[Radiance-general] BSDF question

[Andrew McNeil]

Giuseppe,

The front/back inconsistency is mostly related to the BSDF material
primitive. For the 3-phase method you don't have to worry about front/back
of the fenestration. (unless you want to use a BSDF backwards, which might
be impossible without manually editing the BSDF file).

The BSDF handling has matured quite a bit since the early days of the
three-phase method. These days dctimestep can use either front transmission
or back transmission applying reciprocity principles for the three phase
method.

Andy




On Wed, Jul 2, 2014 at 9:24 AM, CHI-German Molina <gmolina at hdlao.com> wrote:

> Guiseppe,
>
> The three-phase method simulation method does not use the geometry of the
> shading device to work. In fact, one advantage of it is that only the
> BSDF.xml file is needed. If you check Andy's Three-phase method tutorial,
> you will see that the calculation of the V and D matrices do not require
> neither the geometry of the shading device nor the BSDF of it (thus making
> it very easy to try multiple fenestration systems).
>
> Adding Geometry information to the BSDF file is useful for using pkgBSDF;
> not really for the 3phase method. When rays have to go through the
> fenestration system (i.e. rendering a room with venetian blinds, or  when
> calculating the third matrix of the 5 phase method) a combination of two
> illums that "wrap" the geometry and the geometry itself seems to be more
> efficient. My understanding (I might be completely wrong) is that the
> illums are used to transfer the diffuse (indirect??) radiation; and the
> geometry is used for transfering direct radiation, casting shadows.
>
> My answer to the first question:
>
> *1.  in the equation i=VTDs the T matrix has to contain the window
> geometry or take knowledge of these from the other two matrix(V,D)? *
>
> Nope. After the V and D matrices are calculated, the simulation is
> performed by simply multiplying matrices... no geometry.
>
>
> The second question is something that confuses me... it would be good to
> have clarification here.
>
> Hope this helps!
>
> Germán
>
>
> 2014-07-02 11:54 GMT-04:00 Giuseppe De Michele <giudm.87 at gmail.com>:
>
>> Dear all,
>>
>> I am working with the 3 phase method (only from a few weeks) and I am
>> trying to understand the BSDF file format and how the 3 phase method read
>> it.
>>
>>  I have noticed that if I use the bsdf created with the command:
>> genBSDF -n 4 +f +b -geom meter material.rad blinds.rad > blinds.xml
>> the .xml file contain same geometrical dimension (height, width). In fact
>> if I use the command:
>> pkgBSDF -s blinds.xml > blinds_pkg.rad
>> the output file contain the original geometry.
>>
>> Instead if I use the BSDF created or contained  in the database of WINDOW
>> 7 these file do not contain a geometry.
>> With pkgBSDF I got an error.
>>
>> My questions are:
>> 1.  in the equation i=VTDs the T matrix has to contain the window
>> geometry or take knowledge of these from the other two matrix(V,D)?
>> 2.  I have understood that 3 phase method uses only the front
>> transmission data [A. McNeil, Three-Phase Method tutorial]  but in
>>  an other discussion [
>> http://www.radiance-online.org/pipermail/radiance-general/2012-October/008969.html
>> ]  I have discovered that WINDOW and genBSDF use an opposite meaning of
>> front and back, so the front transmission regards radiance or window
>> meaning?And what part of the T matrix I have to use in the 3 phase method
>> for the respective cases (WINDOW or genBSDF)?
>>
>> Kind regards,
>> *Giuseppe*
>>
>> _______________________________________________
>> Radiance-general mailing list
>> Radiance-general at radiance-online.org
>> http://www.radiance-online.org/mailman/listinfo/radiance-general
>>
>>
>
>
> --
> *Germán Molina L.*
> Ingeniero Trainee
> Hunter Douglas Chile S.A.
> Celular +569 89224445
>
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