<p>Ultrasound (US) volume data is noisy, so traditional methods for direct volume rendering (DVR) are less appropriate. Improved methods or new techniques are required. There are furthermore a high performance requirement and limited pre-processing to be considered in order for it to be used interactively, since the volume data might be time-varying.</p><p>There exist numerous techniques for improving visual perception of volume rendering, and while some perform well and produce a visually enhanced result, many are designed and compared for use with medical data that has a high signal-to-noise ratio. This master thesis describe and compare recent methods for DVR illumination, in the form of ambient occlusion or direct/indirect lighting from an external light source. New designs and modifications are introduced for efficiently and effectively enhancing the visual quality of DVR with US data. Furthermore, this thesis addresses the issue of how clipping is performed during rendering and for the different illumination techniques, which is commonly used in ultrasound visualization.</p><p>This diploma work was conducted at Siemens Corporate Research in Princeton, NJ where the partially open source framework XIP is developed. The framework was extended further to include modern methods for DVR illumination that are described in detail within this thesis. Finally, presented results show that several methods can be used to visually enhance the visualization within highly interactive frame-rates.</p>

<p>Detta arbete har gjorts i samarbete med Rikspolisstyrelsen för att ta fram en metod för hur modern medieteknik kan användas för att skapa en ”virtuell brottsplats”. Syftet är att arbetet ska leda till ett förslag till en metod som lämpar sig för att integrera i polisens brottsplatsundersökningar och rättsliga processer, med beaktande av de speciella krav som ställs.</p><p>Arbetet innehåller två huvuddelar där den första delens utgångspunkt är vad som går att göra med utrustning och teknik som redan finns tillgänglig och den andra delen hur det skulle kunna utvecklas vidare. Till första delen har ett förslag på en metod som kan användas för att utnyttja panoramatekniken, tagits fram. Därför har det också genomförts utvärderingar och tester på befintliga programvaror för att utröna vad som passar syftet bäst. För den andra delen togs en egen lösning fram och implementerades i OpenGL/C++. Denna lösning baseras på laserskanningsdata. Resultatet av denna del är inte en färdig metod som kan börja användas direkt utan mer ett exempel på hur panoramatekniken kan användas till något mer än att bara visa hur en plats ser ut. För att knyta samman projektet med verkligheten har båda dessa delar tillämpats på flera riktiga fall.</p><p>En slutsats som kan dras av arbetet är att visualiseringar av denna typ är väldigt användbara och till fördel för utredare och åklagare. Det finns mycket kvar att undersöka men det är ingen tvekan om att den här typen av teknik är användbar för detta syfte.</p>

<p>As the volumes are entering the world of computer graphics the pure volume visualisation becomes a more important tool in for example research and medical applications. But the advance in haptics --- force feedback from the computer --- is behind. In volume haptics no equal to the proxy method so popular in surface haptics has yet emerged. Some implementations of volume haptics even use surfaces as intermediate representations so that surface haptics can be used.</p><p>The intention of this work was to create natural feeling haptic feedback from volumetric density data using pure volume haptics. The haptic algorithm would be implemented in Reachin API for the Reachin Desktop Display, together with other parts to build up a usable volume visualisation environment.</p><p>To achieve the feeling of stiffness and friction dependent on tissue type, a proxy based method was developed. In the volume the proxy is constrained by virtual surfaces defined by the local gradient. This algorithm was implemented in a volume haptics node and for visualisation a volume renderer node was implemented. These nodes can be used to setup different volume visualisation environments using VRML.</p>

For the past few years, with the rapid advance of VLSI and multimedia technology, the applications of three-dimensional (3D) graphic applications have been widely and rapidly spread into various areas, and not longer limited into specific technical areas performed by high-end workstations. In near future, the 3D graphic engine will become an indispensable part of most multimedia systems including the entertainment television sets, the personal electronic appliances etc. A general 3D graphics engine can be divided into the geometry subsystem and the raster sub- system. The main contribution of this thesis is to design an efficient fragment pipeline process. It also helps the development of the vertex processor, and the integration of geometry and raster subsystem. In the design of the per-fragment processor, since it contains vary processing stages, such as fog blending, visible test, and alpha blending. This thesis analyzes the dependence relationship between these stages to allow several stages to run in parallel to reduce the overall pipeline latency and adjust the processing order of these stages to avoid unnecessary texturing access. This thesis also proposes two memory buffer access mechanisms suitable for the tile-based 3D graphic rendering engine to reduce the overall system memory bandwidth. The first method is to include some additional control flags for each tile such that the frequent buffer clear operations can be integrated with the normal rendering processes to avoid the additional memory clear access. The second approach is to identify the non-modified pixels in each tile by building the dirty table to reduce the number of updated pixels. The experimental results show that the proposed methods can cause more than 50% reduction of memory access. The proposed design has been realized using 0.18um technology. The gate count of the vertex processor without special functions and per-fragment processor is 201k and 118k, respectively.

