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NAMEr.external - Links GDAL supported raster data as a pseudo GRASS raster map.KEYWORDSraster, import, externalSYNOPSISr.externalr.external --help r.external [-fojeahvtr] [input=name] [source=name] output=name [band=integer] [title=phrase] [--overwrite] [--help] [--verbose] [--quiet] [--ui] Flags:
Parameters:
DESCRIPTIONr.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.NOTESIn 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 handlingGDAL-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).EXAMPLESRGB 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 exportExternal 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 REFERENCESGDAL Pages: http://www.gdal.org/SEE ALSOr.import, r.in.gdal, r.external.outv.import, v.in.ogr, v.external, v.external.out AUTHORGlynn ClementsSOURCE CODEAvailable at: r.external source code (history)Main index | Raster index | Topics index | Keywords index | Graphical index | Full index © 2003-2021 GRASS Development Team, GRASS GIS 7.8.6 Reference Manual
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