This paper presents an end-to-end, low-cost solution for visualizing time-varying volume data rendered on a parallel computer located at a remote site. Pipelining and careful grouping of processors are used to hide I/O time and to maximize processors utilization. Compression is used to significantly cut down the cost of transferring output images from the parallel computer to a display device through a wide-area network. This complete rendering pipeline makes possible highly efficient rendering and remote viewing of high resolution time-varying data sets in the absence of high-speed network and parallel I/O support. To study the performance of this rendering pipeline and to demonstrate high-performance remote visualization, tests were conducted on a PC cluster in Japan as well as an SGI Origin 2000 operated at the NASA Ames Research Center with the display located at UC Davis. Keywords: High Performance Computing, Image Compression, Parallel Volume Rendering, Pipelining, Remote Visualization, Scientific Visualization, Time-Varying Data, Wide-Area Network 1

Visualization algorithms have seen substantial improvements in the past several years. However, very few algorithms have been developed for directly studying data in dimensions higher than three. Most algorithms require a sampling in three-dimensions before applying any visualization algorithms. This sampling typically ignores vital features that may be present when examined in oblique cross-sections, and places an undo burden on system resources when animation through additional dimensions is desired. For time-varying data of large data sets, smooth animation is desired at interactive rates. This paper provides a fast marchingCubes like algorithm for hypercubes of any dimension. To support this, we have developed a new algorithm to automatically generate the isosurface and triangulation tables for any dimension. This allows the efficient calculation of 4D isosurfaces, which can be interactively sliced to provide smooth animation or slicing through oblique hyper-planes. The former allows for smooth animation in a very compressed format. The latter provide better tools to study time-evolving features as they move downstream. We also provide examples in using this technique to show interval volumes or the sensitivity of a particular iso-value threshold. A formal proof on the correctness of our algorithm and a comparison to the Modified Marching Cubes is also included.

AbstractÐFor large time-varying data sets, memory and disk limitations can lower the performace of visualization applications. Algorithms and data structures must be explicitly designed to handle these data sets in order to achieve more interactive rates. The Temporal Branch-on-Need Octree (T-BON) extends the three-dimensional branch-on-need octree for time-varying isosurface extraction. This data structure minimizes the impact of the I/O bottleneck by reading from disk only those portions of the search structure and data necessary to construct the current isosurface. By performing a minimum of I/O and exploiting the hierarchical memory found in modern CPUs, the T-BON algorithm achieves high performance isosurface extraction in time-varying fields. This paper extends earlier work on the T-BON data structure by including techniques for better memory utilization, out-of-core isosurface extraction, and support for nonrectilinear grids. Results from testing the T-BON algorithm on large data sets show that its performance is similar to that of the three-dimensional branch-on-need octree for static data sets while providing substantial advantages for timevarying fields. Index TermsÐIsosurface, time-dependent scalar field visualization, multiresolution methods, octree, bricking, unstructured grid visualization, out-of-core visualization. æ

Multi-resolution techniques and models have been shown to be effective for the display and transmission of large static geometric object. Dynamic environments with internally deforming objects pose similar challenges in terms of time and space and need the development of similar solutions. We present the T-DAG, an adaptive multi-resolution representation for dynamic meshes with arbitrary deformations including attribute, position, connectivity and topology changes. We also provide an on-line algorithm for constructing the T-DAG, enabling the traversal and use of the multi-resolution model for partial playback while still constructing it.

levels of detail are widely used for large-scale two- and three-dimensional data sets. We present a four-dimensional multiresolution approach for time-varying volume data. This approach supports a hierarchy with spatial and temporal scalability.

We present an algorithm for constructing isosurfaces in any dimension. The input to the algorithm is a set of scalar values in a d-dimensional regular grid of (topological) hypercubes. The output is a set of (d-1)-dimensional simplices forming a piecewise linear approximation to the isosurface. The algorithm constructs the isosurface piecewise within each hypercube in the grid using the convex hull of an appropriate set of points. We prove that our algorithm correctly produces a triangulation of a (d-1)-manifold with boundary. In dimensions three and four, lookup tables with 2 8 and 2 16 entries, respectively, can be used to speed the algorithm’s running time. In three dimensions this gives the popular Marching Cubes algorithm. We discuss applications of four dimensional isosurface construction to time varying isosurfaces, interval volumes and morphing.

Traditionally, time-varying data has been visualized using snapshots of the individual time steps or an animation of the snapshots shown in a sequential manner. For larger datasets with many timevarying features, animation can be limited in its use, as an observer can only track a limited number of features over the last few frames. Visually inspecting each snapshot is not practical either for a large number of time-steps. We propose new techniques inspired from the illustration literature to convey change over time more effectively in a time-varying dataset. Speedlines are used extensively by cartoonists to convey motion, speed, or change over different panels. Flow ribbons are another technique used by cartoonists to depict motion in a single frame. Strobe silhouettes are used to depict previous positions of an object to convey the previous positions of the object to the user. These illustration-inspired techniques can be used in conjunction with animation to convey change over time. Keywords: Flow visualization, Non-photorealistic rendering, time-varying data, illustration

In this paper, we describe a compression scheme for encoding time-varying isosurfaces and amorphous volumetric features (volumes within specified value ranges) in a unified way, which allows for on-line reconstruction and rendering. Since the size of even one frame in a time-varying data set is very large, transmission and online reconstruction are the main bottlenecks for interactive visualization of time-varying volume and surface data. To increase the run-time decompression speed and compression ratio, we decompose the volume into small blocks and encode only the significant blocks that contribute to the isosurface and volumetric features. The result shows that our compression scheme achieves high compression ratio with fast reconstruction, which is effective for client-side rendering of time-varying isosurfaces with amorphous volumetric features.

Wedes5FI e a geometricbast for thevis5076jU7T0 of time-varying volume data of one ors everal variables as they occur ins cientific and engineeringapplications We demonsjU75 a prototype interface for gridded data, extending the contours pectrum interface of Bajaj, PasTF67j and Schikore to higherdimens6T0 and to topological properties that are not decomposmpj7 And we explore the datastaj6T9T Key words: Scientific vis950jU0TT7F computational topology,s implicial mes #Corres onding author.

This paper develops an approach for the splat-based visualization of large scale, non-uniform data. A hierarchical structure is generated that permits detailed treatment at the leaf nodes of the non-uniform distribution. A set of levels of detail (LODs) are generated based on the levels of the hierarchy. These yield two metrics, one in terms of the spatial extent of the bounding box containing the splat and one in terms of the variation of the scalar field over this box. The former yields a view-dependent choice of LODs while the latter yields a view-independent LOD based on the field variation. To show the utility of this general approach it is applied to a set of application data for a whole earth environment and some test data. Performance results are given.