Flags:¶

-f

List supported formats and exit

-o

Override projection check (use current project’s CRS)
Assume that the dataset has the same coordinate reference system as the current project

-j

Perform projection check only and exit

-e

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

-a

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

-h

Flip horizontally

-v

Flip vertically

-t

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

-m

Read data range from metadata
WARNING: metadata are sometimes approximations with wrong data range

-r

Create fast link without data range
WARNING: some modules do not work correctly without known data range

--overwrite

Allow output files to overwrite existing files

--help

Print usage summary

--verbose

Verbose module output

--quiet

Quiet module output

--ui

Force launching GUI dialog

Parameters:¶

input=name

Name of raster file to be linked

source=name

Name of non-file GDAL data source

output=name [required]

Name for output raster map

band=integer

Band to select (default is all bands)

title=phrase

Title for resultant raster map

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 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