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Item Fast Generation of Multiresolution Surfaces from Contours(The Eurographics Association, 1998) Schilling, Andreas; Klein, Reinhard; Bartz, DirkShow more Surface reconstruction from contours is an important problem especially in medical applications. Other uses include reconstruction from topographic data, or isosurface generation in general. The drawback of existing reconstruction algorithms from contours is, that they are relatively complicated and often have numerical problems. Furthermore, algorithms to generate multiresolution surface models do not exploit the special situation having contours. In this paper we describe a new robust and fast reconstruction algorithm from contours that delivers a multiresolution surface with controlled distance from the original contours. Supporting selective refinement in areas of interest, this multiresolution model can be handled interactively without giving up accuracy.Show more Item Three-Dimensional Visualization of Atomic Collision Cascades(The Eurographics Association, 1998) Sroubek, Filip; Slavik, Pavel; Bartz, DirkShow more The paper describes a new approach to the visualization of atomic collision cascades and using the interaction with visualized data. The collision cascade is a physical phenomenon initiated by bombarding the surface of a solid with accelerated atomic particles. The process evolves in time and therefore it is necessary to develop some tools that would allow to investigate and visualize the dynamics of the process. Such tools are classi ers ( lters) that enable to select and visualize objects with specific dynamic properties. As the visualization has been done in a 3D environment a question arises how to specify effectively and user friendly both the properties and the objects in the 3D space. Several techniques are available that allow interaction in the 3D space. It has been necessary to test some of these techniques and to determine which one is the most suitable for the given application class.Show more Item Particle Tracing on Sparse Grids(The Eurographics Association, 1998) Teitzel, Christian; Grosso, Roberto; Ertl, Thomas; Bartz, DirkShow more 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.Show more Item Adaptively Adjusting Marching Cubes Output to Fit A Trilinear Reconstruction Filter(The Eurographics Association, 1998) Allamandri, Fabio; Cignoni, Paolo; Montani, Claudio; Scopigno, Roberto; Bartz, DirkShow more The paper focuses on the improvement of the quality of isosurfaces fitted on volume datasets with respect to standard MC solutions. The new solution presented improves the precision in the reconstruction process using an approach based on mesh re nement and driven by the evaluation of the trilinear reconstruction filter. The iso-surface reconstruction process is adaptive, to ensure that the complexity of the fitted mesh will not become excessive. The proposed approach has been tested on many datasets; we discuss the precision of the obtained meshs and report data on fitted meshes complexity and processing times.Show more Item Data Compression of Multiresolution Surfaces(The Eurographics Association, 1998) Klein, Reinhard; Gumhold, Stefan; Bartz, DirkShow more In this paper we introduce a new compressed representation for multiresolution models (MRM) of triangulated surfaces of 3D-objects. Associated with the representation we present compression and decompression algorithms. Our representation allows us to extract the surface at variable resolution in time linear in the output size. It applies to MRMs generated by di erent simpli cation algorithms like local vertex deletion or edge and triangle collapse. The time required to transmit models over communication lines and the space needed to store the MRMs is signi - cantly reduced.Show more Item Data-Dependent Surface Simplification(The Eurographics Association, 1998) Frank, Karin; Lang, Ulrich; Bartz, DirkShow more In Scientific Visualization, surfaces have often attached data, e. g. cutting surfaces or isosurfaces in numerical simulations with multiple data components. These surfaces can be e. g. the output of a marching cubes algorithm which produces a large number of very small triangles. Existing triangle decimation algorithms use purely geometric criteria to simplify oversampled surfaces. This approach can lead to coarse representations of the surface in areas with high data gradients, thus loosing important information. In this paper, a data-dependent reduction algorithm for arbitrary triangulated surfaces is presented using besides geometric criteria a gradient approximation of the data to de ne the order of geometric elements to be removed. Examples show that the algorithm works su ciently fast to be used interactively in a VR environment and allows relatively high reduction rates keeping a good quality representation of the surface.Show more Item Stereoscopic Volume Rendering(The Eurographics Association, 