Modeling and generating moving trees from video

We present a probabilistic approach for the automatic production of tree models with convincing 3D appearance and motion. The only input is a video of a moving tree that provides us an initial dynamic tree model, which is used to generate new individual trees of the same type. Our approach combines global and local constraints to construct a dynamic 3D tree model from a 2D skeleton. Our modeling takes into account factors such as the shape of branches, the overall shape of the tree, and physically plausible motion. Furthermore, we provide a generative model that creates multiple trees in 3D, given a single example model. This means that users no longer have to make each tree individually, or specify rules to make new trees. Results with different species are presented and compared to both reference input data and state of the art alternatives

Space colonization for the procedural generation of lightning

Dissertação de mestrado integrado em Engenharia InformáticaThe procedural generation of geometry within the space of computer graphics has been a topic of study for quite some time, benefiting from a more unpredictable brand of randomness. Similarly, the exploration of lighting as a phenomenon within virtual space has been a field of study of comparable age. Despite its age and early adoption, there is a surprising lack of research in emulating the phenomenon of lighting past its interactions with the world. Most implementations of procedurally generated lightning within video games are based on randomized data trees. When part of the skybox, 2D meshes or textures are randomly selected from a pre-made pool. There are, however, methods based entirely on the dielectric breakdown model, using approximations to solve a Laplacian equation. This dissertation aims to present an alternative approach to the randomized and procedural generation of lightning bolts based on the Space Colonization algorithm. While the algorithm was first conceived for use in botanical applications, modeling the growth of biological structures, the similarities between the results produced by the dielectric breakdown model and botanic modeling algorithms coupled with the visual likeness of a lightning bolt and certain trees, made for solid groundwork upon which to establish this unique approach. As such, this work largely aims to be a first step into this particular realm, showing Space Colonization as a suitable algorithm for this specific purpose. That being said, a large portion of time was spent iterating, modifying and experimenting with ideas that were either discarded or adapted, an effort primarily dedicated towards controlling and stifling the possible growth of branches in ways beyond the reduction of attractors. The original algorithm was altered, focus put especially on the creation of a singular channel at a time, mixing discoveries from previous research with the work done on manipulating Space Colonization. Instead of the venation patterns observed with the original work, the stifling of any growth means that each node has a chance, when created, of sprouting a branch and each branch is, in turn, a different, modified instance of the same underlying concept providing an additional level of control. Effort was equally placed on showcasing different properties inherent to a lightning strike, such as its iterative construction when descending from its origin. In the rendering section, along with recreating the bloom and glow effect seen in previous works, effort was put into recreating the strobing observed in capturing slow-motion footage of lightning bolts with special detail given to this. In addition, parameters were joined with a waypoint system to allow for a great degree of freedom when generating new bolts.A geração iterativa de geometria no contexto de computação gráfica é um tópico de estudo à já algum tempo apesar de usado em apenas contextos específicos, um ramo que benefícia de um tipo de aleatoriedade imprevisível. Similarmente, a exploração de relâmpagos como um fenómeno em espaço virtual é uma faceta de idade comparável. Apesar disto, o foco quando tratando relâmpagos tem caído marioritariamente nos seus efeitos após impacto. Estudos têm sido conduzidos no âmbito de mitigar o dano causado por estes em fuselagem de aeronaves e analizar o impacto de trovoada em estruturas críticas. No entanto, existe uma falta de investigação sobre a emulação deste fenómeno barra as suas interações com o mundo. A maioria das implementações iterativas em video jogos são baseadas em árvores de dados. Quando fazem parte do cenário, são marioritariamente meshes ou texturas 2D selecionas aleatoriamente de um conjunto. Existem, no entanto, métodos baseados num modelo de colapso elétrico usando apróximações a uma equação de Laplace. Esta dissertação tem como foco apresentar uma alternativa para a geração aleatória e iterativa de relâmpagos baseada no algoritmo de Space Colonization. Apesar deste algoritmo ter sido concebido para uso botânico, modelando o crescimento de estruturas biológicas, as similaridades entre os resultados obtidos pelo modelo de colapso elétrico e estes algoritmos de modelagem, quando considerados com a semelhança entre certos relâmpagos e árvores, constroem uma fundação sólida para o tópico. Neste âmbito, este trabalho é um primeiro passo que tem o intuito de mostrar a capacidade do algoritmo de Space Colonization em simular relâmpagos. Dito isto, uma grande porção do tempo de desenvolvimento dobrou-se sobre a iteração modificação e experimentação de ideias que foram discardadas ou adaptadas, um esforço primariamente dedicado em controlar o crescimento de ramos sem reduzir o número de atratores. O algoritmo original foi alterado, focando especialmente na criação de um único canal e fazendo uso de conhecimento prévio, oriundo de trabalho e investigação feita sobre manipulação de Space Colonization. Em vez de padrões de venação, observados no trabalho original, o impedimento de qualquer crescimento significa que cada nodo tem uma probabilidade, quando criado, de dar origem a um ramo e que cada ramo é uma instância diferente e modificada do mesmo conceito, algo que cria um nível de controlo mais profundo. Um esforço extra foi, também, realizado com o intuito de mostrar todas as propriedades diferentes, inerentes a um relâmpago tal como a construção iterativa durante a sua travessia. Na parte de renderização, foram recriados efeitos de brilho e bloom vistos em trabalhos prévios. Foi também dada especial atenção à recriação do efeito estroboscópico observado durante a análise de imagens em câmera lenta, algo que se tornou no foco principal desta parte. Adicionalmente, a adição de parâmetros foi conjugada com um sistema de pontos que dá um grau superior de liberdade ao utilizador

