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- r.sunmask can be used in two ways:
- a) define sun position:
- r.sunmask elev=dgm25 output=dgm25.shadow alt=47.394203 azim=138.604904
- b) define location, date, time
- r.sunmask -v el=dgm5 out=shadow year=1997 month=9 day=25 hour=11 minute=15 \
- sec=0 timezone=1 east=3570720 north=5766095
- or (using map center coordinates)
- r.sunmask -v el=dgm5 out=shadow year=1997 month=9 day=25 hour=11 minute=15 \
- sec=0 timezone=1
- Calculating sun position... (using solpos (V. 11 April 2001) from NREL)
- 1997.09.25, daynum 268, time: 11:15:00
- long: 10.030458, lat: 52.025555, timezone: 2.000000
- Solar position: sun azimuth 145.121445,
- sun angle above horz.(refraction corrected) 31.662413
- Sunrise time (without refraction): 07:16
- Sunset time (without refraction): 19:07
- Calculating shadows from DEM...
- --------------------------
- Since the solpos algorithm expects lat/long coordinates, the module
- transforms the local coordinates to lat/long on-the-fly
- --------------------------
- daylight savings: Rather than convert time to GMT, the solpos
- algorithm uses what is called Local Standard Time, which is generally
- defined politically as an offset from GMT. So the key is the offset from
- GMT, which the solpos Time Zone parameter. If the user specifies clock time
- (different for winter and summer), he/she would have to change the Time Zone
- parameter seasonally in r.sunmask (timezone parameter).
- --------------------------
- solpos questions can be directed to
- > Steve Wilcox (Stephen_Wilcox@nrel.gov)
- > National Renewable Energy Laboratory
- > 1617 Cole Boulevard, Golden, CO 80401-3393
- > voice: 1-303-275-4061; fax: 1-303-275-4675
- http://rredc.nrel.gov/solar/codes_algs/solpos/
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