Bob Hughes wrote in message <369ECBDE.8FD96178@aol.com>...
>Anyone get a reasonable, and useable, atmospheric media working for
>various situations? I.e., different camera/object distances and number
>of lights so when you make a new scene the media (as used for
>atmosphere) doesn't wreak havoc while adjusting it endlessly?
>I understand the basic scaling syndrome of keeping media density in sync
>with container objects, but I've been lost too many times trying the
>containerless "air", since each scene is not the same as the last.


One thing you have to remember is to scale the densities according to
the scale of the scene. I've found that to have 50% of light absorbed
by a media of thickness "dist" the appropriate definition is
  media { absorption 1/(sqrt(2)*dist) }
I suppose the same applies to scattering media. Since the density is
constant, you can speed up rendering by using "intervals 1". Oh, and
don't use the fade_distance keyword in interior if you want a realistic
scene - the formula used has nothing to do with realistic absorption.

I do agree that the overlap between the values in density{} and the
actual absorption/emission/scattering values can be a bit confusing.
It may be a good idea to treat either of the values as being normalized
to the 0.0-1.0 range and to vary the other.

BTW, whatever were the povray designers thinking when they implemented
light_source fading? For some reasong the realistic formula
  attenuation = pow( fade_distance/d, fade_power )
was replaced by
  attenuation = 2/( 1 + pow( d/fade_distance, fade_power ) )
which has AFAIK absolutely no connection to reality, even though it does
approximate the proper formula at distances far greater than fade_distance
as long as you remember to divide the brightness by two.. (The same cannot
be said for the aforementioned interior fading.)

Hmm.. maybe I should finally get a C compiler for this computer and start
writing my own patches.. my wish list is growing too long to remember.

--
Ilmari Karonen (ilt### [at] scifi)
(not r### [at] hakasaunalahtifi as the IRTC comments list claims..)
http://www.sci.fi/~iltzu/

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