[OSM-talk] Turn restrictions ambiguity
teemu.koskinen at mbnet.fi
Thu Apr 23 20:17:31 BST 2009
On Thu, 23 Apr 2009 21:34:05 +0300, SteveC <steve at asklater.com> wrote:
> I don't see a clear explanation as to why there is ambiguity if you
> don't do turn restrictions at the end of ways on the wiki. There is
> some stuff in the talk page
> Anyone care to provide an explanation?
> The reason I ask is that I've come across some roads where there is a
> restriction every other turn in both directions... and splitting a
> mile long road in to 30 pieces seems nuts. As a follow up, I can
> guess, but what will the renderer do in that situation? I'm guessing
> mapnik will give up trying to put 30 names on a one mile road and
> won't notice they're the same name?
If both from and to ways continue after the via point and neither is
one-way, there's two possible ways to interpret it: the restriction could
apply when coming from either of the ends of the from-way. This of course
doesn't matter if there is similar restriction coming from both
directions, but that's not nearly always the case. And even if there is
symmetry in the real life restrictions, it's not appropriate in my opinion
to map those with just one restriction.
About the splitting, it's already necessary to split the way if some other
property changes, eg. speed limit or number of lanes (which does change
more often in some places than there are restrictions), it's either the
renderer's job to figure out that the pieces belong together or we could
use some relation to group the pieces together but that too would require
support from the renderers.
Regards Teemu Koskinen
More information about the talk