[Radiance-general] rewrite BRDF as .cal file for plasfunc

[Katja Doerschner]

I sent this message earlier - but I think it may have gotten lost. I 
apologize if you receive it twice!

Hello, 

Has anyone an example of how to write a .cal function for plasfunc, 
for a given BRDF?
Specifically, I am not sure which predefined variables correspond to 
the view direction vector.

This is the BRDF I want to use in Radiance: 
V(i,j,n,a)=(1/PI)*(a/(a+(i dot n)(j dot n))
:i is unit vector from the source direction, j is unit vector of view 
direction, n is surface normal, a some other parameter.

I know the Radiance-predefined variable names for the source direction 
(x,y,z) and surface normal (Nx,Ny,Nz), but I am not sure what to use 
for the view direction.

Can anyone help? 
Thank you!
katja