> I am working on a planet earth model, and I found this cool map of the
> cities at night (Thanks Jon Berndt! for the reference). I am using it as a
> mostly transparent shell 0.000001 bigger than my earth image map sphere.
Why?  Can't you use layered textures?

> Now, the question. I of course want to only see the city lights on the
unlit
> side of earth. The easy unelegant way is to cut the sphere in half and
make
> sure that the city lights are applied only opposite the sun, but that
> requires a knowledge of where the sun is, and more calculations than I
care
> to do.
I did it using a slope-dependant texture, but of course you need the
position of the sun for this...

> Then I came up with a briliant (I thought) Idea: Set the ambient of the
> shell to 0.5, then the diffuse to -0.5. My thinking is that a negative
> diffuse setting means that the more light you hit it with, the darker it
> gets. So a full light hitting normal to this shell should result in a
total
> effect of 0.5 Ambient+(-0.5 Diffuse)=0 light.
I once did something similar...  A negative diffuse didn't work, I think,
but a very large negative highlight did!
I can't check it right now, but I think the following code gives more or
less the result you're after...
camera {
 location -z*5
 look_at 0
}
light_source {
 <500,500,-500>
 rgb 1//<0,0,1>
}
sphere {
 0,1
 texture {
  pigment {rgb <1,1,0>}
  finish {diffuse 0 ambient 1}// specular 1 roughness .01}
 }
 texture {
  pigment {rgbt <-2,-2,0,1>}
  finish {diffuse 1 specular 1 roughness 1 metallic}
 }
}




--
ZK
http://www.povplace.be.tf

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