To introduce additional NULL values to a computation based on a GDAL-linked
raster, the user needs to either create a mask with with r.mask and
then "apply" it using e.g. r.resample or r.mapcalc,
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
# 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
v.import, v.in.ogr, v.external, v.external.out