Topology Processing
Polygonize
Finds and registers all faces defined by topology edges.
Synopsis
text Polygonize(varchar toponame)
Description
Registers all faces that can be built out a topology edge primitives.
The target topology is assumed to contain no self-intersecting edges.
Note
Already known faces are recognized, so it is safe to call Polygonize multiple times on the same topology.
Note
This function does not use nor set the next_left_edge and next_right_edge fields of the edge table.
Availability: 2.0.0
See Also
AddNode
Adds a point node to the node table in the specified topology schema and returns the nodeid of new node. If point already exists as node, the existing nodeid is returned.
Synopsis
integer AddNode(varchar toponame, geometry apoint, boolean allowEdgeSplitting=false, boolean computeContainingFace=false)
Description
Adds a point node to the node table in the specified topology schema. The AddEdge function automatically adds start and end points of an edge when called so not necessary to explicitly add nodes of an edge.
If any edge crossing the node is found either an exception is raised or the edge is split, depending on the allowEdgeSplitting parameter value.
If computeContainingFace is true a newly added node would get the correct containing face computed.
Note
If the apoint geometry already exists as a node, the node is not added but the existing nodeid is returned.
Availability: 2.0.0
Examples
SELECT topology.AddNode('ma_topo', ST_GeomFromText('POINT(227641.6 893816.5)', 26986) ) As nodeid;
-- result --
nodeid
--------
4
See Also
AddEdge
Adds a linestring edge to the edge table and associated start and end points to the point nodes table of the specified topology schema using the specified linestring geometry and returns the edgeid of the new (or existing) edge.
Synopsis
integer AddEdge(varchar toponame, geometry aline)
Description
Adds an edge to the edge table and associated nodes to the nodes table of the specified toponame schema using the specified linestring geometry and returns the edgeid of the new or existing record. The newly added edge has "universe" face on both sides and links to itself.
Note
If the aline geometry crosses, overlaps, contains or is contained by an existing linestring edge, then an error is thrown and the edge is not added.
Note
The geometry of aline must have the same srid as defined for the topology otherwise an invalid spatial reference sys error will be thrown.
Performed by the GEOS module.
Warning
AddEdge is deprecated as of 3.5.0. Use TopoGeo_AddLineString instead.
Availability: 2.0.0
Examples
SELECT topology.AddEdge('ma_topo', ST_GeomFromText('LINESTRING(227575.8 893917.2,227591.9 893900.4)', 26986) ) As edgeid;
-- result-
edgeid
--------
1
SELECT topology.AddEdge('ma_topo', ST_GeomFromText('LINESTRING(227591.9 893900.4,227622.6 893844.2,227641.6 893816.5,
227704.5 893778.5)', 26986) ) As edgeid;
-- result --
edgeid
--------
2
SELECT topology.AddEdge('ma_topo', ST_GeomFromText('LINESTRING(227591.2 893900, 227591.9 893900.4,
227704.5 893778.5)', 26986) ) As edgeid;
-- gives error --
ERROR: Edge intersects (not on endpoints) with existing edge 1
See Also
TopoGeo_AddLineString, CreateTopology, Spatial Reference Systems
AddFace
Registers a face primitive to a topology and gets its identifier.
Synopsis
integer AddFace(varchar toponame, geometry apolygon, boolean force_new=false)
Description
Registers a face primitive to a topology and gets its identifier.
For a newly added face, the edges forming its boundaries and the ones contained in the face will be updated to have correct values in the left_face and right_face fields. Isolated nodes contained in the face will also be updated to have a correct containing_face field value.
Note
This function does not use nor set the next_left_edge and next_right_edge fields of the edge table.
The target topology is assumed to be valid (containing no self-intersecting edges). An exception is raised if: The polygon boundary is not fully defined by existing edges or the polygon overlaps an existing face.
If the apolygon geometry already exists as a face, then: if force_new is false (the default) the face id of the existing face is returned; if force_new is true a new id will be assigned to the newly registered face.
Note
When a new registration of an existing face is performed (force_new=true), no action will be taken to resolve dangling references to the existing face in the edge, node an relation tables, nor will the MBR field of the existing face record be updated. It is up to the caller to deal with that.
Note
The apolygon geometry must have the same srid as defined for the topology otherwise an invalid spatial reference sys error will be thrown.
Availability: 2.0.0
Examples
-- first add the edges we use generate_series as an iterator (the below
-- will only work for polygons with < 10000 points because of our max in gs)
SELECT topology.AddEdge('ma_topo', ST_MakeLine(ST_PointN(geom,i), ST_PointN(geom, i + 1) )) As edgeid
FROM (SELECT ST_NPoints(geom) AS npt, geom
FROM
(SELECT ST_Boundary(ST_GeomFromText('POLYGON((234896.5 899456.7,234914 899436.4,234946.6 899356.9,234872.5 899328.7,
234891 899285.4,234992.5 899145, 234890.6 899069,234755.2 899255.4,
234612.7 899379.4,234776.9 899563.7,234896.5 899456.7))', 26986) ) As geom
) As geoms) As facen CROSS JOIN generate_series(1,10000) As i
WHERE i < npt;
-- result --
edgeid
--------
3
4
5
6
7
8
9
10
11
12
(10 rows)
-- then add the face -
SELECT topology.AddFace('ma_topo',
ST_GeomFromText('POLYGON((234896.5 899456.7,234914 899436.4,234946.6 899356.9,234872.5 899328.7,
234891 899285.4,234992.5 899145, 234890.6 899069,234755.2 899255.4,
234612.7 899379.4,234776.9 899563.7,234896.5 899456.7))', 26986) ) As faceid;
-- result --
faceid
--------
1
See Also
AddEdge, CreateTopology, Spatial Reference Systems
ST_Simplify
Returns a "simplified" geometry version of the given TopoGeometry using the Douglas-Peucker algorithm.
Synopsis
geometry ST_Simplify(TopoGeometry tg, float8 tolerance)
Description
Returns a "simplified" geometry version of the given TopoGeometry using the Douglas-Peucker algorithm on each component edge.
Note
The returned geometry may be non-simple or non-valid.
Splitting component edges may help retaining simplicity/validity.
Performed by the GEOS module.
Availability: 2.1.0
See Also
Geometry ST_Simplify, ST_IsSimple, ST_IsValid, ST_ModEdgeSplit
RemoveUnusedPrimitives
Removes topology primitives which not needed to define existing TopoGeometry objects.
Synopsis
int RemoveUnusedPrimitives(text topology_name, geometry bbox)
Description
Finds all primitives (nodes, edges, faces) that are not strictly needed to represent existing TopoGeometry objects and removes them, maintaining topology validity (edge linking, face labeling) and TopoGeometry space occupation.
No new primitive identifiers are created, but rather existing primitives are expanded to include merged faces (upon removing edges) or healed edges (upon removing nodes).
Availability: 3.3.0