On Fri, 13 Feb 1998 00:26:58 +0100, mbr### [at] swipnetse (Mathias Broxvall)
wrote:

>Sorry, I haven't found a macintosh port of the isosurface patch.
>I've started porting it myself but isn't finished. Anyway, correct
>me if I'm wrong, can it realy handle 4000 - 10000 asteroids (tracing
>time) in a fast way?

Perhaps not as fast as a method that can assume local linearity, but
it is fast.  The number of asteroids isn't really as relevant as the
volume is.  Here are the details from the isosurface documentation.
Note that, unless you tell it otherwise, it only finds the first
intersection of a given ray with an isosurface object.

The equipotential-surface finding in POVeq patch is based on a
recursive subdivision method as following. 

   1.POV-Ray calculates the potential values at the two points (d1 and
d2, where d1<d2: the distance from the initial point of the ray). 
   2.If there is a possibility (possibility is calculated with a
testing function T(f(d1),f(d2), MAX_GRADIENT)) of existence of the
equipotential-surface between 'd1' and 'd2', POV-Ray calculates
potential value at another point 'd3' on the ray between the two point
'd1' and 'd2'. 
   3.If there is a possibility between 'd1' and 'd3', POV-Ray
calculates another point 'd4' between 'd1' and 'd3'. 
   4.If there is no possibility between 'd1' and 'd3', POV-Ray looks
for another point 'd4' between 'd3' and 'd2'. 
   5.These calculation (1-4) will be done recursively until
(dn-dn')<"ACCURACY".

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