joto
Multipolygon: handling of closed touching inner rings
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
"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.
"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 … :-)
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.
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.