Volume rendering is quite an old concept of representing images, dating back to the 1980's. It is very useful in the medical field for visualizing the results of a computer tomography (CT) and magnet resonance tomography (MRT) in 3D. Apart from these two major applications for volume rendering, there aren’t many other fields of usage accept from tech demos. Volumetric data does not have any limitations to the shape of an object that ordinary meshes can have. A popular way of representing volume data is through an algorithm that is called volume raycasting. There is a big disadvantage with this algorithm, namely that it is computationally heavy for the hardware. However, there have been vast improvements of the graphic cards (GPUs) in recent years and with the first GPU implementation of volume raycasting in 2003, how does this algorithm perform on modern hardware? Can the performance of the algorithm be improved with the introduction of GPGPU (DirectCompute) in Directx 11? The performance results of the basic version and the DirectCompute version was compared in this thesis and revealed significant improvement in performance. Speedup was indeed possible when using DirectCompute to optimize volume raycasting. / Implementation, optimering och prestandamätning av en volume rendering algoritm som heter volume raycasting. Optimeringen är utförd med hjälp av DirectCompute i Directx 11.

A numerical simulation case involving space plasma and the evolution of instabilities that generates very fast electrons, i.e. approximately at half of the speed of light, is used as a test bed for scientific visualisation techniques. A visualisation system was developed to provide interactive real-time animation and visualisation of the simulation results. The work focuses on two themes and the integration of them. The first theme is the storage and management of the large data sets produced. The second theme deals with how the Visualisation System and Visual Objects are tailored to efficiently visualise the data at hand. The integration of the themes has resulted in an interactive real-time animation and visualisation system which constitutes a very powerful tool for analysis and understanding of the plasma physics processes. The visualisations contained in this work have spawned many new possible research projects and provided insight into previously not fully understood plasma physics phenomena.

Algoritmos para rendering de superfícies são rápidos, mas não são compatíveis com situações em que é necessário investigar estruturas internas em volumes. Algoritmos de rendering volumétrico direto são adequados para a exploração de estruturas volumétricas, mas são lentos quando comparados a um rendering de superfícies. Várias soluções híbridas foram propostas na literatura, sendo que uma delas, conhecida como VoS (Volume on Surface), foi proposta recentemente com o objetivo de aumentar a capacidade de investigação do conteúdo de volumes por meio de superfícies. VoS é uma técnica híbrida que permite mapear o conteúdo de um volume em superfícies extraídas do mesmo. A técnica executa lançamento de raios para mapear as informações do volume na superfície, possibilitando a visualização das estruturas internas do volume utilizando rendering de superfícies convencional. No presente trabalho estudamos a técnica VoS e propomos diversas modificações com o intuito de generalizar a técnica e tratar algumas de suas limitações. As novas soluções apresentadas permitem a utilização da técnica com volumes de voxels regulares, e geram imagens de melhor qualidade. Assim como a VoS, as duas novas versões implementadas, VoSm e VoSm*, têm o objetivo de melhorar o poder de investigação do rendering de superfícies, permitindo a exploração do conteúdo de volumes. A técnica VoS e suas variações oferecem uma ferramenta alternativa para aplicações em que a utilização de superfícies é uma solução natural. / Surface rendering algorithms are fast, but are not suitable in situations where internal volume structures must be displayed for investigation. On the other hand, Direct Volume Rendering algorithms are effective to support exploration of internal volume structures, but software implementations are slow as compared to surface rendering solutions. Several hybrid solutions have been proposed in the literature. One of such hybrid solutions, named as VoS (Volume on Surface), has been recently introduced with the goal of using surfaces to enhance volume investigation capability. VoS is a hybrid technique that maps volume contents to surfaces extracted from this volume. The technique performs ray casting to map the volume information onto the surface, thus enabling the visualization of internal volume structures using standard surface rendering algorithms. In this work we study the VoS technique and propose several modifications in order to generalize the technique and treat some of its limitations. The new solutions presented here enable applying the technique to volumes described as a regular grid of voxels and produce images of superior quality as compared to the original. As with VoS, the two novel implementations, VoSm and VoSm*, have the goal of improving the investigative power of a surface rendering display, supporting exploration of volumetric contents. VoS and its variations are alternative tools for applications where surface rendering is a natural visualization solution.

