1r.external(1)               GRASS GIS User's Manual              r.external(1)
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NAME

6       r.external  - Links GDAL supported raster data as a pseudo GRASS raster
7       map.
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KEYWORDS

10       raster, import, external
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SYNOPSIS

13       r.external
14       r.external --help
15       r.external  [-fojeahvt]   [input=name]     [source=name]    output=name
16       [band=integer]    [title=phrase]   [--overwrite]  [--help]  [--verbose]
17       [--quiet]  [--ui]
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19   Flags:
20       -f
21           List supported formats and exit
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23       -o
24           Override projection check (use current location’s projection)
25           Assume that the dataset has same projection as the current location
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27       -j
28           Perform projection check only and exit
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30       -e
31           Extend region extents based on new dataset
32           Also updates the default region if in the PERMANENT mapset
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34       -a
35           Auto-adjustment for lat/lon
36           Attempt to fix small precision errors in resolution and extents
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38       -h
39           Flip horizontally
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41       -v
42           Flip vertically
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44       -t
45           List available bands including band type in dataset and exit
46           Format: band number,type,projection check
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48       --overwrite
49           Allow output files to overwrite existing files
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51       --help
52           Print usage summary
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54       --verbose
55           Verbose module output
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57       --quiet
58           Quiet module output
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60       --ui
61           Force launching GUI dialog
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63   Parameters:
64       input=name
65           Name of raster file to be linked
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67       source=name
68           Name of non-file GDAL data source
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70       output=name [required]
71           Name for output raster map
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73       band=integer
74           Band to select (default is all bands)
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76       title=phrase
77           Title for resultant raster map
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DESCRIPTION

80       r.external allows a user to link a GDAL  supported  raster  file  to  a
81       binary  raster  map  layer,  from any GDAL supported raster map format,
82       with an optional title. The file is not imported but just registered as
83       GRASS raster map.
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NOTES

86       In essence, r.external creates a read-only link to the original dataset
87       which is only valid if the original dataset remains at  the  originally
88       indicated directory and filename.
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NULL data handling

91       GDAL-linked  (r.external)  maps do not have or use a NULL bitmap, hence
92       r.null cannot manipulate them directly. Here NULL cells are those whose
93       value  matches  the  value  reported  by the GDALGetRasterNoDataValue()
94       function.  To apply the GDAL-linked the user need to  either  create  a
95       MASK  (e.g.  with r.mask) and then "apply" it using e.g. r.resample, or
96       use r.mapcalc to create a copy with the appropriate categories  changed
97       to NULL (if() condition).
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EXAMPLES

100   RGB Orthophoto from GeoTIFF
101       # import of all channels (each channel will become a GRASS raster map):
102       r.external input=/home/user/data/maps/059100.tif output=ortho
103       g.region raster=ortho.3 -p
104       d.rgb r=ortho.1 g=ortho.2 b=ortho.3
105       r.composite r=ortho.1 g=ortho.2 b=ortho.3 output=ortho.rgb
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107   Processing workflow without data import and export
108       External  raster  maps  to  be  processed  can be directly linked using
109       r.external; likewise, results can be written  out  to  standard  raster
110       formats with r.external.out (GDAL supported formats):
111       # register GeoTIFF file to be used in current mapset:
112       r.external input=terra_lst1km20030314.LST_Day.tif output=modis_celsius
113       # define output directory for files resulting from GRASS calculation:
114       r.external.out directory=$HOME/gisoutput/ format="GTiff"
115       # perform GRASS calculation (here: extract pixels > 20 deg C)
116       # this stores the output map directly as GeoTIFF:
117       r.mapcalc "warm.tif = if(modis_celsius > 20.0, modis_celsius, null() )"
118       # cease GDAL output connection and turn back to write GRASS raster files:
119       r.external.out -r
120       # now use the resulting file elsewhere
121       gdalinfo $HOME/gisoutput/warm.tif
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REFERENCES

124       GDAL Pages: http://www.gdal.org/
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SEE ALSO

127        r.import, r.in.gdal, r.external.out
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129        v.import, v.in.ogr, v.external, v.external.out
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AUTHOR

132       Glynn Clements
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SOURCE CODE

135       Available at: r.external source code (history)
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137       Main  index  | Raster index | Topics index | Keywords index | Graphical
138       index | Full index
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140       © 2003-2020 GRASS Development Team, GRASS GIS 7.8.5 Reference Manual
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144GRASS 7.8.5                                                      r.external(1)