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   [-fojeahvt]   [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

       --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)

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       © 2003-2019 GRASS Development Team, GRASS GIS 7.8.2 Reference Manual