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r.sunmask(1grass) | Grass User's Manual | r.sunmask(1grass) |
NAME¶
r.sunmask - Calculates cast shadow areas from sun position and elevation raster map.KEYWORDS¶
raster, sun positionSYNOPSIS¶
r.sunmaskFlags:¶
- -z
-
- -v
-
- -s
-
- -g
-
- --overwrite
-
- --verbose
-
- --quiet
-
Parameters:¶
- elevation=name
-
- output=name
-
- altitude=float
-
- azimuth=float
-
- year=integer
-
- month=integer
-
- day=integer
-
- hour=integer
-
- minute=integer
-
- second=integer
-
- timezone=integer
-
- east=value
-
- north=value
-
DESCRIPTION¶
r.sunmask creates an output map layer based on an input elevation raster map layer and the sun position. The output map layer contains the cast shadow areas arising from sun shine and elevations. The user can define the sun position either directly or the module calculates it from given location and date/time parameters using the NREL sun position algorithm. So either "A:"-parameters to specify the exact known sun position or "B:-parameters" to specify date/time for sun position calculation by r.sunmask itself have to be used. 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.Notes¶
r.sunmask and 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). 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. Note for module usage with -g flag and 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.
Acknowledgements¶
Acknowledgements: National Renewable Energy Laboratory for their SOLPOS 2.0 sun position algorithm.SEE ALSO¶
g.region, r.sun, r.slope.aspectAUTHOR¶
Janne Soimasuo, Finland 1994GRASS 6.4.2 |