Trying to understand why one LinearRing does not contain another

[jrnorth]

Hi all,

I've created a small sample repository that demonstrates my problem: https://github.com/jrnorth/jts-test

I have one 'exterior' LinearRing and one 'interior' LinearRing, and I am trying to understand why JTS says the exterior does not contain the interior (using the contains() method).

I've been using https://arthur-e.github.io/Wicket/sandbox-gmaps3.html to plot my rings on a map, and all the points of the interior are inside the exterior.

[dr-jts]

LinearRings are lines, not areas. So their interior consists of the points in the line, but does not include the area they enclose.

If you turn the exterior ring into a Polygon then the contains() test will work as you are expecting.

[jrnorth]

Thanks. So when would contains() return true for two LinearRings? Would they have to have exactly the same points?

[dr-jts]

Thanks. So when would contains() return true for two LinearRings? Would they have to have exactly the same points?

Yes, or if one ring is a subset of the other (topologically).