[Radiance-general] sorry, again a question about gold mosaic

[Lars O. Grobe]

Hi List!

I am sorry, I have asked so often about this, but as I have to model a 
room with a lot of gold mosaic, which is not an easy material do 
define, here is one more question about this...

So far, I use a gold material (which has 100% specular reflection) 
together with a high roughness value (0.03). This gives me some visual 
impression of a mosiac and the right color of gold (I use the measured 
values by Andrew Glassner).

However, as for the indirect calculation, I wonder if I am completely 
wrong with this material. I have a specularity of 1.0 in my definition, 
while the effect of using this material as mosaic (not large, plane 
sheets of gold ;-) will in fact give a diffuse reflection in the large 
scale of e.g. a complete dome. So there is a difference in the material 
behaviour between the scale of a single piece of mosaic (which is more 
or less planar and may have this 100% specular reflectivity) and the 
scale of the building, where the material is "mosaic" consisting of 
millions of pieces, and diffuse.

I once planned to do some experiments with some kind of a "virtual 
photometer", where I could measure the output of a modeled sample from 
various directions. I did not do so simply because of a lack of time. 
And I was quite pleased by the effect of using the roughness parameter. 
Now I am worried, because I wonder if the diffuse effect of the mosaic 
will be neglected in the indirect calculation?

Thank You for any help, have a nice week-end, CU Lars.