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NAME

v.external - Creates a new pseudo-vector map as a link to an OGR-supported layer.

KEYWORDS

vector, external, ogr

SYNOPSIS

v.external
v.external help
v.external [-flb] dsn=string layer=name [output=name] [--overwrite] [--verbose] [--quiet]

Flags:

-f
List supported OGR formats and exit
-l
List available OGR layers in given data source and exit
-b
Do not build topology
--overwrite
Allow output files to overwrite existing files
--verbose
Verbose module output
--quiet
Quiet module output

Parameters:

dsn=string
Name of input OGR data source
Examples:
ESRI Shapefile: directory containing a shapefile
MapInfo File: directory containing a mapinfo file
PostGIS database: PG:dbname=<database>
layer=name
Name of input OGR layer
Examples:
ESRI Shapefile: shapefile name
MapInfo File: mapinfo file name
PostGIS database: table name
output=name
Name for output GRASS vector map

DESCRIPTION

v.external creates new vector as a link to external OGR layer (read only). OGR (Simple Features Library) is part of the GDAL library, so you need to install GDAL to use v.external and external OGR layers.

Supported OGR Vector Formats

Further available drivers such as UK .NTF, SDTS, TIGER, IHO S-57 (ENC), DGN, GML, AVCBin, REC, Memory, OGDI, and PostgreSQL depend on the local installation (OGR library), for details see OGR web site.

EXAMPLES

SHAPE files
v.external dsn=/home/user/shape_data layer=test_shape output=grass_map 
MapInfo files
v.external dsn=./ layer=mapinfo_test output=grass_map
SDTS files (you have to select the CATD file)
v.external dsn=CITXCATD.DDF output=cities
TIGER files
v.external dsn=input/2000/56015/ layer=CompleteChain,PIP output=t56015_all
PostGIS layers (area example)
v.external dsn="PG:host=localhost user=postgres dbname=postgis" layer=polymap \
output=polygons

NOTES

The simple feature data model used by OGR is very different from the topological format used by GRASS. Instead of true topology, so called 'pseudo topology' is created for data linked by v.external. User should learn the difference between those to formats, because some modules working correctly with GRASS native data, can produce wrong results with input layers created by v.external.

See v.db.connect for an example of maintaining attributes in external DBMS in also writeable mode.

REFERENCES

OGR vector library
OGR vector library C API documentation

SEE ALSO

v.clean, v.db.connect, v.in.db, v.in.ogr, v.out.ogr

AUTHOR

Radim Blazek, ITC-Irst, Trento, Italy

Last changed: $Date: 2009-07-12 02:48:05 -0700 (Sun, 12 Jul 2009) $


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