[Radiance-general] Area lights breaking up?

[Greg Ward]

(Meant to copy this to radiance-general, but I guess I missed.)

Hi Ian,

This behavior is the same as for Radiance 3.6.  (I just checked.)   
You can increase the -dj parameter to 1 and get a better result.   
Decreasing -ds also helps somewhat, but setting -ds 0 makes it look  
unnatural.  Increasing the roughness also alleviates the problem --  
it's just when you're on the boundary that you'll have trouble.

An alternative is to use a perfectly smooth material modified by a  
random texture function that simulates roughness without applying the  
BRDF model in Radiance, like so:

# A glossy surface
void texfunc ball_roughness
4 gloss_dx gloss_dy gloss_dz gloss.cal
0
3 0.01 0.01 0.01

ball_roughness plastic white3
0
0
5       0.9     0.9     0.9
         0.05    0.0

-Greg

P.S.  There are two relevant references for materials in Radiance, as  
Rob mentioned:

SIGGRAPH '92:    http://radsite.lbl.gov/radiance/papers/sg92/paper.html

Materials reference:    http://radsite.lbl.gov/radiance/refer/ 
materials.pdf

> From: Ian Tester <ian at testers.homelinux.net>
> Date: August 23, 2005 5:11:18 PM PDT
>
> The problem appears to be with the roughness of the plastic. If  
> it's set
> to 0, then reflections are shown. As soon as I increase it to as  
> much 0.01,
> the plastic is no longer reflective and all we see is the specular
> highlights of the sub-divided area light pieces. Is this the intended
> behaviour? I remember spending quite some time fine-tuning these  
> parameters
> to look just the way I wanted. Now nothing I can do will bring back  
> the old
> appearance. The billiard balls should be glossy but not too smooth.
>
> I wondered if my problems might be to the mixfuncs and such that I  
> use to
> produce the billiard balls. So I made a super simple scene to test  
> this
> problem and I get the same results. I've attached it to this email.  
> Just
> run rad on the test.rif file.
>
> Here is what I get:
> http://www.ian.testers.homelinux.net/dump/test_main
>
> The left ball has a roughness of 0.01, the one on the right is 0.
>
> And if the mailing list eats the attachment:
> http://www.ian.testers.homelinux.net/dump/spectest.tar.bz2
>
> bye
>
>