[Radiance-general] how to start it using participating media

[Carsten Bauer]

Hi Thomas

nice to hear that the info was useful..

btw, two short clarifications:
my last sentence was maybe a bit ambigous, of course one can set medium 
extinction and albedo globally, but you still need the mist volume and 
mist material with the source list to show scattering. Otherwise only 
the extinction will show up, attenuating the light according to the 
distance the rays have traveled in the scene
In this case, a usual way is setting global extinction, for example  
with -me 0.07 0.07 0.07 and then define a mist material :

void  mist fogdemo
n ... sources
0
6  0 0 0  0.5 0.5 0.5

the zeros for the extinction in the mist materials mean to use the 
global value without changes, only scattering is calculated in tthe 
volume then.

To add further complexity and confusion :-), in limited, well defined 
circumstances also the extinction can be successfully  modified by a 
pattern. A 'colorfunc' modifier to the mist material acts on the 
extinction values, however, they aren't changed over the mist volume, 
just the value at the entry point is set and then holds for that ray 
throughout the mist volume. In special cases, when the gradient of the 
extinction is vertical to the view rays, this can indeed work out well, 
but only then..
Think e.g of a fog layer increasing in densitiy with decrasing height 
above ground, and the looking through it more or less in horizontal 
direction...

-Carsten