[postgis-users] PostGIS Topology Error

[Nicolas Ribot]

Hi,
Indeed, Postgis Topology works well to build topo from clean geometries,
but can fail if input geometries have topological errors.

It could be tricky to clean data with just postGIS and sql queries.
Topological GIS, like GRASS, can load PostGIS data and clean them at a
given precision

HTH
Nicolas

On 4 July 2018 at 14:01, Cameron Green <u15055452 at tuks.co.za> wrote:

> Good day,
>
>
>
> My name is Cameron Green and I am an honours (4th year) student at the
> University of Pretoria in South Africa. I am currently working on a project
> that requires me to assess the quality of data that was downloaded from
> OpenStreetMap (OSM), specifically, various topological errors. I have
> decided to use PostGIS as it does error checks and tells me what the error
> is and where (or at least that is how I understand it).
>
>
>
> Firstly, here is my installation information (Ubuntu 16.04) with
> PostgreSQL 10:
>
> POSTGIS="2.4.4 r16526" PGSQL="100" GEOS="3.5.0-CAPI-1.9.0 r4084"
> SFCGAL="1.2.2" PROJ="Rel. 4.9.2, 08 September 2015" GDAL="GDAL 1.11.3,
> released 2015/09/16" LIBXML="2.9.3" LIBJSON="0.11.99" LIBPROTOBUF="1.2.1"
> TOPOLOGY RASTER
>
>
>
> Using the textbook, Mastering PostGIS chapter 8, where it deals with
> PostGIS Topology. Below is the SQL commands I used. When I used SRID as
> 4026 and 0,00028 as the snap threshold, the commands execute without any
> issues. However, when I change the SRID to 2049 and decrease the snap
> tolerance in the topology.toTopoGeom, I get the following error:
>
>
>
> ERROR: SQL/MM Spatial exception - geometry crosses edge 4469 CONTEXT:
> PL/pgSQL function totopogeom(geometry,topogeometry,double precision) line
> 114 at FOR over SELECT rows PL/pgSQL function totopogeom(geometry,character
> varying,integer,double precision) line 89 at assignment SQL state: XX000
>
>
>
> The line and type of error changes as I increase the snap tolerance to any
> value between 5m and 100m.
>
>
>
> From my understanding, once the topology is created and the geometries are
> loaded into the topology, I should be able to run the
> topology.ValidateTopology function to get a list of errors. Is this
> correct?
>
>
>
> At the moment it seems like the topology errors is what preventing me from
> creating the topology.
>
>
>
> If anyone could please help me or direct me to where I have made an error
> in my SQL commands or there are some settings I must change. Any help
> regarding this would be greatly appreciated.  I have added the commands at
> the end of this email.
>
>
>
> Kind regards,
>
> Cameron Green
> President - CGIS YouthMappers
> BSc(Hons) Geoinformatics, University of Pretoria
> +2783 301 3201
>
> +2712 420 2016
>
>
>
>
>
>
>
> SQL Commands:
>
> topology.CreateTopology ('my_topology', 2049, 5, false)
>
>
>
> // Checked the validity of the input geometries
>
> select ST_IsValidReason(way)
>
> from osm_lines
>
> where ST_IsValid(way) = false
>
>
>
> // Create the TopoGeometry column
>
> select topology.AddTopoGeometryColumn('my_topology', 'public', osm_lines,
> 'topogeom', 'Linestring')
>
>
>
> //  Populate the Topogeometry column from an existing geometry.
>
> // This is where my problem starts
>
> update osm_lines SET topogeom = topology.toTopoGeom(way,'my_topology',1,5)
>
>
>
>
> select topology.TopologySummary('my_topology')
>
>
>
> select * from  topology.ValidateTopology('my_topology')
>
>
>
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