pmap distribution

Hi there,

I would like to measure the illumination from a vertical pipe bringing
daylight into a building. I have two situations, a clear sky with 30 and
60 degrees solar angles - 75,000 and 40,000 Lux reaching the top of the
tube - and would like to measure the transmittance of the pipe at its
bottom, using materials with 95, 96, 97, 98 and 99% reflectance. Using
manual calculations I can fairly expect something between 52-88% and
80-96% transmittance for the 30-degrees and 60-degrees sky,
respectively. I initially used the metal material which has given me
very low numbers. When I switched to the mirror material with a faceted
tube (polygons) replacing the initial round tube, the numbers started to
match (or at least sort of).

For measurements, I divided the ring in the bottom of the tube in
approximately 200 measuring points and retrieved numbers that vary from
5,000 to 150,000 Lux for the first tube and 9,000 to 400,000 Lux for the
later. Dividing the individual values for the number of measuring points
give me exact numbers for the "30-deg" tube, and numbers 20% higher (but
accurate when reduced) for the "60-deg" one. Being a newbie at this, I
am quite puzzled with the photon distribution and if the measurements
are accurate. Is it the bandwidth that is producing numbers that far
low and high? Is it bias that is distributing the photon like this?

I am testing with an 80 degrees solar altitude clear sky and the results
are 100% higher that I expected (but again, accurate when reduced).

My parameters are:

mkpmap -appb <file> 1000000 50 5000 - apc <file> 1000000 -ds 0.001 -dp
32768
rtrace -I+ -ab 1 -ad 32768 -aa 0.001 -ar 32768 -app <file> -apcb 50 5000

Erico Naves Rosa
Doctor of Design Candidate
Harvard Design School

Erico,

How long is the pipe?

How many curves does it have?

What is the degree of curve for each curve?

TracePro has a tutorial that is very similar to your problem. Photopia, Zemax and ASAP should have similar tutorials. Why don't you ask them for their software.

52-88% and 80-96% transmittance sounds too high.

Martin Moeck, Penn State

···

________________________________

From: [email protected] on behalf of Erico Rosa
Sent: Tue 2/7/2006 3:00 PM
To: [email protected]

Hi there,

I would like to measure the illumination from a vertical pipe bringing
daylight into a building. I have two situations, a clear sky with 30 and
60 degrees solar angles - 75,000 and 40,000 Lux reaching the top of the
tube - and would like to measure the transmittance of the pipe at its
bottom, using materials with 95, 96, 97, 98 and 99% reflectance. Using
manual calculations I can fairly expect something between 52-88% and
80-96% transmittance for the 30-degrees and 60-degrees sky,
respectively. I initially used the metal material which has given me
very low numbers. When I switched to the mirror material with a faceted
tube (polygons) replacing the initial round tube, the numbers started to
match (or at least sort of).

For measurements, I divided the ring in the bottom of the tube in
approximately 200 measuring points and retrieved numbers that vary from
5,000 to 150,000 Lux for the first tube and 9,000 to 400,000 Lux for the
later. Dividing the individual values for the number of measuring points
give me exact numbers for the "30-deg" tube, and numbers 20% higher (but
accurate when reduced) for the "60-deg" one. Being a newbie at this, I
am quite puzzled with the photon distribution and if the measurements
are accurate. Is it the bandwidth that is producing numbers that far
low and high? Is it bias that is distributing the photon like this?

I am testing with an 80 degrees solar altitude clear sky and the results
are 100% higher that I expected (but again, accurate when reduced).

My parameters are:

mkpmap -appb <file> 1000000 50 5000 - apc <file> 1000000 -ds 0.001 -dp
32768
rtrace -I+ -ab 1 -ad 32768 -aa 0.001 -ar 32768 -app <file> -apcb 50 5000

Erico Naves Rosa
Doctor of Design Candidate
Harvard Design School

_______________________________________________
[email protected]

Hi Martin,

There are no curves. Its a straight 6-meter-long hollow mirror pipe
with a diameter of 1 meter (fairly large). I've based these
transmittances on a study by Zastrow and Wittwer:

Transmittance of pipe = radius of pipe ^ [(length of pipe/tangent of
solar angle)/(pi x diameter of pipe/4)], which gave me the numbers I've
mentioned.

Thanks for the pointers! I actually requested TracePro sometime ago but
the trial version doesn't allow me to attach any materials, which was
quite upsetting. I could try to contact them for a sponsorship for this
fairly expensive piece of software, although I was hoping the photon map
would do the job...

