FW: Gensky Question

radiance-general
1

Hi All,

I have a GENSKY question that I cant find the answer to in the archives. I
suspect that the answer is straightforward, but I am now challenging all my
old assumptions as I have just switched from old school desktop radiance to
3R7P2 with photon mapping running under Ubuntu on VMware Workstation.
Daunting, but I like it!

Perhaps first I should state that I am aware from the listings that perhaps
I should be using Gendaylit rather than Gensky, but I have not managed to
compile it yet. Compiling makes me anxious. I used Francesco's Linux
binaries in the end as I couldn't get photon map to compile properly after
3R7P2. My /bin and /lib files are not in the standard location, but I have
altered PATH & RAYPATH accordingly.

So, to the questions:

Firstly, I have some data for sky brightness from BRE Availability of
Daylight, for diffuse and direct illuminance. If for example, I have
illuminance values of 34 klux diffuse and 26 klux direct can I explicitly
set these in Gensky (assuming 179lux per watt) with

Gensky (location details, azimuth etc) +s -B 189 -R 145.25 > skyfile.rad

My concern is whether -B or -R overrides the other, or will I ultimately
result in approximately total 60klux horizontal illuminance?

Secondly, do I have to manually add the following to the bottom of
skyfile.rad. I presume that I don't need to alter any of the parameters here
for a basic sky and ground plane and that it references the skyfunc output
from the gensky command.

skyfunc glow skyglow
0
0
4
  .85 1.04 1.2 0

skyglow source sky
0
0
4
  0 0 1 180

skyfunc glow groundglow
0
0
4
  .8 1.1 .8 0

groundglow source ground
0
0
4
  0 0 -1 180

Finally, if I explicitly set -B & -R for an intermediate sky with +i does
the +i setting result in an adjustment to the -B & -R values?

Many thanks in advance

Nick Devlin.

2

Nick,

-R -B are supposed to specify direct and diffuse contribute.
a quick and easy check is to create a -s (diffuse only) and a +s
(global) sky with the same -R -B and check illuminances at a point (0 0
0, 0 0 1)
Now try without the sky dome and +s (direct only) and see...
you should get diffuse and global and direct values.
Please try it.

About the source primitive, you need it all the time.
Coefficients can be just (1 1 1) for the sky
and a reduction like (0.1 0.1 0.1) or (0.2 0.2 0.2) for the ground
depending to the model you are working on.
If you use your coefficients you will be working with colour but you
need to check that the photopic average is correct.

Hope this is +s,
i.e. 'clear'
:slight_smile:

Ciao

···

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Nick
Devlin
Sent: 22 November 2006 09:56
To: [email protected]
Subject: [Radiance-general] FW: Gensky Question

Hi All,

I have a GENSKY question that I cant find the answer to in the archives.
I
suspect that the answer is straightforward, but I am now challenging all
my
old assumptions as I have just switched from old school desktop radiance
to
3R7P2 with photon mapping running under Ubuntu on VMware Workstation.
Daunting, but I like it!

Perhaps first I should state that I am aware from the listings that
perhaps
I should be using Gendaylit rather than Gensky, but I have not managed
to
compile it yet. Compiling makes me anxious. I used Francesco's Linux
binaries in the end as I couldn't get photon map to compile properly
after
3R7P2. My /bin and /lib files are not in the standard location, but I
have
altered PATH & RAYPATH accordingly.

So, to the questions:

Firstly, I have some data for sky brightness from BRE Availability of
Daylight, for diffuse and direct illuminance. If for example, I have
illuminance values of 34 klux diffuse and 26 klux direct can I
explicitly
set these in Gensky (assuming 179lux per watt) with

Gensky (location details, azimuth etc) +s -B 189 -R 145.25 > skyfile.rad

My concern is whether -B or -R overrides the other, or will I ultimately
result in approximately total 60klux horizontal illuminance?

Secondly, do I have to manually add the following to the bottom of
skyfile.rad. I presume that I don't need to alter any of the parameters
here
for a basic sky and ground plane and that it references the skyfunc
output
from the gensky command.

skyfunc glow skyglow
0
0
4
  .85 1.04 1.2 0

skyglow source sky
0
0
4
  0 0 1 180

skyfunc glow groundglow
0
0
4
  .8 1.1 .8 0

groundglow source ground
0
0
4
  0 0 -1 180

Finally, if I explicitly set -B & -R for an intermediate sky with +i
does
the +i setting result in an adjustment to the -B & -R values?

Many thanks in advance

Nick Devlin.

