trans material

Just a quick one..

Dose anyone now the specular transmission and diffuse transmission
parameters of a real glass example.

Thanks,

Miguel Oliveira

NaturalWorks - Consultants

Lisbon:351213971816/914310067

<http://www.natural-works.com/> www.Natural-Works.com

Miguel Oliveira wrote:

Just a quick one..

Dose anyone now the specular transmission and diffuse transmission parameters of a real glass example.

Hi,
Translucent glass comes as structured clear glass, edged, screen printed, sandblasted etc. and its forward scattering varies considerably.
Or are you looking for coated glass, which is non-diffuse, but its directional transmittance ("transmission"- whatever, with or without Fresnel) varies form the rule-of-thumb 10%-reflexion-at-normal-incidence too ?

-Peter

···

--
pab-opto, Freiburg, Germany, http://www.pab-opto.de
[see web page to check digital email signature]

Hi,
I'm looking for diffuse glass used in translucent pyramidal skylights.

Miguel Oliveira

NaturalWorks - Consultants

Lisbon:351213971816/914310067

www.Natural-Works.com

···

-----Original Message-----
From: Peter Apian-Bennewitz [mailto:[email protected]]
Sent: Tuesday, November 02, 2004 3:42 PM
To: Radiance general discussion
Subject: Re: [Radiance-general] trans material

Miguel Oliveira wrote:

Just a quick one..

Dose anyone now the specular transmission and diffuse transmission

parameters of a real glass example.

Hi,
Translucent glass comes as structured clear glass, edged, screen
printed, sandblasted etc. and its forward scattering varies considerably.
Or are you looking for coated glass, which is non-diffuse, but its
directional transmittance ("transmission"- whatever, with or without
Fresnel) varies form the rule-of-thumb 10%-reflexion-at-normal-incidence
too ?

-Peter

--
pab-opto, Freiburg, Germany, http://www.pab-opto.de
[see web page to check digital email signature]

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

Hi all,
I should simulate a screen material with highly specular reflection
(0.8) at one side like aluminized matrial an a totally diffuse
transmission of about 0.1.
The parameter of spec for trans material isn't described very well in
'Rendering with Radiance' so I couldn't understand it. Does a numer of 1
spec means a totally specularity for diffuse and direct light ? If so
should I use somthing like this:

screen trans spec-diff_80-10
0 0 7 1 1 1 .8 0 .1 0

correct? Or does anybody know a BRTDfunc material definition for this
issue?

Thanks for help!

Friedemann Kik
Transsolar Stuttgart

Hi Friedemann,

The trans material is indeed a bit confusing (no offense Greg:)). We did
a validation last year for a translucent material along with some
measurements of a real material. Maybe you'll find the paper useful:
Reinhart C F, Andersen M, "Development and validation of a Radiance
model for a translucent panel", Energy and Buildings 38:7 pp. 890-904,
2006.
http://irc.nrc-cnrc.gc.ca/pubs/fulltext/nrcc48165/nrcc48165.pdf

Also, you might want to have a look at
http://www.schorsch.com/rayfront/manual/transdef.html to bette undrstand
the trans material.

Christoph

···

________________________________

From: [email protected]
[mailto:[email protected]] On Behalf Of
Friedemann Kik
Sent: Friday, January 26, 2007 6:39 AM
To: Radiance general discussion
Subject: [Radiance-general] trans material

Hi all,
I should simulate a screen material with highly specular reflection
(0.8) at one side like aluminized matrial an a totally diffuse
transmission of about 0.1.
The parameter of spec for trans material isn't described very well in
'Rendering with Radiance' so I couldn't understand it. Does a numer of 1
spec means a totally specularity for diffuse and direct light ? If so
should I use somthing like this:

screen trans spec-diff_80-10
0 0 7 1 1 1 .8 0 .1 0

correct? Or does anybody know a BRTDfunc material definition for this
issue?

Thanks for help!

Friedemann Kik
Transsolar Stuttgart

Hi All,

Yes, trans is very confusing. The link to Schorsch's page is very helpful, particularly the diagram. You should also look at pages 325 and 326 of Rendering with Radiance to see how parameters for the trans material can be derived. It would probably also be worthwhile to do a search on the archives as the trans material is a recurring topic of question, discussion and answer.

I am a bit unclear though about the makeup of your material. You use the word "screen" to describe it, this could be interpreted as a material that actually has holes in it, in which case the material would also need to have a specular transmittance component (arg 7), that is the portion of light that pass un-diffused through the material. I am not sure but this might even need a more complex material description.

Also you may have some more basic problems in the definition of your material. You have the following:

    screen trans spec-diff_80-10
    0
    7 1 1 1 .8 0 .1 0

Note that this implies that there is actually some material modifier called "screen" that is modifying the material (of type trans) called "spec-diff_80-10". Is this what you intend? Or do you mean:

    void trans screen
    0
    7 1 1 1 .8 0 .1 0

where "screen" then gets applied to geometry?

Note one other item. I believe that it would be extremely unusual for the first three parameters to be 1 1 1. Schorsch's page indicates a realistic range of .2 to .9. The first three arguments are derived based on the interaction of the "diffuse" reflectance of the material with the "reflected specularity" (arg 4) and along with (arg 6).

Regards,

-Jack de Valpine

Reinhart, Christoph wrote:

···

Hi Friedemann,
The trans material is indeed a bit confusing (no offense Greg:)). We did a validation last year for a translucent material along with some measurements of a real material. Maybe you'll find the paper useful: Reinhart C F, Andersen M, "Development and validation of a Radiance model for a translucent panel", Energy and Buildings 38:7 pp. 890-904, 2006.
http://irc.nrc-cnrc.gc.ca/pubs/fulltext/nrcc48165/nrcc48165.pdf
Also, you might want to have a look at http://www.schorsch.com/rayfront/manual/transdef.html to bette undrstand the trans material.
Christoph
------------------------------------------------------------------------
*From:* [email protected] [mailto:[email protected]] *On Behalf Of *Friedemann Kik
*Sent:* Friday, January 26, 2007 6:39 AM
*To:* Radiance general discussion
*Subject:* [Radiance-general] trans material

Hi all,
I should simulate a screen material with highly specular reflection (0.8) at one side like aluminized matrial an a totally diffuse transmission of about 0.1.
The parameter of spec for trans material isn't described very well in 'Rendering with Radiance' so I couldn't understand it. Does a numer of 1 spec means a totally specularity for diffuse and direct light ? If so should I use somthing like this:
screen trans spec-diff_80-10
0 0 7 1 1 1 .8 0 .1 0
correct? Or does anybody know a BRTDfunc material definition for this issue?
Thanks for help!
Friedemann Kik
Transsolar Stuttgart

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