Erico Naves Rosa
Doctor of Design Candidate
Harvard Design School

···

-----Original Message-----
From: Martin Moeck [mailto:[email protected]]
On Behalf Of Martin Moeck
Sent: Tuesday, February 07, 2006 4:30 PM

Erico,

How long is the pipe?

How many curves does it have?

What is the degree of curve for each curve?

TracePro has a tutorial that is very similar to your problem. Photopia,
Zemax and ASAP should have similar tutorials. Why don't you ask them for
their software.

52-88% and 80-96% transmittance sounds too high.

Martin Moeck, Penn State

From: [email protected] on behalf of Erico
Rosa
Sent: Tue 2/7/2006 3:00 PM
To: [email protected]
Hi there,

I would like to measure the illumination from a vertical pipe bringing
daylight into a building. I have two situations, a clear sky with 30 and
60 degrees solar angles - 75,000 and 40,000 Lux reaching the top of the
tube - and would like to measure the transmittance of the pipe at its
bottom, using materials with 95, 96, 97, 98 and 99% reflectance. Using
manual calculations I can fairly expect something between 52-88% and
80-96% transmittance for the 30-degrees and 60-degrees sky,
respectively. I initially used the metal material which has given me
very low numbers. When I switched to the mirror material with a faceted
tube (polygons) replacing the initial round tube, the numbers started to
match (or at least sort of).

For measurements, I divided the ring in the bottom of the tube in
approximately 200 measuring points and retrieved numbers that vary from
5,000 to 150,000 Lux for the first tube and 9,000 to 400,000 Lux for the
later. Dividing the individual values for the number of measuring points
give me exact numbers for the "30-deg" tube, and numbers 20% higher (but
accurate when reduced) for the "60-deg" one. Being a newbie at this, I
am quite puzzled with the photon distribution and if the measurements
are accurate. Is it the bandwidth that is producing numbers that far
low and high? Is it bias that is distributing the photon like this?

I am testing with an 80 degrees solar altitude clear sky and the results
are 100% higher that I expected (but again, accurate when reduced).

My parameters are:

mkpmap -appb <file> 1000000 50 5000 - apc <file> 1000000 -ds 0.001 -dp
32768
rtrace -I+ -ab 1 -ad 32768 -aa 0.001 -ar 32768 -app <file> -apcb 50 5000

Erico Naves Rosa
Doctor of Design Candidate
Harvard Design School

_______________________________________________
[email protected]

Hi Erico,

where did you put your measuring points exactly? And how do you measure the incoming flux?
If you put the measuring points not directly on a surface and use photon mapping, then it is not surprising that you get strange results. Then photon mapping calculates the density estimate of the nearest photons in the scene (which are per definition always on a surface). So if you wanna get the transmission of a pipe, you should "close" the pipe at its bottom by a disk and put the measuring points directly on it. This disk shouldn't be completely black - even knowing that it reflects the light back to the top.
The same must be done for the incoming flux, so you need an extra run just for that and should put a disk at the top of the pipe.

In that case, you should get reasonable results also by using the metal material.

Jan

Erico Rosa wrote:

···

Hi there,

I would like to measure the illumination from a vertical pipe bringing
daylight into a building. I have two situations, a clear sky with 30 and
60 degrees solar angles - 75,000 and 40,000 Lux reaching the top of the
tube - and would like to measure the transmittance of the pipe at its
bottom, using materials with 95, 96, 97, 98 and 99% reflectance. Using
manual calculations I can fairly expect something between 52-88% and
80-96% transmittance for the 30-degrees and 60-degrees sky,
respectively. I initially used the metal material which has given me
very low numbers. When I switched to the mirror material with a faceted
tube (polygons) replacing the initial round tube, the numbers started to
match (or at least sort of).

For measurements, I divided the ring in the bottom of the tube in
approximately 200 measuring points and retrieved numbers that vary from
5,000 to 150,000 Lux for the first tube and 9,000 to 400,000 Lux for the
later. Dividing the individual values for the number of measuring points
give me exact numbers for the "30-deg" tube, and numbers 20% higher (but
accurate when reduced) for the "60-deg" one. Being a newbie at this, I
am quite puzzled with the photon distribution and if the measurements
are accurate. Is it the bandwidth that is producing numbers that far
low and high? Is it bias that is distributing the photon like this?

I am testing with an 80 degrees solar altitude clear sky and the results
are 100% higher that I expected (but again, accurate when reduced).

