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MathGroup Archive 2000

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Graphics Directives Lost In Certain Cases

  • To: mathgroup at smc.vnet.net
  • Subject: [mg25622] Graphics Directives Lost In Certain Cases
  • From: "David Park" <djmp at earthlink.net>
  • Date: Mon, 16 Oct 2000 03:04:43 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Dear MathGroup,

I have come across a strange behavior of 3D graphics where graphics
directives are lost in certain cases. It has to do with a 3D arrow routine I
am working on, but here is the bare bones essence of the problem.

The following plot gives a second thick blue line plotted on top half of the
first thin black line.

Show[Graphics3D[
{{Line[{{0, 0, 0}, {10, 10, 10}}]},
 RGBColor[0, 0, 1],
 AbsoluteThickness[2], {Line[{{0, 0, 0}, {10, 10, 10}/2}]}}],
   AspectRatio -> Automatic, PlotRange -> All];

If I combine the second line with this polygon, the color and thickness
directives are lost. Why?

Show[Graphics3D[{{Line[{{0, 0, 0}, {10, 10, 10}}]}, RGBColor[0, 0, 1],
     AbsoluteThickness[2], {Line[{{0, 0, 0}, {10, 10, 10}/2}],
      {Polygon[{{5., 5., 5.}, {4., 4.306186217847897, 3.6938137821521027},
         {3.6938137821521027, 4., 4.306186217847897}}]}}}],
   AspectRatio -> Automatic, PlotRange -> All];

But the directives are not lost if the second line is not right on top of
the first line.

Show[Graphics3D[{{Line[{{0, 0, 0}, {10, 10, 10}}]}, RGBColor[0, 0, 1],
     AbsoluteThickness[2], {Line[{{0, 0, 0}, {10, 10, 10.000001}/2}],
      {Polygon[{{5., 5., 5.}, {4., 4.306186217847897, 3.6938137821521027},
         {3.6938137821521027, 4., 4.306186217847897}}]}}}],
   AspectRatio -> Automatic, PlotRange -> All];

Nor are the directives lost if a different polygon is used.

Show[Graphics3D[{{Line[{{0, 0, 0}, {10, 10, 10}}]}, RGBColor[0, 0, 1],
     AbsoluteThickness[2], {Line[{{0, 0, 0}, {10, 10, 10}/2}],
      {Polygon[{{5., 5., 5.}, {4., 4.306186217847897, 3.6938137821521027},
         {4., 3.6938137821521027, 4.306186217847897}}]}}}],
   AspectRatio -> Automatic, PlotRange -> All];

Needless to say, most of the time I lose the directives. Does anyone know
the cause of this?

David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/





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