Dendritic shapes are commonplace in the natural world such as trees, lichens, coral and lightning. Models of dendritic shapes are widely needed in many areas. Because of their branching fractal and erratic structures modeling dendritic shapes is a tricky task. Existing methods for modeling dendritic shapes are slow and complicated.<p>In this thesis we present a procedural algorithm of using path planning to model dendritic shapes. We generate a dendrite by finding the least-cost paths from multiple endpoints to a common generator and use the dendrite to build the geometric model. With the control handles of endpoint placement, fractal shape, edge weights distribution and path width, we create different shapes of dendrites that simulate different kinds of dendritic shapes very well. Compared with some existing methods, our algorithm is fast and simple.

Dendritic shapes are commonplace in the natural world such as trees, lichens, coral and lightning. Models of dendritic shapes are widely needed in many areas. Because of their branching fractal and erratic structures modeling dendritic shapes is a tricky task. Existing methods for modeling dendritic shapes are slow and complicated.<p>In this thesis we present a procedural algorithm of using path planning to model dendritic shapes. We generate a dendrite by finding the least-cost paths from multiple endpoints to a common generator and use the dendrite to build the geometric model. With the control handles of endpoint placement, fractal shape, edge weights distribution and path width, we create different shapes of dendrites that simulate different kinds of dendritic shapes very well. Compared with some existing methods, our algorithm is fast and simple.

A síntese de imagens é uma ferramenta valiosa na compreensão de diversos fenômenos da natureza. Nos últimos anos várias abordagens têm sido propostas para sintetizar tais fenômenos. A grande maioria de tais abordagens têm se centralizado no desenvolvimento de modelos procedurais. Porém, cada uma destas técnicas simula exclusivamente um fenômeno natural. Um dos métodos de síntese de imagens fotorealísticas mais proeminente é denominado de Traçado de Raios (Ray Tracing). Contudo, apesar de produzir imagens de excelente qualidade, este método é computacionalmente muito oneroso. A síntese de fenômenos naturais utilizando-se o traçado de raios é um desafio. É importante que este problema seja abordado, apesar da sua complexidade, pois a simulaçao fotorealista da natureza é muito importante para os cientistas e pesquisadores desde o surgimento dos computadores. Um algoritmo versátil e rápido para a síntese de fenômenos da natureza através do traçado de raios utilizando campos de altitude é proposto. O algoritmo utiliza uma modificação do algoritmo do Analisador Diferencial Digital de Bresenham para atravesar uma matriz bidimensional de valores de altitude. A determinação das primitivas geométricas a serem interseccionadas por um raio é obtida num tempo ( N ) , sendo N o número de altitudes no campo de altitude. Este trabalho faz uma comparação em termos de velocidade e realismo deste método com outras abordagens convencionais; e discute as implicações que a implementação deste método traz. Finalmente, destaca-se a simplicidade e versatilidade que este método proporciona devido à pequena quantidade de parâmetros necessária para a síntese de fenômenos naturais utilizando o traçado de raios. Para a criação de animações basta a especificação de novos parâmetros num intervalo de tempo diferente. / Visualization is a powerful tool for better undestanding of several natural phenomena. In recent years, several techniques have been proposed. Considerable interest in natural scene synthesis has focused on procedural models. However, these techniques produce synthetic scenes of only one natural phenomenon. Ray tracing is one of the most photorealistic methods of image syntesis. While providing images of excellent quality, ray tracing is a computationally intensive task. Natural scene synthesis is a challenging problem within the realm of ray tracing. It is important to tackle this problem, despite of its complexity, because photorealistic simulation have been important to scientific community since the appearance of computers. A fast and versatile algorithm for ray tracing natural scenes through height fields is presented. The algorithm employs a modified Bresenham DDA to traverse a two dimensional array of values. The objects tested for intersection are located in ( N ) time where N is the number of values in the field. This work compares the speed-up and photorealism achieved in natural scene synthesis using this method with other algorithms and discusses the implications of implementing this approach. As a final point, the simplicity and versatility of synthesizing complex natural scenes from a few parameters and data is especially attractive. Animated sequences require only the additional specifications of time modified parameters or data.

