Three-Phase Method - subdivision of window with sensor located close to the window

Hi list - Hope you have time to give me some guidance here :slight_smile:

My question is if any of you have any recommendations or thoughts on how I
should or shouldn't subdivide the window?

*Problem:*

I have a scene with a sensor located close to the window. The window is
placed in y=0.82, and the sensor is located in y=0.84, just behind the
window. Due to the sensor location this close to the window I鈥檓 thinking I
have to subdivide the window to get a correct sensor reading, especially
when solar shading is included in my simulations.

I have run simulations for 4 different cases with different subdivisions of
the window. The transmission matrix is an .xml file generated with window6
for a clear window. Nothing special here, yet! In further simulations I鈥檒l
introduce solar shading.
My simulation results show that the sensor signal differs with the different
subdivisions.

You can see the results and subdivision of window in this link:
http://dl.dropbox.com/u/9713279/ThreePhaseMethod_Subdivision.pdf

And my script if necessary, in this link:
http://dl.dropbox.com/u/9713279/threephasemethod.bash

Thanks in advance,
Anne

Hi Anne,

give Andy's suggestion using the glow material a try - I usually do that for large windows (i.e. in most cases) to avoid the
subsampling problem of the "window lights". Even if you do not put sensors close to the window, you mostly have walls
somewhere close to the window where the same issue arises.
Manually subdividing is only necessary - as Andy states - if it's needed because of changes in the exterior illumination.

Cheers,
David

路路路

Am 28.04.2011 19:38, schrieb Andy McNeil:

Hi Anne,

On my computer the text on your charts show up as black squares. But I think I can still provide some relevant advice.

Generally speaking, subdivision of the window for the three phase method is only necessary when there are nearby external obstructions or for intermediary blind positions. But your case is unusual - your sensor point is so very close to the window.

When generating the view matrix we typically use a light material for the window. Direct (deterministic) sampling is used to calculate the window's contribution. The direct sampling algorithm will automatically divide a light source according to the -ds parameter, however the maximum number of divisions is limited to 64 (as determined by the variable MAXSPARTS in source.h). Given the proximity of your sensor to the window I don't think 64 direct samples will accurately map the window's outgoing klems divisions to illuminance contribution at your sensor. Manually subdividing the window is one approach. Though rather than horizontal bands I'd suggest a pattern of squares that is finer near the sensor and corse away from the sensor (see ascii art below). You also want to set -dt 0 and -dc 1.
____________________
> >__|__|__| |
>______|__|__|__|______|
> > > >
>______|_______|______|

Alternatively you could consider using ambient sampling to sample the window. You could try using a glow material for the window and set -ad 2000 or higher. Roughly half the initial ambient sample rays would hit the window (because your sensor is nearly against the window). -ab can be low and -lw should be less than 1/ad, probably 1/ad^2. I've never tried this, so I don't know how well (or if) it'll work.

If it were me, I'd give the glow material a try. It seems much more elegant and now that I think about it, it might be a better approach for some spaces.

Good luck,
Andy

On Apr 28, 2011, at 8:48 AM, Anne Iversen wrote:

Hi list - Hope you have time to give me some guidance here :slight_smile:

My question is if any of you have any recommendations or thoughts on how I should or shouldn't subdivide the window?

*Problem:*

I have a scene with a sensor located close to the window. The window is placed in y=0.82, and the sensor is located in y=0.84, just behind the window. Due to the sensor location this close to the window I鈥檓 thinking I have to subdivide the window to get a correct sensor reading, especially when solar shading is included in my simulations.

I have run simulations for 4 different cases with different subdivisions of the window. The transmission matrix is an .xml file generated with window6 for a clear window. Nothing special here, yet! In further simulations I鈥檒l introduce solar shading.

My simulation results show that the sensor signal differs with the different subdivisions.

You can see the results and subdivision of window in this link:
http://dl.dropbox.com/u/9713279/ThreePhaseMethod_Subdivision.pdf

And my script if necessary, in this link:
http://dl.dropbox.com/u/9713279/threephasemethod.bash

Thanks in advance,
Anne
_______________________________________________
Radiance-general mailing list
[email protected] <mailto:[email protected]>
http://www.radiance-online.org/mailman/listinfo/radiance-general

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[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general

Thanks Greg, David and Andy for your replies.
Have run simulations with the glow material and find no significant
differences in sensor signal when having no subdivision compared to
different subdivisions. So I'll stick to the glow material for my window and
simulate without any window subdivision. Elegant ;-).

