[Routing] parsing roundabouts

[Marcus Wolschon]

On Mon, 2 Mar 2009 09:50:12 +0100, Guenther Meyer <d.s.e at sordidmusic.com>
wrote:
> Am Montag 02 März 2009 schrieb 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.
> 
> is this relevant?

Yes, it is.
Not for routing but for the driving-instructions.
You need to know the ordering to determine if you count the exits
in ascending or descending waynode-order to get the "second" in
"Then take the second exit!".
..unless I'm missing someting.

> if the routing is implemented properly, the route shouldn't walk into the

> wrong direction (roundabouts are oneway).
> when the route has been calculated, you just count the number of exits
from
> 
> entering until leaving, then you have the number of the needed exit.

mmh... can I actually assume all roundabouts to be drawn in the correct
direction?
This would indeed make my thinking obsolete and this trivial to implement.

Marcus