[Radiance-general] sun positions as calculated by gensky

[Lars O. Grobe]

Hi list...

I just compared the sun positions as given by gensky for Singapore with
those calculated online using a form found under

http://aa.usno.navy.mil/data/docs/AltAz.php

I use the following parameters:

SINGAPORE
E 103deg48', N 1deg17'
Altitude and Azimuth of the Sun
Jun 21, 2008
Zone:  8h East of Greenwich

gives me for 1.30pm
            altitude   azimuth (north->east)
13:30       67.1       346.1

Running gensky like:

gensky 6 21 5.30GMT +s -a 1.25 -o -103.75

results in a command line:

# gensky 6 21 5.30GMT +s -a 1.25 -o -103.75
# Local solar time: 12.19
# Solar altitude and azimuth: 67.6 173.0
# Ground ambient level: 16.1

Where azimuth is given (welcome to radiance world ;-) given in south to west direction.

So I have a difference of .5 degree for elevation and 6.9 degrees for azimuth.

Do I get something wrong here about time zone calculation?

TIA&CU, Lars.