[Radiance-general] Using BRDF measurement representations with Radiance

[Greg Ward]

Sorry, but this is one of those design decisions that is built into  
the code.  Of course, the C source is all there if you want to modify  
it, but there's quite a lot to figure out along the way, like how to  
sample the hemisphere for an arbitrary BRDF.  This is a difficult  
problem, and one that has been tackled by various people over the  
years, so there are some precedents.

If I were to do it myself, I would investigate something like a  
median cut algorithm or kd-tree on the hemisphere, which would  
require presampling the BRDF or performing lazy evaluation.  For  
something like the He-Torrance model, you would likely spend hours  
and hours (perhaps days) just computing the BRDF before you ended up  
tracing your first ray.  This is why Radiance doesn't make the attempt.

-Greg

> From: Jeppe Vesterbaek <j.vesterbaek at cs.ucl.ac.uk>
> Date: October 5, 2005 11:12:03 AM PDT
>
> Hi Greg
>
> Thanks for the quick reply. I'll have a look at "He.cal" tomorrow  
> (been staring too long at this monitor by now :p).
>
> With respect to Radiance's handling of BRDF materials: is there no  
> way (around) to change how Radiance calculates the indirect  
> component? I'll be using Radiance for rendering (relighted) real  
> scenes (in collaboration with Katrien Jacobs) and would like the  
> rendering to be as realistic as possible (no efficiency concerns  
> atm.).
>
> Thanks,
> /Jeppe
>