Koji Koyamada

Automatic isosurface propagation using an extrema graph and sorted boundary cell lists

A high-performance algorithm for generating isosurfaces is presented. In our method, guides to searching for cells intersected by an isosurface are generated as a pre-process. These guides are two kinds of cell lists: an extrema graph, and sorted lists of boundary cells. In an extrema graph, extremum points are connected by arcs, and each arc has a list of cells through which it passes. At the same time, all boundary cells are sorted according to their minimum and maximum values, and two sorted lists are then generated. Isosurfaces are generated by visiting adjacent intersected cells in order. Here, the starting cells for this process are found by searching in an extrema graph and in sorted boundary cell lists. In this process, isosurfaces appear to propagate themselves. Our algorithm is efficient, since it visits only cells that are intersected by an isosurface and cells whose IDs are included in the guides. It is especially efficient when many isosurfaces are interactively generated in a huge volume. Some benchmark tests described in this paper show the efficiency of the algorithm.

Volume thinning for automatic isosurface propagation

An isosurface can be efficiently generated by visiting adjacent intersected cells in order, as if the isosurface were propagating itself. We previously proposed an extrema graph method (T. Itoh and K. Koyamada, 1995), which generates a graph connecting extremum points. The isosurface propagation starts from some of the intersected cells that are found both by visiting the cells through which arcs of the graph pass and by visiting the cells on the boundary of a volume. We propose an efficient method of searching for cells intersected by an isosurface. This method generates a volumetric skeleton. consisting of cells, like an extrema graph, by applying a thinning algorithm used in the image recognition area. Since it preserves the topological features of the volume and the connectivity of the extremum points, it necessarily intersects every isosurface. The method is more efficient than the extrema graph method, since it does not require that cells on the boundary be visited.

Isosurface generation by using extrema graphs

A high-performance algorithm for generating isosurfaces is presented. In this algorithm, extrema points in a scalar field are first extracted. A graph is then generated in which the extrema points are taken as nodes. Each arc of the graph has a list of IDs of the cells that are intersected by the arc. A boundary cell list ordered according to cells values is also generated. The graph and the list generated in this pre-process are used as a guide in searching for seed cells. Isosurfaces are generated from seed cells that are found in arcs of the graph. In this process, isosurfaces appear to propagate themselves. The algorithm visits only cells that are intersected by an isosurface and cells whose IDs an included in cell lists. It is especially efficient when many isosurfaces are interactively generated in a huge volume. Some benchmark tests described show the efficiency of the algorithm.<<ETX>>

Volume visualization of 3D finite element method results

This paper describes a method for visualizing the output data set of a 3D finite element method result. A linear tetrahedral element is used as a primitive for the visualization processing, and a 3D finite element model is subdivided into a set of these primitives, which are generated at every s< îd element. With these primitives, isosurfaces are visualized semltransparentiy from scalar data at each node point. Two methods are developed for the visualization of isosurfaces with and without inteimediate geometries. The methods are applied to output data sets from some simulation results of a semiconductor chip. These are visualized, and the effectiveness of the method is discussed.

Fast traverse of irregular volumes

This paper proposes a fast cell traverse method for volume rendering of irregular volume datasets. All cells of an irregular volume are subdivided into a set of tetrahedral cells for our algorithm. The number of calculations needed to find the intersections of a ray and an irregular volume is reduced by using the exterior faces of cells rather than the ray as a basis for processing. An efficient new method of computing the integration of the brightness equation along a ray takes advantage of the linear distribution of data within a tetrahedral cell. Benchmark tests proved that the proposed method significantly improves the performance of volume rendering.

Visualization of simulated airflow in a clean room

Techniques for visualizing a simulated air flow in a clean room are developed by using an efficient cell traverse of tetrahedral cells generated from irregular volumes. The proposed techniques, probing and stream line display, are related to the measurement techniques used in actual clean rooms. The efficient traverse makes it possible to move freely around a given irregular volume and to spawn off stream lines. A successful application of these techniques to a problem in a clean room is also described.<<ETX>>

Fast generation of spherical slicing surfaces for irregular volume rendering

An efficient algorithm for generating a set of concentric spherical slicing surfaces for volume rendering of irregular volume datasets is presented. Our original algorithm, which approximates volume rendering by accumulating concentric spherical slicing surfaces from back to front, generates these surfaces by means of a conventional isosurface generation algorithm. However, this causes a performance bottleneck. To solve the problem, we propose a proliferous generation of slicing surfaces from seed cells, which are automatically determined according to the extremum points of the values of distances from a viewing point. A benchmark test shows that this approach can improve the performance significantly. In addition, we compare this algorithm with a raycasting algorithm that we proposed previously, and discuss a criterion for selecting which one to use for maximizing the performance

Volume visualization for the unstructured grid data

We propose a method for visualizing 3-D scalar data defmed on unstructured grid data by means of tetrahedral primitives. In these primitives, data are distributed linearly not only along edge lines but along any line segments. This characteristic is well suited to hnëar interpolation, which is a very effective method of visualization in terms of computational cost. Because of the wide use of the 3-D fmite element method (FEM), there is a strong need for volume visualization of the unstructured grid data that is output by 3-D FEM analysis. In this kind of analysis, various kinds of fmite elements, which are composed of unstructured grid data, are used in a mixed form to represent a complicated 3-D space. In a finite element, data are expressed by means of the elements own interpolation function. In terms of data processing, a simple interpolation function is most suitable, because it consumes few computational resources. We therefore select a linear tetrahedral element (LTE), and introduce a concept of element subdivision to other fmite elements. In our method, each fmite element is first reconstructed as a set of LTEs that approximates its interpolation function. We visualize iso-valued surfaces from 3-D scalar data by using an LTE as a processing primitive. For this, we have developed two methods. One is a method for extracting triangular facets as iso-valued surfaces and rendering them by a traditional shading algorithm. The other is a method for rendering LTEs directly in order to visualize iso-valued surfaces. We apply these methods to analysis of thermal stress in a semi-conductor chip and simulation of air-flow in a clean room, and confirm their effectiveness.

Seed specification for displaying a streamline in an irregular volume

Two techniques are presented for specifying seed points, which are the starting points for streamlines, in an irregular volume. One is an interactive seed specification technique, in which efficient data probing is achieved by traversing the adjacency graph of the volume. The other is an automatic seed specification technique. A seed point is placed near a critical point, where the velocity vector is zero. Efficient algorithms are given for finding and classifying the critical point by using a tetrahedral cell. A successful application of these techniques to a problem in a clean room is also described.

A high-speed integrated renderer for interpreting multiple 3D volume data

This paper proposes an integrated rendering algorithm for visualizing 3D volumetric and geometric data, such as surfaces, lines and points, simultaneously with depth information, and other algorithms for improving the performance of the rendering process of the first. The first algorithm extends a volume rendering algorithm based on ray-tracing so that it can handle both 3D volumetric and geometric data. It processes these data in accordance with their original representation formats to eliminate conversion artefacts such as spurious or missing surfaces, and also gives special treatment to volume segments so as to avoid errors in visibility at the intersections between volume segments and geometric data. The other algorithms employ adaptive termination of ray-tracing, elimination of rays that do not intersect the volume, and adaptive undersampling over an image plane. These improve the performance by three to seven times over the brute-force approach. The cost and versatility of the algorithm are evaluated by using data from the results of 3D computational fluid dynamics.