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).
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.
Supported OGR vector formats
To list supported OGR formats, type
For details see
GDAL 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
PostGIS layers
By default, PostGIS links are 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.
List of layers for given data source can be printed by -l
flag.
v.external input="PG:host=localhost user=postgres dbname=postgis" -l
...
polymap
...
v.external input="PG:host=localhost user=postgres dbname=postgis" layer=polymap
Note: Authentication details (user password) can be preferably defined
by db.login.
MapInfo files
Assuming that 'mapinfo_test' MapInfo file is located in the current
directory (".").
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
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
GDAL Library
PostGIS
See
also GRASS user wiki page for more examples.
AUTHORS
Radim Blazek, ITC-Irst, Trento, Italy
PostGIS support by Martin Landa, GeoForAll (OSGeoREL) Lab, Czech
Technical University in Prague, Czech Republic
Last changed: $Date$