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
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: $Date$