# 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

[Description: IES]<http://www.iesve.com/>

Palbinder Sandher
Software Platform Engineer

T:

+44 (0) 141 945 8500

F:

+44 (0) 141 945 8501

**Design, Simulate + Innovate with the <Virtual Environment>**

Integrated Environmental Solutions Limited. Registered in Scotland No. SC151456
Registered Office - Helix Building, West Of Scotland Science Park, Glasgow G20 0SP

Email Disclaimer<http://www.iesve.com/disclaimer.html>

···

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.

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:

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.

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

_______________________________________________

[email protected]

_______________________________________________
[email protected]

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

_______________________________________________