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.
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KEYWORDS

11       raster
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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]
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21   Flags:
22       -z  Zero is a real elevation
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24       -v  verbose output (also print out sun position etc.)
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26       -s  calculate sun position only and exit
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28       -g  Print the sun position output in shell script style
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30       --overwrite
31
32   Parameters:
33       elev=string
34           Name of elevation raster map
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36       output=string
37           Output raster map having shadows
38
39       altitude=float
40           A: altitude of the sun above horizon, degrees Options: 0-89.999
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42       azimuth=float
43           A: azimuth of the sun from the north, degrees Options: 0-360
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45       year=integer
46           B: year (1950..2050)
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48       month=integer
49           B: month (0..12)
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51       day=integer
52           B: day (0..31)
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54       hour=integer
55           B: hour (0..24)
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57       minute=integer
58           B: minutes (0..60)
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60       second=integer
61           B: seconds (0..60)
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63       timezone=integer
64           B: timezone (east positive, offset from GMT,  also  use  to  adjust
65           daylight savings)
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67       east=value
68           east coordinate (point of interest, default: map center)
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70       north=value
71           north coordinate (point of interest, default: map center)
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DESCRIPTION

74       r.sunmask  creates  an  output  map  layer  based on an input elevation
75       raster map layer and the sun position. The output  map  layer  contains
76       the  cast  shadow areas arising from sun shine and elevations. The user
77       can define the sun position either directly or the module calculates it
78       from  given  location and date/time parameters using the NREL sun posi‐
79       tion algorithm. So either "A:"-parameters to specify  the  exact  known
80       sun  position  or "B:-parameters" to specify date/time for sun position
81       calculation by r.sunmask itself have to be used.
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83       The module performs sunset/sunrise checks and refraction correction for
84       sun  position  calculation.  Local  coordinate  systems  are internally
85       transformed to latitude/longitude for the SOLPOS algorithm. The  eleva‐
86       tion is not considered in the sunset/sunrise calculations.
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Notes

89       r.sunmask  and  daylight  savings: Rather than convert time to GMT, the
90       solpos algorithm uses what is called Local Standard Time, which is gen‐
91       erally  defined  politically  as an offset from GMT.  So the key is the
92       offset from GMT, which the solpos Time Zone  parameter.   If  the  user
93       specifies  clock  time  (different for winter and summer), he/she would
94       have to change the Time Zone parameter seasonally in  r.sunmask  (time‐
95       zone parameter).
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97       Note:  In  latitude/longitude  locations  the position coordinates pair
98       (east/west) has to be specified in decimal degree (not D:M:S).  If  not
99       specified, the map center's coordinates will be used.  Also g.region -l
100       displays the map center's coordinates.
101
102       Note for module usage with -g  flag  and  calculations  close  to  sun‐
103       set/sunrise:
104        [...]
105        sunangleabovehorizont=0.434240
106        sunrise=07:59:19
107        sunset=16:25:17
108        Time (07:59:02) is before sunrise (07:59:19)!
109        WARNING: Nothing to calculate. Please verify settings.
110        No map calculation requested. Finished.
111         In above calculation appears to be a mistake as the program indicates
112       that we are before sunrise while the sun angle above horizon is already
113       positive.   The  reason  is  that sun angle above horizon is calculated
114       with correction for atmosphere refraction while sunrise and sunset  are
115       calculated  without  correction  for  atmosphere refraction. The output
116       without -g flag contains related indications.
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Acknowledgements

119       Acknowledgements: National Renewable Energy Laboratory for their SOLPOS
120       2.0 sun position algorithm.
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AUTHOR

126       Janne Soimasuo, Finland 1994
127       update to FP by Huidae Cho 2001
128       added solpos algorithm feature by Markus Neteler 2001
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130       Last changed: $Date: 2004/12/07 16:12:41 $
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132       Full index
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136GRASS 6.2.2                                                       r.sunmask(1)