[Radiance-general] trans

[Greg Ward]

Hi Martin,

Thanks for writing to let me know all is well with trans, if a bit  
confusing...  (But we knew that!)

While I agree that the -i option would be better to show arriving  
irradiance on some trans surfaces, it's a hack to begin with, and the  
behavior is more predictable if it switches based on material type  
rather than material parameters.

Your formulas for the trans arguments look correct, except your A5  
calculation, the specular roughness:

> A5 = (rs * rs_a _ ts * ts_a) / (rs + ts)

Perhaps you meant:

A5 = (rs * rs_a + ts * ts_a) / (rs + ts)

This seems a reasonable way to compute an average value for the  
roughness.

-Greg

------------------ Off-list messages:
> From: "Martin Moeck" <MMoeck at engr.psu.edu>
> Date: January 3, 2006 3:19:22 PM PST
>
> Greg,
>
> I dutifully updated to 3.7 patchlevel 2 today.
>
> Your HDR book is great.
>
> Trans is ok - I made a mistake and got thrown off additionally by  
> the to me yet unfamiliar rview -i trans and glass appearance. In my  
> opinion, these surfaces should show their illuminance levels. They  
> are planes with non-emitting materials.
>
> I hope I did not make a mistake in the trans A1-A7 calculations.
>
> Martin

---------------
> From: Greg Ward <gregoryjward at gmail.com>
> Date: January 2, 2006 12:48:18 PM PST
>
> Hi Martin,
>
> Just so I don't have to recreate it myself and get some detail  
> wrong, could you send me your scene file(s) in a separate e-mail  
> (not to the list)?
>
> Thanks,
> -Greg
>
> P.S.  Why are you 2 releases behind??


------- Original post:
> From: "Martin Moeck" <MMoeck at engr.psu.edu>
> Date: January 2, 2006 12:08:51 PM PST
>
> Radiance 3.5 official LBNL release March 21 2003
>
> Scene = a box 3X3X3 m with a south facing window.
>
> Trans =
> 0.31   0.31   0.31     0.01     0.02     0.3443     0.191
>
> points.inp:
> 1.5 -.5 1.5       0 -1 0
> 1.5 0.1 1.5       0 -1 0
>
> I assume the following formulae:
>
> ts = direct transmittance = 0.02
> td = diffuse transmittance = 0.85
> rs_a = ts_a = roughness = 0.02
> rs = specularity
>
> A1 = A2 = A3 = rd / ( (1-rs)*(1-A6) )
> A4 = rs = 0.01
> A5 = (rs * rs_a _ ts * ts_a) / (rs + ts)
> A6 = (td + ts) / (rd + td  + ts)
> A7 = ts / (td + ts)
>
> Is that correct?
>
> Martin
>
> ________________________________
>
> From: radiance-general-bounces at radiance-online.org on behalf of  
> Greg Ward
> Sent: Mon 1/2/2006 2:42 PM
>
> Hi Martin,
>
> You still aren't giving enough hints as to your problem.  What is
> your scene?  Which version of Radiance are you using?
>
> I just ran a few sanity checks with the rtrace -I option and the
> latest HEAD release on a trans material, and all seems well.
>
> -Greg