[pt] A interpretação de dados sísmicos é de fundamental importância para a industria de óleo e gás. Uma vez que esses tipos de dados possuem um caráter volumétrico, não é tão simples se identificar e selecionar atributos presentes em sua estrutura 3D. Além disso, a grande presença de ruídos e concavidades acentuadas nesse tipo de dado aumenta a complexidade de sua manipulação e visualização. Devido a essas características, a geometria do dado é muito complexa, sendo necessários modelos de iluminação mais realísticos para realizar a iluminação do volume sísmico. Este trabalho consiste em realizar a visualização volumétrica de dados sísmicos baseada no algoritmo de traçado de raios, utilizando um modelo de iluminação por oclusão direcional, calculando a contribuição de luz ambiente que chega a cada elemento do volume. Desta forma, conseguimos realçar a geometria do dado sísmico, sobretudo onde as concavidades e falhas são mais acentuadas. O algoritmo proposto foi inteiramente implementado em placa gráfica, permitindo manipulação a taxas interativas, sem a necessidade de pré-processamento. / [en] The interpretation of seismic volumetric data has a major importance for the oil and gas industry. Since these data types have a volumetric character mode, identify and select attributes present in this struct become a difficult task. Furthemore, the high-frequecy noise and depth information typically found in this type of data, increasesthe complexity of their manipulation and visualization. Due to these characteristics, the geometry of 3D sismic data is very complexy and is necessary more realistic light model to perfom the illumnination of the seismic volume. This work consists of performing a volumetric visualization of seismic data based on ray tracing algorithm, using an illumination model by directional occlusion, computing the ambiente light attenuated by the elements in the light trajetory for all elements in the volume. Thus, we emphasize the geometry of the seismic data, especially the depth cues and spatial relationship. The proposed algorithm was fully implemented on graphics card, allowing at interactive rates, without any pre-processing.

This work deals with the 2D and 3D visualization of simulation outputs from the k-Wave toolbox. This toolbox, designed to accurately model the propagation of ultrasound waves in the human body, usually generates immense amounts of output data (up to hundreds of GB). That is why new methods for both the visualization and the effective data representation are necessary to be developed to help users to easily understand the simulation results. This thesis elaborates on the data format, simulation outputs are stored in, with the use of the HDF5 library and looking for the best way to quickly read the simulation data. Finally, the thesis presents the design and the implementation of the console-based application for big simulation data pre-processing and the GUI-based application for interactive visualization of the pre-processed data. The most significant features of these applications are downsampling data, changing the format of storing, viewing 2D sections, planar and volumetric visualization and animation of the simulation process. The proposed implementation allows parts of the simulation domain to be visualised within tens of milliseconds even if the simulation domain comprises GBs of data - This significantly streamlines the work of scientists and clinicians in the field of HIFU.

Aplikace pro vizualizaci a modelování molekul nejsou dosud příliš poznamenány současným hardware vyvinutým pro potřeby počítačových her. Cílem projektu je navrhnout intuitivní rozhraní s novými widgety specializovanými na atomové struktury a vizualizací využívající moderní hardware grafických karet. Důležitou částí je také dosažení vysoké přesnosti modelování, obvykle dostupné pouze u profesionálních CAD programů.

This thesis deals with accelerated 3D rendering of medical data, e.g. computed tomography, using a graphics processor and OpenGL library. Raw data slices are send to graphic memory and rendered by a ray-casting algorithm. The goal of this project is high quality visual output and full user interaction at the same time. Multiple rendering modes are avaiable to the user: MIP, X-Ray simulation and realistic shading.

[pt] Encontrar manualmente uma boa função de transferência para visualização volumétrica é uma tarefa difícil que exige um conhecimento prévio sobre os dados sendo visualizados. Por isso, muitas pesquisas têm sido desenvolvidas nos últimos anos, com o objetivo de facilitar esse processo. No entanto, poucos trabalhos se esforçaram em obter métodos automáticos para a detecção de funções de transferência. A grande maioria busca melhorar o controle do usuário sobre a função de transferência indicando regiões potencialmente interessantes em histogramas e facilitando sua manipulação através de interfaces. Além disso, os resultados encontrados são geralmente apresentados na área médica, buscando melhorar a visualização dos exames de ressonância magnética, tomografia computadorizada ou ultrassom. Assim, visando mostrar que os conceitos utilizados nesses trabalhos podem ser explorados na área de petróleo e gás, este trabalho propõem um novo método para detecção automática de funções de transferência com o intuito de visualizar as interfaces entre regiões de um reservatório de petróleo. A abordagem proposta também é avaliada na detecção de fronteiras entre diferentes materiais de volumes médicos e outros volumes científicos amplamente utilizados. / [en] Finding a good transfer function for volume rendering is a difficult task that requires previous knowledge about the data domain itself. Therefore, many researches have been developed in the past few years aiming to overcome this barrier. However, only a few of them have concentrated forces into obtaining an automatic transfer function detector. Most of them focus on improving user control over transfer function domain, indicating potentially interesting regions and easing its manipulation through different histograms. Also, the results are often presented in medical field, through MRI, CT scan or ultrasound images. Thus, with the purpose of showing that the concepts used in these works can be exploited on oil and gas research field, this work proposes a novel method to automatically detect transfer functions, aiming to visualize the interfaces between different regions in the reservoir. The proposed approach is also tested in detecting boundaries between different materials of medical datasets and other datasets widely used.

