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From: finn@sunshine.cad.mcc.com (Chris Finn)
Newsgroups: comp.graphics
Subject: Find Surface Normal Which Goes to a Point
Keywords: surface normal
Message-ID: <4696@cadillac.CAD.MCC.COM>
Date: 11 Dec 89 17:46:50 GMT
Sender: news@cadillac.CAD.MCC.COM
Reply-To: finn@MCC.COM (Chris Finn)
Followup-To: comp.graphics
Distribution: comp.graphics
Organization: MCC CAD Program, Austin, TX
Lines: 15

Here is a problem to which I would like to know a fast and
robust solution.
	Given a point (x1,y1,z1), and a surface represented
by z = f(x,y), find the point (or points) on the surface where
the normal points towards (x1,y1,z1). The spatial derivatives
of f(x,y) are easily computed.
	The points and surfaces to which I would like to apply
this are relatively non-pathological (i.e. f(x,y) != a hemisphere
with x1,y1,z1 at the center).

Thanks,
Chris Finn
MCC CAD Program, P.O. Box 200195, Austin, TX 78720 [512] 343-0978
ARPA: finn@mcc.com
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