NAME

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

KEYWORDS

       raster, import, external

SYNOPSIS

       r.external
       r.external --help
       r.external   [-fojeahvtr]    [input=name]     [source=name]   output=name   [band=integer]
       [title=phrase]   [--overwrite]  [--help]  [--verbose]  [--quiet]  [--ui]

   Flags:
       -f
           List supported formats and exit

       -o
           Override projection check (use current location’s projection)
           Assume that the dataset has same projection as the current location

       -j
           Perform projection check only and exit

       -e
           Extend region extents based on new dataset
           Also updates the default region if in the PERMANENT mapset

       -a
           Auto-adjustment for lat/lon
           Attempt to fix small precision errors in resolution and extents

       -h
           Flip horizontally

       -v
           Flip vertically

       -t
           List available bands including band type in dataset and exit
           Format: band number,type,projection check

       -r
           Create fast link without data range
           WARNING: some modules do not work correctly without known data range

       --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:
       input=name
           Name of raster file to be linked

       source=name
           Name of non-file GDAL data source

       output=name [required]
           Name for output raster map

       band=integer
           Band to select (default is all bands)

       title=phrase
           Title for resultant raster map

DESCRIPTION

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

NOTES

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

NULL data handling

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

EXAMPLES

   RGB Orthophoto from GeoTIFF
       # import of all channels (each channel will become a GRASS raster map):
       r.external input=/home/user/data/maps/059100.tif output=ortho
       g.region raster=ortho.3 -p
       d.rgb r=ortho.1 g=ortho.2 b=ortho.3
       r.composite r=ortho.1 g=ortho.2 b=ortho.3 output=ortho.rgb

   Processing workflow without data import and export
       External raster maps to be processed can be directly linked  using  r.external;  likewise,
       results  can be written out to standard raster formats with r.external.out (GDAL supported
       formats):
       # register GeoTIFF file to be used in current mapset:
       r.external input=terra_lst1km20030314.LST_Day.tif output=modis_celsius
       # define output directory for files resulting from GRASS calculation:
       r.external.out directory=$HOME/gisoutput/ format="GTiff"
       # perform GRASS calculation (here: extract pixels > 20 deg C)
       # this stores the output map directly as GeoTIFF:
       r.mapcalc "warm.tif = if(modis_celsius > 20.0, modis_celsius, null() )"
       # cease GDAL output connection and turn back to write GRASS raster files:
       r.external.out -r
       # now use the resulting file elsewhere
       gdalinfo $HOME/gisoutput/warm.tif

REFERENCES

       GDAL Pages: http://www.gdal.org/

SEE ALSO

        r.import, r.in.gdal, r.external.out

        v.import, v.in.ogr, v.external, v.external.out

AUTHOR

       Glynn Clements

SOURCE CODE

       Available at: r.external source code (history)

       Accessed: unknown

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       © 2003-2022 GRASS Development Team, GRASS GIS 7.8.7 Reference Manual