[Radiance-general] virtual light sources with mirror & diffuse component

[Greg Ward]

Hi Lars,

As far as I can tell, your analysis and the parameters you derived are correct.

-Greg

> From: "Lars O. Grobe" <grobe at gmx.net>
> Date: August 2, 2012 3:11:47 AM PDT
> 
> Hi all,
> 
> I am currently setting up a scene where I need the mirror modifier to
> create virtual light sources. This mirror will stand for a metal sheet
> with high specularity - but also some diffuse reflectance. First it
> seams to be obvious, but the more I think about it the less sure I am
> about it.
> 
> I defined a mirror material referencing a metal material, which includes
> both the absolute reflectance and the specularity.
> 
> Example:
> 
> void metal mySheetMetal
> 0
> 0
> 5 .9 .9 .9 .8 0
> 
> That should lead to a specular reflectance of .9 * .8 = .72
> 
> (Typically, one would know the specular and absolute reflectance from
> measurements and have to calculate the specularity from it - the other
> way around.)
> 
> Is it this specular reflectance value of .72 that I have to use in my
> mirror materials definition? Like
> 
> void mirror mySheetMirror
> 1 mySheetMetal
> 0
> 3 .72 .72 .72
> 
> My understanding is that the virtual source should have the value of the
> original source times the specular reflectance, while for all rays not
> hitting the sheet at an angle leading to the source in mirror direction
> would lead to ambient sampling according to the metal definition.
> 
> Is this correct, do the metal and the mirror material match each other
> in my example?
> 
> Cheers, Lars.