PostGIS Topology

PostGIS Topology allows to store topological vector data in PostGIS database. It's available in PostGIS 2.0 and greater. GRASS supports PostGIS Topology in version GRASS 7.0 and greater through GRASS-PostGIS data provider.

Background

Topological models used by GRASS and PostGIS Topology are different - see bellow.

GRASS Topology Model

In GRASS model are defined various topological elements:

• nodes - point elements

  For each node is defined which lines/boundaries starts and ends in this node.

• lines - linear elements which are not forming areas

  For each line is defined by start and end node.

• boundaries - linear elements which can form areas

  For each line is defined by start and end node, and by the area on the left and right.

• centroids - point located inside area

  For each centroid is defined area id within the centroid is located.

• areas - topologically correct areal elements formed by closed set of boundaries and one centroid located inside the area

  For each area is defined list of boundaries which forms the area (outter ring), number of isles and id of isles located in the area

• isle - inner ring (closed set of boundaries) located inside area (note that inner ring is not allowed to touch the area boundary)

  For each isle is defined list of boundaries which forms the isle (it's outter ring) and area id where the isle is located.

For other info and examples see programmer's manual.

PostGIS Topology Model

PostGIS Topology model is based on ISO standard 13249. The model defines only three topological elements:

• nodes - point elements
• edges - linear elements
• faces - area elements

See also

• Working with external data in GRASS 7
• PostGIS

External links

• PostGIS Topology manual
• PostGIS Topology wiki page
• State of the art of FOSS4G for topology and network analysis (FOSS4G 2010)
• strk's page about PostGIS
• PostGIS topology ISO SQL/MM complete (strk's blog)
• Simplifying a map layer using PostGIS topology (strk's blog)
• Topo-Geo-and-Topo-Net - The Concepts • Routine Details
• ISO 13249-3 Information Technology - Database languages - SQL Multimedia and application packages (Text for FDIS)