_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general
____________________________________________________________
Electronic mail messages entering and leaving Arup business
systems are scanned for acceptability of content and viruses

3

Hi Nick, Giulio,

One comment to add to Giulio's message... Just be careful of your
ground definition.

The gensky model includes a default ground reflectance of 0.2. This can
be changed using gensky's -g option. So, the normalised emittance of
Nick's groundglow material should be 1.0, not 0.1 or 0.2 as Giulio
suggested.

Cheers all,
Phil.

···

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of
Giulio Antonutto
Sent: 22 November 2006 10:25
To: Radiance general discussion
Subject: RE: [Radiance-general] FW: Gensky Question

Nick,

-R -B are supposed to specify direct and diffuse contribute.
a quick and easy check is to create a -s (diffuse only) and a +s
(global) sky with the same -R -B and check illuminances at a point (0 0
0, 0 0 1) Now try without the sky dome and +s (direct only) and see...
you should get diffuse and global and direct values.
Please try it.

About the source primitive, you need it all the time.
Coefficients can be just (1 1 1) for the sky and a reduction like (0.1
0.1 0.1) or (0.2 0.2 0.2) for the ground depending to the model you are
working on.
If you use your coefficients you will be working with colour but you
need to check that the photopic average is correct.

Hope this is +s,
i.e. 'clear'
:slight_smile:

Ciao

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Nick
Devlin
Sent: 22 November 2006 09:56
To: [email protected]
Subject: [Radiance-general] FW: Gensky Question

Hi All,

I have a GENSKY question that I cant find the answer to in the archives.
I
suspect that the answer is straightforward, but I am now challenging all
my
old assumptions as I have just switched from old school desktop radiance
to
3R7P2 with photon mapping running under Ubuntu on VMware Workstation.
Daunting, but I like it!

Perhaps first I should state that I am aware from the listings that
perhaps
I should be using Gendaylit rather than Gensky, but I have not managed
to
compile it yet. Compiling makes me anxious. I used Francesco's Linux
binaries in the end as I couldn't get photon map to compile properly
after
3R7P2. My /bin and /lib files are not in the standard location, but I
have
altered PATH & RAYPATH accordingly.

So, to the questions:

Firstly, I have some data for sky brightness from BRE Availability of
Daylight, for diffuse and direct illuminance. If for example, I have
illuminance values of 34 klux diffuse and 26 klux direct can I
explicitly
set these in Gensky (assuming 179lux per watt) with

Gensky (location details, azimuth etc) +s -B 189 -R 145.25 > skyfile.rad

My concern is whether -B or -R overrides the other, or will I ultimately
result in approximately total 60klux horizontal illuminance?

Secondly, do I have to manually add the following to the bottom of
skyfile.rad. I presume that I don't need to alter any of the parameters
here
for a basic sky and ground plane and that it references the skyfunc
output
from the gensky command.

skyfunc glow skyglow
0
0
4
  .85 1.04 1.2 0

skyglow source sky
0
0
4
  0 0 1 180

skyfunc glow groundglow
0
0
4
  .8 1.1 .8 0

groundglow source ground
0
0
4
  0 0 -1 180

Finally, if I explicitly set -B & -R for an intermediate sky with +i
does
the +i setting result in an adjustment to the -B & -R values?

Many thanks in advance

Nick Devlin.

____________________________________________________________
Electronic mail messages entering and leaving Arup business
systems are scanned for acceptability of content and viruses

4

Indeed Phil is right!
oops :slight_smile:

but be careful when you use the options -i and -s, without the sun
you need also to say -R 0.

If not the 20% ratio will not work, because the ground will include the
reflected sun component anyway...

Try to compare:

gensky 12 12 12 -i -B 56

and

gensky 12 12 12 -i -B 56 -R 0

The ground is different.... why is it?

Phil, what do you think? Can we call this a bug?

I never noticed it before because I do not model the ground with a
glow...

Ciao,

:slight_smile:

G.

···

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of
Phillip Greenup
Sent: 22 November 2006 10:47
To: Radiance general discussion
Subject: RE: [Radiance-general] FW: Gensky Question

Hi Nick, Giulio,

One comment to add to Giulio's message... Just be careful of your
ground definition.

The gensky model includes a default ground reflectance of 0.2. This can
be changed using gensky's -g option. So, the normalised emittance of
Nick's groundglow material should be 1.0, not 0.1 or 0.2 as Giulio
suggested.

Cheers all,
Phil.

