You can spatially find points which lie on the surface by using several
methods.  The easiest is the spatial grid (in which you sample in rows and
columns down through the object at set intervals - you can build a shell of
the object by then joining all the points).

There are other methods for producing more accurate and efficient results
but I don't know how hard they are to implement.  Most of them use a simple
point test on the f(x,y,z) to determine if the point is inside or outside
the object.

--
Lance.
The Zone - http://come.to/the.zone

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