Radiance-general Digest, Vol 166, Issue 33

radiance-general
1

Hi,

In your example, you test the irradiance at a single point in *only one
direction* (up) which is not what I am trying to do unfortunately. If I
want to calculate the energy arriving at a point on a plane, calculating
irradiance from a single direction isn't realistic. Thus, I asked about
RSENSOR which you recommended that I use a long time ago. I am thinking
that for each point, I call RTRACE with the view direction -vd changing in
equal increments and then add the irradiances. For example, the view
directions for a very rough calculation would be in spherical
coordinates/degrees: (1, 0, 0), (1, 90, 0), (1, 180, 0), (1, 270, 0), (1,
0, 45), (1, 90, 45), (1, 180, 45), (1, 270, 45), (1, 0, 90).

Also, I am confused about "a list of RGB irradiance values (watts/sr/m^2)."
This looks like radiance, and reputable sources state that the units for
irradiance are (W/m^2).

Thank you!

Best,

Valerie

···

On Dec 28, 2017 3:00 PM, <[email protected]> wrote:

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Today's Topics:

   1. RSENSOR questions (Valerie Tan)
   2. Re: RSENSOR questions ([email protected])
   3. Re: RSENSOR questions (Greg Ward)

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

Message: 1
Date: Thu, 28 Dec 2017 12:17:49 -0500
From: Valerie Tan <[email protected]>
To: [email protected]
Subject: [Radiance-general] RSENSOR questions
Message-ID:
        <CAFWG2TdKo8m2nbA5qfEG-pZRJawA7uBYM9YXyFDV8REGKwLeCA@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"

Hello,

I am using RSENSOR on an array of "test points" for my greenhouse energy
modeling project. In general, I want to model energy arriving at different
points in the greenhouse, given weather conditions, building geometry, etc.
At each test point/sensor, I want to send backwards rays at evenly-spaced
azimuthal angles and polar angles and sum the irradiance contributions from
each ray.

I assumed that RSENSOR does what I intend to do and that my sensor file
will determine what rays are sent and in what direction. But I don't know
whether my assumption is true.

Also, I don't understand what the sensitivity values on the SPOT matrix
really mean. Overall, I just want to calculate irradiance values at each
test point by evenly sampling backwards rays in all directions.

I've looked at this:
https://www.radiance-online.org/community/workshops/2009-bos
ton-ma/Presentations/rogers_SPOT%20on.pdf

However, I don't understand the sin/cosine parts and I am focused and
radiometric units, not human-centered units like luminance.

Thank you!

Best,

Valerie

--
Valerie Tan
Computer Science
College of Engineering
Cornell University '19
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Message: 2
Date: Thu, 28 Dec 2017 18:24:05 +0100 (CET)
From: [email protected]
To: [email protected]
Subject: Re: [Radiance-general] RSENSOR questions
Message-ID: <[email protected]>
Content-Type: text/plain; charset="UTF-8"

Bonjour,

Je suis actuellement en vacances. Je serai de retour le 8 janvier 2018.

En cas d'urgence, vous pouvez toujours appeler le num?ro g?n?ral d'Estia : +41
(0) 21/510.59.59 ou envoyer un mail ? l'adresse [email protected].

Pour toutes questions relatives ? DIAL+, merci d'utiliser l'adresse mail
[email protected].

Cordialement

Julien Boutillier
Estia SA

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

Message: 3
Date: Thu, 28 Dec 2017 09:48:34 -0800
From: Greg Ward <[email protected]>
To: Radiance general discussion <[email protected]>
Subject: Re: [Radiance-general] RSENSOR questions
Message-ID: <[email protected]>
Content-Type: text/plain; charset="us-ascii"

Hi Valerie,

If you just want irradiance at specific points, you should use rtrace with
the -I+ (capital 'i') option. Rsensor is not needed unless you have a
custom sensitivity distribution you are integrating. If you give rtrace a
list of coordinates and hemisphere (surface normal) orientations, you will
get out a list of RGB irradiance values (watts/sr/m^2):

positions.txt:
        10 15 3 0 0 1
        10 20 3 0 0 1
        15 15 3 0 0 1
        15 20 3 0 0 1

command: rtrace -h- -I+ -ab 1 scene.oct < positions.txt > results.txt

The output file will contain 3 values per line, corresponding to RGB
irradiance at each point in the order given.

