AW: [Radiance-general] trans material
Jack de Valpine
jedev at visarc.com
Thu Feb 1 15:04:14 CET 2007
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
>
>
>
>
> -----Ursprüngliche Nachricht-----
> *Von:* radiance-general-bounces at radiance-online.org
> [mailto:radiance-general-bounces at radiance-online.org] *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:* 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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--
# Jack de Valpine
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#
# visarc incorporated
# http://www.visarc.com
#
# channeling technology for superior design and construction
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