# RE: Triangle Normals

From: Anthony D. Martin (amartin@engr.csulb.edu)
Date: Wed Jan 10 1996 - 23:21:51 EET

On Wed, 10 Jan 1996, BROCK ROONEY wrote:
>
> I don't think any normals are necessary at all.
> Using the vertex normals allows you to calculate A curve,
> but not The curve (the original part shape). Reasonable normals
> can be obtained by examining the local situation.
>
But the resulting "improved" part can't be trusted. Sure, you can just
average the normals of the neighboring facets and smooth it out. But
what if there is _supposed_ to be a corner there. You can also assume
that if the angle between facets is greater than some value, then it is
supposed to be a corner, and if it is less than this value then it should
be smooth, but it is likely to guess wrong in some situations.
If the normal data is supplied at each vertex, of course you can only
get A curve that is not likely to match the actual curve, but it will
probably be very close. Trying to add facets to a model with too few
facets will only approximate A curve, not The curve as well, and if you
are not using normal vertices supplied with the data, then this
approximated curve is only a guess. I think that the actual model will
be closer approximated by basing it on _real_ normal data, rather than a
guess.

Tony.

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