I have simply changed the window material from light to glow and set the
settings as recommended by Andy.

void glow windowlight
0
0
4 1 1 1 0

Best,
Anne

路路路

On Thu, Apr 28, 2011 at 9:00 PM, < [email protected]> wrote:

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When replying, please edit your Subject line so it is more specific
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Today's Topics:

聽聽1. Re: Three-Phase Method - subdivision of window with sensor
聽聽聽聽聽located close to the window (David Geisler-Moroder)
聽聽2. Re: Three-Phase Method - subdivision of window with sensor
聽聽聽聽聽located close to the window (Greg Ward)

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

Message: 1
Date: Thu, 28 Apr 2011 20:24:17 +0200
From: David Geisler-Moroder <[email protected]>
To: [email protected]
Subject: Re: [Radiance-general] Three-Phase Method - subdivision of
聽聽聽聽聽聽聽window with sensor located close to the window
Message-ID: <[email protected]>
Content-Type: text/plain; charset="windows-1252"; Format="flowed"

Hi Anne,

give Andy's suggestion using the glow material a try - I usually do that
for large windows (i.e. in most cases) to avoid the
subsampling problem of the "window lights". Even if you do not put
sensors close to the window, you mostly have walls
somewhere close to the window where the same issue arises.
Manually subdividing is only necessary - as Andy states - if it's needed
because of changes in the exterior illumination.

Cheers,
David

Am 28.04.2011 19:38, schrieb Andy McNeil:
> Hi Anne,
>
> On my computer the text on your charts show up as black squares. But
> I think I can still provide some relevant advice.
>
> Generally speaking, subdivision of the window for the three phase
> method is only necessary when there are nearby external obstructions
> or for intermediary blind positions. But your case is unusual - your
> sensor point is so very close to the window.
>
> When generating the view matrix we typically use a light material for
> the window. Direct (deterministic) sampling is used to calculate the
> window's contribution. The direct sampling algorithm will
> automatically divide a light source according to the -ds parameter,
> however the maximum number of divisions is limited to 64 (as
> determined by the variable MAXSPARTS in source.h). Given the
> proximity of your sensor to the window I don't think 64 direct samples
> will accurately map the window's outgoing klems divisions to
> illuminance contribution at your sensor. Manually subdividing the
> window is one approach. Though rather than horizontal bands I'd
> suggest a pattern of squares that is finer near the sensor and corse
> away from the sensor (see ascii art below). You also want to set -dt
> 0 and -dc 1.
> ____________________
> > >__|__|__| |
> >______|__|__|__|______|
> > > > >
> >______|_______|______|
>
> Alternatively you could consider using ambient sampling to sample the
> window. You could try using a glow material for the window and set
> -ad 2000 or higher. Roughly half the initial ambient sample rays
> would hit the window (because your sensor is nearly against the
> window). -ab can be low and -lw should be less than 1/ad, probably
> 1/ad^2. I've never tried this, so I don't know how well (or if)
> it'll work.
>
> If it were me, I'd give the glow material a try. It seems much more
> elegant and now that I think about it, it might be a better approach
> for some spaces.
>
> Good luck,
> Andy
>
>
>
>
> On Apr 28, 2011, at 8:48 AM, Anne Iversen wrote:
>
>> Hi list - Hope you have time to give me some guidance here :slight_smile:
>>
>>
>> My question is if any of you have any recommendations or thoughts on
>> how I should or shouldn't subdivide the window?
>>
>>
>> *Problem:*
>>
>> I have a scene with a sensor located close to the window. The window
>> is placed in y=0.82, and the sensor is located in y=0.84, just behind
>> the window. Due to the sensor location this close to the window I?m
>> thinking I have to subdivide the window to get a correct sensor
>> reading, especially when solar shading is included in my simulations.
>>
>>
>> I have run simulations for 4 different cases with different
>> subdivisions of the window. The transmission matrix is an .xml file
>> generated with window6 for a clear window. Nothing special here, yet!
>> In further simulations I?ll introduce solar shading.
>>
>> My simulation results show that the sensor signal differs with the
>> different subdivisions.
>>
>> You can see the results and subdivision of window in this link:
>> http://dl.dropbox.com/u/9713279/ThreePhaseMethod_Subdivision.pdf
>>
>> And my script if necessary, in this link:
>> http://dl.dropbox.com/u/9713279/threephasemethod.bash
>>
>> Thanks in advance,
>> Anne
>> _______________________________________________
>> Radiance-general mailing list
>> [email protected]
>> <mailto:[email protected]>
>> http://www.radiance-online.org/mailman/listinfo/radiance-general
>
>
> _______________________________________________
> Radiance-general mailing list
> [email protected]
> http://www.radiance-online.org/mailman/listinfo/radiance-general

