indirect/direct photometric

radiance-general
1

Yes, it's me again.

I have yet another question (guaranteed not to be the last). I would not have gotten beyond the basic tutorial if it hadn't been for the support provided by this list. As frightening as it may sound, if I can manage to get enough of the fundamentals down over the summer, I will be trying to introduce the basics of Radiance into the curriculum at my school.

My questions this time are related modeling electric luminaires and accurately applying photometric data.

I have been following the instructions in Section 5.2.3 of Rendering with Radiance, but using my own direct/indirect fluorrescent luminaire photometric file. As usual, I'm having some trouble.

1) The ies2rad command has -di -df -dc and -dm options. Do I set the units according to the units of the model of my space, or according to the units the photometric data was created? I am assuming that it would be according to the units of the model of my space (especially since I don't think photometric data is created in inches or centimeters). However, when I compare the resulting .dat file of using the -df option with the .dat file using -dm, they are identical.

2) I used the command:
ies2rad -df -t white -i .56419 D21998.ies
I then edited the resulting .rad file to use the lboxcorr function. The file reads as follows:

# ies2rad -df -t white -i .56419
# Dimensions in feet
#<IESNA:LM-63-1995
#<[TEST] 21998
#<[DATE] 05/31/2001
#<[LUMCAT] AGDMWU232-F3-120-1/2-EB
#<[LUMINAIRE] DAY-BRITE ADAGIO DIRECT/INDIRECT W/33-CELL SPECULAR LOUVER
#<[LAMP] F32T8
#<[BALLAST] ADVANCE REL-2P32-SC
#<[MANUFAC] DayBrite-Capri-Omega(Genlyte Thomas Group)
#<[_TIFF_FILE_NAME] AGD2
#<[_VERSION] fo2ies 2.01
#<Reflection factor 0.92, Test distance = 26 ft.
# 60 watt luminaire, lamp*ballast factor = 0.88

void brightdata D21998_dist
5 lboxcorr D21998.dat source.cal src_phi4 src_theta
0
4 .816 .141 1.22 .156

D21998_dist illum D21998_light
0
3 1 1 1

!genbox D21998_light D21998.s .141 1.22 .156 \

xform -t -.0705 -.61 -.078

Because this file is in meters, I decided to xform the above file using -s 39.3700787 to convert the file to inches (which my model is in). Is this correct?

The resulting file is:

# xform -s 39.3700787
# ies2rad -df -t white -i .56419
# Dimensions in feet
#<IESNA:LM-63-1995
#<[TEST] 21998
#<[DATE] 05/31/2001
#<[LUMCAT] AGDMWU232-F3-120-1/2-EB
#<[LUMINAIRE] DAY-BRITE ADAGIO DIRECT/INDIRECT W/33-CELL SPECULAR LOUVER
#<[LAMP] F32T8
#<[BALLAST] ADVANCE REL-2P32-SC
#<[MANUFAC] DayBrite-Capri-Omega(Genlyte Thomas Group)
#<[_TIFF_FILE_NAME] AGD2
#<[_VERSION] fo2ies 2.01
#<Reflection factor 0.92, Test distance = 26 ft.
# 60 watt luminaire, lamp*ballast factor = 0.88

void brightdata D21998_dist
9 lboxcorr D21998.dat source.cal src_phi4 src_theta -i 1 -s 39.3700787
0
4 0.816 0.141 1.22 0.156

D21998_dist illum D21998_light
0
3 1 1 1
# xform -t -.0705 -.61 -.078
# genbox D21998_light D21998.s .141 1.22 .156

D21998_light polygon D21998.s.1540
0
12
       2.77559054835 -24.015748007 -3.0708661386
       2.77559054835 -24.015748007 3.0708661386
      -2.77559054835 -24.015748007 3.0708661386
      -2.77559054835 -24.015748007 -3.0708661386

D21998_light polygon D21998.s.4620
0
12
      -2.77559054835 -24.015748007 3.0708661386
      -2.77559054835 24.015748007 3.0708661386
      -2.77559054835 24.015748007 -3.0708661386
      -2.77559054835 -24.015748007 -3.0708661386

D21998_light polygon D21998.s.2310
0
12
      -2.77559054835 24.015748007 -3.0708661386
       2.77559054835 24.015748007 -3.0708661386
       2.77559054835 -24.015748007 -3.0708661386
      -2.77559054835 -24.015748007 -3.0708661386

D21998_light polygon D21998.s.3267
0
12
       2.77559054835 24.015748007 -3.0708661386
      -2.77559054835 24.015748007 -3.0708661386
      -2.77559054835 24.015748007 3.0708661386
       2.77559054835 24.015748007 3.0708661386

D21998_light polygon D21998.s.5137
0
12
       2.77559054835 -24.015748007 3.0708661386
       2.77559054835 -24.015748007 -3.0708661386
       2.77559054835 24.015748007 -3.0708661386
       2.77559054835 24.015748007 3.0708661386

D21998_light polygon D21998.s.6457
0
12
      -2.77559054835 24.015748007 3.0708661386
      -2.77559054835 -24.015748007 3.0708661386
       2.77559054835 -24.015748007 3.0708661386
       2.77559054835 24.015748007 3.0708661386

3) However, when I place the resulting illum close to the floor, it is obvious that the light is being emitted is spherical, not linear. There has to be something that I am missing. Could somebody please inform me?

