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Has files: true × Author: Ertl, Thomas × Start date: 1997 × End date: 1999 ×

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Now showing 1 - 5 of 5
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    A Multiscale Approach to Integrated Volume Segmentation and Rendering
    (Blackwell Publishers Ltd and the Eurographics Association, 1997) Westermann, Rudiger; Ertl, Thomas
    A number of techniques have been proposed for rendering volumetric scalar data sets. Techniques have also been proposed for analyzing the three dimensional information contents of the underlying domain, but traditionally the data analysis part is left as a post-processing step which only involves the rendered two dimensional images. In this paper, we describe a visualization method for scalar volume data which integrates explicit knowledge of the underlying domain into the rendering process. The key of this approach lies in a hierarchical description of the discrete signal, which is decomposed into a sequence of multiscale representations. We describe a technique for the analysis of structures within the data. This allows for the segmentation and classification of the relevant features and can be used to improve their visual sensation. We also address the problem of accelerating the final rendering pass by integrating the extracted object space information into the ray traversal process.
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    Particle Tracing on Sparse Grids
    (The Eurographics Association, 1998) Teitzel, Christian; Grosso, Roberto; Ertl, Thomas; Bartz, Dirk
    These days sparse grids are of increasing interest in numerical simulations. Based upon hierarchical tensor product bases, the sparse grid approach is a very e cient one improving the ratio of invested storage and computing time to the achieved accuracy for many problems in the area of numerical solution of di erential equations, for instance in numerical fluid mechanics. The particle tracing algorithms that are available so far cannot cope with sparse grids. Now we present an approach that directly works on sparse grids. As a second aspect in this paper, we suggest to use sparse grids as a data compression method in order to visualize huge data sets even on small workstations. Because the size of data sets used in numerical simulations is still growing, this feature makes it possible that workstations can continue to handle these data sets.
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    Decoupling Polygon Rendering from Geometry using Rasterization Hardware
    (The Eurographics Association, 1999) Westermann, Rüdiger; Sommer, Ove; Ertl, Thomas; Dani Lischinski and Greg Ward Larson
    The dramatically increasing size of polygonal models resulting from 3D scanning devices and advanced modeling techniques requires new approaches to reduce the load of geometry transfer and processing. In order to supplement methods like polygon reduction or geometry compression we suggest to exploit the processing power and functionality of the rasterization and texture subsystem of advanced graphics hardware. We demonstrate that 3D-texture maps can be used to render voxelized polygon models of arbitrary complexity at interactive rates by extracting isosurfaces from distance volumes. Therefore, we propose two fundamental algorithms to limit the rasterization load: First, the model is partitioned into a hierarchy of axis-aligned bounding boxes that are voxelized in an error controlled multi-resolution representation. Second, rasterization is restricted to the thin boundary regions around the isosurface representing the voxelized geometry. Furthermore, we suggest and simulate an OpenGL extension enabling advanced per-pixel lighting and shading. Although the presented approach exhibits certain limitations we consider it as a starting point for hybrid solutions balancing load between the geometry and the rasterization stage and we expect some influence on future hardware design.
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    Progressive Iso-Surface Extraction from Hierarchical 3D Meshes
    (Blackwell Publishers Ltd and the Eurographics Association, 1998) Grosso, Roberto; Ertl, Thomas
    A multiresolution data decomposition offers a fundamental framework supporting compression, progressive transmission, and level-of-detail (LOD) control for large two or three dimensional data sets discretized on complex meshes. In this paper we extend a previously presented algorithm for 3D mesh reduction for volume data based on multilevel finite element approximations in two ways. First, we present efficient data structures which allow to incrementally construct approximations of the volume data at lower or higher resolutions at interactive rates. An abstract description of the mesh hierarchy in terms of a coarse base mesh and a set of integer records offers a high compression potential which is essential for an efficient storage and a progressive network transmission. Based on this mesh hierarchy we then develop a new progressive iso-surface extraction algorithm. For a given iso-value, the corresponding iso-surface can be computed at different levels of resolution. Changing to a higher or coarser resolution will update the surface only in those regions where the volume data is being refined or coarsened. Our approach allows to interactively visualize very large scalar fields like medical data sets, whereas the conventional algorithms would have required at least an order of magnitude more resources.
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    New Approaches for Particle Tracing on Sparse Grids
    (Springer and The Eurographics Association, 1999) Teitzel, Christian; Ertl, Thomas; Gröller, E., Löffelmann, H., Ribarsky, W.
    Flow visualization tools based on particle methods continue to be an important utility of flow simulation. Additionally, sparse grids are of increasing interest in numerical simulations. In [14] we presented the advontages of particle tracing on uniform sparse grids. Here we present and compare two different approaches to accelerate particle tracing on sparse grids. Furthermore, a new approach is presented in order to perform particle tracing on curvilinear sparse grids. The method for curvilinear sparse grids consists of a modified Stencil Walk algorithm and especially adapted routines to compute, store, and handle the required Jacobians. The accelerating approaches are on the on hand an adaptive method, where an error criterion is used to skip basis functions with minor contribution coefficients, and on the other hand the so-called combination technique, which uses a specific selection of small full grids to emulate sparse grids.