[Radiance-general] better results on genBSDF

Wed Feb 20 11:36:48 PST 2013

I think all you need to do is change  lines 350 and 351 of genBSDF.pl so
they look like this:

Kazi = 360*DEGREE * Kcol / Knaz(Krow);
Kpol = DEGREE * (0.5*Kpola(Krow) + 0.5*Kpola(Krow-1));

(this only changes it for Klems BSDF generation)

Andy

On Wed, Feb 20, 2013 at 5:44 AM, Germán Molina Larrain <gmolina1 at uc.cl>wrote:

> 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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>>>>>
>>>>>
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