Sborník referátů semináře Zimní škola počítačové grafiky a CAD systémů 1992
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Item Creating Convex Hulls in E2 Using Dual Representation(Západočeská univerzita, 1994) Kolingerová, Ivana; Skala, VáclavThe dual representation of points, lines and polygons introduced in [Gun88] can also be used for computing convex hulls of a set of points in E2. The main principles of the dual representation and a sketch of the algorithm for convex hull computation are given in this paper. Algorithm can be used both for statical and semi-dynamical case. More details can be seen in [Kol94].
Item Raytracing 3D Linear Graftals(Západočeská univerzita, 1994) Bekaert, Phillipe; Willems, Y. D.; Skala, VáclavMany objects in nature, like trees, mountains and seashells, have a property called selfsimilarity. Sometimes this property is very pronounced, other natural phenomena exhibit this property to a lesser degree. During the past years much attention has been paid to fractals, purely selfsimilar objects. We present a formalism, based on the well-known object-instancing graph, to represent objects which are not necessarily purely selfsimilar. We show that Iterated Function Systems and some famous variants can be described elegantly in this formalism. We also present an algorithm to raytrace such objects.Item A Mathematical Framework for Global Illumination Algorithms(Západočeská univerzita v Plzni, 1994) Dutré, Philip; Lafortune, E.; Willems, Y. D.; Skala, VáclavThis paper describes a mathematical framework for rendering algorithms. Starting from the rendering equation and the potential equation, we will introduce the Global Reflection Distribution Function (GRDF). By using GRDF, we are able to compute the behaviour of light in an environment, independent of the initial lighting or viewpoint conditions. This framework is able to describe most existing rendering algorithms.Item Cubic Monte Carlo Radiosity(Západočeská univerzita, 1994) Eliáš, Pavol; Feda, Martin; Ferschin, Peter; Purgathofer, Werner; Skala, VáclavA revised radiosity method for curved surfaces is proposed, based on the Monte Carlo approach. In order to improve the accuracy of the solution, a smoothly reconstructed illumination function with selected discontinuities is used during the radiosity computation. The reconstructed function is used as a random number distribution for position sampling to overcome the constant radiosity assumption syndrome. Illumination information stored at the surface control points is used to preserve continuity of the illumination across the boundary of adjacent surfaces and to avoid Mach band effects. Implementation in Flatland is discussed.Item Prehľad normalizovaných grafických systémov(Západočeská univerzita, 1994) Ferko, Andrej; Skala, VáclavThe paper deals with the survey of standardized graphics systems from the point of view of a course for computer graphics students. This Comenius University course is based on a new textbook [ErFe93] on this topic which seems to be a very useful notional and conceptual tool for systematic understanding to the functionality and architecture of any graphics system.Item Fractal Based Procedural Modelling(Západočeská univerzita v Plzni, 1994) Filip, Norbert; Skala, VáclavTwo different methods for procedurally based modelling are presented as an alternative to the interactive modelling. Fractal and graftal techniques are shown to be the possibilities for modelling of natural phenomena as terrain shapes and trees. Different issues of consistency for fractal based terrain modelling are discussed. Second part of the paper shows several problems of graftal and L-systems trees modelling. Attention is focused on modeling of branches, the problem of "twisted" branches and branch connections are solved. The paper contains remarks towards the implementation of presented ideas.Item Coherence in scan-line algorithms for CSG(Západočeská univerzita, 1994) Gröller, Eduard; Brunner, Peter; Skala, VáclavScan-line algorithms for visibility calculation exploit various types of coherence properties. Several scan-line algorithms for Constructive Solid Geometry (CSG)are discussed. In one approach CSG primitives are represented by polygonal approximations. Another technique processes CSG primitives as general quadric surfaces. We investigate the handling of frequently occuring quadric surfaces (cube, cone, sphere, cylinder)as distinct cases. Thus the differing properties of such objects can be used more efficiently than a uniform approach would allow. A so called eBRep (extended Boundary Representation) is defined for the frequently occuring quadric surfaces. An eBRep is an exact representation of of a quadric object and contains curved edges and faces. For each of the above mentioned quadric surfaces a different, geometry dependent eBRep is specified. A comparison between the polygon-based scan-line algorithm for CSG and our eBRep based approach is done. eBRep is a storage efficient exact representation of quadric surfaces, well suited for scan-line visibility determination.Item Graphics Systems PHIGS and PHIGS+(Západočeská univerzita, 1994) Hudec, Bohuslav; Skala, VáclavThe PHIGS (Programmer's Hierarchical Interactive Graphics System) is an international ISO standard of a functional interface between an application program and a configuration of graphical input and output devices. This interface contains basic functions for dynamic interactive 2D and 3D graphics on wide variety of graphics equippment.Item G2 Continuous Beta-spline Curves Defined on the Interval <0,1)(Západočeská univerzita, 1994) Imrišková, Mária; Skala, VáclavIn this paper, the general and special matrices forms of the cubic beta-spline curve defined on the interval <0,1) are described.Item Visualisation of the Volume Datasets in Science(Západočeská univerzita, 1994) Jankovič, Juraj; Skala, VáclavVolume visualisation is one of the fast-growing areas in scientific visualisation. It helps