better validation of roundabouts

[sommerluk]

Please provide a better check/validation of roundabouts.

1.) A so-called “hamburger roundabout”, in spite of its name, isn’t a roundabout. By defination, a roundabout is where the circle traffic has priority and where you have a non-transversable island. So it would be great if JOSM could recognize when doing the check before uploading some data. JOSM could check

– that all the ways that are connected to a way with roundabout=yes are
connected at the same side of the roundabout
– and that they end at the roundabout and do not cross the roundabout
– otherwise (=if you have a so-called “hamburger roundabout” instead of a
real roundabout) the tag junction=roundabout must be removed.

2.) Check if the way(s) of the roundabout form really a circle. The wiki recommands to make roundabouts as one single – closed – way. In OSM there are many cases where peoples split the roundabout in various ways. But maybe JOSM could check at least, if the roundabout (also when it is composed by various ways) has the form of a circle.