David C. Banks

Image-guided streamline placement

Accurate control of streamline density is key to producing several effective forms of visualization of two-dimensional vector fields. We introduce a technique that uses an energy function to guide the placement of streamlines at a specified density. This energy function uses a low-pass filtered version of the image to measure the difference between the current image and the desired visual density. We reduce the energy (and thereby improve the placement of streamlines) by (1) changing the positions and lengths of streamlines, (2) joining streamlines that nearly abut, and (3) creating new streamlines to fill sufficiently large gaps. The entire process is iterated to produce streamlines that are neither too crowded nor too sparse. The resulting streamlines manifest a more hand-placed appearance than do regularlyor randomly-placed streamlines. Arrows can be added to the streamlines to disambiguate flow direction, and flow magnitude can be represented by the thickness, density, or intensity of the lines. CR Categories: I.3.3 [Computer Graphics]: Picture/Image generation; I.4.3 [Image Processing]: Enhancement. Additional

Illumination in diverse codimensions

This paper considers an idealized subclass of surface reflectivities; namely a simple superposition of ideal diffuse and ideal specular, restricted to point light sources. The paper derives a model of diffuse and specular illumination in arbitrarily large dimensions, based on a few characteristics of material and light in 3-space. It describes how to adjust for the anomaly of excess brightness in large codimensions. If a surface is grooved or furry, it can be illuminated with a hybrid model that incorporates both the ID geometry (the grooves or fur) and the 2D geometry (the surface).

Multi-frequency noise for LIC

We present a way to visualize a flow field using Line Integral Convolution (LIC) with a multi frequency noise texture. A broad range of feature sizes can enhance a users perception of the magnitudes and direction of the flow. In addition, the multiple scales of feature size help a user clarify the motion of the flow in an animation.

Selective visualization of vortices in hydrodynamic flows

Vortices are important features in many research and engineering fields. Visualization is an important step in gaining more understanding and control of vortices. Vortex detection criteria fall into two categories: point based scalar quantities, calculated at single points, and curve based geometric criteria, calculated for, e.g., streamlines. The first category is easy to compute, but does not work in all cases. The second category is more intuitive and should work in all cases, but currently only works in 2D (or 3D projected) flows. We show applications of both approaches in hydrodynamic flows.

TennisViewer: a browser for competition trees

A tennis novice watching a match for the first time might be surprised that the crowd erupts with cheers when a player wins one point, then barely applauds when he wins the next. The crowd is not necessarily fickle; some points are genuinely more important than others because a tennis match is hierarchically structured. One match consists of several sets. One set consists of several games. One game consists of several points. The match-winning point is the most important one. How can we make that importance visible? Our goal is to let a fan, a player, or a coach examine tennis data visually, extract the interesting parts, and jump from one item to another quickly and easily. The visualization tool should help parse the elements of a match. We developed an interactive system called TennisViewer to visualize the dynamic, tree-structured data representing a tennis match. It provides an interface for users to quickly explore tennis match information. The visualization tool reveals the overall structure of the match as well as the fine details in a single screen. It uses a 2D display of translucent layers, a design that contains elements of Tree-Maps and of the Visual Scheduler system, which was designed to help faculty and students identify mutually available (transparent) time slots when arranging group meetings. TennisViewer provides MagicLens filters to explore specialized views of the information and a time-varying display to animate all or part of a match.

Extracting iso-valued features in 4-dimensional scalar fields

Isosurfaces are an important tool for finding features in 3D scalar data. The paper describes how recursive contour meshing is applied to extract similar features in 4-dimensional space. In the case of time-varying isosurfaces f(x, y, z, t)=c, the technique constructs a solid mesh for the isosurface that sweeps a volume in space-time. An instance of an isosurface at a particular time results from applying a second constraint against this volume. The envelope defined by the time-varying isosurface can be captured in a similar way: when a time-varying isosurface f=c reaches is maximum extent, the functions partial derivative with respect to time must be zero. This second constraint and produces a surface containing the extrema of the isosurfaces. Multi-resolution models and inter-penetrating blobby objects can also be extracted from 4-dimensional representations.

Complex-valued contour meshing

An isovalue contour of a function of two complex variables defines a surface in four-space. We present a robust technique for creating polygonal contours of complex-valued functions. The technique, contour meshing, generalizes well to larger dimensions.

Two-dimensional sequence compression using MPEG

This paper presents a technique to use the MPEG-2 compression scheme to compress a 2D array of images. The technique operates over two spatial dimensions, instead of the normal temporal dimension. This compression is crucial to interactive image-based rendering techniques, which allow virtual walk-throughs of texture-rich scenes. Since the MPEG schemes can achieve high compression with minimal image degradation, the large storage problems are reduced. This increase the applicability of image-based rendering on standard workstations or personal computers. Results are compared against previously presented compression schemes for image-based rendering.

Visualizing a tennis match

This paper describes our work on visualizing the information of a tennis match. We use competition trees to organize the information of a tennis match and visualize the competition trees by the top-nesting layered maps with translucent colored layers. We create iconic representations to describe the detailed information of athletic events in an intuitive manner. Specialized views of the information are displayed by applying multiple Magic Lens filters on the top-nesting layered maps. The dynamic nature of the tennis match is depicted by the time-varying display. The approach we present in this paper can be used to visualize other sports information, information with competition property, or information with hierarchical structure.

Interactive 3D visualization of optical phenomena

Each year at colleges and universities nationwide, some 10,000 students take a course on optics, typically through a physics department. The method of instruction has changed very little in the past 40 years, and many of the textbook illustrations have remained essentially the same during this time. In particular, the illustrations rely heavily on line drawings and 2D graphs. Certain key concepts in optics possess fundamentally 3D aspects, which instructors typically demonstrate in a classroom laboratory. Currently, several computer-assisted instructional modules support teaching optics by visualizing optical phenomena. We created interactive 3D graphical modules for visualizing optical phenomena by applying 3D visualization techniques to instructional courseware.