[Radiance-general] BSDF question

Mon Jul 7 07:32:10 PDT 2014

Hi Giuseppe,

You only really need either +f or +b, not both.  genBSDF does +b by default
so if you only wanted to do the forward direction you should use +f -b.
Doing one direction takes about half as much time as doing both directions.
However, if you want to import into Window you'll need to do both
directions.

Andy

On Thu, Jul 3, 2014 at 12:45 AM, Giuseppe De Michele <giudm.87 at gmail.com>
wrote:

> Germán and Andy,
>
> meanwhile thank you for the answers and sorry if my questions are a little
> bit confused. I am a newbie of the "lighting art" and I am studying this
> concepts almost alone.
> So if I understood, when I create a BSDF matrix with genBSDF I add the +f
> +b options in order to obtain both transmission matrix and then dctimestep
> does the rest, doesn't it?
>
> Thanks for yours great help,
> Giuseppe
>
>
> 2014-07-02 19:12 GMT+02:00 Andrew McNeil <amcneil at lbl.gov>:
>
> 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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>
>
> --
> *Giuseppe De Michele*
>
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