Provided by: grass-doc_7.4.0-1_all bug


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


       raster, import, external


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

           List supported formats and exit

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

           Perform projection check only and exit

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

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

           Flip horizontally

           Flip vertically

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

           Allow output files to overwrite existing files

           Print usage summary

           Verbose module output

           Quiet module output

           Force launching GUI dialog

           Name of raster file to be linked

           Name of non-file GDAL data source

       output=name [required]
           Name for output raster map

           Band to select (default is all bands)

           Title for resultant raster map


       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.


       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()


   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
       # 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


       GDAL Pages:


        r.import,, r.external.out

        v.import,, v.external, v.external.out


       Glynn Clements

       Last changed: $Date: 2016-01-13 10:18:55 +0100 (Wed, 13 Jan 2016) $


       Available at: r.external source code (history)

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       © 2003-2018 GRASS Development Team, GRASS GIS 7.4.0 Reference Manual