gensky question

radiance-general
1

Hi Everybody,

I have an aim to find out the luminance of the sun after it hits a perfect diffuser. I'm sure i have done this the very long way round, but at least this step by step way i understand what is going on.

I have used gensky to create a sun, and have created a sky and a ground (see bottom).

Aside question- the default for meridian using gensky is -120, and as im in london i have put my meridian to 0. this seems to give me a negative azimuth angle for my early morning sun and a positive for my afternoon sun. this means that the sun is rising in the west and setting in the east…im sure its the other way round??? the first four lines of the 10am automatically generated gensky file can be seen below
# gensky 07 24 10 -a 52 -o 2 -m 0 +s
# Local solar time: 9.76
# Solar altitude and azimuth: 48.8 -52.0
# Ground ambient level: 18.3

I have created different files for the sun throughout one day, started and finishing at 7, so that i have 13 different sun's.
I have then oconv each file to my material file, found a nice view directly at the sun for each time in rview and then rendering the image in rpict and finally pcond each image with a -h- option to get a good exposure level. So i have 13 images all looking directly at the sun. When i then click on a point and press l it gives me a value for (i think???) luminance.

I now want to place a perfect diffuser with a normal pointed directly at the sun in each of these 13 positions and measure the illuminance reflecting off of the diffuser. My big question is, how do i orientate the diffuser so that it is normal to the sun each time, and any recommendations as to what material/values i should make the diffuser from??

My sky.mat file just for completion

skyfunc glow sky_glow
0
0
4 1 1 1 0

sky_glow source sky
0
0
4 0 0 1 180

skyfunc glow ground_glow
0
0
4 1 1 1 0

ground_glow source ground
0
0
4 0 0 -1 180

# ground plane

void plastic ground_mat
0
0
5 .28 .18 .12 0 0

ground_mat ring groundplane
0
0
8 0 0 -.01
  0 0 1
  0 30

Thanks

Chris

···

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2

Hi Chris.

I never checked the angles gensky prints but I remember that Radiance
understands "+" as west and "-" as east. (Remember that it was written
in and for America and it's always good for your ego to have a "+"
associated
with you :wink: So the output should be fine. You can check the output of an
hourly
cycle to see how the value changes.

Your main problem can be solved by using a file with the diffuser as a
vertical
plane at a position "south" of the origin and "!xform" it into place
with the altitude
and azimuth as arguments for the "-ry" and "-rz" options:

!xform -ry <altitude*-1> -rz <azimuth*-1> diffuser.rad

The order of -ry and -rz is important!

To model the "perfect diffuser" have a look at Schorsch excelent
explanation
of the trans material at

http://www.schorsch.com/rayfront/manual/transdef.html

If I understand you right you want a material with 100 % diffuse
transmittance.
I'm not sure Radiance does this correctly as it is physically imposible
but it's
worth a try.

Have fun,
Thomas

···

_____

From: [email protected]
[mailto:[email protected]] On Behalf Of Chris
Foster
Sent: 24 July 2006 13:39
To: Radiance general discussion; Radiance general
Subject: [Radiance-general] gensky question

Hi Everybody,

I have an aim to find out the luminance of the sun after it hits a
perfect diffuser. I'm sure i have done this the very long way round, but
at least this step by step way i understand what is going on.

I have used gensky to create a sun, and have created a sky and a ground
(see bottom).

Aside question- the default for meridian using gensky is -120, and as im
in london i have put my meridian to 0. this seems to give me a negative
azimuth angle for my early morning sun and a positive for my afternoon
sun. this means that the sun is rising in the west and setting in the
east…im sure its the other way round??? the first four lines
of the 10am automatically generated gensky file can be seen below
# gensky 07 24 10 -a 52 -o 2 -m 0 +s
# Local solar time: 9.76
# Solar altitude and azimuth: 48.8 -52.0
# Ground ambient level: 18.3

I have created different files for the sun throughout one day, started
and finishing at 7, so that i have 13 different sun's.
I have then oconv each file to my material file, found a nice view
directly at the sun for each time in rview and then rendering the image
in rpict and finally pcond each image with a -h- option to get a good
exposure level. So i have 13 images all looking directly at the sun.
When i then click on a point and press l it gives me a value for (i
think???) luminance.

I now want to place a perfect diffuser with a normal pointed directly at
the sun in each of these 13 positions and measure the illuminance
reflecting off of the diffuser. My big question is, how do i orientate
the diffuser so that it is normal to the sun each time, and any
recommendations as to what material/values i should make the diffuser
from??

My sky.mat file just for completion

skyfunc glow sky_glow
0
0
4 1 1 1 0

sky_glow source sky
0
0
4 0 0 1 180

skyfunc glow ground_glow
0
0
4 1 1 1 0

ground_glow source ground
0
0
4 0 0 -1 180

# ground plane

void plastic ground_mat
0
0
5 .28 .18 .12 0 0

ground_mat ring groundplane
0
0
8 0 0 -.01
  0 0 1
  0 30

Thanks

Chris

-------------------------------------------------------------------
This e-mail and any attachments may contain confidential and/or
privileged material; it is for the intended addressee(s) only.
If you are not a named addressee, you must not use, retain or
disclose such information.

