Computer Sciences Dept.

Using the ASP for the Interactive Viewing of Polyhedral Scenes

W. Brent Seales and Charles R Dyer

In this paper, we discuss an approach for solving the problem of interactively viewing a polyhedral scene. Interactive viewing is the computation and display of an interactively controlled sequence of views of a scene corresponding to a viewer’s movement along a continuous viewpath. We present an algorithm for generating such views with hidden-lines removed, and consider extensions to solve the problem of generating views with hidden-surfaces removed. The method relies on a precomputation phase which constructs the aspect representation, or asp. This representation can be used to interactively view a polyhedral scene at video rates with hidden-lines or surfaces removed. The method exploits viewpath coherence, a form of frame-to-frame coherence present in such a sequence of views. The display of polyhedral line drawings with hidden lines removed makes use of the topology of the image line drawing and the pre-ordering of visual events which change that topology. This approach is extended to interactive viewing with hidden-surfaces removed and with shading, shadows, and multiple light sources. The set of object resolution polygons representing the visible faces and the shadow polygons for a single frame can be computed efficiently from the previous frame using the asp. The hidden-line and hidden-surface algorithms are closely related via the asp. Interactive viewing with hidden-lines removed is shown to be about as fast as the interactive display of a wire-frame scene. The primary on-line cost of hidden-surface interactive viewing is the cost associated with scan converting the visible surfaces and shadow polygons.

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