IsSimple=true for self-touching polygon

[jratike80]

Issue was found from PostGIS 2.3 with these tests:

select ST_IsValid(
ST_GeomFromText(
'POLYGON (( 320 620, 460 620, 460 500, 320 620, 320 500, 180 500, 180 
620, 320 620 ))'
     ));
Result: "f".

select ST_IsValidReason(
  ST_GeomFromText(
  'POLYGON (( 320 620, 460 620, 460 500, 320 620, 320 500, 180 500, 180 
620, 320 620 ))'
      ));
Result: "Ring Self-intersection[320 620]"

select ST_IsSimple(
  ST_GeomFromText(
  'POLYGON (( 320 620, 460 620, 460 500, 320 620, 320 500, 180 500, 180 
620, 320 620 ))'
      ));
Result: "t"

JTS IsSimpleOp used to return trivially "true" for all polygons but since SVN revision 662 Sept 2012 self-intersecting rings are tested. GEOS should do the same.

See discussion in thread ​https://lists.osgeo.org/pipermail/postgis-users/2017-May/042102.html

[pramsey]

This will be fixed in 3.10 ​https://github.com/libgeos/geos/commit/71369610d46d7962bdff096d1bb1346006d9b7cf