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.
v.external dsn=/home/user/shape_data layer=test_shape output=grass_map
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
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 \
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.
OGR vector library
OGR vector library C API
Radim Blazek, ITC-Irst, Trento, Italy
Last changed: $Date$