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  [-fojeahvtmr]   [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

       -m
           Read data range from metadata
           WARNING: metadata are sometimes approximations with wrong data range

       -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: Monday Apr 01 03:07:31 2024

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       © 2003-2024 GRASS Development Team, GRASS GIS 8.3.2 Reference Manual

GRASS 8.3.2                                                                                   r.external(1grass)