[Radiance-general] Multiple spherical glow sources?

[Mark Stock]

Hello,

I am working on a star map for use with night renderings, and it 
seems like it should be decomposed into two layers: one is a 
high-resolution imagemap showing the stars themselves, the other 
is a low-resolution "light map" that should be used to actually 
illuminate the scene.

The problem is that I want the "light map" layer to do the 
illumination, but I don't want it to be visible. I want the image 
map to appear in the sky in the final rendering.

I know that I can use maxrad=-1 in the image map glow source to 
prevent it from contributing to scene illumination, and maxrad=0 
to allow the light map to illuminate. But mixfunc must be placed 
between the colorpict and the glow source, forcing me to either 
allow both to illuminate, or neither. But when the imagemap 
contributes to illumination, the result is very noisy 
(obviously).

This wouldn't be a problem if I could use two sky-dome sized glow 
sources in the same scene: "skyglow source skydome 0 0 4 0 0 1 
360". But Radiance only sees the last one to be defined.

And I can't make the light map into an "illum" because it then 
gets treated as a point source at the zenith of my "source" 
description (ignoring the 180-degree size of the source disc).

Do I need to add transparency to the imagemap before making it 
into a rad=-1 glow source, so that when a ray is traced between 
the stars, it hits the illuminating light map rad=0 glow source? 
I am reluctant to include another circa-gigabyte imagemap to the 
scene just for that.

Am I missing something else or is this impossible?

Mark

PS. Shouldn't the file size limit for colorpict images be raised? 
I get a warning for using even a 134MB picture file. I intend to 
go much larger.