The following POV code is an adaptation of Mike Andrews clouds.pov code for just the clouds. I have a need to see how it was done, but in units of feet and not miles. I have tried to modify it, but it comes out pure black - though it renders just as slowly as his clouds.pov scene! Anyone know what I am doing wrong?
 
Jon
 
 
// Start of cloud code ... rather a 
mess.
#declare cloudShape = density { spotted ramp_wave }
 
#declare D_Cloud_Center =
density {
   cloudShape triangle_wave
   colour_map {
      [0.5 colour Gray95]
      [1.0 colour Gray75]
   }
}
 
// Calculate 
the correct colour_map values.
#declare NT = floor((groundRad + 6) / 6);
#declare DT = (groundRad + 6)*5280 / NT;
#declare V1 = 1 - (6 - 2.0)*5280 / DT;
#declare V2 = 1 - (6 - 2.5)*5280 / DT;
#declare V3 = 1 - (6 - 3.5)*5280 / DT;
#declare V4 = 1 - (6 - 4.5)*5280 / DT;
#declare V5 = 1 - (6 - 5.5)*5280 / DT;
#declare V6 = 1 - (6 - 6.0)*5280 / DT;
 
// container for cloud.
difference {
   sphere { 0, (groundRad + 6.0)*5280 }
 sphere { 0, (groundRad + 3.5)*5280 }
   pigment { rgbf 1 }
   interior {
      media {
         intervals mSamples
         scattering { 2, rgb 5 extinction 1.0}
         samples 2, mSamples
         confidence 0.9999
         variance 1/1000
         density { D_Cloud_Center scale 2*3*0.2*5280 }   // fine scale cloud detail
   density { D_Cloud_Center scale 2*3*0.08*5280 }
         density {         // confine the cloud to the container
             onion
          &nbs p; colour_map {
          [V1 rgb 0]
        [V2 rgb 0]
        [V3 rgb 0]
        [V4 rgb 1]
        [V5 rgb 1]
        [V6 rgb 0]
            }
            scale DT
         }
         // large scale cloud detail
         density {
            onion
       colour_map {
        [V1 rgb 0]
        [V2 rgb 1]
        [V3 rgb 1]
        [V4 rgb 0]
        [V5 rgb 0]
        [V6 rgb 0]
       }
            warp { turbulence 0.25*0.8 octaves 3 lambda 3 omega 0.7 }
            scale DT
         }
      }
   }
   translate -groundRad*5280*y
   hollow
}
 
// atmosphere 
#declare NT = floor((groundRad + 20.0) / 20.0);
#declare DT = (groundRad + 20.0)*5280 / NT;
#declare V1 = 1 - (20.0 - 5.0)*5280 / DT;
#declare V2 = 1 - (20.0 - 5.0)*5280 / DT;
 
sphere {
   0, (groundRad + 20.0)*5280
   pigment { rgbf 1 }
   interior {
      media {
         intervals mSamples
   scattering { 4, rgb atmCol extinction 1 }
   samples 2, mSamples
   confidence 0.9999
   variance 1/1000
         density {
            onion ramp_wave
             colour_map {
           &n bsp;   [V1 rgb 1]
           & nbsp;   [V2 rgb 0.5]
            ;    [1  rgb 0]
            }
         }
         scale DT
      }
   }
   translate -groundRad*5280*y
   hollow
}