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Re: is the visibility of a Polygon[] exposed?

• To: mathgroup at smc.vnet.net
• Subject: [mg83700] Re: is the visibility of a Polygon[] exposed?
• From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
• Date: Wed, 28 Nov 2007 05:43:28 -0500 (EST)
• References: <figuou$foo$1@smc.vnet.net>

Hi,

take the normal of the polygon and (since the polyhedron
is convex) use only polygon with normals pointing into the viewer.

Regards
   Jens



congruentialuminaire at yahoo.com wrote:
> Hello Mathematica UG:
> 
> Is it possible for my code to tell if a Polygon (in my graphics
> object) is visible?
> 
> I assume that this is based upon (or is affected by) the ViewPoint->
> setting.
> 
> Further, I assume that the kernel is deriving this somewhere to do
> rendering. Do I have any access to this?
> 
> If I evaluate:
> 
> q = PolyhedronData["SnubCube"]
> 
> I can see the component Polygon[] and GraphicsComplex[] objects that
> make up the Graphics3D[]. I want to make a code decision based on
> whether a face is showing.
> 
> TIA.
> 
> Regards..Roger W.
>