Note: This document is for an older version of GRASS GIS that is outdated. You should upgrade, and read the current manual page.
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 09:52:42 -0800 (Fri, 20 Dec 2013) $
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