[PostGIS] #5606: Valid polygons in SQL Server are invalid in POSTGIS

[PostGIS]

#5606: Valid polygons in SQL Server are invalid in POSTGIS
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  Reporter:  samnull10  |      Owner:  pramsey
      Type:  defect     |     Status:  new
  Priority:  high       |  Milestone:  PostGIS 3.4.1
 Component:  postgis    |    Version:  3.4.x
Resolution:             |   Keywords:
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Comment (by mdavis):

 All these cases are invalid because they are polygons with a single ring
 that self-touches when evaluated ''in a planar coordinate system''
 (`geometry`).

 It may be that SQL Server is evaluating these for validity on the WGS84
 geodetic spheroid, where perhaps the self-touches do not occur.  Or
 possibly it uses a tolerance value in some way.  AFAIK SQL Server does not
 allow "self-touching inverted rings" (i.e. it follows the OGC polygon
 model, not the ESRI polygon model).  But possibly that restriction has
 been relaxed?

 In any case, these are invalid in the PostGIS geometry model, so should be
 fixed using `ST_MakeValid` before being used in functions.
-- 
Ticket URL: <https://trac.osgeo.org/postgis/ticket/5606#comment:3>
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