The Hybrid Octree: towards the definition of a multiresolution hybrid framework

The Hybrid Octree (HO) is an octree-based representation scheme for coding in a single model an exact representation of a surface and volume data. The HO is able to efficiently manipulate surface and volume data independently. Moreover, it facilitates the visualization and composition of surface and volume data using graphic hardware. The HO definition and its construction algorithm are provided. Some examples are presented and the goodness of the model is discussed.Postprint (published version

Remuestreo estructurado de contornos de huecos en superficies 3d de objetos de forma libre utilizando bresenham

La etapa de integración dentro del proceso de reconstrucción tridimensional de objetos de forma libre, requiere de la descripción, análisis y corrección de huecos en superficies 3D. Ciertas evaluaciones cuantitativas en este tema implican contar con conjuntos de datos espaciados de forma regular o contenidos en estructuras que garanticen dicha propiedad, por ejemplo voxels, octrees o mallas estructuradas. Lograr lo anterior requiere un proceso de re-muestreo de los puntos que conforman el contorno del hueco en la superficie 3D. En este trabajo se describe un método para obtener conjuntos estructurados de puntos, a partir de los datos de contornos de huecos en objetos de forma libre. El método inicia con el ajuste de una curva NURBS al conjunto inicial de puntos con el fin de asegurar la suavidad del contorno, de lo cual se obtiene un conjunto de puntos ajustados. Finalmente se utiliza el algoritmo de discretización de Bresenham para obtener el conjunto de puntos estructurados. Los resultados obtenidos muestran que el método desarrollado asegura que el conjunto final de puntos estructurados preserven la forma del contorno original con altos niveles de detalle

Three--dimensional medical imaging: Algorithms and computer systems

This paper presents an introduction to the field of three-dimensional medical imaging It presents medical imaging terms and concepts, summarizes the basic operations performed in three-dimensional medical imaging, and describes sample algorithms for accomplishing these operations. The paper contains a synopsis of the architectures and algorithms used in eight machines to render three-dimensional medical images, with particular emphasis paid to their distinctive contributions. It compares the performance of the machines along several dimensions, including image resolution, elapsed time to form an image, imaging algorithms used in the machine, and the degree of parallelism used in the architecture. The paper concludes with general trends for future developments in this field and references on three-dimensional medical imaging

Aquisição e tratamento de dados 3D para modelação acústica de salas

Mestrado em Engenharia Eletrónica e TelecomunicaçõesEsta dissertação tem como objectivo desenvolver ferramentas de apoio à componente de áudio em ambientes de Realidade Virtual. Trata-se de possibilitar a aquisição e configuração de dados 3D para alimentar modelos acústicos de salas. Estes podem ser geométricos (como o método das imagens virtuais, baseado nas reflexões das ondas sonoras nas superfícies que delimitam a sala) ou físicos (como o método das malhas de guias de onda digitais, baseado na discretização da equação de onda numa grelha tridimensional abrangendo o volume da sala). Para a aquisição de modelos poligonais representativos das superfícies delimitadoras de ambientes reais, foi utilizado um sensor Microsoft Kinect associado à aplicação Kinect Fusion. Em seguida, foram desenvolvidas ferramentas de identificação dos materiais constituintes das superfícies presentes, recorrendo ao Visualisation Toolkit (VTK). Este passo permite associar características acústicas, nomeadamente coeficientes de absorção/reflexão, a cada polígono da malha. É assim possível alimentar modelos acústicos geométricos, utilizados em algoritmos de auralização em tempo real. Para alimentar modelos físicos, foi desenvolvido um algoritmo para, a partir dos modelos poligonais das superfícies das salas, gerar uma malha tridimensional de nós, de topologia retangular, abrangendo todo o domínio de propagação por elas delimitado. Cada nó é configurado em função da sua posição no domínio (nó de ar ou nó-fronteira) e, no caso de ser nó-fronteira, do respectivo material. Foi utilizada, para efeitos de teste, uma sala de reuniões situada no IEETA (Instituto de Engenharia Eletrónica e Telemática de Aveiro). Para esta sala, construiu-se um modelo poligonal com os materiais corretamente identificados em cada face, para alimentar o modelo geométrico. Aplicaram-se critérios de limitação do número de polígonos. Construiu-se igualmente uma grelha tridimensional de nós para modelação física. Conjugando as informações proporcionadas pelos dois modelos (absorção das superfícies, por um lado, e volume, por outro), foi possível gerar uma estimativa automática do tempo de reverberação (RT60) de acordo com a fórmula de Sabine (modificada).The goal of this dissertation is the development of tools for audio in Virtual Reality environments, namely the acquisition and configuration of 3D data to feed room acoustic models. These models can be either geometric (such as the mirror-image source method, based on the reflection of sound waves on the surfaces delimiting the room) or physical (such as the digital waveguide mesh method, based on the discretisation of the wave equation on a three-dimensional grid covering the whole volume of the room). A Microsoft Kinect sensor and the Kinect Fusion application were used for acquiring boundary surface polygonal models in real rooms. Tools to identify the surface materials were then developed using the Visualisation Toolkit (VTK). This allowed the assignment of acoustic properties, namely absorption/reflection coefficients, to each mesh polygon, making it possible to configure geometric acoustic models, used in real-time auralization applications. In the physical model configuration front, an algorithm was developed for generating three-dimensional grids of nodes based on the polygonal models of room boundary surfaces. These 3D grids, with rectangular topology, cover the whole volume of the room. Each node is configured according to its position (air node or boundary node) and, for boundary nodes, according to the respective boundary material. A meeting room in IEETA was used for testing purposes. A polygonal model, with surface materials carefully identified, was built to create a geometric model of this room. Polygon number limitation criteria were applied. A 3D grid for physical modelling was also built. Combining the information from both models (surface absorption from one and volume information from the other), it was possible to automatically estimate reverberation time (RT60) according to the (modified) Sabine’s formula

