, W.A.J.Item First Impressions of NeWS(Blackwell Publishing Ltd and the Eurographics Association, 1988) Roberts, W.; Slater, M.; Drake, K.; Simmins, A.; Davison, A.; Williams, P.The SUN Microsystems Network Extensible Window System (NeWS) is a display system that uses the PostScript page description language to provide fully device independent screen and input manipulation as a network service. This system has been available in the UK as a beta test product since April 1987 and this paper reports the work done with NeWS at Queen Mary College. A general introduction to NeWS is given, together with some more detailed information and reports of what each author has been doing with the system. We will try to predict the future of NeWS and its main rival (the MIT X-Windows system) and to suggest changes to the NeWS beta product that will be necessary for it to realise its potential.Item Third Eurographics Workshop on IUVTELLIGENT CAD SYSTEMS"Practical Experience and Evaluation"(Blackwell Publishing Ltd and the Eurographics Association, 1988)Item Calendar of Events(Blackwell Publishing Ltd and the Eurographics Association, 1988)Item Fast Algorithm for Polygon Clipping with 3D Windows(Eurographics Association, 1988) Burkert, Andreas; Noll, StefanMany applications which use 3D graphics, need 3D geometric modeling and hence polygon clipping against 3D Windows or general volumes. The disadvantages of existing clipping algorithms are that they are 2D, slow or produce incorrect results. This paper describes a new 3D clipping algorithm for concave polygons with one contour. The new algorithm is an extension to the algorithm of Liang and Barsky: The necessary condition for the appearance of a corner of the clipping rectangle in the output polygon is replaced by a necessary and sufficient condition and then extended to the three dimensional case. Another advantage of the presented algorithm is the the removal of degenerated edges. The algorithm is useful for implementing the draft international standards GKS-3D and PHIGS and also for 3D Window Systems.Item Construction of Interactive Programs in Computer Graphics(Blackwell Publishing Ltd and the Eurographics Association, 1988) Dufourd, Jean-FrancoisIn interactive computer graphics, one often finds a gap between sophisticated algorithms, using very high level data structures, and poor methods of program and object construction. Particular programming languages are too readily adopted for solving problems, before a precise specification of the problem to be solved has been formulated.This paper shows that progress can be made by using modern engineering methods to specify and develop graphical software. Two programming techniques are studied here: the algebraic specification of data types and a functional static modular method of problem statement.The paper also discusses these proposals in the context of other modes of computer graphics specification and programming.Item A New Algorithm for Converting Boundary Representation to Octree(Eurographics Association, 1988) Tang, Zesheng; Lu, ShengkaiConversion algorithms between different object representations have become Increasingly important In soIid modeling system. In this paper, an algorithm for converting boundary representation of 3D object to octree structure is presented. This algorithm Is based on the transformation of Cartesian coordinates of voxels in the object universe to octant addresses or to node addresses of octree. The surface coherence, edge coherence, voxel coherence are used to speed up the transformation. In order to save memory space, Iinear octree Is used and the Intermediate resulting octant addresses are condensed as early as possible. The resolution of octree structure may also be controled by defining the number of levels of octree. This Is the bottom-up algorithm for converting boundary representation of 3D object to octree structure.Item IFPP TC-2 Working Conference on Visual Database Systems(Blackwell Publishing Ltd and the Eurographics Association, 1988)Item Calendar of Events(Blackwell Publishing Ltd and the Eurographics Association, 1988)Item Conic Beta-Splines with Local Tension Control for Interactive Curve Fitting(Eurographics Association, 1988) Pham, BinhPolynomial Beta-splines were introduced by Barsky as an extension of polynomial B-splines with bias and tension parameters which allow more flexibility in controlling shape in curve fitting. It is possible to show that a quadratic Beta-spline segment is equivalent to a quadratic B-spline segment with suitably modified control vertices. This provides a simple method for evaluating quadratic Beta-splines using De Boor's algorithm for calculating polynomial B-splines. A representation for conic Beta-splines with one tension parameter is introduced and some properties are derived. They form a basis for an efficient algorithm for interactive curve fitting with conic Beta-splines. The results are extended further to cover the case of conic Beta-splines with varying tension where the tension parameter is an interpolating function between the tension values at each end of a segment.Item Continuous Processing of Images through User Sketched Functional Blocks(Blackwell Publishing Ltd and the Eurographics Association, 1988) Kaya, Aydin; Ozguc, BulentItem EUROGRAPHlCS UK Chapter 7th Annual General Meeting 7 April 1988 at the University of Sussex(Blackwell Publishing Ltd and the Eurographics Association, 1988)Item Adding Name Sets and Workstation Filters to GKS a Future Extension(Blackwell Publishing Ltd and the Eurographics Association, 1988) Bakkert, MienteItem Monte-Carlo Integration Applied to an Illumination Model(Eurographics Association, 1988) Bouville, C.; Dubois, J.L.; Marchal, I.; Viaud, M.L.The use of Monte-Carlo integration together with stochastic sampling is very useful for dealing with the scattering phenomena that occur in the propagation and reflection of light. In this paper, these techniques have been applied to the implementation of a physicsbased global illumination model. The theoretical basis of this approach is presented briefly and various applications to realistic image rendering are then described. This concerns the rendering of penumbra and scattered reflection effects, antialiasing and accurate color modelling through spectral integration. For all these applications, both theoretical and implementation aspects are developed and it is shown that stochastic techniques can provide very simple and efficient algorithms.Item Incremental Polygon Rendering on a SIMD Processor Array(Blackwell Publishing Ltd and the Eurographics Association, 1988) Theoharis, Theohaiis; Page, IanWe demonstrate how both area coherence and parallelism can be exploited in order to speed up rendering operations on a SIMD square array of processors. Our algorithms take advantage of the method of differences, in order to incrementally compute the values of a linear polynomial function at discrete intervals and thus implement area rendering operations efficiently. We discuss how filling of convex polygons, hidden surface elimination and smooth shading can be implemented on an N ? N processor array that supports planar arithmetic, that is, arithmetic operations performed on N ? N matrices in parallel for all matrix elements. A major attraction of the method we present is that it is based on a SIMD processor array- such machines are now recognised as highly general purpose given the wide range of applications successfully implemented on them.