v.external(1)

NAME
v.external - Creates a new pseudo-vector map as a link to an OGR-supported layer or a PostGIS feature table.

KEYWORDS
vector, import, external, OGR, PostGIS

SYNOPSIS
v.external
v.external --help
v.external [-fltb] input=string layer=name [output=name] [--overwrite] [--help] [--verbose] [--quiet] [--ui]

  Flags:

-f
    List supported formats and exit

-l
    List available layers in data source and exit

-t
    List available layers including feature type in data source and exit
    Format: layer name,type,projection check,geometry

-b
    Do not build topology

--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=string [required]
    Name of input OGR or PostGIS data source
    Examples:
    ESRI Shapefile: directory containing a shapefile
    MapInfo File: directory containing a mapinfo file
    PostGIS database: connection string, eg. ’PG:dbname=db user=grass’

layer=name [required]
    Name of OGR layer or PostGIS feature table to be linked
    Examples:
    ESRI Shapefile: shapefile name
    MapInfo File: mapinfo file name
    PostGIS database: table name

output=name
    Name for output GRASS vector map (default: input layer)

DESCRIPTION
v.external creates new vector map as a link to external OGR layer or PostGIS feature table. OGR (Simple Features Library) is part of the GDAL library, so you need to install GDAL to use v.external for external OGR layers. Note that a PostGIS feature table can be linked also using built-in GRASS-PostGIS data driver (requires GRASS to be built with PostgreSQL support).

  Supported OGR vector formats
To list supported OGR formats, type

v.external -f

For details see OGR web site.

EXAMPLES

  ESRI Shapefile
Assuming that ’test_shape.shp’ is located in directory ’/home/user/shape_data’.

v.external input=/home/user/shape_data layer=test_shape output=grass_map

  MapInfo files

v.external input=./ layer=mapinfo_test output=grass_map

  SDTS files
Note: you have to select the CATD file

v.external input=CITXCATD.DDF output=cities

  TIGER files

v.external input=input/2000/56015/ layer=CompleteChain,PIP output=t56015_all

  PostGIS layers
PostGIS links are by default created by built-in PostGIS support, ie. using GRASS-PostGIS data driver. If the environment variable GRASS_VECTOR_OGR exists, or GRASS is compiled without PostgreSQL support then GRASS will use OGR-PostgreSQL driver for creating a link.

v.external input="PG:host=localhost user=postgres dbname=postgis" layer=polymap

NOTES
The simple feature data model used by OGR (or PostGIS) 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 two formats, because some modules working correctly with GRASS native data, can produce wrong results with input vector maps 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 C API documentation

SEE ALSO
v.external.out, v.clean, v.db.connect, v.import, v.in.db, v.in.ogr, v.out.ogr

OGR Library
PostGIS

See also GRASS user wiki page for more examples.

AUTHORS
Radim Blazek, ITC-Irst, Trento, Italy
PostGIS support by Martin Landa, Czech Technical University in Prague, Czech Republic

Last changed: $Date: 2016-01-13 10:20:46 +0100 (Wed, 13 Jan 2016) $

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