[Radiance-general] better results on genBSDF

[Germán Molina Larrain]

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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