[OSM-talk] Turn restrictions ambiguity

Andy Allan gravitystorm at gmail.com
Fri Apr 24 11:23:38 BST 2009


On Fri, Apr 24, 2009 at 10:13 AM, kaerast <kaerast at qvox.org> wrote:

> Why do we need to know which way has priority?  Yes it is nice to know
> some times, but no other maps show this and it just isn't necessary.  It
> tends to be "slower" roads which you need to give way on, and these are
> already given a lower priority in routing algorithms.

Imagine a grid of residential streets, and you're going from one
corner to the opposite corner. There are two long-axis roads, one of
which has priority at every intersection, the other parallel option
has a give-way at every intersection. It's pretty obvious that you
want to know priority so the routing algorithm picks the correct
street. Classification and distance are otherwise identical.

 |   |   |   |
-S-------------
 |   |   |   |
-|---|---|---F-
 |   |   |   |

Also, if you're barrelling through the countryside it's nice to be
told what to do at junctions. But not every time there's a little side
road. So again knowing how long this road has priority ("continue for
3 miles") or not ("in 100 yards, cross the junction") is important.

Cheers,
Andy




More information about the talk mailing list