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r.sunmask(1)		    GRASS GIS User's Manual		  r.sunmask(1)

NAME
       r.sunmask   - Calculates	cast shadow areas from sun position and	eleva-
       tion raster map.
       Either exact sun	position (A) is	specified, or date/time	 to  calculate
       the sun position	(B) by r.sunmask itself.

KEYWORDS
       raster, solar, sun position, shadow

SYNOPSIS
       r.sunmask
       r.sunmask --help
       r.sunmask   [-zsg]   elevation=name   [output=name]    [altitude=float]
       [azimuth=float]	  [year=integer]     [month=integer]	 [day=integer]
       [hour=integer]	 [minute=integer]   [second=integer]   [timezone=inte-
       ger]   [east=value]   [north=value]   [--overwrite]  [--help]   [--ver-
       bose]  [--quiet]	 [--ui]

   Flags:
       -z
	   Do not ignore zero elevation

       -s
	   Calculate sun position only and exit

       -g
	   Print the sun position output in shell script style

       --overwrite
	   Allow output	files to overwrite existing files

       --help
	   Print usage summary

       --verbose
	   Verbose module output

       --quiet
	   Quiet module	output

       --ui
	   Force launching GUI dialog

   Parameters:
       elevation=nameA [required]
	   Name	of input elevation raster map

       output=name
	   Name	for output raster map

       altitude=float
	   Altitude of the sun in degrees above	the horizon (A)
	   Options: 0-89.999

       azimuth=float
	   Azimuth of the sun in degrees from north (A)
	   Options: 0-360

       year=integer
	   Year	(B)
	   Options: 1950-2050

       month=integer
	   Month (B)
	   Options: 0-12

       day=integer
	   Day (B)
	   Options: 0-31

       hour=integer
	   Hour	(B)
	   Options: 0-24

       minute=integer
	   Minutes (B)
	   Options: 0-60

       second=integer
	   Seconds (B)
	   Options: 0-60
	   Default: 0

       timezone=integer
	   Timezone
	   East	positive, offset from GMT, also	use to adjust daylight savings

       east=value
	   Easting coordinate (point of	interest)
	   Default: map	center

       north=value
	   Northing coordinate (point of interest)
	   Default: map	center

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 posi-
       tion 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	eleva-
       tion is not considered in the sunset/sunrise calculations.

NOTES
       r.sunmask  and  daylight	savings: Rather	than converting	the local time
       to GMT, the SOLPOS algorithm uses what is called	Local  Standard	 Time,
       which  is  generally politically	defined	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), s/he
       would have to change the	Time Zone parameter  seasonally	 in  r.sunmask
       (timezone parameter). See also Daylight saving time by region and coun-
       try.

       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.re-
       gion -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.
       In  above  calculation  it appears to be	a mistake as the program indi-
       cates that we are before	sunrise	while the sun angle above  horizon  is
       already positive.  The reason is	that sun angle above horizon is	calcu-
       lated with correction for atmosphere refraction while sunrise and  sun-
       set  are	 calculated  without correction	for atmosphere refraction. The
       output without -g flag contains related indications.

EXAMPLE
       Example for North Carolina sample data set for the calculation  of  sun
       position	angles and more:
       # 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

Acknowledgements
       Acknowledgements: National Renewable Energy Laboratory for their	SOLPOS
       2.0 sun position	algorithm.

SEE ALSO
	g.region, r.sun, r.sunhours, r.slope.aspect

AUTHOR
       Janne Soimasuo, Finland 1994
       update to FP by Huidae Cho 2001
       added solpos algorithm feature by Markus	Neteler	2001

SOURCE CODE
       Available at: r.sunmask source code (history)

       Main index | Raster index | Topics index	| Keywords index  |  Graphical
       index | Full index

       A(C) 2003-2020 GRASS Development	Team, GRASS GIS	7.8.4 Reference	Manual

GRASS 7.8.4							  r.sunmask(1)

NAME | KEYWORDS | SYNOPSIS | DESCRIPTION | NOTES | EXAMPLE | Acknowledgements | SEE ALSO | AUTHOR | SOURCE CODE

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