Re: Problem with 3D Polygon

• To: mathgroup at smc.vnet.net
• Subject: [mg33456] Re: Problem with 3D Polygon
• From: "Allan Hayes" <hay at haystack.demon.co.uk>
• Date: Fri, 22 Mar 2002 04:06:31 -0500 (EST)
• References: <a79cit\$7ug\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Kevin,
When showing a Polygon[{p1,p2,p3,p4,...pn}] in 3D, Mathematica superimposes
the insides of the triangles
Polygon[{p1,p2,p3}], Polygon[{p1,p3,p4}, ....,Polygon[{p1, p(n-1), pn}]
This accounts for the solid rectangle that you get.
How it decides on the edges, or parts of the edges, to show, I have not yet
worked  out in detail but it looks to be based on parts of the line
Line[{p1,p2,p3,...,pn}].
--
Allan

---------------------
Allan Hayes
Mathematica Training and Consulting
Leicester UK
www.haystack.demon.co.uk
hay at haystack.demon.co.uk
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565

"Kevin J. McCann" <kmccann at umbc.edu> wrote in message
news:a79cit\$7ug\$1 at smc.vnet.net...
> When I plot the following
>
> Graphics3D[{LightBlue,
>         Polygon[{{1,0,0},{1,0,1},{-1,0,1},{-1,0,0},{-1/2,0,0},{-1/2,0,
>               1/2},{1/2,0,1/2},{1/2,0,0},{1,0,0}}]}],Lighting->False,
>     Boxed->False];
>
> I get just a blue rectangle with some of the boundary drawn, not an
inverted
> "U" shape. Can someone explain this please.
>
> Kevin
>
>
>

```

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