Thanks .... Warning message and glass definition

Hi Arvinder,

It's funny you should write this morning, as I just realized that I made a mistake (two, actually) in my formula for the normal reflectance of a simple glazing, and I was just about to post a correction.

There are actually two files in the ray/src/cal/cal directory that should be helpful, which I forgot were there:

trans.cal - the exact solution for transmissivity based on normal transmittance and index of refraction

trans2.cal - an approximate solution for the index of refraction and transmissivity based on normal reflectance and transmittance

If you run "calc trans2.cal" in the ray/src/cal/cal directory and enter:

Tn = 0.85
Rn = 0.05

Typing in "n" and "tn" will give you these results:

n
\$1=1.39992615
tn
\$2=0.894736842
^D

Checking this against the file trans.cal, to which I've added the corrected formula for Rn:

% calc trans.cal
Rn = rn + rn*sq((1-rn)*tn)/(1-sq(tn*rn));

n = 1.4
Tn = 0.85

Rn
\$1=0.0489971986
tn
\$2=0.898704882

We can see there's just a slight error in the approximations made in trans2.cal. Playing around with these values in trans.cal, I was able to get closer to the correct parameters for your glass type:

n = 1.405
Rn
\$9=0.0500464342
tn
\$10=0.899753993

Actually, the first approximate result is probably good enough, but anyway, the correct glass specification should be:

void glass class_lglass
0
4 0.900 0.900 0.900 1.405

Sorry for the screw-up. The advantage of programming is that you can fix your errors (usually) before they do irreperable harm.

-Greg

···

From: Arvinder Dang <ashudang@yahoo.com>
Date: Wed Oct 8, 2003 9:50:41 AM US/Pacific

Thanks a lot Greg for responding to my questions and actually calculating the transmittivity for me .Your explanation of the same would definitely help to calculate it myself in the future. My results in comparison to Superlite seem reasonable unlike intially when there was a difference of about 25%.
I 'm sure there will be lots more coming your way
Thanks Again
Arvinder