[postgis-users] Method to remove overlaps in a layer

[Pierre Racine]

So I have been creating a very simple example based on the example in the toTopoGeom() documentation page:

http://www.postgis.org/documentation/manual-svn/toTopoGeom.html

SELECT CreateTopology('topo1',31467, 10);

CREATE TABLE ovlp.test02_topo (id integer);

SELECT AddTopoGeometryColumn('topo1', 'ovlp', 'test02_topo', 'topo', 'POLYGON');

INSERT INTO ovlp.test02_topo (id, topo)
SELECT id, topology.toTopoGeom(geom, 'topo1', 1)
FROM ovlp.test02

And I get:

********** Error **********

ERROR: interpolate_point4d: invalid F (1)
SQL state: XX000
Context: PL/pgSQL function "st_modedgesplit" line 94 at assignment
PL/pgSQL function "topogeo_addpoint" line 91 at assignment
PL/pgSQL function "topogeo_addlinestring" line 132 at assignment
SQL statement "SELECT array_cat(edges, array_agg(x)) FROM ( select topology.TopoGeo_addLinestring(atopology, rec.geom, tol) as x ) as foo"
PL/pgSQL function "topogeo_addpolygon" line 27 at assignment
SQL statement "INSERT INTO topo1.relation(topogeo_id, layer_id, element_type, element_id) SELECT 5, 1, 3, topogeo_addPolygon('topo1', '0103000020EB7A0000010000000800000000000080FD384B4100000000F461544100000000D84B4B41000000405069544100000000B55D4B41000000005C63544100000000BD594B4100000000965B544100000000C8694B41000000006255544100000080E15C4B4100000080474D544100000080ED404B41000000006C50544100000080FD384B4100000000F4615441'::geometry, 10);"
PL/pgSQL function "totopogeom" line 129 at EXECUTE statement

I join a picture of the original layer to be converted to a topologic layer.

I'm still at beta 5... Should upgrading solve that particular problem?

Pierre

> > So what would be the normal/easiest steps to convert a messy polygon
> coverage into a clean topology? Is it documented somewhere?
> >
> > My guess:
> >
> > 1- SET search_path TO topology,public;
> 
> You shouldn't need this, when you load topology.sql you should
> get "topology" already appended to the end of the search_path
> associated with the database.
> 
> > 2- SELECT CreateTopoGeom('test')
> 
> Yep.
> 
> > 3- SELECT toTopoGeom(geom, 'test', 1)
> > FROM mymessyone;
> 
> You didn't create a layer, see AddTopoGeometryColumn.
> The third argument is a layer id, as returned by that function.
> 
> > or
> >
> > SELECT ST_CreateTopoGeo('test', geom)
> > FROM mymessyone;
> 
> This one only works starting with an empty topology so
> you'll need to pass it a full collection:
> 
> SELECT ST_CreateTopoGeo('test', ST_Collect(geom)) FROM mymessyone;
> 
> But I'd recommend using toTopoGeom instead, to keep the linking
> between attributes and geometries.
> 
> > What happens when a polygon to be added to the topology overlaps a
> polygon already in the topology?
> 
> Two overlapping rectangles would produce a total of 3 faces.
> If you're returning TopoGeometry objects (your step 2) both
> of them will be defined by 2 faces, having one face in common.


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