The module performs sunset/sunrise checks and refraction correction for sun position calculation. Local coordinate systems are internally transformed to latitude/longitude for the SOLPOS algorithm. The elevation is not considered in the sunset/sunrise calculations.
Note: In latitude/longitude locations the position coordinates pair (east/west) has to be specified in decimal degree (not D:M:S). If not specified, the map center's coordinates will be used. Also g.region -l displays the map center's coordinates in latitude/longitude (or g.region -c in the actual coordinate system).
Note for module usage with the -g flag, when performing calculations close to sunset/sunrise:
[...] sunangleabovehorizont=0.434240 sunrise=07:59:19 sunset=16:25:17 Time (07:59:02) is before sunrise (07:59:19)! WARNING: Nothing to calculate. Please verify settings. No map calculation requested. Finished.
# set the region to a place near Raleigh (NC) g.region raster=elev_lid792_1m -p # compute only sun position and no output map r.sunmask -s elev_lid792_1m year=2012 month=2 \ day=22 hour=10 minute=30 timezone=-5 Using map center coordinates: 638650.000000 220375.000000 Calculating sun position... (using solpos (V. 11 April 2001) from NREL) 2012/02/22, daynum: 53, time: 10:30:00 (decimal time: 10.500000) long: -78.678856, lat: 35.736160, timezone: -5.000000 Solar position: sun azimuth: 143.006409, sun angle above horz. (refraction corrected): 36.233879 Sunrise time (without refraction): 06:58:11 Sunset time (without refraction): 17:58:47 # with -g flag, useful for eval() shell function r.sunmask -s -g elev_lid792_1m year=2012 month=2 \ day=22 hour=10 minute=30 timezone=-5 Using map center coordinates: 638650.000000 220375.000000 Calculating sun position... (using solpos (V. 11 April 2001) from NREL) date=2012/02/22 daynum=53 time=10:30:00 decimaltime=10.500000 longitudine=-78.678856 latitude=35.736160 timezone=-5.000000 sunazimuth=143.006409 sunangleabovehorizon=36.233879 sunrise=06:58:11 sunset=17:58:47
Last changed: $Date$