[Radiance-general] trans material

[Jack de Valpine]

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
    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
    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:* radiance-general-bounces at radiance-online.org 
> [mailto:radiance-general-bounces at radiance-online.org] *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
>  
>  
> ------------------------------------------------------------------------
>
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-- 
# Jack de Valpine
# president
#
# visarc incorporated
# http://www.visarc.com
#
# channeling technology for superior design and construction

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