Radiance-general Digest, Vol 166, Issue 13

Hello Greg,

I unfortunately use two computers with different rtrace versions (to speed
things up). One has 5.1a and the other 5.1.0.

As of the bsdf generation options. It has been generated through genBSDF
with only -dim option. I want to note that the BSDF was only used for the
3-phase method, and the system's depth has been neglected (2mm depth seems
neglectible in regards to scene's dimensions).

Rtrace scene used the real geometry (the one I generated from the BSDF) as
I want to validate against it. I didn't use the proxy geometry. I don't
know if it answers your question.

Thank you for your time!

Sincerely,
Marouane.

···

Von: [email protected]
An: [email protected]
Datum: 10.12.2017 21:04
Betreff: Radiance-general Digest, Vol 166, Issue 13

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Today's Topics:

   1. Re: rtrace values too low compared to 3-phase method (Greg Ward)

----------------------------------------------------------------------

Message: 1
Date: Sat, 9 Dec 2017 12:58:18 -0800
From: Greg Ward <[email protected]>
To: Radiance general discussion <[email protected]>
Subject: Re: [Radiance-general] rtrace values too low compared to
                 3-phase method
Message-ID: <[email protected]>
Content-Type: text/plain; charset="windows-1252"

Hi Marouane,

Which version of Radiance are you using? (I.e., what does "rtrace
-version" say?)

There are difficulties finding transmitted solar radiation through
unproxied BSDF materials before the 5.1 release. The latest release adds
a new calculation called "peak extraction" that attempts to identify
strong peaks in the BSDF view component that it treats separately. The
solution is not perfect, but it generally leads to more correct results in
such cases.

Another approach if you are starting from a geometric description of your
fenestration and using genBSDF is the +geom option, which includes the
system geometry in the XML file. You can then apply "pkgBSDF" to
translate this geometry and surround it with appropriate proxy surfaces,
so that your rays will pass through and generate the correct patterns on
your interior surfaces, as well as giving you a correct view through the
fenestration system.

If you are using genBSDF, what options did you include? How did you
describe the actual BSDF surface(s) in your model?

Best,
-Greg

From: [email protected]
Date: December 8, 2017 8:08:22 AM PST

Hello,

I?m trying to calculate vertical illuminance with 3-phase method and

validate it against rtrace results. My results are very different.
3-phase method has illuminance values two order of magnitudes higher. I
can only see the the direct solar illuminance on the floor. I suspect that
my rtrace command fails to find the sky, because of the complexity of the
geometry of my fenestration system. I was wondering if anyone here has
already had such a problem in the past with rtrace giving too low
illuminance values.

My CFS geometry consists of uniformly spaced boxes of 5 cm (picture in

the end). The gap between the boxes allow 4% normal transmittance (tested
with 20% too and it?s still dark, 30% start giving some light).

Here are the parameters used to calculate the vertical illuminance (and

which I suspect may be wrong)

1st way : 3PM : View matrix of the picture (on which I use evalglare to

get the vertical illuminance) : -n 35 -ab 10 -ad 65536 -lw 1.52e-5 -c 9

2nd way : Vertical illuminance with rtrace : rtrace -h -I -n 40 -ab 10

-ad 8192 -ar 1024 -as 4096 -aa 0.1

3rd way : Rtrace picture (I use evalglare on it) : rtrace -n 40 -ab 5

-ad 512 -ar 128 -as 256 -aa 0.15 -dc 1

Needless to say I made the parameters vary many times before contacting

the mailing list, but there are so much parameters and simulation times
increase a lot (I mainly increased ab and ar). I have already tried the
parameters on the old and new 3pm/5pm tutorials to be sure my 3-pm results
are not wrong. Has anyone else had similar experience with rtrace and know
how to solve it ?

Sincerely,
Marouane.

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Hi Marouane,

Looking at your original post again, I would say that relying on rtrace and the default calculation to determine the tiny bit of light that bounces many times between closely-spaced diffuse surfaces and makes it into your room is the problem. This is very close to a "worst case" scenario for indirect irradiance caching, so I would switch this off, at least for your rtrace calculation. It will still be very expensive to compute the light through this system, but you can try something like:

  rtrace -I+ -aa 0 -ad 1024 -as 1024 -ab 10 -lw 1e-4 -lr -12

The other option is to use a more modest irradiance caching operation with the BSDF you have computed. You do not need to use the system geometry, as it seems the elements are too thick to let direct light through in any case, which was my initial (incorrect) assumption.

Best,
-Greg

···

From: [email protected]
Date: December 10, 2017 8:09:30 PM PST

Hello Greg,

I unfortunately use two computers with different rtrace versions (to speed things up). One has 5.1a and the other 5.1.0.

As of the bsdf generation options. It has been generated through genBSDF with only -dim option. I want to note that the BSDF was only used for the 3-phase method, and the system's depth has been neglected (2mm depth seems neglectible in regards to scene's dimensions).

Rtrace scene used the real geometry (the one I generated from the BSDF) as I want to validate against it. I didn't use the proxy geometry. I don't know if it answers your question.

Thank you for your time!

Sincerely,
Marouane.

Date: Sat, 9 Dec 2017 12:58:18 -0800
From: Greg Ward <[email protected]>
To: Radiance general discussion <[email protected]>

Hi Marouane,

Which version of Radiance are you using? (I.e., what does "rtrace -version" say?)

There are difficulties finding transmitted solar radiation through unproxied BSDF materials before the 5.1 release. The latest release adds a new calculation called "peak extraction" that attempts to identify strong peaks in the BSDF view component that it treats separately. The solution is not perfect, but it generally leads to more correct results in such cases.

Another approach if you are starting from a geometric description of your fenestration and using genBSDF is the +geom option, which includes the system geometry in the XML file. You can then apply "pkgBSDF" to translate this geometry and surround it with appropriate proxy surfaces, so that your rays will pass through and generate the correct patterns on your interior surfaces, as well as giving you a correct view through the fenestration system.

If you are using genBSDF, what options did you include? How did you describe the actual BSDF surface(s) in your model?

Best,
-Greg