[postgis-users] Self-intersecting polygon gives ST_IsSimple=true

[Sandro Santilli]

On Fri, May 05, 2017 at 10:28:03AM +0300, Jukka Rahkonen wrote:

> select ST_IsSimple(
>  ST_GeomFromText(
>  'POLYGON (( 320 620, 460 620, 460 500, 320 620, 320 500, 180 500, 180 620,
> 320 620 ))'
>      ));
> Result: "t"
> 
> 
> Shouldn't ST_IsSimple return "false"? OpenJUMP reports that this polygon is
> "Not Simple Geometry"
> I tried PostGIS versions 2.1 and 2.3, both versions give "true".

Polygons are simple by definition, see here:
https://locationtech.github.io/jts/javadoc/org/locationtech/jts/operation/IsSimpleOp.html

 " this means that isSimple cannot be used to test for (invalid)
   self-intersections in Polygons "

--strk;