ShieldTester: cell-to-cell visibility test for surface occluders

Abstract

We present a novel Cell-To-Cell Visibility (C2CV) algorithm, which given two polyhedra,A and B and a connected and oriented manifold triangle mesh, S offers a simple, fast, and conservative test for detecting when A and B are occluded from each other by S. Previously disclosed C2CV algorithms either relied on costly occlusion fusion or were restricted to convex or “apparently convex” occluders, which makes them inappropriate for scenes where potential occluders are arbitrary triangulated surfaces, such as the body of a car or a portion of a terrain. The simplicity of our C2CV algorithm, named ShieldTester, stems from a new Occlusion Theorem, introduced here which permits to establish occlusion by computing the intersection of S with a single ray from a vertex of A to a vertex of B. ShieldTester may be used to establish that pairs of cells in a subdivision of space are hidden from each other by a relatively large surface occluder, so that when the viewer is in one cell, the objects in the other cell need not be displayed.