The "-ab 1" option is needed to turn on interreflections. A more accurate
calculation will result from "-ab 2" or "-ab 3". You can also employ
multiple processors using the "-n" option, but be sure to add a "-af
scene.amb" option to share cached values for a more efficient calculation
if you do that.

There are many other options you may consider changing to improve the
speed/accuracy trade-off. If you have only a few points, I might suggest
something like this:

        rtrace -h- -I+ -ab 3 -aa 0 -ad 4096 -lw 1e-5 -n 8 scene.oct <
positions.txt > results.txt

The "-n 8" is appropriate for an 8-core machine, but if you only have a few
points, the calculation will take just seconds in any case.

Hope this helps!
-Greg

From: Valerie Tan <[email protected]>
Date: December 28, 2017 9:17:49 AM PST

Hello,

I am using RSENSOR on an array of "test points" for my greenhouse energy

modeling project. In general, I want to model energy arriving at different
points in the greenhouse, given weather conditions, building geometry, etc.
At each test point/sensor, I want to send backwards rays at evenly-spaced
azimuthal angles and polar angles and sum the irradiance contributions from
each ray.

I assumed that RSENSOR does what I intend to do and that my sensor file

will determine what rays are sent and in what direction. But I don't know
whether my assumption is true.

Also, I don't understand what the sensitivity values on the SPOT matrix

really mean. Overall, I just want to calculate irradiance values at each
test point by evenly sampling backwards rays in all directions.

I've looked at this: https://www.radiance-online.or

g/community/workshops/2009-boston-ma/Presentations/rogers_SPOT%20on.pdf

However, I don't understand the sin/cosine parts and I am focused and

radiometric units, not human-centered units like luminance.

Thank you!

Best,

Valerie

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2

Hi Valerie,

You are correct about irradiance units, which are watts/meter^2. That was my mistake.

If you wish to add up irradiance, I would still recommend doing this with rtrace rather than rsensor, unless you have a specific spherical sensitivity in mind. You can give rtrace any hemisphere orientations you like and average the results using "total" or your own program.

However, the light arriving on a plane *is* irradiance, which is a sum over the hemisphere of incoming directions with a cosine weighting. If you were to give rtrace a set of different directions for irradiance, then you would arrive at something more like total incident radiation at a point, which is an unusual quantity. What do you need this value for, exactly?

Cheers,
-Greg

···

From: Valerie Tan <[email protected]>
Date: December 28, 2017 1:55:24 PM PST

Hi,

In your example, you test the irradiance at a single point in only one direction (up) which is not what I am trying to do unfortunately. If I want to calculate the energy arriving at a point on a plane, calculating irradiance from a single direction isn't realistic. Thus, I asked about RSENSOR which you recommended that I use a long time ago. I am thinking that for each point, I call RTRACE with the view direction -vd changing in equal increments and then add the irradiances. For example, the view directions for a very rough calculation would be in spherical coordinates/degrees: (1, 0, 0), (1, 90, 0), (1, 180, 0), (1, 270, 0), (1, 0, 45), (1, 90, 45), (1, 180, 45), (1, 270, 45), (1, 0, 90).

Also, I am confused about "a list of RGB irradiance values (watts/sr/m^2)." This looks like radiance, and reputable sources state that the units for irradiance are (W/m^2).

Thank you!

Best,

Valerie

3

Bonjour,

Je suis actuellement en vacances. Je serai de retour le 8 janvier 2018.

En cas d'urgence, vous pouvez toujours appeler le numéro général d'Estia : +41 (0) 21/510.59.59 ou envoyer un mail à l'adresse [email protected].

Pour toutes questions relatives à DIAL+, merci d'utiliser l'adresse mail [email protected].

Cordialement

Julien Boutillier
Estia SA