I have a sun include file defined thusly:

#ifndef (sun_radius_m)
#declare sun_radius_m = 6.96e8;
#end

#ifndef (sun_distance_m)
#declare sun_distance_m = 1.5e11;
#end

#ifndef (sun_render_distance_m)
#declare sun_render_distance_m = sun_distance_m;
#end

#declare sun_render_radius_m = sun_render_distance_m * sun_radius_m /
sun_distance_m;

#declare sun_color = rgb< 1, 1, .5 >;

#declare sun_sphere =
sphere
{
  <0,0,0>, sun_render_radius_m
  pigment { color sun_color }
  finish { ambient 1 }
}

#declare sun =
light_source
{
  < 0, sun_render_distance_m, 0 >
  color sun_color
  looks_like { sun_sphere }
}

I wanted to use this to easily create a sun light source for outdoor scenes.
If I declare
a sun object at the default render distance with a camera say at the origin
and then rotate
the sun into the camera's view ( I have to reduce the angle quite a bit ),
things in the scene
will be illuminated but the sun itself will not be visible.  If I make the
render distance around
10000000 or less, the sun is visible.  Can someone explain this to me?

Also, does anyone have any examples of how to create a photo-realistic
atmosphere like the
ones from terragen in POV?  Specifically how to make the atmosphere scatter
blue and thus make
the sun redder as it has to shine through more atmospheric media.  Also the
creation of sun rays
through clouds.

Any help is much appreciated...

J.D.

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J.D. Herron <boo### [at] gci-netcom> wrote:
: will be illuminated but the sun itself will not be visible.  If I make the
: render distance around
: 10000000 or less, the sun is visible.  Can someone explain this to me?

  There's an internal limit in povray. If an object is farther away than
a certain distance, it's not traced.
  I don't know the specific reasons for this. There may be some accuracy
issues here.

  With that big values your sun might not look like a perfect circle, anyways.
You should be aware that the accuracu of floating point numbers is quite
limited.

-- 
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):_;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/

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"J.D. Herron" wrote:
>
> Also, does anyone have any examples of how to create a photo-realistic
> atmosphere like the
> ones from terragen in POV?

Here you will find description of the algorithm and c code
for reasonably realistic atmospheric effects.

http://www.cs.utah.edu/vissim/papers/sunsky/

______________________________________________________________________
Kari Kivisalo                                  http://www.kivisalo.net

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Hi Folks,

The atmosphere model looks very good. It could possibly be incorporated
as a patch to the current scattering media code. I haven't looked at
this code closely enough to be sure. Any comments from those who have?

There is another (of the many) interesting paper on this site which
describes how to do fairly robust conversion from RGB triples to spectra
for reflectances. This could be used to expand and standardise the
chromatic dispersion patch to use 'proper' spectral responses.

Bye for now,
	Mike Andrews.

Kari Kivisalo wrote:
> 
> "J.D. Herron" wrote:
> >
> > Also, does anyone have any examples of how to create a photo-realistic
> > atmosphere like the
> > ones from terragen in POV?
> 
> Here you will find description of the algorithm and c code
> for reasonably realistic atmospheric effects.
> 
> http://www.cs.utah.edu/vissim/papers/sunsky/
> 
> ______________________________________________________________________
> Kari Kivisalo                                  http://www.kivisalo.net

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In article <39E43B9B.80740C07@reading.ac.uk>, Michael Andrews 
<M.C### [at] readingacuk> wrote:

> The atmosphere model looks very good. It could possibly be incorporated
> as a patch to the current scattering media code. I haven't looked at
> this code closely enough to be sure. Any comments from those who have?

I glanced at the paper, but didn't understand much of it...but it seems 
like more of a fog effect than media.


> There is another (of the many) interesting paper on this site which
> describes how to do fairly robust conversion from RGB triples to spectra
> for reflectances. This could be used to expand and standardise the
> chromatic dispersion patch to use 'proper' spectral responses.

I didn't see that...it could be interesting.

-- 
Christopher James Huff
Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tagpovrayorg, http://tag.povray.org/

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