[Radiance-general] an invisible glow

[Carsten Bauer]

Hi Schorsch and Alex !

Independent of what Alex really wants large area sources are a
problematic case for the direct calculation in the region near to the
source, as then the simplification of the inverse square law is not
valid anymore. Of course, they can be subdivided with -ds/dj, but if you
have objects very close to the source, especially transparent stuff
covering the source, you see the subdivision effect. So it can make
sense to treat a large area source with the indirect calculation only,
and so there might be the need of an invisible indirect source material
just as there's an invisible direct source material (illum). It's a
rather exceptional case though. And it all sounds pretty much of
cheating and faking, but for image generation, this is allowed :).

I have to admit, however, that the secondary ambient hack which I have
mentioned doesn't seem to work correctly for this purpose, you see the
effect of the glow but not with the correct illumination levels. But as
this hack wasn't meant to be used in this way (I just tried to 'abuse'
it for fun after reading Alex's mail) I don't have to feel guilty about
it... 

:-).


-Carsten