[Radiance-general] Re: why I got such blotchy results?

[Lars O. Grobe]

Hi Huang,

I think what you observe is a problem of the indirect calculation. If I 
guess that the only light source in your room is the descended light, 
which may be defined by using a manufacturers ies (is this the case?), 
than it is not that easy for the software to calculate the indirect 
illumination of the room correctly without finetuning a bit. First try 
to set a reasonable -ab value, maybe 2, depending on how many bounces 
you need to come from a surface to the source (it is just a simple 
room, so try 2 for the beginning). More important settings may be the 
-ad, -ar and -ad values, which define, generally speaking, the accuracy 
of the calculation of the indirect values (imagine a resolution used in 
the step of the indirect calculation, which is not the same as the 
final image resolution but must be coarse enough to find all the 
differences in the indirect values over your surfaces). On the other 
hand, setting these values to too accurate numbers is dangerous and 
will give terrible rendering times.

Just take a look at this list's archives, also at the documentation 
(there should be a small text file in the software documentation just 
about rpict settings), and, if possible, at the book Rendering with 
Radiance.

And try to find out what values are actually used by Desktop Radiance 
and how to influence them. If you want to rely on the GUI and it's 
defaults, this is the wrong list here, you need to know what's 
happening.

Good luck ;-)

CU Lars.