Modeling dendritic shapes - using path planning

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.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

Real-time rendering and simulation of trees and snow

Tree models created by an industry used package are exported and the structure extracted in order to procedurally regenerate the geometric mesh, addressing the limitations of the application's standard output. The structure, once extracted, is used to fully generate a high quality skeleton for the tree, individually representing each section in every branch to give the greatest achievable level of freedom of deformation and animation. Around the generated skeleton, a new geometric mesh is wrapped using a single, continuous surface resulting in the removal of intersection based render artefacts. Surface smoothing and enhanced detail is added to the model dynamically using the GPU enhanced tessellation engine. A real-time snow accumulation system is developed to generate snow cover on a dynamic, animated scene. Occlusion techniques are used to project snow accumulating faces and map exposed areas to applied accumulation maps in the form of dynamic textures. Accumulation maps are xed to applied surfaces, allowing moving objects to maintain accumulated snow cover. Mesh generation is performed dynamically during the rendering pass using surface o�setting and tessellation to enhance required detail

Sparse Volumetric Deformation

Volume rendering is becoming increasingly popular as applications require realistic solid shape representations with seamless texture mapping and accurate filtering. However rendering sparse volumetric data is difficult because of the limited memory and processing capabilities of current hardware. To address these limitations, the volumetric information can be stored at progressive resolutions in the hierarchical branches of a tree structure, and sampled according to the region of interest. This means that only a partial region of the full dataset is processed, and therefore massive volumetric scenes can be rendered efficiently. The problem with this approach is that it currently only supports static scenes. This is because it is difficult to accurately deform massive amounts of volume elements and reconstruct the scene hierarchy in real-time. Another problem is that deformation operations distort the shape where more than one volume element tries to occupy the same location, and similarly gaps occur where deformation stretches the elements further than one discrete location. It is also challenging to efficiently support sophisticated deformations at hierarchical resolutions, such as character skinning or physically based animation. These types of deformation are expensive and require a control structure (for example a cage or skeleton) that maps to a set of features to accelerate the deformation process. The problems with this technique are that the varying volume hierarchy reflects different feature sizes, and manipulating the features at the original resolution is too expensive; therefore the control structure must also hierarchically capture features according to the varying volumetric resolution. This thesis investigates the area of deforming and rendering massive amounts of dynamic volumetric content. The proposed approach efficiently deforms hierarchical volume elements without introducing artifacts and supports both ray casting and rasterization renderers. This enables light transport to be modeled both accurately and efficiently with applications in the fields of real-time rendering and computer animation. Sophisticated volumetric deformation, including character animation, is also supported in real-time. This is achieved by automatically generating a control skeleton which is mapped to the varying feature resolution of the volume hierarchy. The output deformations are demonstrated in massive dynamic volumetric scenes

Boxelization: folding 3D objects into boxes

We present a method for transforming a 3D object into a cube or a box using a continuous folding sequence. Our method produces a single, connected object that can be physically fabricated and folded from one shape to the other. We segment the object into voxels and search for a voxel-tree that can fold from the input shape to the target shape. This involves three major steps: finding a good voxelization, finding the tree structure that can form the input and target shapes' configurations, and finding a non-intersecting folding sequence. We demonstrate our results on several input 3D objects and also physically fabricate some using a 3D printer

Connectivity Compression for Irregular Quadrilateral Meshes

Applications that require Internet access to remote 3D datasets are often limited by the storage costs of 3D models. Several compression methods are available to address these limits for objects represented by triangle meshes. Many CAD and VRML models, however, are represented as quadrilateral meshes or mixed triangle/quadrilateral meshes, and these models may also require compression. We present an algorithm for encoding the connectivity of such quadrilateral meshes, and we demonstrate that by preserving and exploiting the original quad structure, our approach achieves encodings 30 - 80% smaller than an approach based on randomly splitting quads into triangles. We present both a code with a proven worst-case cost of 3 bits per vertex (or 2.75 bits per vertex for meshes without valence-two vertices) and entropy-coding results for typical meshes ranging from 0.3 to 0.9 bits per vertex, depending on the regularity of the mesh. Our method may be implemented by a rule for a particular splitting of quads into triangles and by using the compression and decompression algorithms introduced in [Rossignac99] and [Rossignac&Szymczak99]. We also present extensions to the algorithm to compress meshes with holes and handles and meshes containing triangles and other polygons as well as quads