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

Message: 2
Date: Thu, 28 Apr 2011 11:42:03 -0700
From: Greg Ward <[email protected]>
To: Radiance general discussion <[email protected]>
Subject: Re: [Radiance-general] Three-Phase Method - subdivision of
聽聽聽聽聽聽聽window with sensor located close to the window
Message-ID: <[email protected]>
Content-Type: text/plain; charset=us-ascii

Hi Anne,

I agree that you should try the glow window. If you are using the rsensor
program as your script seems to indicate, rays will be distributed over the
window independently from how you've defined it. Only the secondary bounces
will care if it's a light source or a glow and whether it's subdivided, and
those should not matter to the results. This leaves the puzzle of why your
output varies so much in the first place.

Have you tried generating hemispherical fisheye views from the sensor
position under the different simulation conditions? This is always my
favorite way of debugging such problems.

Best,
-Greg

> From: David Geisler-Moroder <[email protected]>
> Date: April 28, 2011 11:24:17 AM PDT
>
> Hi Anne,
>
> give Andy's suggestion using the glow material a try - I usually do that
for large windows (i.e. in most cases) to avoid the
> subsampling problem of the "window lights". Even if you do not put
sensors close to the window, you mostly have walls
> somewhere close to the window where the same issue arises.
> Manually subdividing is only necessary - as Andy states - if it's needed
because of changes in the exterior illumination.
>
> Cheers,
> David

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

_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general

End of Radiance-general Digest, Vol 86, Issue 23
************************************************

Hi,
Maybe I was a bit fast concluding that I'll use glow. Comparing the glow
material to the light material reveals a lower sensor signal when the direct
irradiation is low and the opposite when direct irradiation is high. Do you
know why I get this? Due to the 鈥榮ubsampling鈥 problem of window lights as
David mentioned because of my sensor location very close to the window?? And
therefore I should stick to glow?

I have included the results from the glow simulations in the document:
http://dl.dropbox.com/u/9713279/ThreePhaseMethod_Subdivision.pdf
(the non-readable legends and axes must be a mac thing...the same happens
when I open the documet on my mac, I can read the graphs nicely in the pdf
on my pc. ...have included some text in the captions, if you want to know
what you are looking at ;-))

And to your question about my sensor, Andy. The sensor is located on the
window head, just behind the glass. The major detection area is to the
outside through the window. The sensor used right now comes along with the
SPOT distribution, and is the WattStopper LD290C - the spatial distribution
can be seen from the image linked to below. I wouldn't call it a
narrow/peaky/tight sensitivity distribution:
http://dl.dropbox.com/u/9713279/SensorSpatialResponse.png
and I have placed the .dat file here:
http://dl.dropbox.com/u/9713279/WattStopper_LS-290C.dat
Why do you believe that using glow probably won't make much difference -
unless my sensor has a tight and/or peaky sensitivity distribution?

Enjoy the weekend. It is pre-summer in Denmark; we've had blue sky for the
last 14 days, 20C and sun ....who said I miss California?? :wink:

Best,
Anne

路路路

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

Message: 1
Date: Fri, 29 Apr 2011 09:30:48 -0700
From: Andy McNeil <[email protected]>
To: Radiance general discussion <[email protected]>
Subject: Re: [Radiance-general] Three-Phase Method - subdivision of
聽聽聽聽聽聽聽window with sensor located close to the window
Message-ID: <[email protected]>
Content-Type: text/plain; charset="us-ascii"

Hi Anne,
Just curious, how do the glow results compare to the light sources? Could
you update the graph with the sensor signals using the glow material?
Andy

Hi Anne,

another thing that came to my mind...

