On Thu, Jul 23, 2009 at 11:22 AM, Steve Hill<st...@nexusuk.org> wrote: > 1. It is one way in the appropriate direction (clockwise in the UK) > 2. All the roads leave/join the outside of the loop (*) > 3. It generally isn't very built-up in the middle (**) > 4. It has a reasonably circular shape (***) > 5. It is signposted as such
Fwiw even (1) isn't necessarily true. The Magic Roundabout famously has a counter-clockwise loop in the centre. And there are other such roundabouts where the central loop isn't even one-way. I do think (5) is kind of important. Critically there are special laws dictating right-of-way and rules for navigating roundabouts which aren't necessarily the same as for a simple loop of one-way roads. (One would hope they're consistent but it's not 100% true.) I experimented once with a road that had a bunch of inconsequential bridges I wanted to mark with instead of breaking it up, adding extra ways which re-used the points for the bridges. Those extra ways were just marked "bridge=yes". I think this actually rendered correctly though I didn't way for all the renderers to update before putting it back to normal. I have to say I find it awfully annoying to edit ways in an area where every path is broken up into ten million single segment paths because there are bridges, tunnels, surface changes, hazards, etc. It would be awfully nice to have one reasonably big way and then shorter ways marking the exceptions. One problem with breaking them up and then detecting roundabouts heuristically is that it will become awfully difficult to distinguish double and triple roundabouts, let alone hamburger roundabouts and more, shall we say, creative roundabouts. -- greg http://mit.edu/~gsstark/resume.pdf _______________________________________________ Talk-GB mailing list Talk-GB@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-gb
