trans

Hello,

Since about 10 months, I am having an unexpected problem with the material trans. The direct component (argument 7) always cases 0 illuminance values. Was there a change in the material definition?

Martin Moeck

Hi Martin,

I'm not sure I understand your question. Could you restate it more clearly?

Are you speaking of the rpict/rtrace -i+ rendering option? In this case, trans materials will be ignored, treated as if they were not there at all, regardless of the real arguments. The same is true for dielectric and glass materials. This is designed to avoid the confusing situation where you see the irradiance arriving at a window rather than the irradiance on the objects visible through it.

-Greg

···

From: "Martin Moeck" <[email protected]>
Date: January 2, 2006 10:32:51 AM PST

Hello,

Since about 10 months, I am having an unexpected problem with the material trans. The direct component (argument 7) always cases 0 illuminance values. Was there a change in the material definition?

Martin Moeck

Example:
rtrace -h -w -I -ab 2 -dr 2 -ds 2 octree < points.inp | rcalc ...

points.inp contains the location and direction of a sensor in front of and then behind the trans material for the calculation of total transmittance.

Martin

···

________________________________

From: [email protected] on behalf of Greg Ward
Sent: Mon 1/2/2006 1:47 PM
To: Radiance general discussion
Subject: Re: [Radiance-general] trans

Hi Martin,

I'm not sure I understand your question. Could you restate it more
clearly?

Are you speaking of the rpict/rtrace -i+ rendering option? In this
case, trans materials will be ignored, treated as if they were not
there at all, regardless of the real arguments. The same is true for
dielectric and glass materials. This is designed to avoid the
confusing situation where you see the irradiance arriving at a window
rather than the irradiance on the objects visible through it.

-Greg

From: "Martin Moeck" <[email protected]>
Date: January 2, 2006 10:32:51 AM PST

Hello,

Since about 10 months, I am having an unexpected problem with the
material trans. The direct component (argument 7) always cases 0
illuminance values. Was there a change in the material definition?

Martin Moeck

_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general

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

···

From: "Martin Moeck" <[email protected]>
Date: January 2, 2006 11:17:34 AM PST

Example:
rtrace -h -w -I -ab 2 -dr 2 -ds 2 octree < points.inp | rcalc ...

points.inp contains the location and direction of a sensor in front of and then behind the trans material for the calculation of total transmittance.

Martin

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: [email protected] on behalf of Greg Ward
Sent: Mon 1/2/2006 2:42 PM
To: Radiance general discussion
Subject: Re: [Radiance-general] trans

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

From: "Martin Moeck" <[email protected]>
Date: January 2, 2006 11:17:34 AM PST

Example:
rtrace -h -w -I -ab 2 -dr 2 -ds 2 octree < points.inp | rcalc ...

points.inp contains the location and direction of a sensor in front
of and then behind the trans material for the calculation of total
transmittance.

Martin

_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general

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" <[email protected]>
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 <[email protected]>
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" <[email protected]>
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: [email protected] 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