From: srp@travis.csd.harris.com (Stephen Pietrowicz)
Subject: Surface normal orientations
Article-I.D.: travis.1pscti$aqe
Organization: Harris CSD, Ft. Lauderdale, FL
Lines: 20
NNTP-Posting-Host: travis.csd.harris.com

Some rendering programs require that all surface normals point in the same
direction.  (ie: On a closed cube, all normals point outwards).  You can use
the points on the faces to determine the direction of the normal, by making
sure that all points are either in clockwise or counter-clockwise order.

How do you go about orienting all normals in the same direction, given a 
set of points, edges and faces?   Say that you had a cube with all faces that 
have their normals facing outwards, except for one face.  What's the
best way to realize that face is "flipped", and should have it's points
re-ordered?   I thought I had a good way of telling this, but then realized
that the algorithm I had would only tell you if you had points in clockwise
order for a 2d polygon.  I'd like something for 3d data.

Any hints, tips, references would be appreciated.

Steve
-- 
Where humor is concerned there are no standards -- no one can say what is good 
or bad, although you can be sure that everyone will.  -- John Kenneth Galbraith
------- These opinions are my own.