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of
Giulio Antonutto
Sent: 22 November 2006 10:25
To: Radiance general discussion
Subject: RE: [Radiance-general] FW: Gensky Question

Nick,

-R -B are supposed to specify direct and diffuse contribute.
a quick and easy check is to create a -s (diffuse only) and a +s
(global) sky with the same -R -B and check illuminances at a point (0 0
0, 0 0 1) Now try without the sky dome and +s (direct only) and see...
you should get diffuse and global and direct values.
Please try it.

About the source primitive, you need it all the time.
Coefficients can be just (1 1 1) for the sky and a reduction like (0.1
0.1 0.1) or (0.2 0.2 0.2) for the ground depending to the model you are
working on.
If you use your coefficients you will be working with colour but you
need to check that the photopic average is correct.

Hope this is +s,
i.e. 'clear'
:slight_smile:

Ciao

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Nick
Devlin
Sent: 22 November 2006 09:56
To: [email protected]
Subject: [Radiance-general] FW: Gensky Question

Hi All,

I have a GENSKY question that I cant find the answer to in the archives.
I
suspect that the answer is straightforward, but I am now challenging all
my
old assumptions as I have just switched from old school desktop radiance
to
3R7P2 with photon mapping running under Ubuntu on VMware Workstation.
Daunting, but I like it!

Perhaps first I should state that I am aware from the listings that
perhaps
I should be using Gendaylit rather than Gensky, but I have not managed
to
compile it yet. Compiling makes me anxious. I used Francesco's Linux
binaries in the end as I couldn't get photon map to compile properly
after
3R7P2. My /bin and /lib files are not in the standard location, but I
have
altered PATH & RAYPATH accordingly.

So, to the questions:

Firstly, I have some data for sky brightness from BRE Availability of
Daylight, for diffuse and direct illuminance. If for example, I have
illuminance values of 34 klux diffuse and 26 klux direct can I
explicitly
set these in Gensky (assuming 179lux per watt) with

Gensky (location details, azimuth etc) +s -B 189 -R 145.25 > skyfile.rad

My concern is whether -B or -R overrides the other, or will I ultimately
result in approximately total 60klux horizontal illuminance?

Secondly, do I have to manually add the following to the bottom of
skyfile.rad. I presume that I don't need to alter any of the parameters
here
for a basic sky and ground plane and that it references the skyfunc
output
from the gensky command.

skyfunc glow skyglow
0
0
4
  .85 1.04 1.2 0

skyglow source sky
0
0
4
  0 0 1 180

skyfunc glow groundglow
0
0
4
  .8 1.1 .8 0

groundglow source ground
0
0
4
  0 0 -1 180

Finally, if I explicitly set -B & -R for an intermediate sky with +i
does
the +i setting result in an adjustment to the -B & -R values?

Many thanks in advance

Nick Devlin.

____________________________________________________________
Electronic mail messages entering and leaving Arup business
systems are scanned for acceptability of content and viruses

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

5

Well this is a funny little thing... Giulio has found something
strange!

Having followed his test below, both sky definitions provided a global
irrad of 55.7 W/m2. The reflected ground glow was 5.27 W/m2/sr for the
former model and 3.57 W/m2/sr for the latter. These correspond to
ground reflectances of ~30 and 20% resp...

Like Giulio, I have never noticed this as I prefer to use a local ground
plane, particularly where sunlight is involved...

What's going on here?
Hmmmmm...

Phil.

···

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of
Giulio Antonutto
Sent: 22 November 2006 11:27
To: Radiance general discussion
Subject: RE: [Radiance-general] FW: Gensky Question

Indeed Phil is right!
oops :slight_smile:

but be careful when you use the options -i and -s, without the sun you
need also to say -R 0.

If not the 20% ratio will not work, because the ground will include the
reflected sun component anyway...

Try to compare:

gensky 12 12 12 -i -B 56

and

gensky 12 12 12 -i -B 56 -R 0

The ground is different.... why is it?

Phil, what do you think? Can we call this a bug?

I never noticed it before because I do not model the ground with a
glow...

Ciao,

:slight_smile:

G.

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of
Phillip Greenup
Sent: 22 November 2006 10:47
To: Radiance general discussion
Subject: RE: [Radiance-general] FW: Gensky Question

Hi Nick, Giulio,

One comment to add to Giulio's message... Just be careful of your
ground definition.

The gensky model includes a default ground reflectance of 0.2. This can
be changed using gensky's -g option. So, the normalised emittance of
Nick's groundglow material should be 1.0, not 0.1 or 0.2 as Giulio
suggested.

