Changes between Initial Version and Version 1 of UsersWikiPostgisTopology

Timestamp:

Apr 14, 2009, 11:19:22 AM (15 years ago)

Author:

pierre

Comment:

—

UsersWikiPostgisTopology

@@ +1 @@
+= Postgis Topology =
+
+
+PostGIS topology support is in pre-alpha stage.
+It consists in a topology schema model and accessory functions.
+
+With topology support enabled you can store [wiki:UsersWikiTopologicalPrimitives topological elements],
+define TopoGeometry objects as being composed by these elements,
+convert TopoGeometry objects to simple [wiki:UsersWikiGeometryType Geometry] objects
+to use all functions defined on the latter.
+
+Topological elements are Faces, Edges and Nodes.
+
+An entity-relationship diagram of the topology concepts can
+be found in the CVS repository of PostGIS (head branch), under
+the topology/ER directory.
+
+The CVS 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 order to enable postgis support you need to be equipped with the following:
+
+ * A schema-aware postgresql installation (7.3 and up)
+ * PostGIS-1.1.x (current HEAD branch in CVS)
+ * 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 [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
+  * 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
+  * node_id integer PRIMARY KEY
+  * containing_face integer REFERENCES Face.face_id
+  * geom geometry ( a point )
+
+ * Face
+  * face_id integer PRIMARY KEY
+  * mbr box2d ( can be NULL )
+
+Details on semantic are contained in the SQL/MM specification, which
+this implementation follows as for these views structure.
+
+== Validating Topology ==
+
+To verify validity of a topology:
+
+{{{
+SELECT * FROM topology.ValidateTopology(name);
+
+}}}
+
+The return set will contain references to elements involved in the invalidity.
+
+== Editing a Topology ==
+
+See TopologyEditing
+
+= Working with !TopoGeometry objects =
+
+See CreatingTopoGeometryObjects
+
+== 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:
+
+{{{
+SELECT topology.Geometry(TopoGeometry);
+
+}}}
+
+= Testing Topology implementation =
+
+Tests are included under the topology/test/ directory.
+Run make w/out args to see a list of supported targets.