[postgis-users] Topology: cannot delete slivers (or gaps)

Guillaume Drolet droletguillaume at gmail.com
Mon Nov 3 08:04:16 PST 2014

Sandro Santilli wrote
>> I suggest you take a look at edges having face 1831 on either
>> the right or left edge. Do any edge exist ? 
> edge 5187 has face 1831 as its right face
>> The correct procedure to drop those slivers would be to assign
>> those small areas to the (closest|biggest|leftmost|youpickit)
>> TopoGeometry object, to one and only one, and then, if you really
>> need it, drop the edge internal to the TopoGeometry.
>> I made a QGIS plugin which may help you do some of these things
>> manually, which is useful in some cases, mainly to understand the
>> issues.
> The plugin you made is a great tool (thanks). I will first try to get the
> number of slivers down to 
> a manageable number, which I had with setting the tolerance at 2.0 m, and
> then apply the
> TopoGeometry approach above.
>> So the error was right about there being another edge attached to the
>> node:
>>  ERROR:  SQL/MM Spatial exception - other edges connected (3912)
>> I'm guessing 3912 and 3908 are the two parallel edges in the picture
>> you attached: https://dl.dropboxusercontent.com/u/5196336/example1.bmp
> You're right, they are the two parallel edges. And it's the same for most
> of
> the some 650 slivers I have.
>> Again, QGIS may help you getting more info out of the visual, enable
>> the DBManager core plugin, select your topology schema and select
>> Schema->TopoViewer from the menu.
> I didn't know about the TopoViewer tool. I was importing the topology
> tables (node, edge, face)
> like any other PG geometry tables. Will explore with this new tool.
>> It's probably easier to clean up nodes for an areal topology than to
>> clean up faces. With my QGIS plugin (PostGIS Topology Editor) you can
>> select all nodes and click on a button which will drop all the ones
>> that are safe to drop.
> You're right! I'll create my topology again but with the 2.0 m tolerance,
> then run
> my function for getting rid of nodes that are not at intersections and
> finally,
> I will use the approach you suggested of working with the TopoGeometry
> objects and the
> relation table to eliminate the remaining slivers.
> Will keep you posted on how it goes. Again, I really appreciate your help.
> Thanks.
> Guillaume.

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