[Qgis-developer] Valid or invalid geom in PostGIS?

[Mark Johnson]

This is a GEOS error that is being reported
- your Geometry has a Topological error

> 2017-01-16T11:34:52   1       NOTA: NOTICE:  Self-intersection at or near
> point
> > 619746.32941695023 4869530.4882389866
> > 2017-01-16T11:34:52   1       NOTA: NOTICE:  IllegalArgumentException:
> Invalid
> > number of points in LinearRing found 3 - must be 0 or >= 4


Look for  'ST_SelfIntersections(..)' in PostGis
- it will show the points that cause such errors
-- not sure of PostGis has this command

The first error
- is often a POLYGON that has been created from single LINESTRINGs
-- 1 or more of these LINESTRINGs have been included more than once
--- remove the double LINESTRINGs to correct
---> will start at the given point: 619746.32941695023 4869530.4882389866

The error message will only show the first POINT, if there are more than
one you should look for the next.

The second error means that the ExteriorRing of the POLYGON only has 3
POINTs
- 4 are required to be Topologicaly correct
SELECT ST_NumPoints(ST_ExteriorRing(geometry))
- should return 3 in this case, but should be 4 at least

Certain functions, that use GEOS, will not bring correct results
- when Topological error exists
-- and should be corrected

Mark Johnson
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