Wasn't it Barron Gillon who wrote:
>not trace!  I need to find the normal at an arbitrary point that
>_may_or_may_not be on the surface.  Trace finds an intersection with a
>surface and then returns the normal at the intersection, but I need the
>normal from an arbitrary point given an arbitrary function.  Trace is good,
>but not quite what I'm looking for.  Thanks anyway.

If the point isn't on the surface, then there's obviously no normal at
that point.

Do you mean that you want to know if its possible to determine the
direction of the Grad vector of an arbitrary scalar field?

-- 
Mike Williams
Gentleman of Leisure

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