Метод растеризації зрізів тривимірних медичних зображень

Дана дисертація присвячена тривимірному моделюванню медичних зображень та, зокрема, розробленню методу растеризації зрізів воксельних моделей даних. У роботі виконано дослідження воксельних моделей даних та проведено порівняльний аналіз існуючих рішень для растеризації довільно орієнтованих зрізів воксельних моделей даних. Були проаналізовані переваги та недоліки існуючих рішень, на основі чого були висунуті відповідні гіпотези. Дані гіпотези були перевірені і на їх основі запропоновано власний метод для растеризації зрізів воксельних моделей даних, що базується на використанні ткацьких технологій. За найближчий аналог було взято точний ткацький алгоритм растеризації. На основі проведеного дослідження було викладено теоретичний матеріал, що описує запропонований метод, та програмно реалізовано відповідний алгоритм для растеризації зрізів. У даній дисертації виконано порівняльну характеристику алгоритму для запропонованого методу із точним ткацьким алгоритмом растеризації, виконано оцінку запропонованого методу та вказано шляхи подальшого вдосконалення.This dissertation is devoted to the three-dimensional modeling of medical images and, in particular, the development of a rasterization method for the cuts of voxel datasets. In this work the study of voxel datasets was completed and a comparative analysis of existing solutions for rasterization of arbitrarily oriented cuts of voxel datasets was performed. The advantages and disadvantages of existing solutions were analyzed and the corresponding hypotheses were advanced. These hypotheses have been tested and own method for rasterization of the cuts of voxel datasets based on the use of weaving techniques was introduced. An exact weaving rasterization algorithm was considered as the nearest analogue. On the basis of the research theoretical material that describes the proposed method was presented, and the corresponding algorithm for rasterization of the cuts was implemented. In this dissertation comparative characteristic between the algorithm for the proposed method and an exact weaving rasterization algorithm is performed. An estimation of the proposed method is described and the ways of further improvement are proposed as well

Intelligent Computational Transportation

Transportation is commonplace around our world. Numerous researchers dedicate great efforts to vast transportation research topics. The purpose of this dissertation is to investigate and address a couple of transportation problems with respect to geographic discretization, pavement surface automatic examination, and traffic ow simulation, using advanced computational technologies. Many applications require a discretized 2D geographic map such that local information can be accessed efficiently. For example, map matching, which aligns a sequence of observed positions to a real-world road network, needs to find all the nearby road segments to the individual positions. To this end, the map is discretized by cells and each cell retains a list of road segments coincident with this cell. An efficient method is proposed to form such lists for the cells without costly overlapping tests. Furthermore, the method can be easily extended to 3D scenarios for fast triangle mesh voxelization. Pavement surface distress conditions are critical inputs for quantifying roadway infrastructure serviceability. Existing computer-aided automatic examination techniques are mainly based on 2D image analysis or 3D georeferenced data set. The disadvantage of information losses or extremely high costs impedes their effectiveness iv and applicability. In this study, a cost-effective Kinect-based approach is proposed for 3D pavement surface reconstruction and cracking recognition. Various cracking measurements such as alligator cracking, traverse cracking, longitudinal cracking, etc., are identified and recognized for their severity examinations based on associated geometrical features. Smart transportation is one of the core components in modern urbanization processes. Under this context, the Connected Autonomous Vehicle (CAV) system presents a promising solution towards the enhanced traffic safety and mobility through state-of-the-art wireless communications and autonomous driving techniques. Due to the different nature between the CAVs and the conventional Human- Driven-Vehicles (HDVs), it is believed that CAV-enabled transportation systems will revolutionize the existing understanding of network-wide traffic operations and re-establish traffic ow theory. This study presents a new continuum dynamics model for the future CAV-enabled traffic system, realized by encapsulating mutually-coupled vehicle interactions using virtual internal and external forces. A Smoothed Particle Hydrodynamics (SPH)-based numerical simulation and an interactive traffic visualization framework are also developed

