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MathGroup Archive 2000

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fade to mauve

  • To: mathgroup at smc.vnet.net
  • Subject: [mg24393] fade to mauve
  • From: "Christopher J. Purcell" <purcell at drea.dnd.ca>
  • Date: Wed, 12 Jul 2000 23:13:35 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Using Vers 4.0 and i think all the way back to 2.2, if you ParametricPlot
anything, say a hemisphere:

radius = 1;
ParametricPlot3D[
  radius{Sin[theta]Cos[phi], Sin[theta]Sin[phi], Cos[theta]}, {theta, Pi,
    2 Pi}, {phi, 0, Pi}, ViewPoint -> radius *{1.3, -2.4, 2.}]

where the ViewPoint is close to the default {1.3, -2.4, 2.} you get the
usual nice shaded image. But when you increase the magnitude of Viewpoint,
the colors and shading start to fade. For example if you repeat the above
with radius = 10,
the shading has now faded to an ugly mauve (on a mac) even though the
sphere has been scaled the same amount as ViewPoint. The same holds if you
use Graphics3D to plot filled shaded polygons.

When I draw big things and need to use big Viewpoints to get the
perspective right, they lose their lighting.

I don't see why it has to be this way.

Dr. C. J. Purcell
Group Leader/Transducers
Defence Research Establishment Atlantic
9 Grove St., Dartmouth, NS Canada B2Y 3Z7
Tel: 902-426-3100-x389
Fax: 902-426-9654




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