Dear list,

May I ask what is the exact algorithm used by gensky and gendaylit to

calculate sun position in Radiance?

i.e. given the latitude, longitude, standard meridian, month, day, hour,

what's the formula used in Radiance to produce solar altitude and azimuth

angles?

Thanks!

- Ji

Download the sources & take a look for yourself -> http://radsite.lbl.gov/radiance/framed.html

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## ···

From: Ji Zhang [mailto:[email protected]]

Sent: 29 May 2012 09:15

To: Radiance general discussion

Subject: [Radiance-general] the solar position algorithm used in Radiance

Dear list,

May I ask what is the exact algorithm used by gensky and gendaylit to calculate sun position in Radiance?

i.e. given the latitude, longitude, standard meridian, month, day, hour, what's the formula used in Radiance to produce solar altitude and azimuth angles?

Thanks!

- Ji

Ji,

If you are interested in this in a more general sense, you should consult the libnova library for astronomical calculations from Girdwood and Kubanek:

http://libnova.sourceforge.net/

I used this library to compute sun, moon, and planet positions for my "genutahsky" program, which implements most of the features of gensky and additionally outputs a colored sky, the moon and bright planets, and a star field.

http://markjstock.org/radiance/

Mark

## ···

On Tue, 29 May 2012, Ji Zhang wrote:

Dear list,

May I ask what is the exact algorithm used by gensky and gendaylit to

calculate sun position in Radiance?

i.e. given the latitude, longitude, standard meridian, month, day, hour,

what's the formula used in Radiance to produce solar altitude and azimuth

angles?

Thanks!

- Ji

Thanks for the advice, Mark and Pally, I'll take a look! It seems there's a

sun.cal file in Radiance library. I'll try to figure it out how it works.

- Cheers, Ji

## ···

On Tue, May 29, 2012 at 9:58 PM, Mark Stock <[email protected]> wrote:

Ji,

If you are interested in this in a more general sense, you should consult

the libnova library for astronomical calculations from Girdwood and Kubanek:

http://libnova.sourceforge.**net/ <http://libnova.sourceforge.net/>

I used this library to compute sun, moon, and planet positions for my

"genutahsky" program, which implements most of the features of gensky and

additionally outputs a colored sky, the moon and bright planets, and a star

field.

http://markjstock.org/**radiance/ <http://markjstock.org/radiance/>

Mark

On Tue, 29 May 2012, Ji Zhang wrote:

Dear list,

May I ask what is the exact algorithm used by gensky and gendaylit to

calculate sun position in Radiance?

i.e. given the latitude, longitude, standard meridian, month, day, hour,

what's the formula used in Radiance to produce solar altitude and azimuth

angles?

Thanks!

- Ji

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http://www.radiance-online.org/mailman/listinfo/radiance-general

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Radiance-general mailing list

[email protected]

http://www.radiance-online.org/mailman/listinfo/radiance-general

Ji

I think you will find what you are looking for also in the source code file

src/gen/sun.c if C is easier to understand for you.

Both files don't contain much of an explanation. I copied these functions

to Python few years back and I think I could find all of the equations

documented and explained on the net somewhere. It's worth a Google if you

don't understand what's going on.

Regards,

Thomas

## ···

On Tue, May 29, 2012 at 9:57 AM, Ji Zhang <[email protected]> wrote:

Thanks for the advice, Mark and Pally, I'll take a look! It seems there's

a sun.cal file in Radiance library. I'll try to figure it out how it works.

- Cheers, Ji

Thank you very much, Thomas! I'll take a look of the C file.

- Cheers, Ji

## ···

On Mon, Jun 4, 2012 at 5:13 AM, Thomas Bleicher <[email protected]>wrote:

Ji

I think you will find what you are looking for also in the source code

file src/gen/sun.c if C is easier to understand for you.

Both files don't contain much of an explanation. I copied these functions

to Python few years back and I think I could find all of the equations

documented and explained on the net somewhere. It's worth a Google if you

don't understand what's going on.

Regards,

Thomas

On Tue, May 29, 2012 at 9:57 AM, Ji Zhang <[email protected]> wrote:

Thanks for the advice, Mark and Pally, I'll take a look! It seems there's

a sun.cal file in Radiance library. I'll try to figure it out how it works.

- Cheers, Ji

_______________________________________________

Radiance-general mailing list

[email protected]

http://www.radiance-online.org/mailman/listinfo/radiance-general