This study used qualitative (interviews) and quantitative methods (questionnaires) to investigate and describe (a) Papua New Guinea (PNG) village elders' traditional ideas and beliefs on natural phenomena, (b) PNG secondary school student's traditional science beliefs, (c) the sources of PNG secondary school students' explanations of natural phenomena, (d) the types of explanations PNG secondary school students provide to describe natural phenomena, and the views of science teachers and curriculum officers on the inclusion of traditional knowledge in the science curriculum.. Analysis of data included interviews with eight village elders and completed questionnaires from approximately 200 secondary school students in one rural provincial high school in the Gulf Province. Village elders' beliefs were analysed and categorised into (a) spirits, magic spells and sorcery, (b) Christianity, (c) personal experience, and (d) modern science. Secondary school students' sources of explanations were based on what they have heard at (a) home, (b) in the family and village, (c) in church and (d) from school. Approximately half of the secondary school students strongly hold on to traditional beliefs while learning formal school science and these were related to spirits, magic spells and sorcery that were similar to those of the village elders. Students also used scientific explanations of natural phenomena based on their learning in school and from their own personal experiences and interactions with the physical world. / Interviews with science teachers and curriculum officers supported the need to include traditional knowledge in the science curricula. The study identified students holding both traditional and scientific explanations of natural phenomena. There is both a need and value for traditional knowledge being incorporated in science education programs that harmonise with school science. The thesis concludes with six recommendations to bring these ideas to fruition.

This thesis describes a novel terrain synthesis method based on distances in a weighted graph. The method begins with a regular lattice with arbitrary edge weights; heights are determined by path cost from a set of generator nodes. The shapes of individual terrain features, such as mountains, hills, and craters, are specified by a monotonically decreasing profile describing the cross-sectional shape of a feature, while the locations of features in the terrain are specified by placing the generators. Pathing places ridges whose initial location have a dendritic shape. The method is robust and easy to control, making it possible to create pareidolia effects. It can produce a wide range of realistic synthetic terrains such as mountain ranges, craters, faults, cinder cones, and hills. The algorithm incorporates random graph edge weights, permits the inclusion of multiple topography profiles, and allows precise control over placement of terrain features and their heights. These properties all allow the artist to create highly heterogeneous terrains that compare quite favorably to existing methods.

Despite the notable progress in physically-based rendering, there is still a long way to go before we can automatically generate predictable images of biological materials. In this thesis, we address an open problem in this area, namely the spectral simulation of light interaction with human skin, and propose a novel biophysically-based model that accounts for all components of light propagation in skin tissues, namely surface reflectance, subsurface reflectance and transmittance, and the biological mechanisms of light absorption by pigments in these tissues. The model is controlled by biologically meaningful parameters, and its formulation, based on standard Monte Carlo techniques, enables its straightforward incorporation into realistic image synthesis frameworks. Besides its biophysicallybased nature, the key difference between the proposed model and the existing skin models is its comprehensiveness, i. e. , it computes both spectral (reflectance and transmittance) and scattering (bidirectional surface-scattering distribution function) quantities for skin specimens. In order to assess the predictability of our simulations, we evaluate their accuracy by comparing results from the model with actual skin measured data. We also present computer generated images to illustrate the flexibility of the proposed model with respect to variations in the biological input data, and its applicability not only in the predictive image synthesis of different skin tones, but also in the spectral simulation of medical conditions.

