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From: ritter@versatc.versatec.COM (Jack Ritter)
Newsgroups: comp.graphics
Subject: World Cordinate Resolution
Keywords: Accuracy, floating point VS real numbers
Message-ID: <20582@versatc.versatec.COM>
Date: 11 Apr 90 22:25:08 GMT
Organization: Versatec, Santa Clara, Ca. 95051
Lines: 31

In most image synthesizers, 
you have the freedom to pick the overall
scale of your world coordinates. (The image-space
to screen-space transformation compensates.)
Most raytracers I've seen use a span of about
-10.0 to 10.0 for each world dimension. This
makes sense because it uses all of the accuracy
bits (where a span of, say, -.1 to .1, throws away
1 decimal digit of accuracy). It also allows more
elbow room for intermediate calculations as far
as over/under flow. Assume you're using doubles.

If your're careful about over/under flow, you dont
need all those exponent bits. What if you define
your world space span as: -10000 to 10000, for
example? Does this convert surplus exponent bits
into additional accuracy bits, or does it just
make the holes in floating-point-space bigger?
-- 
   Versatec, Inc.
   Jack Ritter, M.S. 1-7
   2710 Walsh Ave.
   P.O. Box 58091
   Santa Clara, CA 95052-8091
   (408)982-4332, or (408)988-2800 X 5743
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