features in a volume of data. The visualizations are controlled by interactive tools, which "emit" collections of visualizations. It is these tools the user manipulates directly.

There are several features of the VWT architecture critical to its success: the computation and graphics are implemented in separate, asynchronous, concurrent processes so that a slowdown in the computation does not impede the head-tracked aspects of the display; the visualizations and tools are implemented in an object-oriented class hierarchy designed so that new visualizations or tools may be added without having to modify existing visualizations or tools; and a number of display and interaction technologies are supported, ranging from conventional workstation and mouse through head-mounted displays and gloves, with a unified interaction paradigm.

The VWT currently is under evaluation release at a number of NASA sites, with a general release expected in early 1997. For more information on the VWT, contact the Web at www.nas.nasa.gov/NAS/VWT. For papers on the VWT, contact the Web at www.nas.nasa.gov/~bryson/home.html.