We present a novel presence acceleration for volumetric ray casting. A highly accurate estimation for object presence is obtained by projecting all grid cells associated with the object boundary on the image plane. Memory space and access time are reduced by run-length encoding of the boundary cells, while boundary cell projection time is reduced by exploiting projection templates and multiresolution volumes. Efforts have also been made towards a fast perspective projection as well as interactive classification. We further present task partitioning schemes for effective parallelization of both boundary cell projection and ray traversal procedures. Good load balancing has been reached by taking full advantage of both the optimizations in the serial rendering algorithm and shared-memory architecture. Our experimental results on a 16-processor SGI Power Challenge have shown interactive rendering rates for 256/sup 3/ volumetric data sets at 10-30 Hz. We describe the theory and implementation of our algorithm, and shows its superiority over the shear-warp factorization approach.

The paper describes time management and time critical computing for a near real time interactive unsteady visualization environment. Subtle issues regarding the flow of time are described, formalized and addressed. The resulting system correctly reflects time behavior while allowing the user to control the flow of time. The problem of time critical computation is discussed and a solution is presented. These time critical algorithms provide control over the frame rate of a visualization system, allowing interactive exploration.

The paper describes the Field Encapsulation Library (FEL), which provides a grid independent application programmer's interface to gridded three dimensional field data. The C++ implementation of FEL is described, stressing the way in which the class hierarchy hides the underlying grid structure in a way that allows visualization algorithms to be written in a completely grid independent manner. Appropriately defined coordinate classes play an important role in providing this grid independence. High performance point location routines for data access are described and performance times are provided.

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No abstract available.

An implementation of a distributed virtual environment for the shared interactive visualization of large unsteady three-dimensional flowfields is described. Computation of the visualizations is performed on a Convex C3240 computer and the visualization data are transferred over a high-speed network to a Silicon Graphics Iris workstation for rendering. A boom-mounted six-degree-of-freedom head-position-sensitive stereo CRT (cathode ray tube) system is used for display. A hand-position-sensitive glove controller is used for controlling various tracers (e.g., 'smoke') for the visualization of the flow. User commands are sent to the Convex, which interprets these commands and computes the corresponding visualization. With this architecture, several users may share and cooperatively control the visualization generated by the Convex. The distributed architecture is also interesting to those using conventional screen and mouse interfaces.>

An implementation of a virtual environment for visualizing the geometry of curved spacetime by the display of interactive geodesics is described. This technique displays the paths of particles under the influence of gravity as described by the general theory of relativity and is useful in the investigation of solutions to the field equations of that theory. A boom-mounted six-degree-of-freedom head-position-sensitive stereo CRT system is used for display. A hand-position-sensitive glove controller is used to control the initial positions and directions of geodesics in spacetime. A multiprocessor graphics workstation is used for computation and rendering. Several techniques for visualizing the geometry of spacetime using geodesics are discussed. Although this work is described exclusively in the context of physical four-dimensional spacetimes, it extends to arbitrary geometries in arbitrary dimensions. While this work is intended for researchers, it is also useful for the teaching of general relativity.>

A recently completed implementation of a virtual environment for exploring numerically generated three-dimensional unsteady flowfields is described. A boom-mounted six-degree-of-freedom head-position-sensitive stereo CRT system is used for viewing. A hand-position-sensitive glove controller is used for injecting various tracers (e.g. smoke) into the virtual flowfield. A multiprocessor graphics workstation is used for computation and rendering. The techniques for visualizing unsteady flows are described, and the computer requirements for a variety of visualization techniques are discussed. These techniques generalize to visualization of other 3D vector fields.>

This paper reports on the development of a hand to machine interface device that provides real-time gesture, position and orientation information. The key element is a glove and the device as a whole incorporates a collection of technologies. Analog flex sensors on the glove measure finger bending. Hand position and orientation are measured either by ultrasonics, providing five degrees of freedom, or magnetic flux sensors, which provide six degrees of freedom. Piezoceramic benders provide the wearer of the glove with tactile feedback. These sensors are mounted on the light-weight glove and connected to the driving hardware via a small cable.