Stuttgart, Univ., Diss., 2007. / Druckausg. bei Shaker, Aachen erschienen.

Universiẗat, Diss., 2004--Bonn.

Thema dieser Arbeit sind echtzeitfähige 3D-Renderingverfahren, die 3D-Geometrie mit über der Standarddarstellung hinausgehenden Qualitäts- und Gestaltungsmerkmalen rendern können. Beispiele sind Verfahren zur Darstellung von Schatten, Reflexionen oder Transparenz. Mit heutigen computergraphischen Software-Basissystemen ist ihre Integration in 3D-Anwendungssysteme sehr aufwändig: Dies liegt einerseits an der technischen, algorithmischen Komplexität der Einzelverfahren, andererseits an Ressourcenkonflikten und Seiteneffekten bei der Kombination mehrerer Verfahren. Szenengraphsysteme, intendiert als computergraphische Softwareschicht zur Abstraktion von der Graphikhardware, stellen derzeit keine Mechanismen zur Nutzung dieser Renderingverfahren zur Verfügung.<br><br> Ziel dieser Arbeit ist es, eine Software-Architektur für ein Szenengraphsystem zu konzipieren und umzusetzen, die echtzeitfähige 3D-Renderingverfahren als Komponenten modelliert und es damit erlaubt, diese Verfahren innerhalb des Szenengraphsystems für die Anwendungsentwicklung effektiv zu nutzen. Ein Entwickler, der ein solches Szenengraphsystem nutzt, steuert diese Komponenten durch Elemente in der Szenenbeschreibung an, die die sichtbare Wirkung eines Renderingverfahrens auf die Geometrie in der Szene angeben, aber keine Hinweise auf die algorithmische Implementierung des Verfahrens enthalten. Damit werden Renderingverfahren in 3D-Anwendungssystemen nutzbar, ohne dass ein Entwickler detaillierte Kenntnisse über sie benötigt, so dass der Aufwand für ihre Entwicklung drastisch reduziert wird.<br><br> Ein besonderer Augenmerk der Arbeit liegt darauf, auf diese Weise auch verschiedene Renderingverfahren in einer Szene kombiniert einsetzen zu können. Hierzu ist eine Unterteilung der Renderingverfahren in mehrere Kategorien erforderlich, die mit Hilfe unterschiedlicher Ansätze ausgewertet werden. Dies erlaubt die Abstimmung verschiedener Komponenten für Renderingverfahren und ihrer verwendeten Ressourcen.<br><br> Die Zusammenarbeit mehrerer Renderingverfahren hat dort ihre Grenzen, wo die Kombination von Renderingverfahren graphisch nicht sinnvoll ist oder fundamentale technische Beschränkungen der Verfahren eine gleichzeitige Verwendung unmöglich machen. Die in dieser Arbeit vorgestellte Software-Architektur kann diese Grenzen nicht verschieben, aber sie ermöglicht den gleichzeitigen Einsatz vieler Verfahren, bei denen eine Kombination aufgrund der hohen Komplexität der Implementierung bislang nicht erreicht wurde. Das Vermögen zur Zusammenarbeit ist dabei allerdings von der Art eines Einzelverfahrens abhängig: Verfahren zur Darstellung transparenter Geometrie beispielsweise erfordern bei der Kombination mit anderen Verfahren in der Regel vollständig neuentwickelte Renderingverfahren; entsprechende Komponenten für das Szenengraphsystem können daher nur eingeschränkt mit Komponenten für andere Renderingverfahren verwendet werden.<br><br> Das in dieser Arbeit entwickelte System integriert und kombiniert Verfahren zur Darstellung von Bumpmapping, verschiedene Schatten- und Reflexionsverfahren sowie bildbasiertes CSG-Rendering. Damit stehen wesentliche Renderingverfahren in einem Szenengraphsystem erstmalig komponentenbasiert und auf einem hohen Abstraktionsniveau zur Verfügung. Das System ist trotz des zusätzlichen Verwaltungsaufwandes in der Lage, die Renderingverfahren einzeln und in Kombination grundsätzlich in Echtzeit auszuführen. / This thesis is about real-time rendering algorithms that can render 3D-geometry with quality and design features beyond standard display. Examples include algorithms to render shadows, reflections, or transparency. Integrating these algorithms into 3D-applications using today’s rendering libraries for real-time computer graphics is exceedingly difficult: On the one hand, the rendering algorithms are technically and algorithmically complicated for their own, on the other hand, combining several algorithms causes resource conflicts and side effects that are very difficult to handle. Scene graph libraries, which intend to provide a software layer to abstract from computer graphics hardware, currently offer no mechanisms for using these rendering algorithms, either.<br><br> The objective of this thesis is to design and to implement a software architecture for a scene graph library that models real-time rendering algorithms as software components allowing an effective usage of these algorithms for 3D-application development within the scene graph library. An application developer using the scene graph library controls these components with elements in a scene description that describe the effect of a rendering algorithm for some geometry in the scene graph, but that do not contain hints about the actual implementation of the rendering algorithm. This allows for deploying rendering algorithms in 3D-applications even for application developers that do not have detailed knowledge about them. In this way, the complexity of development of rendering algorithms can be drastically reduced.<br><br> In particular, the thesis focuses on the feasibility of combining several rendering algorithms within a scene at the same time. This requires to classify rendering algorithms into different categories, which are, each, evaluated using different approaches. In this way, components for different rendering algorithms can collaborate and adjust their usage of common graphics resources.<br><br> The possibility of combining different rendering algorithms can be limited in several ways: The graphical result of the combination can be undefined, or fundamental technical restrictions can render it impossible to use two rendering algorithms at the same time. The software architecture described in this work is not able to remove these limitations, but it allows to combine a lot of different rendering algorithms that, until now, could not be combined due to the high complexities of the required implementation. The capability of collaboration, however, depends on the kind of rendering algorithm: For instance, algorithms for rendering transparent geometry can be combined with other algorithms only with a complete redesign of the algorithm. Therefore, components in the scene graph library for displaying transparency can be combined with components for other rendering algorithms in a limited way only.<br><br> The system developed in this work integrates and combines algorithms for displaying bump mapping, several variants of shadow and reflection algorithms, and image-based CSG algorithms. Hence, major rendering algorithms are available for the first time in a scene graph library as components with high abstraction level. Despite the required additional indirections and abstraction layers, the system, in principle, allows for using and combining the rendering algorithms in real-time.