You are calling rtcontrib for the VMX using rsensor in your script like
that:
聽聽聽聽rsensor -h -rd 1000 -vf views/luxstat.vf sensors/WattStopper_LS-290C.dat
. |\
聽聽聽聽聽聽聽rtcontrib -c 1000 -f klems_int.cal -bn Nkbins -fo -o
results/"$vmxname"_%s.vmx \
聽聽聽聽聽聽聽-b kbinS -m windowlight -b kbinS -m windowlightsens \
聽聽聽聽聽聽聽-I+ -ab 3 -ad 2000 -ds .15 -lw 1e-4 model_vmx.oct

Do you want to obtain the sensor signal split up into the Klems bins?
If yes, I'm not sure if it works like that...

You are using rsensor to generate 1000 rays (i.e. origin and direction)
according to the sensor-file.
These points and directions are then given to rtcontrib, where you use -c
1000 to accumulate all
1000 results and -I+ to switch to irradiances.
However, this means that rtcontrib calculates irradiances for 1000 pairs of
points and directions as
if it was e.g. a grid for illuminance calculations. So you do not obtain the
sensor signal, but a mean
of the 1000 calculated irradiances.

I hope I'm not missing anything...

Cheers,
David

路路路

2011/4/30 Anne Iversen <[email protected]>

Hi,
Maybe I was a bit fast concluding that I'll use glow. Comparing the glow
material to the light material reveals a lower sensor signal when the direct
irradiation is low and the opposite when direct irradiation is high. Do you
know why I get this? Due to the 鈥榮ubsampling鈥 problem of window lights as
David mentioned because of my sensor location very close to the window?? And
therefore I should stick to glow?

I have included the results from the glow simulations in the document:
http://dl.dropbox.com/u/9713279/ThreePhaseMethod_Subdivision.pdf
(the non-readable legends and axes must be a mac thing...the same happens
when I open the documet on my mac, I can read the graphs nicely in the pdf
on my pc. ...have included some text in the captions, if you want to know
what you are looking at ;-))

And to your question about my sensor, Andy. The sensor is located on the
window head, just behind the glass. The major detection area is to the
outside through the window. The sensor used right now comes along with the
SPOT distribution, and is the WattStopper LD290C - the spatial distribution
can be seen from the image linked to below. I wouldn't call it a
narrow/peaky/tight sensitivity distribution:
http://dl.dropbox.com/u/9713279/SensorSpatialResponse.png
and I have placed the .dat file here:
http://dl.dropbox.com/u/9713279/WattStopper_LS-290C.dat
Why do you believe that using glow probably won't make much difference -
unless my sensor has a tight and/or peaky sensitivity distribution?

Enjoy the weekend. It is pre-summer in Denmark; we've had blue sky for the
last 14 days, 20C and sun ....who said I miss California?? :wink:

Best,
Anne

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

Message: 1
Date: Fri, 29 Apr 2011 09:30:48 -0700
From: Andy McNeil <[email protected]>

To: Radiance general discussion <[email protected]>
Subject: Re: [Radiance-general] Three-Phase Method - subdivision of
聽聽聽聽聽聽聽window with sensor located close to the window
Message-ID: <[email protected]>

Content-Type: text/plain; charset="us-ascii"

Hi Anne,
Just curious, how do the glow results compare to the light sources? Could
you update the graph with the sensor signals using the glow material?
Andy

_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general

Hi David, Greg and Andy,
Have been in Lausanne for a great Daylight Symposium, so it's first now I
find the time to look at your comments.

My bummer! You're right, the -I does not belong. Thanks for noticing the
mistake and explain the reason why :slight_smile: :-). This is no excuse, but I did
find it myself when comparing rsensor 'cosine distribution' (from SPOT
distribution) to a simulation with a standard sensor point, and have been
wondering why??

And yep - Andy, I'll run it all again. Both three phase method and standard
Radiance technique. I'll let you know how it works out.

THANKS :slight_smile:
Best,
Anne

路路路

On Mon, May 2, 2011 at 9:00 PM, < [email protected]> wrote:

Send Radiance-general mailing list submissions to
聽聽聽聽聽聽聽[email protected]

To subscribe or unsubscribe via the World Wide Web, visit
聽聽聽聽聽聽聽http://www.radiance-online.org/mailman/listinfo/radiance-general
or, via email, send a message with subject or body 'help' to
聽聽聽聽聽聽聽[email protected]

You can reach the person managing the list at
聽聽聽聽聽聽聽[email protected]

When replying, please edit your Subject line so it is more specific
than "Re: Contents of Radiance-general digest..."

