[Radiance-general] illum-like behaviour for sky dome

[Axel Jacobs]

Dear list,

I have a brightfunc applied to the glow of the sky dome. I would like 
this pattern to be visible to the camera, but use a normal gensky 
generated sky for all sample rays.

Conceptually, this is similar to the illum type where a different 
material is applied when the object (the sky in my case) is viewed directly.

I did try with illum:

skyfunc glow skyglow
0
0
4  1 1 1  0

skyglow brightfunc bracelet
2 band bracelet.cal
0
0

skyfunc illum skymat
1 bracelet
0
3  1 1 1

skymat source sky
0
0
4  0 0 1  180

This works, but results in about twice the horizontal illuminance 
compared to a normal glow sky. The sky now takes part in the direct 
calculation (this works with -ab 0), and all light expectedly emenates 
from the zenith. So using illum is not an option.

Many thanks for your ideas

Axel