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--></style></head><body lang=EN-ZA><div class=WordSection1><p class=MsoNormal>Good day,<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><span style='color:#222222'>My name is Cameron Green and I am an honours (4<sup>th</sup> 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). <o:p></o:p></span></p><p class=MsoNormal><span style='color:#222222'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#222222'>Firstly, here is my installation information (Ubuntu 16.04) with PostgreSQL 10:<o:p></o:p></span></p><p class=MsoNormal><span style='color:#222222'>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<o:p></o:p></span></p><p class=MsoNormal><span style='color:#222222'> <o:p></o:p></span></p><p class=MsoNormal><span style='color:#222222'>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: <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#222222'> <o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Times New Roman",serif;color:#333333;background:white'>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</span><span style='font-family:"Arial",sans-serif;color:#222222'><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#222222'> <o:p></o:p></span></p><p class=MsoNormal><span style='color:#222222'>The line and type of error changes as I increase the snap tolerance to any value between 5m and 100m.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#222222'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#222222'>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? <o:p></o:p></span></p><p class=MsoNormal><span style='color:#222222'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#222222'>At the moment it seems like the topology errors is what preventing me from creating the topology. <o:p></o:p></span></p><p class=MsoNormal><span style='color:#222222'> <o:p></o:p></span></p><p class=MsoNormal><span style='color:#222222'>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. <o:p></o:p></span></p><p class=MsoNormal><span style='color:#222222'> <o:p></o:p></span></p><p class=MsoNormal>Kind regards,<o:p></o:p></p><p class=MsoNormal>Cameron Green<br>President - CGIS YouthMappers<br>BSc(Hons) Geoinformatics, University of Pretoria<br>+2783 301 3201<o:p></o:p></p><p class=MsoNormal>+2712 420 2016<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><span style='color:#222222'>SQL Commands: <o:p></o:p></span></p><p class=MsoNormal><span style='color:#222222'>topology.CreateTopology ('my_topology', 2049, 5, false) <o:p></o:p></span></p><p class=MsoNormal><span style='color:#222222'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#222222'>// Checked the validity of the input geometries <o:p></o:p></span></p><p class=MsoNormal><span style='color:#222222'>select ST_IsValidReason(way) <o:p></o:p></span></p><p class=MsoNormal><span style='color:#222222'>from osm_lines<o:p></o:p></span></p><p class=MsoNormal><span style='color:#222222'>where ST_IsValid(way) = false<o:p></o:p></span></p><p class=MsoNormal><span style='color:#222222'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#222222'>// Create the TopoGeometry column <o:p></o:p></span></p><p class=MsoNormal><span style='color:#222222'>select topology.AddTopoGeometryColumn('my_topology', 'public', osm_lines, 'topogeom', 'Linestring')<o:p></o:p></span></p><p class=MsoNormal><span style='color:#222222'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#222222'>// Populate the Topogeometry column from an existing geometry. <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#222222'>// This is where my problem starts<o:p></o:p></span></p><p class=MsoNormal><span style='color:#222222'>update osm_lines SET topogeom = topology.toTopoGeom(way,'my_topology',1,5) <o:p></o:p></span></p><p class=MsoNormal><span style='color:#222222'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#222222'>select topology.TopologySummary('my_topology')<o:p></o:p></span></p><p class=MsoNormal><span style='color:#222222'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#222222'>select * from topology.ValidateTopology('my_topology')<o:p></o:p></span></p><p class=MsoNormal><o:p> </o:p></p></div></body></html>
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