This work deals with an efficient and robust technique of performing Boolean operations on polygonal models. Full robustness is achieved within an internal representation based on planes and BSP (binary space partitioning) trees, in which operations can be carried out exactly in mere fixed precision arithmetic. Necessary conversions from the usual representation to the inner one and back, including their consequences are analyzed in detail. The performance of the method is optimized by a localization scheme in the form of an adaptive octree. The resulting implementation RazeCSG is experimentally compared with implementations used in practice Carve and Maya, which are not fully robust. For large models, RazeCSG shows only twice lower performance in the worst case than Carve, and is at least 130 times faster than Maya.

A new approach to image-space hardware-based rendering of Constructive Solid Geometry (CSG) models is presented. The work is motivated by the evolving functionality and performance of computer graphics hardware. This work is also motivated by a specific industrial application --- interactive verification of five axis grinding machine tool programs. The goal is to minimise the amount of time required to render each frame in an animation or interactive application involving boolean combinations of three dimensional shapes. The Sequenced Convex Subtraction (SCS) algorithm utilises sequenced subtraction of convex objects for the purpose of interactive CSG rendering. Concave shapes must be decomposed into convex shapes for the purpose of rendering. The length of Permutation Embedding Sequences (PESs) used as subtraction sequences are shown to have a quadratic lower bound. In many situations shorter sequences can be used, in the best case linear. Approaches to s ubtraction sequence encoding are presented including the use of object-space overlap information. The implementation of the algorithm is experimentally shown to perform better on modern commodity graphics hardware than previously reported methods. This work also examines performance aspects of the SCS algorithm itself. Overall performance depends on hardware characteristics, the number and spatial arrangement of primitives, and the structure and boolean operators of the CSG tree.

