The current potlach version is generating sometimes circles, that goes several times round.
In Potlatch you have to zoom to very high level to see this, so user are generating the circle and saving it, without any doubt in in correctness.
Here are all examples i have collected, the version before I (TheFive) edited it will be the wrong one.
I have asked some Mapper, how they produced that error, but what they told sounds totally normal.
“Draw a quadrate and use the make circular function”.
I have no really idea how to reproduce this error, as i do not use potlatch. My simple try did not work.
In the german forum the question occurred, simply to skip the make circular function from the front page.
This sounds plausible to me,
a) The nice drawed roundabouts are only relevant in high zoom mode.
b) the wrong mapped circles will result in crazy routings i believe, so this error is relevant in many use cases, not only in high zoom mode.
the problem potlatch generating here seems bigger to me than the win in high zoom mode in nice circles.
c) As Potlatch users arn’t able to see this error, they won’t go fixing it by themselves, all users have to wait, that this error is found by a mapper in OSMI.
If the roundabout is poorly drawn before using the circle tool, more than one circle will be produced, also after using the tool, if the streets connected to the roundabout are moved around the circle, then the circle tool used a second time, this will produce the bug. I only found that there was a problem in the last week when I started using OSM inspector. The bug can be seen in Potlatch if you no what to look for. The arrows will have multiple heads.
I’ve been running Gary68’s self intersecting ways script on parts of the UK and I’ve seen a number of these cropping up. I’ve fixed about 10 in the last day or two but a quick scan of a couple of the reports for other parts of the UK suggest there are more out there. At least I know where they are coming from now.
After playing around I can consistently reproduce on a couple of roundabouts so I’ve added some information to Trac (first time on Trac so I hope it is right). Broadly it looks to me if you have a roundabout with a node that is incorrectly placed such that the roundabout goes back on itself then multiple circles are created.
Going back on itself seems to depend on latitude / longitude point of view, so moving a node sufficiently out of the initial “circle” means that improving the circle causes potlatch to draw multiple circles.
I’d guess it initially goes wrong because a node is accidentally dragged to the wrong place in the initial roundabout. A user then clicks circle to fix this and get everything back into a circle (seems a logical thing to do to me) which results in something that looks better but is actually worse.