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From: rice@swatsun (Dan Rice)
Newsgroups: comp.graphics
Subject: Wanted: Clever Intersection Tests
Message-ID: <1222@byzantium.swatsun.UUCP>
Date: Wed, 15-Jul-87 14:30:48 EDT
Article-I.D.: byzantiu.1222
Posted: Wed Jul 15 14:30:48 1987
Date-Received: Sat, 18-Jul-87 01:47:58 EDT
Organization: Swarthmore College, Swarthmore PA
Lines: 17
Keywords: ray tracing


	I'm in the midst of writing a ray-tracer, and I would be very interested
in any clever and unusual intersection tests that people have come across.  For
example, one I saw recently calculated the intersection of a ray with a sphere
by finding the closest approach of the ray to the center of the sphere with two
dot products, and then found the actual intersection point by forming a triangle
with the intersection point, the sphere center, and the point of closest
approach.  Other ray-tracers that I've seen calculate this intersection by
solving a quadratic equation for the intersection point directly.  I'm curious
to see if there are similar examples of clever intersection tests beating brute-
force tests.  I'd appreciate examples or source, or pointers to literature about
geometric intersection tests.

-- 
- Dan Rice, Swarthmore College, Swarthmore PA 19081
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