PostGIS

See also working with external data in GRASS 7.

Help pages

• Database management in GRASS GIS help page
• SQL support in GRASS GIS help page

• PostgreSQL driver in GRASS help page
• ODBC driver in GRASS help page

Link to external dataset

• input maps: v.external

  (in GRASS 6 links are read only, for GRASS 7 see working with external data in GRASS 7)

• output maps: v.external.out (GRASS 7 only)

Import into GRASS

1. v.in.ogr (import only geometry column from postgresql/postgis)
2. v.clean

There is a fundamental difference between the PostGIS format which is non-topological (OGC simple feature-based) and the internal GRASS format which is topological and which, thus, does not really allow for overlapping polygons. You can digitize them, but they are not really useful...

Link into GRASS

You can register a PostGIS layer into GRASS using v.external, eg. PostGIS layer 'lakes' from database 'pgis_nc'

v.external dsn=PG:dbname=pgis_nc layer=lakes

It will create in the current mapset new vector map 'lakes', the module also builds pseudo-topology for this map,

Important note: In GRASS 6 this link is read-only, in GRASS 7 it's possible to modify linked layers directly via OGR library, see working with external data in GRASS 7.

You can also link a GRASS layer to a PostgreSQL attribute table, though v.db.connect.

Export to PostGIS

To export GRASS vector map layer to PostGIS layer can be used v.out.ogr, eg.

v.out.ogr in=lakes@PERMANENT dsn=PG:dbname=pgis_nc format=PostgreSQL type=area

See also

• Tutorial by Micha Silver