Cheers all,
Phil.

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of
Giulio Antonutto
Sent: 22 November 2006 10:25
To: Radiance general discussion
Subject: RE: [Radiance-general] FW: Gensky Question

Nick,

-R -B are supposed to specify direct and diffuse contribute.
a quick and easy check is to create a -s (diffuse only) and a +s
(global) sky with the same -R -B and check illuminances at a point (0 0
0, 0 0 1) Now try without the sky dome and +s (direct only) and see...
you should get diffuse and global and direct values.
Please try it.

About the source primitive, you need it all the time.
Coefficients can be just (1 1 1) for the sky and a reduction like (0.1
0.1 0.1) or (0.2 0.2 0.2) for the ground depending to the model you are
working on.
If you use your coefficients you will be working with colour but you
need to check that the photopic average is correct.

Hope this is +s,
i.e. 'clear'
:slight_smile:

Ciao

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Nick
Devlin
Sent: 22 November 2006 09:56
To: [email protected]
Subject: [Radiance-general] FW: Gensky Question

Hi All,

I have a GENSKY question that I cant find the answer to in the archives.
I
suspect that the answer is straightforward, but I am now challenging all
my old assumptions as I have just switched from old school desktop
radiance to
3R7P2 with photon mapping running under Ubuntu on VMware Workstation.
Daunting, but I like it!

Perhaps first I should state that I am aware from the listings that
perhaps I should be using Gendaylit rather than Gensky, but I have not
managed to compile it yet. Compiling makes me anxious. I used
Francesco's Linux binaries in the end as I couldn't get photon map to
compile properly after 3R7P2. My /bin and /lib files are not in the
standard location, but I have altered PATH & RAYPATH accordingly.

So, to the questions:

Firstly, I have some data for sky brightness from BRE Availability of
Daylight, for diffuse and direct illuminance. If for example, I have
illuminance values of 34 klux diffuse and 26 klux direct can I
explicitly set these in Gensky (assuming 179lux per watt) with

Gensky (location details, azimuth etc) +s -B 189 -R 145.25 > skyfile.rad

My concern is whether -B or -R overrides the other, or will I ultimately
result in approximately total 60klux horizontal illuminance?

Secondly, do I have to manually add the following to the bottom of
skyfile.rad. I presume that I don't need to alter any of the parameters
here for a basic sky and ground plane and that it references the skyfunc
output from the gensky command.

skyfunc glow skyglow
0
0
4
  .85 1.04 1.2 0

skyglow source sky
0
0
4
  0 0 1 180

skyfunc glow groundglow
0
0
4
  .8 1.1 .8 0

groundglow source ground
0
0
4
  0 0 -1 180

Finally, if I explicitly set -B & -R for an intermediate sky with +i
does the +i setting result in an adjustment to the -B & -R values?

Many thanks in advance

Nick Devlin.

____________________________________________________________
Electronic mail messages entering and leaving Arup business systems are
scanned for acceptability of content and viruses

_______________________________________________
Radiance-general mailing list
[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

6

The glow computed for the ground includes whatever sunlight should be falling on it. An intermediate sky has some sun, so the solar irradiance (-R) setting has an effect. (Even if you use -i or -s, gensky still computes the ground radiance based on the sun being out -- it just leaves off the solar source.)

-Greg

···

From: "Phillip Greenup" <[email protected]>
Date: November 22, 2006 4:08:25 AM PST

Well this is a funny little thing... Giulio has found something
strange!

Having followed his test below, both sky definitions provided a global
irrad of 55.7 W/m2. The reflected ground glow was 5.27 W/m2/sr for the
former model and 3.57 W/m2/sr for the latter. These correspond to
ground reflectances of ~30 and 20% resp...

Like Giulio, I have never noticed this as I prefer to use a local ground
plane, particularly where sunlight is involved...

What's going on here?
Hmmmmm...

Phil.

-----Original Message-----
From: On Behalf Of Giulio Antonutto
Sent: 22 November 2006 11:27

Indeed Phil is right!
oops :slight_smile:

but be careful when you use the options -i and -s, without the sun you
need also to say -R 0.

If not the 20% ratio will not work, because the ground will include the
reflected sun component anyway...

Try to compare:

gensky 12 12 12 -i -B 56

and

gensky 12 12 12 -i -B 56 -R 0

The ground is different.... why is it?

Phil, what do you think? Can we call this a bug?

I never noticed it before because I do not model the ground with a
glow...

Ciao,

:slight_smile:

G.