Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!samsung!usc!wuarchive!hsdndev!cmcl2!uupsi!sunic!liuida!isy!jonas-y
From: jonas-y@isy.liu.se (Jonas Yngvesson)
Newsgroups: comp.graphics
Subject: Re: newell plane equation
Keywords: graphics, plane eqation
Message-ID: <1991Mar8.164739.19270@isy.liu.se>
Date: 8 Mar 91 16:47:39 GMT
References: <9283@exodus.Eng.Sun.COM> <1991Mar7.203947.27550@csrd.uiuc.edu>
Organization: Dept of EE, University of Linkoping
Lines: 28

neeman@s5.csrd.uiuc.edu (Henry J. Neeman) writes:

>Actually, I think D = -(Ax[k] + By[k] + Cz[k]), for any k in 1..N.

Correct.

>Anyway, your problem is that you're overdetermining your plane.  A plane
>can be described by three points, and I'm guessing that Newell's technique
>takes advantage of that.  Let's try it:

Nope. As I pointed out in another posting, the problem was that the points
were used in wrong order. The great *advantage* with Newell's method is
that you use *all* the points around the polygon, *not* just three of them.
If the three points you choose happends to lie on a straight line in the
plane your computations will fail. This is avoided in Newell's method (if
*all* the points in the polygon is on a straight line in the plane it fails
too, of course, but then it's not really a polygon).

The important thing is to take the points in the correct order, walking
clockwize, or counterclockwize, around the polygon. In the example, the
points were taken in an order that created an 8-shaped polygon.

--Jonas
-- 
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 J o n a s   Y n g v e s s o n
Dept. of Electrical Engineering	                         jonas-y@isy.liu.se
University of Linkoping, Sweden                   ...!uunet!isy.liu.se!jonas-y