Eurovis: Eurographics Conference on Visualization

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Three-Dimensional Visualization of Atomic Collision Cascades
(The Eurographics Association, 1998) Sroubek, Filip; Slavik, Pavel; Bartz, Dirk
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.
Adaptively Adjusting Marching Cubes Output to Fit A Trilinear Reconstruction Filter
(The Eurographics Association, 1998) Allamandri, Fabio; Cignoni, Paolo; Montani, Claudio; Scopigno, Roberto; Bartz, Dirk
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.
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.
Fast Generation of Multiresolution Surfaces from Contours
(The Eurographics Association, 1998) Schilling, Andreas; Klein, Reinhard; Bartz, Dirk
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.
Experiments on the Accuracy of Feature Extraction
(The Eurographics Association, 1998) Reinders, Freek; Spoelder, Hans J.W.; Post, Frits H.; Bartz, Dirk
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.
Stereoscopic Volume Rendering
(The Eurographics Association, 1998) Hubbold, Roger J.; Hancock, David J.; Moore, Christopher J.; Bartz, Dirk
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.
Visualization of Time-Dependent Velocity Fields by Texture Transport
(The Eurographics Association, 1998) Becker, Joachim; Rumpf, Martin; Bartz, Dirk
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.
Data-Dependent Surface Simplification
(The Eurographics Association, 1998) Frank, Karin; Lang, Ulrich; Bartz, Dirk
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.
Data Compression of Multiresolution Surfaces
(The Eurographics Association, 1998) Klein, Reinhard; Gumhold, Stefan; Bartz, Dirk
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.
Enhancing the Visualization of Characteristic Structures in Dynamical Systems
(The Eurographics Association, 1998) Löffelmann, Helwig; Gröller, Eduard; Bartz, Dirk
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.
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, Dirk
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.
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, Dirk
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.
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.
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.
Efficiently Rendering Large Volume Data Using Texture Mapping Hardware
(Springer and The Eurographics Association, 1999) Tong, Xin; Wang, Wenping; Tsang, Waiwan; Tang, Zesheng; Gröller, E., Löffelmann, H., Ribarsky, W.
Volume rendering with texture mapping hardware is a fast volume rendering method available on high-end workstations. However, limited texture memory often prevents the method from being used to render large volume data efficiently. In this paper, we propose a new approach to fast rendering of large volume data with texture mapping hardware. Based on a new volume-loading pipeline, the volume data is preprocessed in such a way that only the volume data that contains object voxels are loaded into texture memory and resampled for rendering. Moreover, if classification threshold is changed, our algorithm classifies and processes the raw volume data accordingly nearly in real time. Our tests show that about 40% to 60% rendering time is saved in our method for large volume data.
Exploring Instationary Fluid Flows by Interactive Volume Movies
(Springer and The Eurographics Association, 1999) Glau, Thomas; Gröller, E., Löffelmann, H., Ribarsky, W.
Volume rendering offers the unique ability to represent inner object data and to realize enclosed structures ""at first glance"". Unlike software-based methods, the use of more and more available specialpurpose hardware allows volume rendering at interactive frame rates - a crucial criterion for acceptance in industrial applications,e,g. CFD analysis, Careful optimizations and the exclusive use of hardware-accelerated data manipulation facilities even enable volume rendered movies supporting real time interactivity. This article presents the most important features and implementation issues of an OpenInventor-based stereoscopic, VR-featured volume rendering system for instationary datasets.
Visualization of Global Flow Structures Using Multiple Levels of Topology
(Springer and The Eurographics Association, 1999) Leeuw, Wim de; Liere, Robert van; Gröller, E., Löffelmann, H., Ribarsky, W.
The technique for visualizing topological information in fluid flows is well known. However, when the technique is used in complex and information rich data sets, the result will be a cluttered image which is difficult to interpet. This paper presents a technique for the visualization of multi-level topology in flow data sets. It provides the user with a mechanism to visualize the topology without excessive cluttering while maintaining the global structure of the flow.
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.
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.
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.
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.
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.
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.
Parallel Multipipe Rendering for Very Large Isosurface Visualization
(Springer and The Eurographics Association, 1999) Udeshi, Tushar; Hansen, Charles D.; Gröller, E., Löffelmann, H., Ribarsky, W.
In exploratory scientific visualization, isosurfaces are typi- cally created with an explicit polygonal representation for the surface using a technique such as Marching Cubes. For even moderate data sets, Marchching Cubes can generate an extraordinary number of poly- gons, which take time to construct, and to render. To address the ren- dering bottleneck, we have developed a multipipe strategy for parallel rendering using a combination of CPUs and parallel graphics adaptors. The multipipe system uses multiple graphics adapters in parallel, the so called SGI Onyx2 Reality Monster. In this paper, we discuss the issues of using the multiple pipes in a Sort-Last fashion which out performs a single graphics adaptor for a surprisingly low number of polygons.

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