[Radiance-general] BSDF question

Wed Jul 9 00:30:37 PDT 2014

Andy,

now is all clear. Thanks.

Giuseppe

2014-07-07 17:42 GMT+02:00 CHI-German Molina <gmolina at hdlao.com>:

> Awesome.
>
> Thanks Greg!
>
>
> 2014-07-07 11:39 GMT-04:00 Greg Ward <gregoryjward at gmail.com>:
>
> Reciprocity works for every BSDF type in Radiance except isotropic tensor
>> trees, so specify +f with the -t3 option if you want transmission to go
>> both ways.  Also, you need +f to get the reflected rays on the opposite
>> side of the surface, so you may want it under some other circumstances as
>> well.
>>
>> The geometry (if present) is used for shadow calculation during the
>> direct calculation and for viewing the system, while the BSDF is used for
>> all other purposes.
>>
>> Cheers,
>> -Greg
>>
>> *From: *CHI-German Molina <gmolina at hdlao.com>
>>
>> *Subject: *Re: [Radiance-general] BSDF question
>>
>> *Date: *July 7, 2014 7:39:33 AM PDT
>>
>>
>>  Andy,
>>
>> How about using BSDFs for ray-tracing calculations? Does it use
>> reciprocity as well? or should we calculate +b ?
>>
>> Also, was I correct when I said that the BSDFd "Proxy Geometry" is only
>> used for ambient calculations, and the geometry for Direct?
>>
>> THANKS!
>>
>> German
>>
>>
>> 2014-07-07 10:32 GMT-04:00 Andrew McNeil <amcneil at lbl.gov>:
>>
>>> 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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>>>>>
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>>>>>
>>>>
>>>>
>>>> --
>>>> *Giuseppe De Michele*
>>>>
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>> --
>> *Germán Molina L.*
>> Ingeniero Trainee
>> Hunter Douglas Chile S.A.
>> Celular +569 89224445
>>
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>
>
> --
> *Germán Molina L.*
> Ingeniero Trainee
> Hunter Douglas Chile S.A.
> Celular +569 89224445
>
> *Nota de Confidencialidad:* Este mensaje incluído los archivos adjuntos
> son confidenciales y pueden contener informacion privilegiada protegida por
> ley. Si Ud. no es el destinatario, deberia abstenerse de copiarlo,
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> gracias.
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> message, including any attachment, is confidential and is intended only for
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-- 
*Giuseppe De Michele*
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