Henry Sowizral

Efficient collision detection using bounding volume hierarchies of k-DOPs

Collision detection is of paramount importance for many applications in computer graphics and visualization. Typically, the input to a collision detection algorithm is a large number of geometric objects comprising an environment, together with a set of objects moving within the environment. In addition to determining accurately the contacts that occur between pairs of objects, one needs also to do so at real-time rates. Applications such as haptic force feedback can require over 1000 collision queries per second. We develop and analyze a method, based on bounding-volume hierarchies, for efficient collision detection for objects moving within highly complex environments. Our choice of bounding volume is to use a discrete orientation polytope (k-DOP), a convex polytope whose facets are determined by halfspaces whose outward normals come from a small fixed set of k orientations. We compare a variety of methods for constructing hierarchies (BV-trees) of bounding k-DOPs. Further, we propose algorithms for maintaining an effective BV-tree of k-DOPs for moving objects, as they rotate, and for performing fast collision detection using BV-trees of the moving objects and of the environment. Our algorithms have been implemented and tested. We provide experimental evidence showing that our approach yields substantially faster collision detection than previous methods.

Scene graphs in the new millennium

Hardware 3D graphics accelerators will be ubiquitous in the new millennium. The great majority of 3D graphics programs will, almost exclusively, use scene graphs. Rarely will graphics programs use immediate mode-if at all-and then only for very special effects, and scene graphs will grow to support new modalities such as sound and haptics. Outrageous? Probably. Predicting the future is never easy. By looking at where we are today and analyzing technology trends, these predictions may seem even more outrageous, outrageously mundane. The author considers how graphics technologies, hardware and software, are evolving at exponential rates.

The Java 3D API and virtual reality

Java programmers can quickly and easily define graphics programs using Java 3Ds scene graph classes. An expanded view model lets applications seamlessly operate in a variety of single- and multiple-display, nonhead-tracked and head-tracked, display environments. This view model relies on the flexible InputDevice interface that Java 3D provides to remove most of the vagaries of hardware trackers.

Adapting computer graphics curricula to changes in graphics

Abstract Introductory computer graphics courses are changing their focus and learning environments. Improvements in hardware and software technology coupled with changes in preparation, interest, and abilities of incoming students are driving the need for curriculum change. Past courses focussed on low- and intermediate-level rendering principles, algorithms, and software development tools. Many of these algorithms have migrated into hardware. Though important knowledge for advanced graphics programmers, most graphics applications programmers have no need to study at this level, much as application programmers have no need to study hardware systems or assembly level programming. Courses need to focus on intermediate- and high-level principles, algorithms, and tools. A fundamental need in modern graphics curricula is integration of a 3D graphics API into the instruction. This paper presents experiences teaching this focus with both low and high level graphics programming APIs. The experiences were gained in courses at an undergraduate university and in multi-day industrial courses for experienced professional programmers.

Fusion of absolute and incremental position and orientation sensors

We describe a theoretical basis for combining absolute and incremental position and orientation data, based on optimization and the maximum likelihood principle. We present algorithms for carrying out the computations, and discuss associated computational issues. We treat separately the translation and rotation problems. For the translation problem, we postulate that we have a sensor of absolute (position) and a sensor of first-difference (velocity) data. We also bring in the second-difference (acceleration) when we consider a possible dynamics assumption. For the rotation problem, we postulate only that we have a sensor of orientation and a sensor of first-order rotation changes. We obtain sensor averages by solving a nonlinearly constrained quadratic optimization problem.

Note on dynamics of human head motions and on predictive filtering of head-set orientations

We investigate the problem of predicting future head orientations from past and current data because the use of raw sensor data in a virtual environment creates visual misalignment due to system time-lag. We develop a form of a generalized calculus where we can investigate trajectories of orientations in their most natural setting. Using a generalization of the Taylor expansion, we derive first- and second-order dynamics, that we then test against real data. Empirically, we discovered that both kinds of dynamics give fairly accurate predictions and that the first-order dynamic gives consistently better predictions than the second-order dynamic. We explain this result by forming a hypothesis: that changes in the orientation of a human head tend to be very simple. Expect for very brief surges of muscle energy when acceleration or deceleration occurs, the orientation of a human head is either fixed, or it changes in a linear, constant-angle motion about a fixed axis. We also test our first-order predictor against a published extended Kalman filter and we find that the first-order dynamic predictions are approximately 20% more accurate and have smaller variance.

Look Ma! four hands! new models for interacting with 3D environments

The most important shift over the last few years is that the World Wide Web has changed the basis on which ideas can be disseminated and communicated. The presence of the Web means that code now can be practically developed that will run everywhere. In terms of 3D interaction, VRML 2.0 provides mechanisms for rudimentary interaction, and Java 3D increases the common base of what’s possible. Thus, instead of interface paradigm development being localized to particular laboratories, technologies can easily be distributed unilaterally, and in a networked fashion.

What 3D API for Java should I use and why? (panel)

Application programmers may use Java bindings to OpenGL++, a scene graph toolkit for OpenGLtm, to render and to provide interaction with 3D objects and scenes. OpenGL++ provides interaction features similar to the Inventor interactive toolkit and features derived from Silicon Graphics’ experience with the highperformance Performer visual simulation toolkit. Developers have control over their 3D application from as high a level as “load and render this VRML 2.0 database” to as low a level as “draw these polygons with these colors, viewed from this location”.