[geos-devel] Polygon simplicity and validity

Fri Sep 7 12:06:27 PDT 2012

The OGC SFS specifies that valid polygons are simple by definition, 
presumably because valid polygons cannot contain any 
self-intersections.  Because of this, JTS/GEOS simply returns true for 
Polygon.isSimple(), without attempting any inspection of the actual 
linework.  isValid can be used to detect self-intersections.

On 8/29/2012 11:19 AM, Sean Gillies wrote:
> Is simplicity meaningful for polygons or only for lines? Here's a
> single ring bowtie that GEOS 3.3.0 reports as invalid but simple:
>
> POLYGON ((39.1451330299999967 23.7510081600000014, 97.0537220899999937
> 40.5455008799999987, 105.2652701399999984 48.1330221300000005,
> 100.9175268500000016 58.4333681499999997, 71.5608144800000048
> 83.5511480100000057, 60.7118916800000008 86.2531609899999978,
> 62.0046980799999972 75.1478175999999962, 83.1631000699999987
> 42.8207167300000009, 92.8230586199999976 37.1917558199999974,
> 95.9940112900000031 26.4705124599999984, 106.2205448200000006
> 15.5197519199999991, 39.1451330299999967 23.7510081600000014))
>
> https://github.com/Toblerity/Shapely/issues/16#issuecomment-8116396
>