1998) Hubbold, Roger J.; Hancock, David J.; Moore, Christopher J.; Bartz, DirkShow more In this paper we describe the extension of a parallel, distributed, direct volume renderer for use with a novel auto-stereoscopic display. We begin by brie y describing the target application of our research, radiation therapy planning, why we believe that stereoscopic viewing may be helpful for this, and the design of our DVR system. We then report on some of the problems we have encountered, and the results we have obtained in experiments. These demonstrate that stereoscopic viewing is beneficial for perceiving depth in transparent DVR images. We illustrate the application of the system to the visualisation of prostate cancer treatment plans. Finally, we describe the use of head-tracking to implement 3D stereo look-around.Show more Item Enhancing the Visualization of Characteristic Structures in Dynamical Systems(The Eurographics Association, 1998) Löffelmann, Helwig; Gröller, Eduard; Bartz, DirkShow more We present a thread of streamlets as a new technique to visualize dynamical systems in three-dimensional space. A trade-off is made between solely visualizing a mathematical abstraction through lowerdimensional manifolds, i.e., characteristic structures such as fixed points, separatrices, etc., and directly encoding the flow through stream lines or stream surfaces. Bundles of streamlets are selectively placed near characteristic trajectories. An over-population of phase space with occlusion problems as a consequence is omitted. On the other hand, information loss is minimized since characteristic structures of the flow are still illustrated in the visualization.Show more Item Visualization of Time-Dependent Velocity Fields by Texture Transport(The Eurographics Association, 1998) Becker, Joachim; Rumpf, Martin; Bartz, DirkShow more Vector field visualization is an important topic in scientific visualization. The aim is to graphically represent field data in an intuitively understandable and precise way, which should be closely related to the physical interpretation. A new tool, the texture transport method is presented, which especially applies to time-dependent velocity fields. It is based on an accurate numerical scheme for convection equations, which is used to compute Lagrangian coordinates in space time. These coordinates are then used as texture coordinates referring to some prescribed texture in the Lagrangian reference space. The method is combined with a reliability indicator. This indicator in uences the final appearance of the texture and thereby leads to reliable visual information. At first the method applies to 2D problems. It can be generalized to 3D.Show more Item Particle Tracing in σ-Transformed Grids using Tetrahedral 6-Decomposition(The Eurographics Association, 1998) Sadarjoen, Ari; Boer, Alex J. de; Post, Frits H.; Mynett, Arthur E.; Bartz, DirkShow more Particle tracing in curvilinear grids often employs decomposition of hexahedral cells into 5 tetrahedra. This method has shortcomings when applied to sigma-transformed grids, a grid type having strongly sheared cells, commonly used in hydrodynamic simulations. This paper describes an improved decomposition method into 6 tetrahedra. It is shown that this method is robust in sigma-transformed grids, however large the shear- ing. Results are presented of applying the technique to a real world sim- ulation. Comparisons are made between the accuracy and speed of the 5-decomposition and the 6-decomposition methods.Show more Item Experiments on the Accuracy of Feature Extraction(The Eurographics Association, 1998) Reinders, Freek; Spoelder, Hans J.W.; Post, Frits H.; Bartz, DirkShow more Feature extraction is an approach to visualization that ex- tracts important regions or objects of interest algorithmically from large data sets. In our feature extraction process, high-level attributes are cal- culated for the features, thus resulting in averaged quantitative measures. The usability of these measures depends on their robustness with noise and their dependency on parameters like the density of the grid that is used. In this paper experiments are described to investigate the accuracy and robustness of the feature extraction method. Synthetic data is gener- ated with prede ned features, this data is used in the feature extraction procedure, and the obtained attributes of the feature are compared to the input attributes. This has been done for several grid resolutions, for di erent noise levels, and with di erent feature extraction parameters. We present the results of the experiments, and also derive a number of guidelines for setting the extraction parameters.Show more Item Mirror, Mirror on the Wall, Who Has the Best Visualization of All?