This work aims at rendering 3D scene using ray tracing. It describes advantages and disadvantages of this technology and its alternation known as distributed ray tracing. Other part deals with method from different branch, which are closely related to distributed ray tracing - constructive solid geometry and procedural texturing.

[pt] Sistemas CAD – Computer-Aided Design Systems – são muito utilizados nas diferentes etapas do ciclo de vida de um empreendimento de engenharia, como a elaboração do projeto conceitual, a construção da estrutura física e a operação da planta. A manutenção das instalações é uma tarefa de muita importância durante a operação, onde a pintura de equipamentos e estruturas é essencial. Estimar a área de pintura dos diferentes objetos possui um custo elevado se feito manualmente, com a utilização de trenas e lasers. Uma forma mais eficiente de calcular essas áreas é através do uso das ferramentas CAD. Entretanto, o processo de modelagem do modelo CAD, utilizando objetos paramétricos e malhas tridimensionais, insere superfícies que estão encobertas por outros objetos. Essas superfícies encobertas não são pintadas, e considerar suas áreas na orçamentação da pintura resulta em erros consideráveis. Portanto, o uso de um cálculo simples de todas as áreas de superfícies que compõem os objetos não é adequado. Com o objetivo de eliminar as superfícies escondidas do cálculo da área de pintura, este trabalho propõe uma abordagem baseada em campos de distância adaptativos juntamente com operações de geometria sólida construtiva. Primeiramente, as malhas passam por uma fase de pré-processamento, no qual são ajustadas de forma que cumpram com os requisitos necessários para a construção do campo de distância adaptativo, e em seguida os seus campos são calculados. Objetos parametrizados não necessitam dessa etapa pois já possuem um campo de distância implícito. Operações de geometria sólida construtiva foram então utilizadas para obter o campo da diferença e da interseção de cada objeto com a cena. De posse desses dados, foi desenvolvida uma fórmula que utiliza as áreas da diferença com a cena, da interseção e a área superficial de cada objeto para calcular a sua área de pintura. Em testes controlados, as áreas de pintura obtidas diferenciaram em no máximo 0,84 por cento das áreas reais. Nos testes com modelos reais, foi obtido uma redução de até 38 por cento da área estimada em relação a abordagem simplista de não tratar as superfícies ocultas. / [en] CAD Systems – Computer-Aided Design Systems – are widely used in the different life cycle stages of an engineering enterprise, such as conceptual design, physical structure construction, and plant operation. The maintenance of the facility is a very important task during the operation, where painting the equipments and structures is essential. Estimating the painting area of the different objects has a high cost if done manually, using measuring tapes and lasers. A more efficiently way to calculate these areas is through the use of CAD tools. However, the modeling process of the CAD model, using parametric objects and three-dimensional meshes, inserts surfaces that are hidden by other objects. These hidden surfaces are not painted, and considering their areas in the painting budgeting leads to considerable errors. Therefore, the use of a simple calculation of all the surfaces areas that compose the objects is not adequate. With the objective of eliminating the hidden surfaces of the painting area computation, this work proposes an approach based on adaptive distance fields together with constructive solid geometry operations. Firstly, the meshes pass through a preprocessing phase, in which they are adjusted to fulfill the requirements for the adaptive distance field construction, and then their fields are computed. Parametrized objects do not need this step because they already have an implicit distance field. Constructive solid geometry operations were then used to obtain the difference and the intersection fields of each object with the scene. With this data, the painting areas are calculated considering the areas of the difference with the scene, the intersection and the surface area of each object. In controlled tests, the painting areas obtained differs of a maximum of 0.84 percent of the real areas. In tests with real models, a reduction of up to 38 percent of the estimated area was obtained in relation to the simplistic approach of not treating hidden surfaces.