The effectiveness of direct volume rendered images depends on finding transfer functions which emphasize structures in the underlying data. In order to support this process, we present a spreadsheet-like constructive visual component-based interface, which also allows novice users to efficiently find meaningful transfer functions. The interface uses a programming-by-example style approach and exploits the domain knowledge of the user without requiring visualization knowledge. Therefore, our application automatically analysis histograms with the Douglas-Peucker algorithm in order to identify potential structures in the data set. Sample visualizations of the resulting structures are presented to the user who can refine and combine them to more complex visualizations. Preliminary tests confirm that the interface is easy to use, and enables non-expert users to identify structures which they could not reveal with traditional transfer function editors. / <p>Short paper</p>

There is a growing need for custom visualization applications to deal with the rising amounts of volume data to be analyzed in fields like medicine, seismology, and meteorology. Visual programming techniques have been used in visualization and other fields to analyze and visualize data in an intuitive manner. However, this additional step of abstraction often results in a performance penalty during the actual rendering. In order to prevent this impact, a careful modularization of the required processing steps is necessary, which provides flexibility and good performance at the same time. In this paper, we will describe the technical foundations as well as the possible applications of such a modularization for GPU-based volume raycasting, which can be considered the state-of-the-art technique for interactive volume rendering. Based on the proposed modularization on a functional level, we will show how to integrate GPU-based volume ray-casting in a visual programming environment in such a way that a high degree of flexibility is achieved without any performance impact.

Modeling of natural phenomena has been of particular interest in the graphics ommunity in recent years. This thesis will explore a method for creating and animating orb webs using a coupled spring-mass system. Using a spring-mass system for creating the orb web is ideal as we can represent each web strand using coupled spring-mass pairs. This allows the orb web simulator to be physically based, i.e., the simulation follows the laws that act on objects in the real world. This in turn simplifies the process of animating the web, as the animation emerges from the simulator without anyone having to set it up explicitly. Since this model is physically based, it would allow for realistic visualization of effects such as observing an orb web under a wind. In the children's book ``Charlotte's Web', the spider creates orb webs with words inscribed on them. Charlotte's web is used as an inspiration, in this thesis, to create webs which no real world spider could possibly create, while keeping the model physically based. This involves modifying the orb web such that the target text shows up on the orb web while keeping the web looking as natural as possible.

In recent years, multiresolution models have progressed substantially. At the beginning, discrete models were employed in graphics applications, due mainly to the low degree of complexity involved in implementing them, which is the reason why nowadays they are still used in applications without high graphics requirements. Nevertheless, the increase in realism in graphics applications makes it necessary to use multiresolution models which are more exact in their approximations, which do not call for high storage costs and which are faster in visualization. This has given way to continuous models, where two consecutive levels of detail only differ by a few polygons and where, additionally, the duplication of information is avoided to a considerable extent, thus improving on the spatial cost offered by most discrete models.Advances have been made in the use of new graphics primitives which minimize the data transfer between the CPU and the GPU, apart from trying to make use of the connectivity information given by a polygonal mesh. For this purpose, graphics primitives with implicit connectivity, such as triangle strips and triangle fans, have been developed. Many continuous models based on this type of primitives have been recently developed. In these last few years, graphics hardware performance has evolved outstandingly, giving rise to new techniques which allow the continuous models to accelerate even more. In this work, we have improved the interactive render of polygonal meshes. To tackle the problem, we firstly studied fundamental techniques to efficiently render polygonal meshes and we later made use of geometry simplification and level of detail techniques. Thus, we defined a multiresolution model that represents a polygonal mesh at any given resolution. This approach is able to manage continuous level-of-detail by smoothly adapting mesh resolution to the application requirements. Moreover, the model was modified to take the maximum advantage of the recent GPU features. We also created a modified version of the model for being used in deforming meshes. Finally, we developed an independent library to integrate our model in real-time applications.

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.

In this physically-based tornado simulation, the tornado-scale approach techniques are applied to simulate the tornado formation environment. The three-dimensional Navier-Stokes equations for incompressible viscous fluid flows are used to model the tornado dynamics. The boundary conditions applied in this simulation lead to rotating and uplifting flow movement as found in real tornadoes and tornado research literatures. Moreover, a particle system is incorporated with the model equation solutions to model the irregular tornado shapes. Also, together with appropriate boundary conditions, varied particle control schemes produce tornadoes with different shapes. Furthermore, a modified metaball scheme is used to smooth the density distribution. Texture mapping, antialising, animation and volume rendering are applied to produce realistic visual results. The rendering algorithm is implemented in OpenGL.