[Radiance-general] better results on genBSDF

Wed Feb 20 11:56:30 PST 2013

Ok, I will try those changes, and let you know my results.

THANKS ANDY!

2013/2/20 Andrew McNeil <amcneil at lbl.gov>

> 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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