PostGIS
Synopsis
topogeometry +`*`+toTopoGeom*(`geometry `geom, varchar
toponame, integer layer_id, float8 tolerance`)`;
topogeometry +`*`+toTopoGeom*(`geometry `geom, topogeometry
topogeom, float8 tolerance`)`;
Description
Converts a simple Geometry into a TopoGeometry.
Topological primitives required to represent the input geometry will be
added to the underlying topology, possibly splitting existing ones, and
they will be associated with the output TopoGeometry in the relation
table.
Existing TopoGeometry objects (with the possible exception of
topogeom, if given) will retain their shapes.
When tolerance is given it will be used to snap the input geometry
to existing primitives.
In the first form a new TopoGeometry will be created for the given layer
(layer_id) of the given topology (toponame).
In the second form the primitives resulting from the conversion will be
added to the pre-existing TopoGeometry (topogeom), possibly adding
space to its final shape. To have the new shape completely replace the
old one see clearTopoGeom.
Availability: 2.0
Enhanced: 2.1.0 adds the version taking an existing TopoGeometry.
Examples
This is a full self-contained workflow
-- do this if you don't have a topology setup already
-- creates topology not allowing any tolerance
SELECT topology.CreateTopology('topo_boston_test', 2249);
-- create a new table
CREATE TABLE nei_topo(gid serial primary key, nei varchar(30));
--add a topogeometry column to it
SELECT topology.AddTopoGeometryColumn('topo_boston_test', 'public', 'nei_topo', 'topo', 'MULTIPOLYGON') As new_layer_id;
new_layer_id
-----------
1
--use new layer id in populating the new topogeometry column
-- we add the topogeoms to the new layer with 0 tolerance
INSERT INTO nei_topo(nei, topo)
SELECT nei, topology.toTopoGeom(geom, 'topo_boston_test', 1)
FROM neighborhoods
WHERE gid BETWEEN 1 and 15;
--use to verify what has happened --
SELECT * FROM
topology.TopologySummary('topo_boston_test');
-- summary--
Topology topo_boston_test (5), SRID 2249, precision 0
61 nodes, 87 edges, 35 faces, 15 topogeoms in 1 layers
Layer 1, type Polygonal (3), 15 topogeoms
Deploy: public.nei_topo.topo-- Shrink all TopoGeometry polygons by 10 meters
UPDATE nei_topo SET topo = ST_Buffer(clearTopoGeom(topo), -10);
-- Get the no-one-lands left by the above operation
-- I think GRASS calls this "polygon0 layer"
SELECT ST_GetFaceGeometry('topo_boston_test', f.face_id)
FROM topo_boston_test.face f
WHERE f.face_id > 0 -- don't consider the universe face
AND NOT EXISTS ( -- check that no TopoGeometry references the face
SELECT * FROM topo_boston_test.relation
WHERE layer_id = 1 AND element_id = f.face_id
);