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

[Greg Ward]

Hi Lars,

Without the benefit of photometric measurements, or having seen the  
material of which you speak, it is quite impossible to usefully  
speculate as to its behavior.  All I can say is that far-field  
reflectance should be an average of near-field behavior that is  
appropriately computed (averaged) in Radiance.  There can be issues  
with noise depending on the model, but you shouldn't require two  
types of model for near and far field.

-Greg

> From: Lars O. Grobe <grobe at gmx.net>
> Date: May 21, 2005 5:57:08 AM PDT
>
> 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.