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

[Pierre Racine]

So I reprocessed the two polygons below in a topology have tolerance=0. However I still get the two same geometries in ovlp.test03_topo. I was expecting three polygons: 1 non-overlapping part for each and 1 representing the overlapping shared part with I don't know which attribute. 

I though topology would prevent the insertion of any overlapping part and remove (or aggregate) them. I thought at least the mbr column of the topo3.face table would contain the three geometries but no, they are just mbrs...

How can I fix my overlapping problem with topology?

Pierre

> So as of r9630 this topology of yours builds.
> Of course your input geometries are not going to being fully
> represented as the tolerance of 10 units on the topology is
> chewing them badly.
> 
> Use tolerance with care !
> 
> Let me know how your next topos go :)
> 
> --strk;
> 
>   ,------o-.
>   |   __/  |    Delivering high quality PostGIS 2.0 !
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> 
> 
> On Wed, Apr 11, 2012 at 02:53:07PM -0400, Pierre Racine wrote:
> > An even simpler example leads to another type of error:
> >
> > SELECT CreateTopology('topo3',0, 10);
> >
> > DROP TABLE IF EXISTS ovlp.test03;
> > CREATE TABLE ovlp.test03 AS
> > SELECT 1 id, ST_GeomFromText('POLYGON((0 1, 2 2, 2 0, 0 1))') geom
> > UNION ALL
> > SELECT 2 id, ST_GeomFromText('POLYGON((1 1, 3 2, 3 0, 1 1))') geom
> >
> > CREATE TABLE ovlp.test03_topo (id integer);
> >
> > SELECT AddTopoGeometryColumn('topo3', 'ovlp', 'test03_topo', 'topo',
> 'POLYGON'); -- 1
> >
> > INSERT INTO ovlp.test03_topo (id, topo)
> > SELECT id, topology.toTopoGeom(geom, 'topo3', 1)
> > FROM ovlp.test03
> >
> > gives:
> >
> > ********** Error **********
> >
> > ERROR: SQL/MM Spatial exception - edge crosses node.
> > SQL state: P0001
> > Context: PL/pgSQL function "topogeo_addpoint" line 96 at assignment
> > PL/pgSQL function "topogeo_addlinestring" line 125 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 topo3.relation(topogeo_id, layer_id,
> element_type, element_id) SELECT 2, 1, 3, topogeo_addPolygon('topo3',
> '01030000000100000004000000000000000000F03F000000000000F03F0000000
> 00000084000000000000000400000000000000840000000000000000000000000
> 0000F03F000000000000F03F'::geometry, 10);"
> > PL/pgSQL function "totopogeom" line 129 at EXECUTE statement
> >
> > Pierre
> >
> > > -----Original Message-----
> > > From: postgis-users-bounces at postgis.refractions.net [mailto:postgis-users-
> > > bounces at postgis.refractions.net] On Behalf Of Pierre Racine
> > > Sent: Wednesday, April 11, 2012 2:40 PM
> > > To: PostGIS Users Discussion
> > > Subject: Re: [postgis-users] Method to remove overlaps in a layer
> > >
> > > 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',
> > >
> '0103000020EB7A0000010000000800000000000080FD384B4100000000F46154
> > >
> 4100000000D84B4B41000000405069544100000000B55D4B41000000005C6354
> > >
> 4100000000BD594B4100000000965B544100000000C8694B4100000000625554
> > >
> 4100000080E15C4B4100000080474D544100000080ED404B41000000006C5054
> > > 4100000080FD384B4100000000F4615441'::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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