[Radiance-general] Specular instead of lambertian for indirect

[loscotec at libero.it]

Thank you for your reply greg !

Actually I think mixfunc wouldn't fit my needs.

I try to explain what I would like to obtain from another perspective. 

I would like to use a specular material representing asphalt (not mirror-like specular material). This will be obtained by trial and errors with metal primitives, using the closer rapresentation, if possible. It will lead surely to a certain error in representation, then, to minimize it, as i will have photometrics values and then BRDF definitions, I would like to use BRDF too. 

If I am right, right now, BRDF can just be considered lambertian for the indirect calculation. I would like than to force Radiance to consider them specular (defining specular values by hand). 


Is it possible? Is it hard? ANy suggestion for a different approach?

As about using mixfunc, if understood it right, the problem would be that direct calculation would be performed on both brdf and specular, leading me to a quite correct result (due to brdf), but influenced form the specular_bit.

As about the indirect calculation it would be influenced by specular (which is ok) but also from lambertian (indirect calculation of brdf). 

Am I wrong? 

Lucio


.Hi Lucio,
.
.> I know that I could run two simulations and then combine the  
.> results, but it would be much cleaner to be able to use a new kind  
.> of primitive able to use BRDF for direct light and a specular  
.> material for indirect light. Is it possible to develop such  
.> primitive? I'm not very skilled about programming , but I can  
.> always learn and help in developing such primitive, if you like. I  
.> guess that such kind of primitives could be handy even for other  
.> applications. What do you think about it?
.
.Do you want the specular part to be 'pure' -- that is, mirror-like?   
.If so, this can be achieved easily enough by specifying a mixfunc  
.with a fixed parameter, e.g.:
.
.void metal specular_bit
.0
.0
.5 0.1 0.1 0.1 1 0
.
.void plasdata brdf_data
.{your arguments here}
.
.void mixfunc asphalt
.4 specular_bit brdf_data 0.5 .
.0
.0
.
.Since we are mixing half of each, you need to double each component  
.(the specular_bit and the brdf_data), but otherwise this should work.
.
.If, on the other hand, you want a specular component with a soft  
.lobe, it gets a little trickier.  Essentially, you want to modify  
.your BRDF data such that the Gaussian model you are using for the  
.specular_bit is taken out.  The basic principle still applies, however.
.
.I hope this makes sense.
.-Greg
.
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