Today's Topics:

聽聽1. Re: Three-Phase Method - subdivision of window with sensor
聽聽聽聽聽located close to the window (David Geisler-Moroder)
聽聽2. Re: Three-Phase Method - subdivision of window with sensor
聽聽聽聽聽located close to the window (Greg Ward)
聽聽3. Re: Three-Phase Method - subdivision of window with sensor
聽聽聽聽聽located close to the window (Andy McNeil)

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

Message: 1
Date: Mon, 2 May 2011 11:41:44 +0200
From: David Geisler-Moroder <[email protected]>
To: Radiance general discussion <[email protected]>
Subject: Re: [Radiance-general] Three-Phase Method - subdivision of
聽聽聽聽聽聽聽window with sensor located close to the window
Message-ID: <[email protected]>
Content-Type: text/plain; charset="windows-1252"

Hi Anne,

another thing that came to my mind...

You are calling rtcontrib for the VMX using rsensor in your script like
that:
聽聽聽rsensor -h -rd 1000 -vf views/luxstat.vf sensors/WattStopper_LS-290C.dat
. |\
聽聽聽聽聽聽rtcontrib -c 1000 -f klems_int.cal -bn Nkbins -fo -o
results/"$vmxname"_%s.vmx \
聽聽聽聽聽聽-b kbinS -m windowlight -b kbinS -m windowlightsens \
聽聽聽聽聽聽-I+ -ab 3 -ad 2000 -ds .15 -lw 1e-4 model_vmx.oct

Do you want to obtain the sensor signal split up into the Klems bins?
If yes, I'm not sure if it works like that...

You are using rsensor to generate 1000 rays (i.e. origin and direction)
according to the sensor-file.
These points and directions are then given to rtcontrib, where you use -c
1000 to accumulate all
1000 results and -I+ to switch to irradiances.
However, this means that rtcontrib calculates irradiances for 1000 pairs of
points and directions as
if it was e.g. a grid for illuminance calculations. So you do not obtain
the
sensor signal, but a mean
of the 1000 calculated irradiances.

I hope I'm not missing anything...

Cheers,
David

2011/4/30 Anne Iversen <[email protected]>

> Hi,
> Maybe I was a bit fast concluding that I'll use glow. Comparing the glow
> material to the light material reveals a lower sensor signal when the
direct
> irradiation is low and the opposite when direct irradiation is high. Do
you
> know why I get this? Due to the ?subsampling? problem of window lights as
> David mentioned because of my sensor location very close to the window??
And
> therefore I should stick to glow?
>
> I have included the results from the glow simulations in the document:
> http://dl.dropbox.com/u/9713279/ThreePhaseMethod_Subdivision.pdf
> (the non-readable legends and axes must be a mac thing...the same happens
> when I open the documet on my mac, I can read the graphs nicely in the
pdf
> on my pc. ...have included some text in the captions, if you want to know
> what you are looking at ;-))
>
> And to your question about my sensor, Andy. The sensor is located on the
> window head, just behind the glass. The major detection area is to the
> outside through the window. The sensor used right now comes along with
the
> SPOT distribution, and is the WattStopper LD290C - the spatial
distribution
> can be seen from the image linked to below. I wouldn't call it a
> narrow/peaky/tight sensitivity distribution:
> http://dl.dropbox.com/u/9713279/SensorSpatialResponse.png
> and I have placed the .dat file here:
> http://dl.dropbox.com/u/9713279/WattStopper_LS-290C.dat
> Why do you believe that using glow probably won't make much difference -
> unless my sensor has a tight and/or peaky sensitivity distribution?
>
>
> Enjoy the weekend. It is pre-summer in Denmark; we've had blue sky for
the
> last 14 days, 20C and sun ....who said I miss California?? :wink:
>
> Best,
> Anne
>
>
> ----------------------------------------------------------------------
>>
>> Message: 1
>> Date: Fri, 29 Apr 2011 09:30:48 -0700
>> From: Andy McNeil <[email protected]>
>>
>> To: Radiance general discussion <[email protected]>
>> Subject: Re: [Radiance-general] Three-Phase Method - subdivision of
>> window with sensor located close to the window
>> Message-ID: <[email protected]>
>>
>> Content-Type: text/plain; charset="us-ascii"
>>
>> Hi Anne,
>> Just curious, how do the glow results compare to the light sources?
Could
>> you update the graph with the sensor signals using the glow material?
>> Andy
>>
>>
>>
>>
>
> _______________________________________________
> Radiance-general mailing list
> [email protected]
> http://www.radiance-online.org/mailman/listinfo/radiance-general
>
>
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------------------------------

