AW: trans material

Thanks for help, Jack and Christoph,

I know about the wonderful rayfront user manuel from Schorsch, espacially the nice diagram, but
the description of trans I found there is a little bit imprecise if "spec" is speciefied with "Values greater than 0.1 are unusual". Does "unusual" mean impossible for RADIANCE to calculate correct if a greater values is set? Is there an other reason which I should know?
An other question about "trans" is if it transmits only direct source rays or additionally diffuse one (i.e. from sky hemisphere)
Jack, I wasn't interrested about the absorption caused by color filtering, my focus was only on reflected specularity. For more realistic renderings I should use other parameters, of course. By the way: I can count myself lucky to say that there are no "other basic problems" to assign the matirial to my model...

Thanks for additional comments!
Friedemann

···

-----Ursprüngliche Nachricht-----
  Von: [email protected] [mailto:[email protected]] Im Auftrag von Jack de Valpine
  Gesendet: Freitag, 26. Januar 2007 14:59
  An: Radiance general discussion
  Betreff: Re: [Radiance-general] trans material
  
  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: [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
      
  --
  # Jack de Valpine
  # president
  #
  # visarc incorporated
  # http://www.visarc.com
  #
  # channeling technology for superior design and construction

Hi Friedmann,

I believe that the specularity of common uncoated glass is around .06, so perhaps this is where this range is coming from. Perhaps if the system was a translucent glazing system with some kind of additional coating the specular component might be higher.

Regarding your comment on absorption. It is actually important to base your material on reasonable estimates for the initial parameters as described in RwR, as these have impact on the values used for the arguments to the material. As you see in the formula's in the book the parameters all interact with each other.

-Jack

Friedemann Kik wrote:

···

Thanks for help, Jack and Christoph,
I know about the wonderful rayfront user manuel from Schorsch, espacially the nice diagram, but
the description of trans I found there is a little bit imprecise if "spec" is speciefied with "Values greater than 0.1 are unusual". Does "unusual" mean impossible for RADIANCE to calculate correct if a greater values is set? Is there an other reason which I should know?
An other question about "trans" is if it transmits only direct source rays or additionally diffuse one (i.e. from sky hemisphere)
Jack, I wasn't interrested about the absorption caused by color filtering, my focus was only on reflected specularity. For more realistic renderings I should use other parameters, of course. By the way: I can count myself lucky to say that there are no "other basic problems" to assign the matirial to my model...
Thanks for additional comments!
Friedemann

    -----Urspr�ngliche Nachricht-----
    *Von:* [email protected]
    [mailto:[email protected]] *Im Auftrag
    von *Jack de Valpine
    *Gesendet:* Freitag, 26. Januar 2007 14:59
    *An:* Radiance general discussion
    *Betreff:* Re: [Radiance-general] trans material

    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
      
    -- # Jack de Valpine
    # president
    #
    # visarc incorporated
    # http://www.visarc.com
    #
    # channeling technology for superior design and construction
        
------------------------------------------------------------------------

_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general
  
--
# Jack de Valpine
# president
#
# visarc incorporated
# http://www.visarc.com
#
# channeling technology for superior design and construction