ritter@versatc.UUCP (Jack Ritter) (06/08/89)
I've come up with a fast, approximation to
3D Euclidian distance ( sqrt(dx*dx+dy*dy+dz*dz) ).
(It's probably not original, but .....)
1) find these 3 values: abs(dx), abs(dy), abs(dz).
2) Sort them (3 compares, 0-3 swaps)
3) Approx E.D. = max + (1/4)med + (1/4)min.
(error: +/- 13%)
max + (5/16)med + (1/4)min has 9% error.
max + (11/32)med + (1/4)min has 8% error.
As you can see, only shifts & adds are used, and
it can be done with integer arithmetic.
It could be used in ray tracing as a preliminary
test before using the exact form.
We all have our dirty little tricks.
--
-> B O Y C O T T E X X O N <-
Jack Ritter, S/W Eng. Versatec, 2710 Walsh Av, Santa Clara, CA 95051
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