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The Surface corresponding to the region of obscuration when a solid is illuminated from a point light source (located at the Radiant Point). A Disk is the Shadow of a Sphere on a Plane perpendicular to the Sphere-Radiant Point line. If the Plane is tilted, the shadow can be the interior of an Ellipse or a Parabola.

See also Projective Geometry

© 1996-9 Eric W. Weisstein