[Radiance-general] better results on genBSDF

Tue Feb 19 14:47:54 PST 2013

Andy, indeed I did not do that; probably that is what causes the problem...

Could you explain me how to do that?

THANKS

2013/2/19 Andrew McNeil <amcneil at lbl.gov>

> German,
> Did you consider that genBSDF integrates over the incident Klems patch
> while radiosity method used in window 6 just uses the center of the patch
> for incident energy?
> It is easy to modify genBSDF to use the ceter of the Klems patch by
> removing a couple of the random variables in incident ray generation.
>
> Andy
>
>
> On Sat, Feb 16, 2013 at 12:49 PM, Greg Ward <gregoryjward at gmail.com>wrote:
>
>> The 3-phase method is restricted to matrix (Klems) BSDFs for the time
>> being.  A more sophisticated method is in the works, but won't be ready for
>> several months.
>>
>> Cheers,
>> -Greg
>>
>> *From: *Germán Molina Larrain <gmolina1 at uc.cl>
>>
>> *Date: *February 16, 2013 12:27:02 PM PST
>>
>> *
>> *
>>
>> Thanks Greg and Lars!
>>
>> I intend to use these BSDFs for annual simulations (three-phase method).
>> Is it possible to use the Tensor-tree implementation on that? I think I can
>> live with the claimed error anyway...
>>
>> THANKS AGAIN
>>
>> Germán
>>
>> 2013/2/16 Greg Ward <gregoryjward at gmail.com>
>>
>>> The genBSDF program produces a limited resolution matrix representation
>>> using the options you've given.  This is appropriate if you want to use it
>>> with WINDOW (although I think some modifications to the output are still
>>> required) or if your material is fairly diffusing.  It will not resolve the
>>> direct peak to anything finer than 10 degrees, which is the resolution of
>>> the full Klems matrix basis.  Some spreading of the direct is unavoidable.
>>>
>>> You can improve upon this using the tensor tree formulation by setting
>>> the -t3 or -t4 option.  If your system produces an isotropic distribution
>>> (i.e., you can rotate the system about its center with no change to the
>>> output), you can try "genBSDF -t3 6" or so.  In the more general case, you
>>> can use "genBSDF -t4 6", which will resolve the direct component to within
>>> a few degrees.  You can increase to "-t4 7" to get twice the resolution,
>>> but you'll have to increase the -c parameter as well, and I can't predict
>>> when the calculation will finish.
>>>
>>> The real solution is to incorporate and employ the actual system
>>> geometry using the proxy method described near slide 7 in my 2011 workshop
>>> presentation:
>>>
>>>
>>> http://www.radiance-online.org/community/workshops/2011-berkeley-ca/presentations/day2/GW5_BSDFFirstClass.pdf
>>>
>>> Cheers,
>>> -Greg
>>>
>>> *From: *Germán Molina Larrain <gmolina1 at uc.cl>
>>>
>>> *Date: *February 16, 2013 11:49:09 AM PST
>>>
>>> *
>>> *
>>>
>>> Hi Lars,
>>>
>>> considering that the specular transmission is that light that does not
>>> touch any surface, the analytical solution would be the exact one (am I
>>> right?). Also, HERE<http://windows.lbl.gov/materials/optics/Bidirectional%20Properties%20of%20Slat%20Shading.pdf>,
>>> those results were compared agains TracePro, and the results of the forward
>>> ray-tracing gave, basically, the same results as the model I am using.
>>>
>>> THANKS
>>>
>>> German
>>>
>>> 2013/2/16 Lars O. Grobe <grobe at gmx.net>
>>>
>>>> Hi German!
>>>>
>>>> > I am using genBSDF to get the BTDF of a shading system, comparing it
>>>> to
>>>> > an analytical model using the radiosity method. No surprise, the
>>>> > calculations seem to be really good, nevertheless, there are some
>>>> > important differences on directly transmitted (specular)
>>>> calculations. I
>>>>
>>>> Why do you think that "an analytical model using the radiosity method"
>>>> results in "better" results than raytracing does for specular
>>>> transmission?
>>>>
>>>> Cheers, Lars.
>>>>
>>>>
>>> ---------------------------
>>>
>>> *From: *Germán Molina Larrain <gmolina1 at uc.cl>
>>>
>>> *Date: *February 16, 2013 7:06:26 AM PST
>>>
>>> *
>>> *
>>>
>>> Dear list,
>>>
>>> I am using genBSDF to get the BTDF of a shading system, comparing it to
>>> an analytical model using the radiosity method. No surprise, the
>>> calculations seem to be really good, nevertheless, there are some important
>>> differences on directly transmitted (specular) calculations. I am using the
>>> following parameters:
>>>
>>> genBSDF -n 4 -c 4000 -r '-ab 4 -ad 512 -as 0 -aa 0 -ds 0.01 -dj 0'
>>> material.mat geometry.rad > ../TMX/file.xml
>>>
>>> I tried modifying the -c option, but it did not show any improvements,
>>> so I stayed on 4000. Any suggestions from gurus?
>>>
>>> THANKS
>>>
>>> German
>>>
>>>
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>>>
>>>
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