to look at scalar or vector datasets and understand them more easily. An overview of basic algorithms used for this purpose, some of enhancements and optimizations are described here.Item Semiregular Grids in 2D and 3D(Západočeská univerzita, 1994) Kolcun, Alexej; Skala, VáclavAdvantages of grids used in finite element analysis ( FEM ), which are similar to regular, are described in [5]. We show posibilities of generation and transformation of such grids and we make comparison of them in 2D. We show dificulties arising in 3D.Item Fractal Volumes(Západočeská univerzita v Plzni, 1994) Kose, C.; Willis, C. P.; Paddon, D. J.; Skala, VáclavA Mandelbrot set, in quaternion representation, is used as a test data set to research the necessary characteristics of a system that visualises large and complex data sets. An image space software solution is developed that uses dynamic data partitioning across a distributed system of processors. A system configuration is used that minimised the network diameter in order to reduce the communications overhead.Item Simple Graphic CAM System Controlling the Cutting Machine(Západočeská univerzita, 1994) Košek, Miloslav; Skala, VáclavA CAM system using a personal computer for the control of a cutting machine is described. The key part of the system is a database of suits. It contains commands that areprocessed by a personal computer. The computer can control a drawing or cutting machine that draws or cuts contours of style parts. The attention is focused namely to the transform of standard instructions that are understood by a tailor to commands that drive the computer.Item X Window System(Západočeská univerzita, 1994) Limpouch, Aleš; Skala, VáclavThe X Window System has, over the last few years, become increasingly important and it is now accepted as THE window system for workstations, mainframes and supercomputers. It has become the standard means of providing graphical facilities on UNIX systems. This paper gives a brief overview of fundamental principles, concepts and architecture of the X system and describes in detail essential characteristics of the X server.Item Použitie octree struktury na urychlenie metody ray tracing(Západočeská univerzita, 1994) Martinka, Jozef; Skala, VáclavNiektoré spôsoby urychlenia metody ray tracing využivajú priestorové rozdelenie scény a jej reprezentáciu pomocou octree štruktúry. Hlavné problémy spojené s použitím uctree sú: vhodná reprezentácia, efektivny spósob vytvorenia (rozdelenia scény na kocky octree) a rychly "prechod" stedovaného lúča cez štruktúru. V článku sú stručne popisané niektoré prístupy k riešeniu týchto problémov.Item Triangtular Patches under Tension(Západočeská univerzita, 1994) Schindler, F.; Skala, VáclavGiven a triangular surface scheme that only approximates the initial data the resulting surfaces do not reflect the shape of control vertices as much as the user would have liked. By supplying tension parameters, or what in this case might be called "shape" parameters, the user is able to force the triangular surface patch to follow the control vertices as close as desired without moving or introducing additional control point A revised radiosity method for curved surfaces is proposed, based on the Monte Carlo approach. In order to improve the accuracy of the solution, a smoothly reconstructed illumination function with selected discontinuities is used during the radiosity computation. The reconstructed function is used as a random number distribution for position sampling to overcome the constant radiosity assumption syndrome. Illumination information stored at the surface control points is used to preserve continuity of the illumination across the boundary of adjacent surfaces and to avoid Mach band effects. Implementation in Flatland is discussed.Item O(lg N) Line Clipping Algorithm in E2(Západočeská univerzita, 1994) Skala, Václav; Skala, VáclavA new O(lg N) line clipping algorithm in E2 against a convex window is presented. The main advantage of the presented algorithm is the principal acceleration of the line clipping problem solution. A comparison of the proposed algorithm with others shows a significant improvement in run-time. Experimental results for selected known algorithms are also shown.Item Graf potenciálu viditelnosti(Západočeská univerzita, 1994) Sojka, Eduard; Skala, VáclavČlánek podává nový pohled na teorii potenciálu viditelnosti. Tento pohled předpokládá, že na množině obrazů dané scény lze zavést relaci ekvivalence. Tato relace pal. indukuje rozklad množiny obrazů, která je nekonečná, na konečný počet tříd. Také prostor obklopující scénu je dekomponován na třídy. Ze všech bodů jedné třídy vnímá pozorovatel ekvivalentní obrazy. Graf potenciálu viditelnosti zachycuje informaci o těchto třídách a vztazích mezí nimi. Předkládaná teorie umožňuje zasadit dosud publikované přístupy do jednotného rámce. Použití teorie je ilustrováno na několika příkladech. Graf potenciálu viditelnosti může být použit jako alternativní nebo doplňkový model scény a může být užitečný při řešení' různých problémů jako je například problém viditelnosti, problém navigace ve scéně a problém rozpoznání trojrozměrných objektů.Item Parallel Visibility Computations for Parallel Radiosity(Západočeská univerzita, 1994) Stürzlinger, W.; Wild, C.; Skala, VáclavThe radiosity method models the interaction of light between diffuse reflecting surfaces, thereby accurately predicting global illumination effects. Due to the high computational effort to calculate the transfer of light between surfaces and the memory requirements for the scene description, a distributed, parallelized version of the algoritm is needed for scenes consisting of thousands of surfaces. We present a distributed, parallel radiosity algoritm, which can subdivide the surface adaptively. Aditionally we present a scheme for paralel visibility calculations. Adaptive load redistribution is also discussed.
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