- A Reference Model for Visualization Quality(The Eurographics Association, 1998) Haase, Helmut; Bartz, DirkShow more What is a 'good' visualization, one which leads to desired insights? How can we evaluate the quality of a scientific visualization or compare two visualizations (or visualization systems) to each other? In the following, the importance of considering the 'visualization context' is stressed. It consists of the prior knowledge of the user; the aims of the user; the application domain; amount, structure, and distribution of the data; and the available hardware and software. Then, six subqualities are identified: data resolution quality, semantic quality, mapping quality, image quality, presentation and interaction quality, and multi-user quality. The QV IS reference model de nes a weight value C (i.e., importance) and a quality value Q for each subquality. The QV IS graph is introduced as a compact, easy to perceive representation of the so-de ned visualization quality. An example illustrates all concepts. The reference model and the graph can help to evaluate visualizations and thus to further improve the quality of scientific visualizations.Show more Item Procedural Shape Generation for Multi-dimensional Data Visualization(Springer and The Eurographics Association, 1999) Ebert, David S.; Rohrer, Randall M.; Shaw, Christopher D.; Panda, Pradyut; Kulda, James M.; Roberts, D. Aaron; Gröller, E., Löffelmann, H., Ribarsky, W.Show more Visualization of multi-dimensional data is a challenging task. The goal is not the display of multiple data dimensions, but user comprehension of the multi-dimensional data. This paper explores several techniques for perceptually motivated procedural generation of shapes to increase the comprehension of multi-dimensional data. Our glyph-based system allows the visualization of both regular and irregular grids of volumetric data. A glyph`s location, 3D size, color, and opacity encode up to 8 attributes of scalar data per glyph. We have extended the system's capabilities to explore shape variation as a visualization attribute. We use procedural shape generation techniques because they allow flexibility, data abstraction, and freedom from specification of detailed shapes, We have explored three procedural shape generation techniques: fractal detail generation, superquadrics, and implicit surfaces. These techniques allow front 1 to 14 additional data dimensions to be visualized using glyph shape.Show more Item VISSION: An Object Oriented Dataflow System for Simulation and Visualization(Springer and The Eurographics Association, 1999) Telea, Alexandru; Wijk, Jarke J. van; Gröller, E., Löffelmann, H., Ribarsky, W.Show more Scientific visualization and simulation speciification and monitoring are sometimes addressed by object-oriented environments. Even though object orientation powerfully and elegantly models many application domains, integration of 00 libraries in such systems remains a difficult task. The elegance and simplicity of object orientation is often lost in the integration phase, so combining 00 and dataflow concepts is usually limited. We propose a system for visualization and simulation with a generic object-oriented way to simulation design, control and interactivity, which merges 00 and dataflow modelling in a single abstraction. Advantages of the proposed system over similar tools are presented and illustrated by a comprehensive set of examples.Show more Item Analysis and Visualization of the Brain Shift Phenomenon in Neurosurgery(Springer and The Eurographics Association, 1999) Lürig, C.; Hastreiter, P.; Nimsky, C.; Ertl, T.; Gröller, E., Löffelmann, H., Ribarsky, W.Show more In this paper we present a method for analyzing the brain shift. The brain shift is a brain deformation phenomenon, that occurs during surgical operations on the opened head. This deformation makes navigation within the brain very difficult for the surgeon, as preoperative magnetic resonance images invalidate very quickly after the beginning of the operation. Up to now not enough is known about this deformation phenomenon in order to come up with solutions for corrective action. The aim of the tool which is presented here is to prepare ground for a better understanding by visualizing the deformation between two 3D brain data sets, where one has been taken preoperatively and the second one during the operation after the brain shift has occured. We propose a new method for the modeling of the deformation by means of efficient distance determination of two deformable surface approximations. Color coding and semi-transparent overlay of the surfaces provides qualitative and quantitative information about the brain shift. The provided insight may lead to a prediction method in future.Show more Item 2D Vector Field Visualization Using Furlike Texture(Springer and The Eurographics Association, 1999) Khouas, Leila; Odet, Christophe; Friboulet, Denis; Gröller, E., Löffelmann, H., Ribarsky, W.Show more This paper presents a new technique for 2D vector field visualization. Our approach is based on the use of a furlike texture. For this purpose, we have first developed a texture model that allows two dimensional synthesis of 