r.sunmask(1)

1r.sunmask(1)                  Grass User's Manual                 r.sunmask(1)
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NAME

6       r.sunmask   -  Calculates  cast shadow areas from sun position and DEM.
7       Either A: exact sun position is specified, or B: date/time to calculate
8       the sun position by r.sunmask itself.
9

KEYWORDS

11       raster
12

SYNOPSIS

14       r.sunmask
15       r.sunmask help
16       r.sunmask    [-zvsg]    elev=string   output=string    [altitude=float]
17       [azimuth=float]    [year=integer]     [month=integer]     [day=integer]
18       [hour=integer]    [minute=integer]   [second=integer]   [timezone=inte‐
19       ger]    [east=value]     [north=value]     [--overwrite]    [--verbose]
20       [--quiet]
21
22   Flags:
23       -z
24           Zero is a real elevation
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26       -v
27           verbose output (also print out sun position etc.)
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29       -s
30           calculate sun position only and exit
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32       -g
33           Print the sun position output in shell script style
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35       --overwrite
36           Allow output files to overwrite existing files
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38       --verbose
39           Verbose module output
40
41       --quiet
42           Quiet module output
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44   Parameters:
45       elev=string
46           Name of elevation raster map
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48       output=string
49           Output raster map having shadows
50
51       altitude=float
52           A: altitude of the sun above horizon, degrees
53           Options: 0-89.999
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55       azimuth=float
56           A: azimuth of the sun from the north, degrees
57           Options: 0-360
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59       year=integer
60           B: year (1950..2050)
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62       month=integer
63           B: month (0..12)
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65       day=integer
66           B: day (0..31)
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68       hour=integer
69           B: hour (0..24)
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71       minute=integer
72           B: minutes (0..60)
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74       second=integer
75           B: seconds (0..60)
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77       timezone=integer
78           B:  timezone  (east  positive,  offset from GMT, also use to adjust
79           daylight savings)
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81       east=value
82           east coordinate (point of interest, default: map center)
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84       north=value
85           north coordinate (point of interest, default: map center)
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DESCRIPTION

88       r.sunmask creates an output map  layer  based  on  an  input  elevation
89       raster  map  layer  and the sun position. The output map layer contains
90       the cast shadow areas arising from sun shine and elevations.  The  user
91       can define the sun position either directly or the module calculates it
92       from given location and date/time parameters using the NREL  sun  posi‐
93       tion  algorithm.  So  either "A:"-parameters to specify the exact known
94       sun position or "B:-parameters" to specify date/time for  sun  position
95       calculation by r.sunmask itself have to be used.
96
97       The module performs sunset/sunrise checks and refraction correction for
98       sun position  calculation.  Local  coordinate  systems  are  internally
99       transformed  to latitude/longitude for the SOLPOS algorithm. The eleva‐
100       tion is not considered in the sunset/sunrise calculations.
101

Notes

103       r.sunmask and daylight savings: Rather than convert time  to  GMT,  the
104       solpos algorithm uses what is called Local Standard Time, which is gen‐
105       erally defined politically as an offset from GMT.  So the  key  is  the
106       offset  from  GMT,  which  the solpos Time Zone parameter.  If the user
107       specifies clock time (different for winter and  summer),  he/she  would
108       have  to  change the Time Zone parameter seasonally in r.sunmask (time‐
109       zone parameter).
110
111       Note: In latitude/longitude locations  the  position  coordinates  pair
112       (east/west)  has  to be specified in decimal degree (not D:M:S). If not
113       specified, the map center's coordinates will be used.  Also g.region -l
114       displays the map center's coordinates.
115
116       Note  for  module  usage  with  -g  flag and calculations close to sun‐
117       set/sunrise:
118        [...]
119        sunangleabovehorizont=0.434240
120        sunrise=07:59:19
121        sunset=16:25:17
122        Time (07:59:02) is before sunrise (07:59:19)!
123        WARNING: Nothing to calculate. Please verify settings.
124        No map calculation requested. Finished.
125        In above calculation appears to be a mistake as the program  indicates
126       that we are before sunrise while the sun angle above horizon is already
127       positive.  The reason is that sun angle  above  horizon  is  calculated
128       with  correction for atmosphere refraction while sunrise and sunset are
129       calculated without correction for  atmosphere  refraction.  The  output
130       without -g flag contains related indications.
131

Acknowledgements

133       Acknowledgements: National Renewable Energy Laboratory for their SOLPOS
134       2.0 sun position algorithm.
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AUTHOR

140       Janne Soimasuo, Finland 1994
141       update to FP by Huidae Cho 2001
142       added solpos algorithm feature by Markus Neteler 2001
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144       Last changed: $Date: 2004-12-07 17:12:41 +0100 (Tue, 07 Dec 2004) $
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146       Full index
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148       © 2003-2008 GRASS Development Team
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152GRASS 6.3.0                                                       r.sunmask(1)