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 > _______________________________________________ > grass-user mailing list > grass-user@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/grass-user > -- -------------------------------------------------- Thomas Huld Joint Research Centre of the European Commission T.P. 450 I-21027 Ispra, Italy phone: +39 0332785273 e-mail: thomas.h...@jrc.ec.europa.eu -------------------------------------------------- _______________________________________________ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user