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NAME

r.external - Link GDAL supported raster file to a binary raster map layer.

KEYWORDS

raster, import

SYNOPSIS

r.external
r.external help
r.external [-oerf] [input=name] [source=string] [output=name] [band=integer] [title="phrase"] [--overwrite] [--verbose] [--quiet]

Flags:

-o
Override projection (use location's projection)
-e
Extend region extents based on new dataset
Also updates the default region if in the PERMANENT mapset
-r
Require exact range
-f
List supported formats and exit
--overwrite
Allow output files to overwrite existing files
--verbose
Verbose module output
--quiet
Quiet module output

Parameters:

input=name
Raster file to be linked
source=string
Name of non-file GDAL data source
output=name
Name for output raster map
band=integer
Band to select (default: all)
title="phrase"
Title for resultant raster map

DESCRIPTION

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.

NOTES

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.

NULL data handling

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).

EXAMPLES

RGB Orthophoto from GeoTIFF

# import of all channels (each channel will become a GRASS raster map):
r.external  /home/user/data/maps/059100.tif out=ortho
g.region rast=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

SEE ALSO

r.in.gdal, v.external

REFERENCES

GDAL Pages: http://www.gdal.org/

AUTHOR

Glynn Clements

Last changed: $Date: 2013-12-20 09:52:08 -0800 (Fri, 20 Dec 2013) $


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