Subdivision Surface based One-Piece Representation

Subdivision surfaces are capable of modeling and representing complex shapes of arbi-trary topology. However, methods on how to build the control mesh of a complex surfaceare not studied much. Currently, most meshes of complicated objects come from trian-gulation and simplification of raster scanned data points, like the Stanford 3D ScanningRepository. This approach is costly and leads to very dense meshes.Subdivision surface based one-piece representation means to represent the final objectin a design process with only one subdivision surface, no matter how complicated theobject\u27s topology or shape. Hence the number of parts in the final representation isalways one.In this dissertation we present necessary mathematical theories and geometric algo-rithms to support subdivision surface based one-piece representation. First, an explicitparametrization method is presented for exact evaluation of Catmull-Clark subdivisionsurfaces. Based on it, two approaches are proposed for constructing the one-piece rep-resentation of a given object with arbitrary topology. One approach is to construct theone-piece representation by using the interpolation technique. Interpolation is a naturalway to build models, but the fairness of the interpolating surface is a big concern inprevious methods. With similarity based interpolation technique, we can obtain bet-ter modeling results with less undesired artifacts and undulations. Another approachis through performing Boolean operations. Up to this point, accurate Boolean oper-ations over subdivision surfaces are not approached yet in the literature. We presenta robust and error controllable Boolean operation method which results in a one-piecerepresentation. Because one-piece representations resulting from the above two methodsare usually dense, error controllable simplification of one-piece representations is needed.Two methods are presented for this purpose: adaptive tessellation and multiresolutionanalysis. Both methods can significantly reduce the complexity of a one-piece represen-tation and while having accurate error estimation.A system that performs subdivision surface based one-piece representation was im-plemented and a lot of examples have been tested. All the examples show that our ap-proaches can obtain very good subdivision based one-piece representation results. Eventhough our methods are based on Catmull-Clark subdivision scheme, we believe they canbe adapted to other subdivision schemes as well with small modifications

Doctor of Philosophy

dissertationWhile boundary representations, such as nonuniform rational B-spline (NURBS) surfaces, have traditionally well served the needs of the modeling community, they have not seen widespread adoption among the wider engineering discipline. There is a common perception that NURBS are slow to evaluate and complex to implement. Whereas computer-aided design commonly deals with surfaces, the engineering community must deal with materials that have thickness. Traditional visualization techniques have avoided NURBS, and there has been little cross-talk between the rich spline approximation community and the larger engineering field. Recently there has been a strong desire to marry the modeling and analysis phases of the iterative design cycle, be it in car design, turbulent flow simulation around an airfoil, or lighting design. Research has demonstrated that employing a single representation throughout the cycle has key advantages. Furthermore, novel manufacturing techniques employing heterogeneous materials require the introduction of volumetric modeling representations. There is little question that fields such as scientific visualization and mechanical engineering could benefit from the powerful approximation properties of splines. In this dissertation, we remove several hurdles to the application of NURBS to problems in engineering and demonstrate how their unique properties can be leveraged to solve problems of interest

Positioning articulated figures

Many animation systems rely on key-frames or poses to produce animated sequences of figures we interpret as articulated, e.g. the skeleton of a character. The production of poses is a difficult problem which can be solved by using techniques such as forward and inverse kinematics. However, animators often find these techniques difficult to work with. The work, presented in this thesis, proposes an innovative technique which approaches this problem from a totally different direction from conventional techniques, and is based on Interactive Genetic Algorithms (IGAs). IGAs are evolutionary tools based on the theory of evolution which was first described by Darwin in 1859. They are derived from Genetic Algorithms (GAs) themselves based on the theory of evolution. IGAs have been successfully used to produce abstract pictures, sculptures and abstract animation sequences. Conventional techniques assist the animator in producing poses. On the contrary, when working with IGAs, users assist the computer in its search for a good solution. Unfortunately, this concept is too weak to allow for an efficient exploration of the space of poses as the user requires more control over the evolutionary process. So, a new concept was introduced to let the user specify directly what is of interest, that is a limb or a set of limbs. This information is efficiently used by the computer to greatly enhance the search. Users build a pose by selecting limbs which are of interest. That pose is provided to the computer as a seed to produce a new generation of poses. The degree of similarity is specified directly by the user. Typically, it is small at the beginning and increases as the process reaches convergences. The power of this new technique is demonstrated by two evaluations, one which uses a set of non expert users and another one which uses myself as the sole but expert user. The first evaluation highlighted the high cognitive requirement of the new technique whereas the second evaluation showed that given sufficient training, the new technique becomes much faster than the other two conventional techniques