[Radiance-general] Transmittance and reflectance dependent on incidence angle

[Greg Ward]

Dumb question, but are you sure your rays are passing through the  
window at all angles?  Is it possible that when the angle is greater  
than 45, the test ray misses the sample?

-Greg

> From: Anne Iversen <iversen.anne at gmail.com>
> Date: May 23, 2009 5:26:11 AM PDT
>
> Thanks for your reply Chris, I have tried to alter my specular  
> treshold (-st) to 0.05, 0.01 or even 0.
> However I still get that with an incidence angle higher than 45  
> degress no reflectance occur, and my transmittance increases! This  
> was not what I would have expected. I would have expected an  
> increase in reflectance and a decrease in transmittance with higher  
> incidence angle.
> My question is therefore, am I using a wrong approach to test the  
> incidence angle-dependency on transmittance and reflectance of my  
> "sample"?
>
>
> My approach has been to vary the rotation of the sample from 'seq  
> 10 10 80' plus 87 around the x-axis, and do the rtrace from "above"  
> to achieve the reflectance and from "below" to achieve the  
> transmittance:
>     xform -rx $ROT -t 0 0 0 LamellaGlowTRANS.rad > lamellaGlow.rad
>     oconv Materials.mat Glow.sky lamellaGlow.rad > glow.oct
>
>     echo "reflectance:"
>     echo '1.75 0.1 4 0 0 -1' | rtrace -h -w -dt 0.05 -st 0.01 glow.oct
>     echo "transmittance:"
>     echo '1.75 0.1 -4 0 0 1' | rtrace -h -w -dt 0.05 -st 0.01 glow.oct
> ...