Hello,
Sorry for the late reply, I tried to send this once but something must have
gone wrong.
By default r.sun calculates times as true solar time, whereby solar noon is
always exactly 12 o'clock everywhere. Depending on where you are in your time
zone, this may cause differences of up to an hour, in some cases (like Western
Spain) even more. On top of this, the offset varies during the year according
to the Equation of Time.
You can use the option civiltime=<timezone_offset> in r.sun to make it use
wall clock time. For Central Europe the timezone offset is +1, +2 when
daylight saving time is in effect.
I'm not completely sure about this, but if you use civiltime you may have to
supply the longitude as a raster with the "longin" option. With latlon
projection you can make a longitude raster simply with
r.mapcalc lon_raster='x()'
Hope this helps.
Thomas
On Monday 02 January 2012 12:57:27 pm Büro Seling wrote:
Dear Group!
Happy New Year @all!
I work on a Linux GRASS 6.4.2 RC1. The area of interest is in central
Europe and
the projection is WGS84(EPSG:4326).
When I use the r.sun module and let it show the sunset/sunrise time and
compare
it with the sunset/sunrise from a map created with r.sunmask I see great
differences (up to 50 minutes).
It is not the timezone (which is set correctly) in r.sunmask.
The results from r.sunmask seem to be, according to other sources, seem
to be
right, but the results from r.sun are fare off.
Please give a suggestions or help!
Stefan
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Thomas Huld
Joint Research Centre of the European Commission
T.P. 450
I-21027 Ispra, Italy
phone: +39 0332785273
e-mail: Thomas.Huld@jrc.ec.europa.eu
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