My POV-ray tutorial told me that if I wanted the sun created by the
sky_sphere command to emit an apparent shadow through clouds, I'd have to
make a really large sky_sphere with the proper texture,and put the
light_source outside the sky_sphere. How do I do that, since the tutorial
never told me? Here's the programming language below I used to create the
sky_sphere with the sun and clouds, but the clouds do not cast shadows.

#include "colors.inc"
#include "finish.inc"
camera {
  location <0,1,-10>
  look_at <0,4,0>
  angle 80
}
light_source {<0,1e4,10000>White scale 1300}
sphere {
  <0,2,0>,1
  pigment {color rgb <1,1,1>}
  finish {ambient .2 diffuse 0 reflection .6}
}
sky_sphere {
  pigment {
    gradient y
    color_map {
      [0,.002 color rgb<1,.2,0>
              color rgb<1,.2,0>]
      [.002,.2 color rgb<.8,.1,0>
               color rgb<.2,.2,.3>]
    }
  }
  scale 2
  translate -1
  pigment {
  bozo
  turbulence .65
  octaves 6
  omega .7
  lambda 2
  color_map {
    [0,.1 color rgb<.5,.5,.5>
          color rgb<.75,.75,.75>]
    [.1,.5 color rgb<1,1,1>
           color rgbt<1,1,1,1>]
    [.5,1  color rgbt<1,1,1,1>
           color rgbt<1,1,1,1>]
  }
  scale .1
}
rotate -135*x
}
plane {
  y,0
  pigment {color Green}
  finish {ambient .3 diffuse .7}
}

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On Wed, 12 May 2004 13:03:43 EDT, "CFM" <nomail@nomail> wrote:

>My POV-ray tutorial told me that if I wanted the sun created by the
>sky_sphere command to emit an apparent shadow through clouds, I'd have to
>make a really large sky_sphere with the proper texture,and put the
>light_source outside the sky_sphere.

The Pov-Ray sky_sphere is a background sort of thing. You cannot put
anything behind it. 
The Pov-Ray documentation Section 3.11.2.3  Adding Some Clouds
Says;
The sky sphere has one drawback as you might notice when looking at
the final image (skysph3.pov). The sun doesn't emit any light and the
clouds will not cast any shadows. If you want to have clouds that cast
shadows you'll have to use a real, large sphere with an appropriate
texture and a light source somewhere outside the sphere. 
I wonder where you got your tutorial it seems to be leading you
astray.

Regards
        Stephen

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Hash: SHA1

CFM wrote:
| My POV-ray tutorial told me that if I wanted the sun created by the
| sky_sphere command to emit an apparent shadow through clouds, I'd
have to
| make a really large sky_sphere with the proper texture,and put the
| light_source outside the sky_sphere. How do I do that, since the
tutorial
| never told me? Here's the programming language below I used to
create the
| sky_sphere with the sun and clouds, but the clouds do not cast shadows.
|
	You can't do it with a sky_sphere, since by definition it is infinite
and therefore behind the clouds. So what you do is use a regular
sphere with a large radius and your cloud texture with the blue parts
replaced by a transparent color. Then all you have to do is put your
light source further out. Something like that (the texture will almpst
certainly require tweaking):

sky_sphere {
~  pigment {
~    gradient y
~    color_map {
~      [0,.002 color rgb<1,.2,0>
~              color rgb<1,.2,0>]
~      [.002,.2 color rgb<.8,.1,0>
~               color rgb<.2,.2,.3>]
~    }
~  }
~  scale 2
~  translate -1
}
sphere {
~  0, 1000000000
~  pigment {
~  bozo
~  turbulence .65
~  octaves 6
~  omega .7
~  lambda 2
~  color_map {
~    [0,.1 color rgb<.5,.5,.5>
~          color rgb<.75,.75,.75>]
~    [.1,.5 color rgb<1,1,1>
~           color rgbt<1,1,1,1>]
~    [.5,1  color rgbt<1,1,1,1>
~           color rgbt<1,1,1,1>]
~  }
~  scale .1
~  }
~  rotate -135*x
}

