[Radiance-general] better results on genBSDF

Wed Feb 20 05:44:55 PST 2013

actually, now that you mention it, I think that the errors I thought were
caused by the borders can be explained by what you say.

2013/2/19 Germán Molina Larrain <gmolina1 at uc.cl>

> 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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