GRASS GIS manual: v.external

Note: A new GRASS GIS stable version has been released: GRASS GIS 7. Go directly to the new manual page here

NAME

v.external - Creates a new vector as a read-only link to OGR layer.

KEYWORDS

vector, external, import

SYNOPSIS

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

Flags:

-f: List supported formats and exit
--overwrite: Allow output files to overwrite existing files
--verbose: Verbose module output
--quiet: Quiet module output

Parameters:

dsn=string: OGR datasource name. Examples:
ESRI Shapefile: directory containing shapefiles
MapInfo File: directory containing mapinfo files
output=name: Output vector. If not given, available layers are printed only.
layer=string: OGR layer name. If not given, available layers are printed only. Examples:
ESRI Shapefile: shapefile name
MapInfo File: mapinfo file name

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

ESRI Shapefile
Mapinfo File

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 maps (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 writable mode.

REFERENCES

OGR vector library
OGR vector library C API documentation

AUTHOR

Radim Blazek, ITC-Irst, Trento, Italy

Last changed: $Date: 2012-02-25 05:38:11 -0800 (Sat, 25 Feb 2012) $

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