NPL Management Ltd cannot guarantee that the e-mail or any
attachments are free from viruses.

NPL Management Ltd. Registered in England and Wales. No: 2937881
Registered Office: Serco House, 16 Bartley Wood Business Park,
Hook, Hampshire, United Kingdom RG27 9UY
-------------------------------------------------------------------

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This e-mail, (and any attachments) is confidential and may be privileged. It may be read, copied and used by the intended addressee only. If you have received this in error please contact BDP immediately.

If you have any queries, please contact the sender.
***********************************************************************************
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Registered in England No 2207415:
Registered Office: Building Design Partnership Ltd, Sunlight House, PO Box 85, Quay Street, Manchester, M60 3JA, http://www.bdp.co.uk
***********************************************************************************

3

Hi Tom,

Thanks for your help. The angles thing has sorted itself out now. I thought i read somewhere that east of south was positive, but obviously not! From my results it makes sense if it were your way.

I near enough did what you recommended already, but i dont think i clarified what i wanted judging by your response.

If I understand you right you want a material with 100 % diffuse transmittance.

I am after a material with 100% diffuse reflectance

My material,reflector.rad

void plastic reflector_mat
0
0
5 1 1 1 0 0

reflector_mat ring reflector
0
0
8 0 0 0
  0 -1 0
  5 0

An example of one of my xforms,

!xform -n reflector -t 0 0 10 -rz 38 -rx -48.8 reflector.rad

These angles are following the azimuth and altitude of the sun, i used rz and rx because of the way my ring was made. I have made my plastic material with a 0,0 spec and roughness value to get a perflectly reflecting diffuse surface (r,g,b are 1,1,1). Im now aim to look directly at my surface and measure the luminance from it.
  
There isnt really a question in this email, just thought id reply to yours, thanks for your help!

Chris

···

-------------------------------------------------------------------
This e-mail and any attachments may contain confidential and/or
privileged material; it is for the intended addressee(s) only.
If you are not a named addressee, you must not use, retain or
disclose such information.

NPL Management Ltd cannot guarantee that the e-mail or any
attachments are free from viruses.

NPL Management Ltd. Registered in England and Wales. No: 2937881
Registered Office: Serco House, 16 Bartley Wood Business Park,
                   Hook, Hampshire, United Kingdom RG27 9UY
-------------------------------------------------------------------

4

Chris.

Glad you solved your problem, sort of.

I just want to add one comment:

If you add the "-i" switch to rpict/rtrace the surface properties
for the last bounce will be replaced with a Lambertian surface
which is what you are looking for (completely diffuse reflection).

For you it might be the simplest solution to do an irridience
calculation with only one bounce. The real properties of the
diffuser (your plastic definition) don't make any difference then.

For an illustration of this see the color prints of the reception
desk in RwR (plate 15).

Thomas

···

_____

From: [email protected]
[mailto:[email protected]] On Behalf Of Chris
Foster
Sent: 25 July 2006 09:30
To: Radiance general discussion; Radiance general discussion
Subject: RE: [Radiance-general] gensky question

Hi Tom,

Thanks for your help. The angles thing has sorted itself out now. I
thought i read somewhere that east of south was positive, but obviously
not! From my results it makes sense if it were your way.

I near enough did what you recommended already, but i dont think i
clarified what i wanted judging by your response.

If I understand you right you want a material with 100 % diffuse

transmittance.

I am after a material with 100% diffuse reflectance

My material,reflector.rad

void plastic reflector_mat
0
0
5 1 1 1 0 0

reflector_mat ring reflector
0
0
8 0 0 0
  0 -1 0
  5 0

An example of one of my xforms,

!xform -n reflector -t 0 0 10 -rz 38 -rx -48.8 reflector.rad

These angles are following the azimuth and altitude of the sun, i used
rz and rx because of the way my ring was made. I have made my plastic
material with a 0,0 spec and roughness value to get a perflectly
reflecting diffuse surface (r,g,b are 1,1,1). Im now aim to look
directly at my surface and measure the luminance from it.

There isnt really a question in this email, just thought id reply to
yours, thanks for your help!

Chris

-------------------------------------------------------------------
This e-mail and any attachments may contain confidential and/or
privileged material; it is for the intended addressee(s) only.
If you are not a named addressee, you must not use, retain or
disclose such information.

NPL Management Ltd cannot guarantee that the e-mail or any
attachments are free from viruses.

NPL Management Ltd. Registered in England and Wales. No: 2937881
Registered Office: Serco House, 16 Bartley Wood Business Park,
Hook, Hampshire, United Kingdom RG27 9UY
-------------------------------------------------------------------

***********************************************************************************
This e-mail, (and any attachments) is confidential and may be privileged. It may be read, copied and used by the intended addressee only. If you have received this in error please contact BDP immediately.

If you have any queries, please contact the sender.
***********************************************************************************
Building Design Partnership
Registered in England No 2207415:
Registered Office: Building Design Partnership Ltd, Sunlight House, PO Box 85, Quay Street, Manchester, M60 3JA, http://www.bdp.co.uk
***********************************************************************************