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  [-fojeahvtmr]   [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       -m
49           Read data range from metadata
50           WARNING: metadata are  sometimes  approximations  with  wrong  data
51           range
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53       -r
54           Create fast link without data range
55           WARNING:  some  modules  do  not  work correctly without known data
56           range
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58       --overwrite
59           Allow output files to overwrite existing files
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61       --help
62           Print usage summary
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64       --verbose
65           Verbose module output
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67       --quiet
68           Quiet module output
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70       --ui
71           Force launching GUI dialog
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73   Parameters:
74       input=name
75           Name of raster file to be linked
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77       source=name
78           Name of non-file GDAL data source
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80       output=name [required]
81           Name for output raster map
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83       band=integer
84           Band to select (default is all bands)
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86       title=phrase
87           Title for resultant raster map
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DESCRIPTION

90       r.external allows a user to link a GDAL supported raster file to a  bi‐
91       nary  raster map layer, from any GDAL supported raster map format, with
92       an optional title. The file is not  imported  but  just  registered  as
93       GRASS raster map.
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NOTES

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

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

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

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

137        r.import, r.in.gdal, r.external.out
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139        v.import, v.in.ogr, v.external, v.external.out
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AUTHOR

142       Glynn Clements
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SOURCE CODE

145       Available at: r.external source code (history)
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147       Accessed: Saturday Jan 21 21:14:34 2023
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149       Main  index  | Raster index | Topics index | Keywords index | Graphical
150       index | Full index
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152       © 2003-2023 GRASS Development Team, GRASS GIS 8.2.1 Reference Manual
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156GRASS 8.2.1                                                      r.external(1)