3D furlike texture. The technique is based on a non stationary two dimensional Autoregressive synthesis (2D AR). The texture generator allows local control of orientation and length of the synthesized texture (the orientation and length of filaments). This texture model is then used to represent 2D vector fields. We can use orientation, length, density and color attributes of our furlike texture to visualize local orientation and magnitude of a 2D vector field. The visual representations produced are satisfying since complete information about local orientation is easily perceived. We will show that the technique can also produce LIC-like texture. In addition, due to the AR formulation, the obtained technique is computationally efficient.Show more Item Interactive Direct Volume Rendering of Time-Varying Data(Springer and The Eurographics Association, 1999) Clyne, John; Dennis, John M.; Gröller, E., Löffelmann, H., Ribarsky, W.Show more Previous efforts aimed at improving direct volume rendering performance have focused largely on time-invariant, 3D data. Little work has been done in the area of interactive direct volume rendering of timevarying data, such as is commonly found in Computational Fluid Dynamics (CFD) simulations. Until recently, the additional costs imposed by time-varying data have made consideration of interactive direct volume rendering impracticaL. We present a volume rendering system based on a parallel implementation of the Shear-Warp Factorization algorithm that is capable of rendering time-varying 128 3 data at interactive speeds.Show more Item Parallel Ray Casting of Visible Human on Distributed Memory Architectures(Springer and The Eurographics Association, 1999) Bajaj, Chandrajit; Ihm, Insung; Koo, Gee-bum; Park, Sanghun; Gröller, E., Löffelmann, H., Ribarsky, W.Show more This paper proposes a new parallel ray-casting scheme for very large volume data on distributed-memory architectures. Our method, based on data compression, attempts to enhance the speedup of parallel rendering by quickly reconstructing data from local memory rather than expensively fetching them from remote memory spaces. Furthermore, it takes the advantages of both object-order and image-order traversal algorithms: It exploits object-space and image-space coherence, respectively, by traversing a min-max octrce block-wise and using a runtime quadtree which is maintained dynamically against pixels' opacity values. Our compression-based parallel volume rendering scheme minimizes conmUnications between processing elements during rendering, hence is also very appropriate for more practical distributed systems, such as dusters of PCs and/or workstations, in which data conmlUnications between processors are regarded as quite costly. We report experimental results on a Cray T3E for the Visible Man dataset.Show more Item On Simulated Annealing and the Construction of Linear Spline Approximations for Scattered Data(Springer and The Eurographics Association, 1999) Kreylos, Oliver; Hamann, Bernd; Gröller, E., Löffelmann, H., Ribarsky, W.Show more We describe a method to create optimal linear spline approximations to arbitrary functions of one or two variables, given as scattered data without known connectivity.We start with an initial approximation consisting of a fixed number of vertices and improve this approximation by choosing different vertices, governed by a simulated annealing algorithm. In the case of one variable, the approximation is defined by line segments; in the case of two variables, the vertices are connected to define a Delaunay triangulation of the selected subset of sites in the plane. In a second version of this algorithm, specifically designed for the bivariate case, we choose vertex sets and also change the triangulation to achieve both optimal vertex placement and optimal triangulation. We then create a hierarchy of linear spline approximations, each one being a superset of all lower-resolution ones.Show more Item Efficient Ray Intersection for Visualization and Navigation of Global Terrain using Spheroidal Height-Augmented Quadtrees(Springer and The Eurographics Association, 1999) Wartell, Zachary; Ribarsky, William; Hodges, Larry; Gröller, E., Löffelmann, H., Ribarsky, W.Show more We present an algorithm for efficiently computing ray intersections with multi-resolution global terrain partitioned by spheroidal height-augmented quadtrees. While previous methods support terrain defined on a Cartesian coordinate system, our methods support terrain defined on a two-parameter ellipsoidal coordinate system. This curvilinear system is necessary for an accurate model of global terrain. Supporting multi-resolution terrain and quadtrees on this curvilinear coordinate system raises a surprising number of complications.We describe the complex- ities and present solutions. The final algorithm is suited for interactive terrain selection, collision detection and simple LOS (line-of-site) queries on global terrain.Show more