“Path specification and path coherence” by Shelley and Greenberg

This paper presents an interactive method for specifying a path in space and time through a three-dimensional environment. A sequence is generated by showing the series of views along the path. The sequence is previewed on a vector scope, and after it is interactively refined, each frame is rendered on a raster device. The path is represented by a B-spline to provide smooth, continuous motion. The timing along the path is also defined by a B-spline so that changes in velocity are smooth. The use of “path coherence” is introduced. The utilization of the available data from the a priori temporal and spatial path definition holds great promise for frame to frame coherence. The path coherence can be used to reduce the number of polygons which need to be considered in a viewed environment. This reduction makes the previewing of complex environments appear less cluttered. Furthermore, the computational expense of the culling and sorting operations in the visible line/surface determination is reduced. One sample usage of this is a tree-structured partitioned environment where the priority ordering of the environment must be changed only when the path crosses a partition boundary.

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