[Radiance-general] better results on genBSDF

[Andrew McNeil]

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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