r.external.out - GRASS manual
Author: GRASS Development Team
Description: r.external.out: Redirects raster output to file utilizing GDAL library rather than storing in GRASS raster format.
Keywords: raster, export, output, external

## NAME

r.external.out - Redirects raster output to file utilizing GDAL library rather than storing in GRASS raster format.

## KEYWORDS

raster, export, output, external

## SYNOPSIS

r.external.out
r.external.out --help
r.external.out [-frp] directory=path [extension=string] format=string [options=string[,string,...]] [--help] [--verbose] [--quiet] [--ui]

### Flags:

-f
  List supported formats and exit
-r
  Cease using GDAL and revert to native output
-p
  Print current status
--help
  Print usage summary
--verbose
  Verbose module output
--quiet
  Quiet module output
--ui
  Force launching GUI dialog

### Parameters:

directory=path [required]
  Name of output directory
extension=string
  Extension for output files
format=string [required]
  Format of output files
  Options: VRT, GTiff, COG, NITF, HFA, ELAS, AAIGrid, DTED, PNG, JPEG, MEM, GIF, FITS, XPM, BMP, PCIDSK, PCRaster, ILWIS, SGI, SRTMHGT, Leveller, Terragen, netCDF, HDF4Image, ISIS3, ISIS2, PDS4, VICAR, ERS, JP2OpenJPEG, FIT, GRIB, RMF, WMS, RST, GSAG, GSBG, GS7BG, R, KMLSUPEROVERLAY, WEBP, PDF, Rasterlite, MBTiles, CALS, WMTS, MRF, PNM, PAux, MFF, MFF2, BT, LAN, LCP, GTX, NTv2, CTable2, KRO, ROI_PAC, RRASTER, BYN, USGSDEM, BAG, NWT_GRD, ADRG, BLX, PostGISRaster, SAGA, XYZ, HF2, ZMap, SIGDEM, AVIF, GPKG, OpenFileGDB, NGW, ENVI, EHdr, ISCE, Zarr
options=string[,string,...]
  Creation options

## DESCRIPTION

r.external.out instructs GRASS to write subsequently generated raster maps as data files (e.g. GeoTIFF) using GDAL instead of storing them in GRASS raster format in the current mapset.

Any new raster map is immediately written out through GDAL as a file.

## NOTES

A relative directory path (parameter directory) is interpreted relative to the current mapset directory, not the current directory where the command was launched. An unspecified or empty directory (which will occur if the user passes a simple filename for output) results in the output file being placed in the "gdal/" subdirectory of the current mapset directory.

## EXAMPLES

### Storing results from raster data analysis directly as GeoTIFF

The module r.external.out is used to write out processing results directly in GeoTIFF format (any GDAL supported format can be used here):

    # define output directory for files resulting from GRASS calculation(s)
    # and target format:
    mkdir $HOME/gisoutput/
    # hint: the create options are not mandatory
    r.external.out directory=$HOME/gisoutput/ format="GTiff" option="BIGTIFF=YES,COMPRESS=DEFLATE"
    # prepare sample analysis
    g.region raster=elevation -p

    # perform GRASS calculation (here: filter by height, write > 120m, NULL otherwise)
    # this will store the output map directly as GeoTIFF, so we use .tif extension:
    r.mapcalc "elev_filt.tif = if(elevation > 120.0, elevation, null() )"

    # ...the "elev_filt.tif" is immediately written.

    # cease GDAL output connection and turn back to write out GRASS raster files:
    r.external.out -r

    # verify resulting file
    gdalinfo $HOME/gisoutput/elev_filt.tif

### Complete workflow using only external geodata while processing in GRASS

The module r.external.out can be used along with r.external to process external geodata in GRASS while writing out the results directly in GeoTIFF:

    # 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: https://gdal.org/

## SEE ALSO

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

## AUTHOR

Glynn Clements

## SOURCE CODE

Available at: r.external.out source code (history)

Latest change: Thursday Dec 04 09:43:11 2025 in commit: 8b4d7c3e310ec3122a5e870e724c50bd716f9513

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