Military training trends are placing increasing emphasis on use of simulators for full-crew, full-mission training. Visual scene simulation must provide effective visual cues with a high degree of realism and a minimum of distracting effects.

The relationships between objects and their shadows, and the changes in these relationships as the observer moves in the gaming area, have been demonstrated to be extremely effective in contributing to the mental correlation process by which an observer extracts knowledge of the world from visual observations. Computer Image Generation (CIG) applied to visual scene simulation has always had the capability to validly portray shadows modeled as part of a fixed environment — but has had difficulty coping with changing illumination or shadows of moving objects.

The optical laws which apply to transmission of light through translucent faces are quite simple, and it was readily demonstrated that such faces could be used to provide excellent simulation of shadows. This provided the incentive to devise algorithms for such simulation which would be feasible for implementation in real-time hardware.

After the capability to simulate translucent faces was developed, ideas arose for their use in applications other than shadows. They were used for windows, with very realistic results. Overlapping translucent spheres and ellipsoids were used for smoke and cloud simulation. For this application to be satisfactory, the processing must be modified from that process conforming to the laws of physics.

An extremely fruitful use for translucent faces is in implementation of gradual transition between versions of three-dimensional models. This application is expected to be of even greater significance than the use for which they were developed. As in the case of cloud simulation, processing must depart from physical laws for graudal transition - but in a different manner than for clouds.

In summary, techniques have been developed for simulation of translucent faces. Three modes of operation apply different rules when more than one translucent face is imaged on the same portion of a view window. This allows extended use of the techniques in providing improved CIG effects.

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