We present an out-of-core, point-based approach for interactive rendering of very large volumetric datasets. Our approach is based on the assumption that the density of voxels with the same function-value in large discretized volumetric scalar fields is high enough to be used to render contour and volume approximations using points to represent the voxels. This approach allows us to visualize isovalue-structures in high-resolution datasets at full resolution and interactive frame rates.

We present a new fast algorithm for rendering the depthof -field effect for point-based surfaces. The algorithm is' able to handle partial occlusion correctly, it does not suffer from intensity leakage and it is also capable of depth-of-field rendering in presence of transparent surfaces. The algorithm is' new in that it exploits' the level-ofdetail paradigm to select the surface detail according to the amount of depth-blur applied. This' makes the speed of the algorithm practically independent of the amount of depthblur. The proposed algorithm is an extension of the Elliptical Weighted Average (EWA) surface splatting, We present a mathematical analysis that extends' the screen space EWA surface splatting to handle the depth-of-field rendering, we modify the definition of surface texture to take the level-of-detail into account, allowing us' to use the level-of-detail for depth-of-field rendering, and we demonstrate the algorithm on example renderings of point-based objects'.

Die Dissertation wurde am 26.04.2007 bei der Technischen Universität München eingereicht und durch die Fakultät für Informatik am 12.09.2007 angenommen. ii Copyright c ○ 2007 Bartosz von Rymon Lipiński. Alle Rechte vorbehalten.

show the images in pairs to emphasize the absence of artifacts where the boundaries of our axes lists meet. (a) and (b) classic splatting; (c) and (d) image-based rendering of range data with estimated depth uncertainty. In (b) and (d), Red = X axis, Blue = Z axis, Green = Y axis. This paper presents a method to accelerate algorithms that need a correct and complete visibility ordering of their data for rendering. The technique works by first pre-sorting primitives using three lists- one for each axis, and then combining them using graphics hardware, by either clipping the projected primitives while rendering, according to the current list being processed, or by rendering each list to a texture and merging the textures in the end. We show that our algorithm works by applying it to the splatting technique using several types of rendering, including classic splatting and volume rendering. 1.

Abstract Ray tracing a volume scene graph composed of multiple point-based volume objects (PBVO) can produce high quality images with effects such as shadows and constructive operations. A naive approach, however, would demand an overwhelming amount of memory to accommodate all point datasets and their associated control structures such as octrees. This paper describes an out-of-core system for rendering such a scene graph in a scalable manner. In order to address the difficulty in pre-determining the order of data caching, we introduce a technique based on a dynamic, in-core working set. We present a ray-driven algorithm for predicting the working set automatically. This allows both the data and the control structures required for ray tracing to be dynamically pre-fetched according to access patterns determined based on captured knowledge of ray-data intersection. We have conducted a series of experiments on the scalability of the technique using working sets and datasets of different sizes. With the aid of both qualitative and quantitative analysis, we demonstrate that this approach allows the rendering of multiple large PBVOs in a volume scene graph be performed on desktop computers. Keywords out-of-core · very large dataset visualization · octree · point-based modeling · point-based rendering · ray tracing · volume scene graph

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The amount of data available from simulation and measurement is growing at an incredible rate. A major challenge for the visualization community is to develop methods that allow users to explore these data interactively. For three-dimensional scalar fields, direct volume rendering has become an important technique in research and commercial settings. Interactive volume rendering requires the efficient use of available computational resources to keep pace with the disparity, resolution, and complexity of the volumes that are commonly produced from simulations (e.g., computational fluid dynamics or structural mechanics) and measurements (e.g., environmental observation and forecasting systems). For structured grids, direct volume rendering is well-studied and sufficiently straightforward with modern graphics hardware. This is not the case with unstructured volumes, because the elements that compose the mesh do not so easily map to current hardware. These datasets may be extremely large and contain more than a single static instance. Therefore, advanced solutions are required to achieve interactive visualization of this type of data. The goal of this dissertation is to provide several new techniques to facilitate the visualization of disparate unstructured meshes. Two new methods are proposed to accelerate volume rendering

Figure 1: CT scan with insufficient resolution of a stag beetle as specimen. Figure (a) to (d) show DVR using different reconstruction schemes: (a) using nearest neighbor reconstruction, (b) using trilinear-, (c) using Catmull-Rom-, and (d) using polynomial interpolation of degree five. (e) shows D 2 VR of projection-based volumetric data. Figure (a)- (d) were rendered from grids with a resolution of 64 3. Figure (e) was rendered from 64 projections each with a resolution of 64 2. Volume rendering techniques are conventionally classified as either direct or indirect methods. Indirect methods require to transform the initial volumetric model into an intermediate geometrical model in order to efficiently visualize it. In contrast, direct volume rendering (DVR) methods can directly process the volumetric data. Modern CT scanners usually provide data as a set of samples on a rectilinear grid, which is computed from the measured projections by discrete tomographic reconstruction. Therefore the rectilinear grid can already be considered as an intermediate volume representation. In this paper we introduce direct direct volume rendering (D 2 VR). D 2 VR does not require a rectilinear grid, since it is based on an immediate processing of the measured projections. Arbitrary samples for ray casting are reconstructed from the projections by using the Filtered Back-Projection algorithm. Our method removes a lossy resampling step from the classical volume rendering pipeline. It provides much higher accuracy than traditional grid-based resampling techniques do. Furthermore we also present a novel high-quality gradient estimation scheme, which is also based on the Filtered Back-Projection algorithm. Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism, I.3.3 [Computer Graphics]: Picture/Image Generation 1.

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First of all, I would like to thank my mentors, who provided leadership and inspiration when it was needed the most. Jürgen Waser and Raphael Fuchs helped out with both the theory and implementation, and were willing to put aside a large amount of time for discussion and assistance. Their help was invaluable, and I feel that I’ve learned a lot from the time spent with them. Meister Eduard Gröller accepted me as his student, and provided insightful comments about the thesis. His ability to spot weak spots in a thesis is both useful and frightening. My mentor at my home university, ˇ Zeljka Mihajlović, provided valuable comments and references. I’d like to thank her for always being supportive and helpful, and especially so during the writing of this thesis. It is also necessary to mention the people I’ve worked with- thanks go out to the entire Visdom team, in particular to Benjamin Schindler, whose coding and software engineerings skills I hope to reach someday. I would also like to thank the VRVis for allowing me to do my internship there, preparing me for the thesis. The ERASMUS programme allowed me to visit Austria and led to this thesis, so I’d like to thank all the people involved in the exchange programme as well.