Explosions are one of the most powerful and devastating natural phenomena. The pressure front from the blast wave of an explosion can cause fracture of objects in its vicinity and create flying debris. In this thesis, I outline a previously proposed explosion model. An explosion is treated as a fluid with its behaviour governed by the Navier-Stokes equations and the gaseous products modeled using particles. Explosions are simulated as a means for initiating fracture of rigid bodies in the vicinity of an explosion. <br /><br /> In contrast to fracture models that are based on physics, I propose a new approach to simulating fracture which treats fracturing the rigid body as a pre-processing step. A rigid body can be pre-fractured by treating it as graph and using one of the two proposed graph partitioning algorithms to divide the object into the desired number of pieces. By treating fracture as a pre-processing step, much less computation need be done during the simulation than models based on physics. <br /><br /> It is shown that the recursive breadth-first search graph partitioning algorithm produces physically realistic results for shattering windows that are consistent with observations of real broken windows. The curvature-driven spectral partitioning algorithm fractures objects into two pieces where the object is weakest, where weakest is defined by the area with largest curvature. Numerical simulations of explosions and fracture were conducted to produce data that was used by a ray tracer and volume renderer to create images which were assembled into animations.

Explosions are one of the most powerful and devastating natural phenomena. The pressure front from the blast wave of an explosion can cause fracture of objects in its vicinity and create flying debris. In this thesis, I outline a previously proposed explosion model. An explosion is treated as a fluid with its behaviour governed by the Navier-Stokes equations and the gaseous products modeled using particles. Explosions are simulated as a means for initiating fracture of rigid bodies in the vicinity of an explosion. <br /><br /> In contrast to fracture models that are based on physics, I propose a new approach to simulating fracture which treats fracturing the rigid body as a pre-processing step. A rigid body can be pre-fractured by treating it as graph and using one of the two proposed graph partitioning algorithms to divide the object into the desired number of pieces. By treating fracture as a pre-processing step, much less computation need be done during the simulation than models based on physics. <br /><br /> It is shown that the recursive breadth-first search graph partitioning algorithm produces physically realistic results for shattering windows that are consistent with observations of real broken windows. The curvature-driven spectral partitioning algorithm fractures objects into two pieces where the object is weakest, where weakest is defined by the area with largest curvature. Numerical simulations of explosions and fracture were conducted to produce data that was used by a ray tracer and volume renderer to create images which were assembled into animations.

Despite the notable progress in physically-based rendering, there is still a long way to go before we can automatically generate predictable images of biological materials. In this thesis, we address an open problem in this area, namely the spectral simulation of light interaction with human skin, and propose a novel biophysically-based model that accounts for all components of light propagation in skin tissues, namely surface reflectance, subsurface reflectance and transmittance, and the biological mechanisms of light absorption by pigments in these tissues. The model is controlled by biologically meaningful parameters, and its formulation, based on standard Monte Carlo techniques, enables its straightforward incorporation into realistic image synthesis frameworks. Besides its biophysicallybased nature, the key difference between the proposed model and the existing skin models is its comprehensiveness, i. e. , it computes both spectral (reflectance and transmittance) and scattering (bidirectional surface-scattering distribution function) quantities for skin specimens. In order to assess the predictability of our simulations, we evaluate their accuracy by comparing results from the model with actual skin measured data. We also present computer generated images to illustrate the flexibility of the proposed model with respect to variations in the biological input data, and its applicability not only in the predictive image synthesis of different skin tones, but also in the spectral simulation of medical conditions.

This thesis describes a novel terrain synthesis method based on distances in a weighted graph. The method begins with a regular lattice with arbitrary edge weights; heights are determined by path cost from a set of generator nodes. The shapes of individual terrain features, such as mountains, hills, and craters, are specified by a monotonically decreasing profile describing the cross-sectional shape of a feature, while the locations of features in the terrain are specified by placing the generators. Pathing places ridges whose initial location have a dendritic shape. The method is robust and easy to control, making it possible to create pareidolia effects. It can produce a wide range of realistic synthetic terrains such as mountain ranges, craters, faults, cinder cones, and hills. The algorithm incorporates random graph edge weights, permits the inclusion of multiple topography profiles, and allows precise control over placement of terrain features and their heights. These properties all allow the artist to create highly heterogeneous terrains that compare quite favorably to existing methods.