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Hi Rob,<br>
<br>
[snip]<br>
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<pre wrap="">In Autocad (for example) 3dfaces that
are built in a clockwise manner will have the normal pointing out of
the clockwise face (I hope I am remembering this correctly).
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It's hard to tell from your description if you are or not. Think of it
this way: let's say you are drawing a polygon that represents the face
(screen) of the computer monitor you are now staring at. If you draw the
points in a clockwise fashion, the surface normal will be pointing away
from you (out the back of the monitor). If you define it with points in a
COUNTER-clockwise fashion, the polygon's surface normal will be pointing
at you. IOW, in the first example, with a glow applied, the monitor face
would render black. In the latter example, the monitor face would glow.
This can be reinforced by a permutation of the so-called "right hand
rule". Take your right hand and point at your face with your thumb, and
then curve your fingers around the axis defined by your thumb; if you
imagine your fingers pointing in the direction of rotation (and direction
of point creation), your thumb describes the surface normal (vector).
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<br>
Ack, yes you are absolutely correct! I knew I should have gone and
actually checked.... Another way to consider this, if you are working
in the XY plane (Autocad based example here) then counter clockwise
gets you a normal point in positive Z.<br>
<br>
Of course this really applies to surface generated geometry. Solid
modeling will bring its own set of issues with geometry management....<br>
<br>
-Jack<br>
<pre class="moz-signature" cols="72">--
# Jack de Valpine
# president
#
# visarc incorporated
# <a class="moz-txt-link-freetext" href="http://www.visarc.com">http://www.visarc.com</a>
#
# channeling technology for superior design and construction
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