- --
******************************
*      Jerome M. Berger      *
* mailto:jbe### [at] ifrancecom *
*  http://jeberger.free.fr/  *
******************************
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>  You can't do it with a sky_sphere, since by definition it is infinite
> and therefore behind the clouds. So what you do is use a regular
> sphere with a large radius and your cloud texture with the blue parts
> replaced by a transparent color. Then all you have to do is put your
> light source further out. Something like that (the texture will almpst
> certainly require tweaking):
>
> sky_sphere {
> ~  pigment {
> ~    gradient y
> ~    color_map {
> ~      [0,.002 color rgb<1,.2,0>
> ~              color rgb<1,.2,0>]
> ~      [.002,.2 color rgb<.8,.1,0>
> ~               color rgb<.2,.2,.3>]
> ~    }
> ~  }
> ~  scale 2
> ~  translate -1
> }
> sphere {
> ~  0, 1000000000
> ~  pigment {
> ~  bozo
> ~  turbulence .65
> ~  octaves 6
> ~  omega .7
> ~  lambda 2
> ~  color_map {
> ~    [0,.1 color rgb<.5,.5,.5>
> ~          color rgb<.75,.75,.75>]
> ~    [.1,.5 color rgb<1,1,1>
> ~           color rgbt<1,1,1,1>]
> ~    [.5,1  color rgbt<1,1,1,1>
> ~           color rgbt<1,1,1,1>]
> ~  }
> ~  scale .1
> ~  }
> ~  rotate -135*x
> }
>
> - --
> ******************************
> *      Jerome M. Berger      *
> * mailto:jbe### [at] ifrancecom *
> *  http://jeberger.free.fr/  *
> ******************************
>
OK, I created a very large sphere with a pigment and color_map in many
similarities to yours. Unfortunately, the clouds always show up as dark.
What tweaking is necessary to lighten them up?

And I realize that my tutorial, which I downloaded with POV-ray for Windows
v3.5 told me something that seemed a bit off, but now I realize that the
tutorial meant a literal "sphere," not a "skysphere."

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"CFM" <nomail@nomail> wrote in message
news:web.40a276f4f48fa4edf438a2280@news.povray.org...
> OK, I created a very large sphere with a pigment and color_map in many
> similarities to yours. Unfortunately, the clouds always show up as dark.
> What tweaking is necessary to lighten them up?
>

If the only light in your scene is the "sun" then maybe only the back of the
clouds are recieving light. You could try to add lights between the ground
and the clouds, to illuminate the visible parts of the clouds

Post a reply to this message

> If the only light in your scene is the "sun" then maybe only the back of
the
> clouds are recieving light. You could try to add lights between the ground
> and the clouds, to illuminate the visible parts of the clouds

Or use double_illuminate, so that both sides of a surface are lit.

-- 
"Tim Nikias v2.0"
Homepage: <http://www.nolights.de>

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Tim Nikias v2.0 wrote:
|>If the only light in your scene is the "sun" then maybe only the back of
|
| the
|
|>clouds are recieving light. You could try to add lights between the
ground
|>and the clouds, to illuminate the visible parts of the clouds
|
|
| Or use double_illuminate, so that both sides of a surface are lit.
|
	Or add: finish { ambient 1.0 diffuse 0.0 } to get the same effect as
with the sky_sphere

		Jerome

- --
******************************
*      Jerome M. Berger      *
* mailto:jbe### [at] ifrancecom *
*  http://jeberger.free.fr/  *
******************************
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In article <40a28795$1@news.povray.org>,
 "Tim Nikias v2.0" <#macro timnikias (@) #local = "gmx.net" #end> 
 wrote:

> > If the only light in your scene is the "sun" then maybe only the back of
> the
> > clouds are recieving light. You could try to add lights between the ground
> > and the clouds, to illuminate the visible parts of the clouds
> 
> Or use double_illuminate, so that both sides of a surface are lit.

Both of these will cause additional shading effects due to the angle of 
incidence of the light rays varying over the surface of the sphere. The 
correct solution is to use ambient 1 and diffuse 0 in the finish, as 

lighting.

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: <chr### [at] tagpovrayorg>
http://tag.povray.org/

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Christopher James Huff nous apporta ses lumieres ainsi en ce 2004/05/12 
17:05... :

>In article <40a28795$1@news.povray.org>,
> "Tim Nikias v2.0" <#macro timnikias (@) #local = "gmx.net" #end> 
> wrote:
>
>  
>
>>>If the only light in your scene is the "sun" then maybe only the back of
>>>      
>>>
>>the
>>    
>>
>>>clouds are recieving light. You could try to add lights between the ground
>>>and the clouds, to illuminate the visible parts of the clouds
>>>      
>>>
>>Or use double_illuminate, so that both sides of a surface are lit.
>>    
>>
>
>Both of these will cause additional shading effects due to the angle of 
>incidence of the light rays varying over the surface of the sphere. The 
>correct solution is to use ambient 1 and diffuse 0 in the finish, as 

>lighting.
>
>  
>
Using that technique, don't forget to put the main light *far* outside 
the big sphere. If you don't, the shadows will get blown up to gigantic 
proportions. Placing the main light around 10 times the sphere radius 
should give you fair results, as well as using parallel light.

Alain

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In some cases using one (or more) y planes will produce better looking clouds 
than a sphere. And it's easy to animate too - you can translate the texture in 
x/z to simulate wind and in y to make the clouds change their shape...
-sascha

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