[PostGIS] #5868: Add Function to Detect Valid Polygons with Point Touching Rings

[PostGIS]

#5868: Add Function to Detect Valid Polygons with Point Touching Rings
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  Reporter:  gravitystorm  |      Owner:  pramsey
      Type:  defect        |     Status:  new
  Priority:  medium        |  Milestone:  PostGIS 3.5.3
 Component:  postgis       |    Version:  3.4.x
Resolution:                |   Keywords:
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Comment (by mdavis):

 Can you just use `ST_IsValid`? It will report `false` for self-touching
 rings.

 There is also a flag on `ST_IsValid` which allows polygons with self-
 touching rings to be considered valid.  You could combine this with the
 default `ST_Valid` to test whether a geometry is valid but with a self-
 touch (i.e. to identify geometries to be ignored or fixed):
 {{{
 SELECT (NOT ST_IsValid(geom)) AND ST_IsValid(geom, 1) AS
 is_valid_with_selftouch
 FROM ST_GeomFromText('POLYGON ((5 9, 9 1, 1 1, 5 6, 3 2, 5 2, 5 9))') AS
 t(geom);


 is_valid_with_selftouch
 ---------------------
 t
 }}}
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Ticket URL: <https://trac.osgeo.org/postgis/ticket/5868#comment:2>
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