[Radiance-general] Multiple spherical glow sources?

[Lars O. Grobe]

Hi Mark!
> Yes, I have that paper. I aim to include the atmospheric horizon glow 
> in another step (mixfunc with the stars), and not even include the 
> stars when their influence is negligible. The illumination from the 
> stars will also only be effective when there is no moon (or a new moon).

So would you expect any difference when using stars clustered into 
groups by mksource and just averaging all the stars contribution over 
the whole hemisphere?

One way would be to use mkillum on a facetted hemisphere. The resolution 
of this hemisphere could be adjusted (use gensurf) until you see no 
further improvements by increasing the resolution. I guess running 
mksource would create more or less the same result, as there will not be 
very concentrated regions on the night sky that mksource could optimize 
for. Maybe you would use the 145-patch sky dome for mkillum.

One other way you could go (please do not beat me for this Greg, I know 
that I tend to do funny things with Radiance :-) ) is to create such a 
simplified but correct sky dome, and using the photon map extension 
create a global photon map for your scene that will account for the 
ambient calculation (the one which gets noisy with the high-res image 
map). Then you replace the simplified sky dome by the one showing all 
detail, but keeping the old global pmap render our image. This should 
give a good result, as for the direct calculation having the high-res 
image map does not cause problems. To help distributing the photons in 
the first step, creating a big photon-port box around the area that will 
be visible in your image would be very helpful of course.

I am not sure whether it is possible to force radiance to reuse an 
ambient file without doing further refinement on it (ok, no it gets 
evil...). I would guess that you could do the trick I tried with the 
photon map by rendering the image first with the simplified glow sky, 
filling up your ambient file (without the noise that you would get from 
the high-res light probe). If you would re-use this ambient file in a 
second step with the high-res map, even if new values are written to it 
there should be much less noise, and in my understanding the result 
should still be correct. But - I have not tried it... ;-) Any comments 
on this?

Cheers,

Lars.