[Radiance-general] Sampling thorugh TRANS material

[Germán Molina Larrain]

Very cool. Thanks a lot, Greg!

2016-03-09 16:06 GMT-03:00 Greg Ward <gregoryjward at gmail.com>:

> Hi Germán,
>
> The default -lw setting for rcontrib is actually just 0.002, which means
> that at most 500 rays will be sampled in the initial scattering, no matter
> what -ad is set to.  You really need to adjust these settings in tandem
> when the irradiance cache is turned off, as it must be for rcontrib.
>
> Illuminating the interior via a BSDF material means that you are randomly
> sampling something that is also randomly sampling, so you have two major
> contributors to variance.  You can see some of these effects in my 2011
> Radiance Workshop talk, "The Bidirectional Scattering Distribution Function
> as a First-class Citizen in Radiance":
>
>
> http://www.radiance-online.org/community/workshops/2011-berkeley-ca/presentations/day2/GW5_BSDFFirstClass.pdf
>
> Best,
> -Greg
>
> *From: *Germán Molina Larrain <germolinal at gmail.com>
>
> *Subject: *Re: [Radiance-general] Sampling thorugh TRANS material
>
> *Date: *March 9, 2016 10:32:22 AM PST
>
>
> Thanks, Greg... It worked. Is there any special thing about TRANS that
> requres so many ADs? This is the first time I have required a value that
> high to converge.
>
> Best,
>
> 2016-03-04 22:35 GMT-03:00 Greg Ward <gregoryjward at gmail.com>:
>
>> Hi Germán,
>>
>> I'm really only guessing, but I would say you need to increase your -ad
>> value (a lot) to get a good result for your workplane in this situation.
>> You have the noise of the BSDF on the window to filter, which requires a
>> great many samples.  Setting -ab 12 is probably higher than needed.  What
>> is your -lw setting?  This is important for determining the number of rays
>> actually traced.  Also, -aa gets set forcibly to zero by rcontrib, since it
>> doesn't support the ambient cache.  Try:
>>
>> -ad 20000 -lw 2e-5 -ab 5
>>
>> to see if this produces smoother results.
>>
>> Cheers,
>> -Greg
>>
>> *From: *Germán Molina Larrain <germolinal at gmail.com>
>>
>> *Subject: *[Radiance-general] Sampling thorugh TRANS material
>>
>> *Date: *March 4, 2016 12:33:12 PM PST
>>
>>
>> Hello everyone,
>>
>> I have a question about trans material... The story is the following:
>>
>>    1. I already read what Axel Jacobs has to say about Trans, read the
>>    Radiance Reference Manual and also Googled a bit.
>>    2. After all that, I found out how to model Fabric materials using
>>    Trans (I need some uncolored specular transmission and a bit colored
>>    Diffuse transmission). After the research, I noticed that Trans, as I
>>    wanted to model Fabrics, would only work for gray textiles... but that is
>>    good enough for me.
>>    3. I managed to do all that, and actually run genBSDF to check if the
>>    diffuse and direct parts were OK.... they came very close, but not quite
>>    perfect, even if my parameters were pretty high.
>>    4. Assuming it was as good as it would get, I continued with my
>>    simulation... I am using rcontrib's 2-phase method, with "-ab 12 -ad 4096
>>    -aa 0.1" parameters... but I get some NOT SMOOTH results. LINK TO
>>    PICTURE
>>    <https://drive.google.com/file/d/0B2NfkTSl19hQSF9rbTF4S0tMWXc/view?usp=sharing>
>>
>> Any hints on the parameters I have to use in order to model this product
>> well? Is this caused by the fact that there is no direct light in the
>> calculation of the DC matrix? Will my approach work?
>>
>> Regards,
>>
>> Germán
>>
>>
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