[Routing] parsing roundabouts

[marcus.wolschon at googlemail.com]

Hello everyone.

I'm thinking about how to add support for
proper driving-instructions for roundabouts
to Traveling Salesman.
"In 200m enter the roundabout! Then take the second exit!"

There are 2 issues:

1 How to determine if the roundabout is drawn clock-wise
  or counter-clock-wise.
2 How to determine if we drive on the left or right road-side.
3 Did anyone else on this list implement support for roundabouts already?


1) I guess the best way for this it so calculate the cross-product
   and see if it's >0?
   (http://debian.fmi.uni-sofia.bg/~sergei/cgsr/docs/clockwise.htm)
   Can we assume that all roundabouts are drawn convex? Even deformed
   ones? (I have one roundabout in my home-town that is quite an elipsis.
   Maybe there are more extreme cases.)

2) Does anyone have a list of all countries where we drive on the
   left side?
   For GB a bounding-box would be simple. How is the state of the
   border-polygon in OSM for the other countries?


Marcus