PostGIS data provider in GRASS 7

PostGIS data can be accessed in GRASS 7 using GRASS-OGR data provider or preferably by native GRASS-PostGIS data provider. Note that GRASS-OGR data provider supports only simple feature access.

Development of PostGIS data provider has been supported by ​Fondazione Edmund Mach and ​Comune di Trento (Italy).

This data provider allows GRASS to read (see read_pg.c​) and write (see write_pg.c​) PostGIS data directly without any external library (like in the case of GRASS-OGR data provider). GRASS-PostGIS data provider is implemented using ​libpq library.

Note that GRASS-PostGIS data provider is compiled only when GRASS is configured with --with-postgres switch.

Overview of subroutines to read PostGIS data:

Level	Sequantial access	Random access
1 (without topology)	​V1_read_next_line_pg()	​V1_read_line_pg()
2 (with pseudo-topology/topology)	​V2_read_next_line_pg()	​V2_read_line_pg()

Overview of subroutines to write PostGIS data:

Level	Write new feature	Delete existing feature	Rewrite existing feature
1 (without topology)	​V1_write_line_pg()	​V1_rewrite_line_pg()	​V1_delete_line_pg()
2 (with pseudo-topology - simple feature access)	​V2_write_line_sfa()	​V2_rewrite_line_sfa()	​V2_delete_line_sfa()
2 (with topology - PostGIS Topology)	​V2_write_line_pg()

By default data are read/write as simple features. If PostGIS Topology schema is defined then the data provider reads/writes topological elements from provided schema.

Note that direct access like for GRASS-OGR data provider is not currently implemented. In other words to access PostGIS data (using GRASS-PostGIS data provider) is required to create a link using v.external command.

Simple features access

GRASS-PostGIS provider allows to read and write PostGIS data stored as simple features on level 1 (without topology) and also on level 2 (in this case a pseudo-topology is built over simple features).

Export example:

Read example:

Write example:

For more examples see ​wiki page from GRASS Wiki.

Topological access

For more information see PostGIS Topology page.supports