[Radiance-general] usage of plasdata material

[Uta Poppe]

Hello,

I have some questions regarding the plasdata material. I couldn' t find a documentation about it, thats why i must ask you.
The material definition is:

void plasdata blue
6 noop daten2.dat blue.cal sigma phi theta 
0
4 0.1973 0.35612 0.6353 1

The unit of the values is (1/sr), I think no further computation is needed in this case, thats why I took the "noop"-Argument. 

the cal-file contains only the three angles:
sigma(x,y,z) = acos(x*Nx+y*Ny+z*Nz)*180/PI;
phi(x,y,z) = acos( -(x*Dx+y*Dy+ z*Dz));

theta(x,y,z) = acos(Dx*Nx+Dy*Ny+Dz*Nz)*180/PI;

sigma should define the angle between incoming light and surface normal, theta is the one between leaving light and normal and phi is the one between theta and sigma ... and I'm not sure, wheter the above calculation is right.

The next thing is, that I'm a little confused about  the meaning of the last argument in the last line of the plasdata material. The materials describtion says, that it is a parameter for defining specularity (?). But when I have a huge amount of reflectance data, why do i need another parameter? In which way does it influence the computation of my reflectance values? In the current material definition it is set to one because, setting it to zero I have a plastic material as it seems. How can I obtain the right value?

Please take the noob out of the dark :)

Cheers,

Uta
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