PostGIS topology support has shipped in PostGIS 2.0. It consists in a topology schema model and accessory functions. A lot of working is going on in the PostGIS 2.0 release. Please refer to PostGIS 2.0 Topology section of manual for details.
With topology support enabled you can store topological elements, define TopoGeometry objects as being composed by these elements, convert TopoGeometry objects to simple Geometry objects to use all functions defined on the latter.
Topological elements are Faces, Edges and Nodes.
The SVN repository also contains initial code, being a set of definitions and pl/pgsql functions. A README file therein contains usage and test notes.
Enabling PostGIS Topology in Versions Earlier Than 2.0
In order to enable PostGIS support you need to be equipped with the following:
- A schema-aware PostgreSQL installation (7.3 and up)
- PostGIS 1.3.x or up
- GEOS 2.1 or up
Move under the topology/ directory and run:
$ make $ psql -f topology.sql <your_test_database>
No C libs involved so far, so no need to make install.
To uninstall/disable just drop the 'topology' schema. It contains all the objects installed by the topology.sql script (remember to cascade).
Creating a Topology
Topology data are stored in named SCHEMAs, where the topology name is the name of the SCHEMA containing its data.
A catalogue of avalable topologies is kept under the "topology"."topology" table.
To create/destroy a topology:
SELECT topology.CreateTopology(name, [srid], [tolerance]); SELECT topology.DropTopology(name);
Loading Topology data
To load topology data in a topology you can use INSERT statements filling up the Edge, Node and Face relations under your topology schema:
- edge_id integer PRIMARY KEY
- start_node integer REFERENCES Node.node_id)
- end_node integer REFERENCES Node.node_id)
- next_left_edge integer REFERENCES abs(Edge.edge_id)
- next_right_edge integer REFERENCES abs(Edge.edge_id)
- left_face integer REFERENCES Face.face_id
- right_face integer REFERENCES Face.face_id
- geom geometry ( a linestring )
- node_id integer PRIMARY KEY
- containing_face integer REFERENCES Face.face_id
- geom geometry ( a point )
- face_id integer PRIMARY KEY
- mbr geometry ( can be NULL )
Details on semantic are contained in the SQL/MM specification, which this implementation follows as for these views structure.
To verify validity of a topology:
SELECT * FROM topology.ValidateTopology(name);
The return set will contain references to elements involved in the invalidity.
Copying a Topology
Editing a Topology
Working with TopoGeometry objects
Getting simple Geometry values from TopoGeometry objects
You currently need to explicit call the TopoGeometry=>Geometry cast function. This will probably be made implicit when the code is more tested:
Testing Topology implementation
Tests are included under the topology/test directory. Run make w/out args to see a list of supported targets.