Thanks again.

John

2

Hi John,

I'll skip for now the question of why you're altering the output of ies2rad, and just try to answer your questions, first.

From: John An <whollycow@mac.com>

1) The ies2rad command has -di -df -dc and -dm options. Do I set the units according to the units of the model of my space, or according to the units the photometric data was created? I am assuming that it would be according to the units of the model of my space (especially since I don't think photometric data is created in inches or centimeters). However, when I compare the resulting .dat file of using the -df option with the .dat file using -dm, they are identical.

The -d? options affect the geometric dimensions that are output when you use the geometry supplied in the ies file. When you specify your own illum sphere with the -i option, it assumes you mean to use the units you specify with the -d? option. All that really changes is the first real argument to the brightdata primitive, which scales the vaues in the *.dat file appropriately. The data file itself is (as you noted) unchanged.

2) I used the command:
ies2rad -df -t white -i .56419 D21998.ies
I then edited the resulting .rad file to use the lboxcorr function. The file reads as follows:

# ies2rad -df -t white -i .56419
...
!genbox D21998_light D21998.s .141 1.22 .156 \
> xform -t -.0705 -.61 -.078

Because this file is in meters, I decided to xform the above file using -s 39.3700787 to convert the file to inches (which my model is in). Is this correct?

The resulting file is:

# xform -s 39.3700787
# ies2rad -df -t white -i .56419
...

3) However, when I place the resulting illum close to the floor, it is obvious that the light is being emitted is spherical, not linear. There has to be something that I am missing. Could somebody please inform me?

Are you visualizing the source in rview? If so, the defaults of -ds 0 and -dj 0 mean that all light soruces will appear as if eminating from a point. If you set -ds .2 and -dj .6 or so, you should get the result you expect.

-Greg

3

From: John An <jan@gsd.harvard.edu>
Date: Sun May 25, 2003 2:41:57 AM America/New_York
To: radiance-general@radiance-online.org
Subject: indirect/direct photometric

Greg,

Thanks again.

Greg Ward wrote:
I'll skip for now the question of why you're altering the output of
ies2rad, and just try to answer your questions, first.

I was following the instructions in Section 5.3.2. It noted that for direct/indirect luminaires, this special method should be used. Besides, when I tried using the ies2rad command without modifying the results, I ended up with visible geometry emitting the light. While I don't have a luminaire modeled yet, I eventually want to be able to look at the luminaire once it is modeled, so I assumed that altering the output of ies2rad so that an illum would eventually envelop the luminaire was the way to go. Is there a better way of doing this?

Also, when I examined the dimensions of the luminaire contained in the .ies file, it showed that the height was 0. I'm assuming that the height of 0 is to address the shadow banding effect. However, a non-existent height would mean that the geometry resulting from the ies2rad would never enclose the geometry of the luminaire unless the output of the ies2rad file was modified.

So I guess my question now is, what is the best process of mapping the photometric data to a 'complex' luminaire so that the luminaire is visible?

Greg Ward wrote:
The -d? options affect the geometric dimensions that are output when
you use the geometry supplied in the ies file. When you specify your
own illum sphere with the -i option, it assumes you mean to use the
units you specify with the -d? option. All that really changes is the
first real argument to the brightdata primitive, which scales the vaues
in the *.dat file appropriately. The data file itself is (as you
noted) unchanged.

Understood. Since my model is in inches, I should be using the -di option.

Greg Ward wrote:
Are you visualizing the source in rview? If so, the defaults of -ds 0
and -dj 0 mean that all light soruces will appear as if eminating from
a point. If you set -ds .2 and -dj .6 or so, you should get the result
you expect.

Yes, I was using rview (rview -vf *.vf -ab 3 *.oct). As soon as I added the -ds .2 and -dj .6 options, I saw a linear profile.

Thanks again, for putting up with my naive questions.

John

4

From: John An <whollycow@mac.com>

I was following the instructions in Section 5.3.2. It noted that for direct/indirect luminaires, this special method should be used. Besides, when I tried using the ies2rad command without modifying the results, I ended up with visible geometry emitting the light. While I don't have a luminaire modeled yet, I eventually want to be able to look at the luminaire once it is modeled, so I assumed that altering the output of ies2rad so that an illum would eventually envelop the luminaire was the way to go. Is there a better way of doing this?

Also, when I examined the dimensions of the luminaire contained in the .ies file, it showed that the height was 0. I'm assuming that the height of 0 is to address the shadow banding effect. However, a non-existent height would mean that the geometry resulting from the ies2rad would never enclose the geometry of the luminaire unless the output of the ies2rad file was modified.

So I guess my question now is, what is the best process of mapping the photometric data to a 'complex' luminaire so that the luminaire is visible?

Some improvements have been made to ies2rad since the book was published, and direct/indirect fixtures should produce better renderings now, I believe.

However, if you want to insert your own visible luminaire geometry, the -i option is the way, but do not replace the geometry that ies2rad produces. Instead, make sure that the illum sphere you specify encloses the geometry you add for your visible fixture, and create this fixture using "glow" modifiers for the emitting surfaces rather than "light" or "illum" materials.

I hope this helps.
-Greg