Multipolygon: handling of closed touching inner rings

[simon04]

According to https://wiki.openstreetmap.org/wiki/Relation:multipolygon#Touching_inner_rings, touching inner rings may be used if the ways are closed.

Osmium, however, fails on such multipolygons, e.g., http://www.openstreetmap.org/browse/relation/1517038:

Building multipolygon based on relation 1517038 failed: invalid ring

[joto]

"fails on such multipolygons" is a bit of a generalization. Osmium works fine in all other "touching inner rings" cases that I have seen. But you are right, in this case it doesn't work. Geometry of the multipolygon looks fine, so this should work. So this is a bug that needs looking into.

[simon04]

"fails on such multipolygons" is a bit of a generalization.

It wasn't meant as an insult of Osmium nor as overly generalization, but I experienced this behaviour on several multipolygons of this type in my region … :-)

[joto]

Can you give some more examples? Maybe we can figure out what they have in common and this way figure out where the problem might be.

[simon04]

Those are the errors reported by the OSM Inspector as Multipolygon/Touching inner rings. All examples I've seen have at least two inner rings with a common way segment.