r.external(1grass) | Grass User's Manual | r.external(1grass) |
r.external - Links GDAL supported raster data as a pseudo GRASS raster map.
raster, import, external
r.external
r.external --help
r.external [-fojeahvt] [input=name]
[source=name] output=name
[band=integer] [title=phrase]
[--overwrite] [--help] [--verbose] [--quiet]
[--ui]
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.
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).
# 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
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
GDAL Pages: http://www.gdal.org/
r.import, r.in.gdal, r.external.out
v.import, v.in.ogr, 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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© 2003-2019 GRASS Development Team, GRASS GIS 7.6.0 Reference Manual
GRASS 7.6.0 |