Explorer et comprendre des données volumétriques ou surfaciques est un des nombreux enjeux du domaine de l'informatique graphique. L'apparence de telles données peut être modélisée et visualisée en utilisant la théorie du transport lumineux. Afin de rendre une telle visualisation compréhensible, le recours à des matériaux transparents est très répandu. Si des solutions existent pour simuler correctement la propagation de la lumière et ainsi afficher des objets semi-transparents, offrir une visualisation compréhensible reste un sujet de recherche ouvert. Le but de cette thèse est double. Tout d'abord, une analyse approfondie du modèle optique pour le transport de la lumière et ses implications sur la génération d'images par ordinateur doit être effectuée. Ensuite, cette connaissance pourra être utilisée pour proposer des solutions efficaces et fiables pour visualiser des milieux transparents et semi-transparents. Dans ce manuscrit, premièrement, nous présentons le modèle optique communément utilisé pour modéliser le transport de la lumière dans des milieux participatifs, sa simplification si l'on réduit la situation à des surfaces et la manière dont ces modèles sont utilisés en informatique graphique pour générer des images. Deuxièmement, nous présentons une solution pour améliorer la représentation des formes dans le cas particulier des surfaces. La technique proposée utilise le transport lumineux comme base pour modifier le processus d'éclairage et modifier l'apparence et l'opacité des matériaux. Troisièmement, nous nous concentrons sur la problématique de l’utilisation de données volumétriques au lieu du cas simplifié des surfaces. Dans ce cas, le fait de ne modifier que les propriétés du matériau a un impact limité. Nous étudions donc comment le transport lumineux peut être utilisé pour fournir des informations utiles à la compréhension de milieux participatifs. Enfin, nous présentons notre modèle de transport lumineux pour les milieux participatifs, qui vise à explorer une région d'intérêt d’un volume. / Exploring and understanding volumetric or surface data is one of the challenges of Computer Graphics. The appearance of these data can be modeled and visualized using light transport theory. For the sake of understanding such a data visualization, transparent materials are widely used. If solutions exist to correctly simulate the light propagation and display semi-transparent objects, offering a understandable visualization remains an open research topic. The goal of this thesis is twofold. First, an in-depth analysis of the optical model for light transport and its implication on computer generated images is performed. Second, this knowledge can be used to tackle the problematic of providing efficient and reliable solution to visualize transparent and semi-transparent media. In this manuscript, we first introduce the general optical model for light transport in participating media, its simplification to surfaces, and how it is used in computer graphics to generate images. Second, we present a solution to improve shape depiction in the special case of surfaces. The proposed technique uses light transport as a basis to change the lighting process and modify the materials appearance and opacity. Third, we focus on the problematic of using full volumetric data instead of the simplified case of surfaces. In this case, changing only the material properties has a limited impact, thus we study how light transport can be used to provide useful information for participating media. Last, we present our light transport model for participating media that aims at exploring part of interest of a volume.

Direct Volume Rendering (DVR) is a visualization technique that has proved to be a very powerful tool in many scientific visualization applications. Diagnostic medical imaging is one domain where DVR could provide clear benefits in terms of unprecedented possibilities for analysis of complex cases and highly efficient work flow for certain routine examinations. The full potential of DVR in the clinical environment has not been reached, however, primarily due to limitations in conventional DVR methods and tools. This thesis presents methods addressing four major challenges for DVR in clinical use. The foundation of all methods is to incorporate the domain knowledge of the medical professional in the technical solutions. The first challenge is the very large data sets routinely produced in medical imaging today. To this end a multiresolution DVR pipeline is proposed, which dynamically prioritizes data according to the actual impact in the rendered image to be reviewed. Using this prioritization the system can reduce the data requirements throughout the pipeline and provide high performance and visual quality in any environment. Another problem addressed is how to achieve simple yet powerful interactive tissue classification in DVR. The methods presented define additional attributes that effectively captures readily available medical knowledge. The task of tissue detection is also important to solve in order to improve efficiency and consistency of diagnostic image review. Histogram-based techniques that exploit spatial relations in the data to achieve accurate and robust tissue detection are presented in this thesis. The final challenge is uncertainty visualization, which is very pertinent in clinical work for patient safety reasons. An animation method has been developed that automatically conveys feasible alternative renderings. The basis of this method is a probabilistic interpretation of the visualization parameters. Several clinically relevant evaluations of the developed techniques have been performed demonstrating their usefulness. Although there is a clear focus on DVR and medical imaging, most of the methods provide similar benefits also for other visualization techniques and application domains.