[Radiance-general] transdata formula & sky component

[radiance-general@radiance-online.org]

Hi!

1) I am using the transdata material for incorporating measured 
BTDF's [1/sr] in Radiance. With the help of 'rtrace', I will verify the 
results. Is it possible to compute luminance values with 'rtrace'? 

2) In the Radiance Digest I have found a formula for the metdata 
material:

radiance (watts/sr/m^2) Lo = spec * cos(theta_i) * omega_i * Li * f

where:
        f = BTDF in 1/sr
mega_i = solid angle of source in sr
       Li = avg. radiance of source in watts/sr/m^2
theta_i = angle between surface normal and source direction
   spec = multiplier for specular component from material arguments

I would like to calculate the luminance values back to the 
measured BTDF's using the transdata formula. How can I get the 
transdata formula?

3) Another question concerns the diffuse sky component. How will 
Radiance compute this component with the transdata material?

Could anybody answer my questions or give me reference how I 
can solve these problems?

Best regards,

Frank