My parameters are:

mkpmap -appb <file> 1000000 50 5000 - apc <file> 1000000 -ds 0.001 -dp
32768
rtrace -I+ -ab 1 -ad 32768 -aa 0.001 -ar 32768 -app <file> -apcb 50 5000

Erico Naves Rosa
Doctor of Design Candidate
Harvard Design School

_______________________________________________
[email protected]

--
Dipl.-Ing. Jan Wienold
Project Manager
Fraunhofer-Institut f�r Solare Energiesysteme
Thermal Systems and Buildings, Lighting and Daylighting
Heidenhofstr. 2, 79110 Freiburg, Germany
Phone: +49(0)761 4588 5133 Fax:+49(0)761 4588 9133
[email protected]

In office: Mo,Tue: 9:00-18:00
We-Fr: 8:30-14:00

Hi Jan,

Thanks again for the help. I realize early on the need for the surface
and my measuring points match the ring surface (plastic, 0.1 0.1 0.1 0
0) on the bottom of the pipe. On the other hand, the pipe is open at the
top (well, there is the antimatter ring port on the top). Would clear
glass do the job on the top?

I am reading some of the early threads on the issue and on a previous
message you mentioned:

"The quick instruction is:

0. You can use the standard radiance description (except user defined
1. To distribute photon and store them in files (global and caustic
photons separately). e.g.
~/bin/radiance/pmap/mkpmap -apg f81_z.gp 700000 -apc f81_z.cp 700000
test.oct
700000 is the number of the photos emitted, gp : global photons, cp
caustic photons
2. Count the photons, make a density estimate and generate a picture
with the modified rpict:
~/bin/radiance/pmap/rpict -apg f81_z.gp 500 -apc f81_z.cp 500 -ab 1 -x
1200 -y 1200 -vf test.vf -o test.pic test.oct"

How would I 'count' the photons and make a density estimate?
Erico

···

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Jan
Wienold
Sent: Tuesday, February 07, 2006 6:46 PM

Hi Erico,

where did you put your measuring points exactly? And how do you measure
the incoming flux?
If you put the measuring points not directly on a surface and use photon

mapping, then it is not surprising that you get strange results. Then
photon mapping calculates the density estimate of the nearest photons in

the scene (which are per definition always on a surface).
So if you wanna get the transmission of a pipe, you should "close" the
pipe at its bottom by a disk and put the measuring points directly on
it. This disk shouldn't be completely black - even knowing that it
reflects the light back to the top.
The same must be done for the incoming flux, so you need an extra run
just for that and should put a disk at the top of the pipe.

In that case, you should get reasonable results also by using the metal
material.

Jan

Erico Rosa wrote:

Hi there,

I would like to measure the illumination from a vertical pipe bringing
daylight into a building. I have two situations, a clear sky with 30

and

60 degrees solar angles - 75,000 and 40,000 Lux reaching the top of the
tube - and would like to measure the transmittance of the pipe at its
bottom, using materials with 95, 96, 97, 98 and 99% reflectance. Using
manual calculations I can fairly expect something between 52-88% and
80-96% transmittance for the 30-degrees and 60-degrees sky,
respectively. I initially used the metal material which has given me
very low numbers. When I switched to the mirror material with a faceted
tube (polygons) replacing the initial round tube, the numbers started

to

match (or at least sort of).

For measurements, I divided the ring in the bottom of the tube in
approximately 200 measuring points and retrieved numbers that vary from
5,000 to 150,000 Lux for the first tube and 9,000 to 400,000 Lux for

the

later. Dividing the individual values for the number of measuring

points

give me exact numbers for the "30-deg" tube, and numbers 20% higher

(but

accurate when reduced) for the "60-deg" one. Being a newbie at this, I
am quite puzzled with the photon distribution and if the measurements
are accurate. Is it the bandwidth that is producing numbers that far
low and high? Is it bias that is distributing the photon like this?

I am testing with an 80 degrees solar altitude clear sky and the

results

are 100% higher that I expected (but again, accurate when reduced).

My parameters are:

mkpmap -appb <file> 1000000 50 5000 - apc <file> 1000000 -ds 0.001 -dp
32768
rtrace -I+ -ab 1 -ad 32768 -aa 0.001 -ar 32768 -app <file> -apcb 50

5000

Erico Naves Rosa
Doctor of Design Candidate
Harvard Design School

_______________________________________________
[email protected]

--
Dipl.-Ing. Jan Wienold
Project Manager
Fraunhofer-Institut für Solare Energiesysteme
Thermal Systems and Buildings, Lighting and Daylighting
Heidenhofstr. 2, 79110 Freiburg, Germany
Phone: +49(0)761 4588 5133 Fax:+49(0)761 4588 9133
[email protected]

In office:
Mo,Tue: 9:00-18:00
We-Fr: 8:30-14:00

_______________________________________________