Message: 2
Date: Mon, 2 May 2011 09:14:35 -0700
From: Greg Ward <[email protected]>
To: Radiance general discussion <[email protected]>
Subject: Re: [Radiance-general] Three-Phase Method - subdivision of
聽聽聽聽聽聽聽window with sensor located close to the window
Message-ID: <[email protected]>
Content-Type: text/plain; charset=us-ascii

Hi Anne,

I believe David is correct. I should have looked at your command more
closely. The -I+ switch does not belong. If you remove it (or set -I-),
then the computed radiance values will be accumulated according to the
distributed rays out of rsensor, then split again into Klems direction bins
by rtcontrib. The *.vmx files will each contain a single row of 145 RGB
coefficients, which processed through dctimestep with the window's BTDF file
will ultimately yield a single sensor value at each time step.

I hope this makes sense. I find it a bit confusing, myself!

Best,
-Greg

> From: David Geisler-Moroder <[email protected]>
> Date: May 2, 2011 2:41:44 AM PDT
>
> Hi Anne,
>
> another thing that came to my mind...
>
> You are calling rtcontrib for the VMX using rsensor in your script like
that:
> rsensor -h -rd 1000 -vf views/luxstat.vf
sensors/WattStopper_LS-290C.dat . |\
> rtcontrib -c 1000 -f klems_int.cal -bn Nkbins -fo -o
results/"$vmxname"_%s.vmx \
> -b kbinS -m windowlight -b kbinS -m windowlightsens \
> -I+ -ab 3 -ad 2000 -ds .15 -lw 1e-4 model_vmx.oct
>
> Do you want to obtain the sensor signal split up into the Klems bins?
> If yes, I'm not sure if it works like that...
>
> You are using rsensor to generate 1000 rays (i.e. origin and direction)
according to the sensor-file.
> These points and directions are then given to rtcontrib, where you use -c
1000 to accumulate all
> 1000 results and -I+ to switch to irradiances.
> However, this means that rtcontrib calculates irradiances for 1000 pairs
of points and directions as
> if it was e.g. a grid for illuminance calculations. So you do not obtain
the sensor signal, but a mean
> of the 1000 calculated irradiances.
>
> I hope I'm not missing anything...
>
> Cheers,
> David

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

Message: 3
Date: Mon, 2 May 2011 10:07:55 -0700
From: Andy McNeil <[email protected]>
To: Radiance general discussion <[email protected]>
Subject: Re: [Radiance-general] Three-Phase Method - subdivision of
聽聽聽聽聽聽聽window with sensor located close to the window
Message-ID: <[email protected]>
Content-Type: text/plain; charset=us-ascii

On Apr 30, 2011, at 6:11 AM, Anne Iversen wrote:

> Why do you believe that using glow probably won't make much difference -
unless my sensor has a tight and/or peaky sensitivity distribution?

Low resolution sampling of the outgoing window directions will only affect
calculations on surfaces near the window. And they should just cause noise
that is a fraction of the values from the direct sampling of the window by
rsensor. So the only way I can think that glow vs. light would make a
sizable difference is if your sensor is somewhat shielded from the window
(by sensitivity or by placement) and/or most of the rsensor samples a sent
to surfaces near the window ( ie focused sensitivity). Neither of these
seem to be the cause though using -I+ would have had the effect of masking
the direct contribution from the window in a similar way because rsensor
rays that hit the window don't return a direct value but instead start an
iluminance calculation on the window.

I'd suggest that while you are running everything again without -I that you
also simulate using classic Radiance techniques (ie not the three-phase
method).

Andy

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End of Radiance-general Digest, Vol 87, Issue 1
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