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Re: Mathematica Lightning Model?

  • To: mathgroup at
  • Subject: [mg14742] Re: Mathematica Lightning Model?
  • From: Martin Kraus <mkraus at>
  • Date: Thu, 12 Nov 1998 02:17:41 -0500
  • Organization: Regionales Rechenzentrum Erlangen, Germany
  • References: <72bdtl$>
  • Sender: owner-wri-mathgroup at

Alexander Otte wrote:
> Hi!
> How can it be, that the shading of an object depends on the distance
> between object and viewer?
> The following line of code shows the problem:
> Plot3D[Sin[x] Cos[y],{x,0,2 Pi},{y,0,2 Pi},
> LightSources->{{{1,0,1},RGBColor[1,0,0]}},ViewPoint->1000{1.3,-2.4,2.0}]
> The surface is rendered with a single color. Even if an object is far
> away - should't the intensity of diffuse reflected light depend on the
> angle between the surface normals and the direction of light?
> So what kind of lightning model (lightning equation) does Mathematica
> use?
> Thanks
>     Alex


as far as I understand, the problem is that the ViewPoint vector is not
properly normalized in the calculation of shadings. For long ViewPoint
vectors this leads to a squeezing of the graphics in the direction of
the ViewPoint vector with respect to the lightning.  Therefore, the
graphics in your case are shaded as if they were flat; thus, they are
uniformly colored.

This is a known bug. Hopefully it will be corrected somewhen. 


Martin Kraus

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