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Old 24th May 2004, 03:07 AM   #1
INNIS
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Default Vertices Surfaces and Normals

Hi Guys
After spending sometime getting acquainted with
AC3D I have some questions that I don't seem to find
definitive answers to in the manual.
This has to do with Vertice order , surfaces and normals.
I would like to know when the magenta normal arrow is
indicating the correct orentation of the surface.I find with a
4 vertice poly if I keep changing the vertex order the normal
arrow will cycle through about six stages.Three when the normal
is pointing in the correct direction and three when the normal points in the
incorrect direction also there seems to be a couple of times when the
normal arrow is pointing along the surface is this correct.
The question I have is how do I know of the three times the normal
is pointing in the correct direction which is the correct vertex order for
the surface or is it a trial and error situation.I hope the above makes
sense.
What does a surface with a red border mean and how can it be corrected
other than deleting it.

Thanks for any help you may be able to give.

Cheers
Innis
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Old 25th May 2004, 03:27 PM   #2
Andy
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A surface normal is calculated using only the first three vertices of a surface.

The vertex order only really matters if you have a concave polygon i.e. one with a 'dent' in the side. If that 'dent' is defined by the first three vertices, the normal will be the opposite to what you expected - and you may get a black surface (because the lighting gets confused).

A red outline on a surface either indicates crossing edges (move some vertices) or that it failed to triangulate - possibly because the vertices are not on the same plane.

Andy
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Old 26th May 2004, 06:08 AM   #3
INNIS
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Hi Andy
Thanks
The red edges must have been because it failed to
triangulate.Can this be fixed by the triangulate command
or do you need to redo the surface.

Cheers
Innis
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Old 26th May 2004, 11:55 AM   #4
Andy
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Yes - manually triangulating the surface (menu Surface->triangulate) should fix it.

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