Margus Ramst wrote in message <36d04c43.0@news.povray.org>...
>The clouds look a bit too solid. They should also have a red hue in a
sunset
>(dawn?) image. Of course, for this to look right, they would have to be 3D
>media objects.
>Still, it's a lot better than any sky image I've come up with. How did you
>get this  yellow/violet banding near the sun?
>
>Margus
>
Well, to start with...

  I used a gradient pigment as pigment 1:

#declare Sun = pigment { gradient y
   color_map

      [0.000 color rgbt 2*<1, .4, 0, -1>]
      [0.0009 color rgbt 2*<1, .4, 0, -.25>]
      [0.0045 color rgbt <1, .4, 0, .2>]
      [0.05 color rgbt <1, .2, 0, .325>]
      [0.1 color rgbt <1, 0, -.05, .5>]
      [1 color rgbt <1, -.2, -.1, 1>] }
   scale 2 translate -1 rotate -85.5*x rotate 12.5*y }

  A z gradient would work just as well.
  Pigment 2 is intended to be a color filter to set up the sky atmosphere,
but I haven't used it right (obviously):

#declare Sky_Map = pigment { gradient y
   color_map {
      [0 color rgbft -4*<1,.8,-1,-1,-1>]
      [0.00045 color rgbft -4*<1,.4,-1,-1,-.25>]
      [0.00225 color rgbft 2*<-.25,-.4,.75,.75,-.2>]
      [0.025 color rgbft 2*<-.5,-.2,.5,.5,-.325>]
      [0.1 color rgbft 2*<-.75,0,.05,.25,-.5>]
      [1 color rgbft 2*<-1,.2,-.5,0,-1>] }
   scale 4 translate -1 rotate -85.5*x rotate 12.5*y }

  Finally, I put it all together with the clouds you can see:

sky_sphere

   pigment { Sun }
   pigment { Sky_Map }
   pigment { wrinkles turbulence 1.3 octaves 7 omega .6 lambda 4.5
      color_map {
         [0,.5 color color rgb <.9,.75,0> filter .8 transmit .25 color rgb
.5 filter .035 transmit .25]
         [.5,.7 color rgb .9 filter .035 transmit .25 color rgb 1 filter
.035 transmit .25]
         [.7,1 color rgb 1 filter .035 transmit .25 color rgb 1 filter .035
transmit .25] }
      scale <1,.254,10> } }

  AND, what really helps get the effect right:

sphere { 0,3600 texture { pigment { color rgbf 1 }
   finish { ambient 0 diffuse 0 reflection .4 specular .5 } }
   interior { ior 1.00229 fade_power .5 fade_distance 1000 }  hollow on }

AND

light_source { <0,-1000,0> color Pink media_interaction on rotate -85.5*x
rotate 12.5*y }

  I have found that MandarinOrange, for the light_source color, works best
(after I posted). I'm still playing, though.

  I hope that helps!

GrimDude
vos### [at] arkansasnet

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