[OSM-talk] Obvious turn restrictions

Anthony osm at inbox.org
Fri Jul 8 22:24:23 BST 2011


On Fri, Jul 8, 2011 at 1:04 PM, Ed Avis <eda at waniasset.com> wrote:
> Nathan Edgars II <neroute2 <at> gmail.com> writes:
>
>>http://www.openstreetmap.org/browse/relation/1591319/history
>>North Elk Vale has been split into three ways with four relations on
>>each side of the overpass. And for what? To prevent a router from
>>telling you to turn right in the wrong part of the intersection?
>
> I think the essential problem is that you need to split a way into several bits
> to add these restrictions.  It would be better if the schema for restrictions
> didn't require you to break ways in two.  For example it might take a 'from' and
> 'to' way, an intersection node and an optional direction such as 'northbound'
> to disambiguate.  That is slightly unclean in a strict geodata sense but
> perhaps better than the death by a thousand cuts we currently suffer when
> modelling complex junctions with the need to split a way at each point there is
> a junction node with some kind of restriction.
>
> That's just one idea.  Another would be a 'lightweight' turn restriction schema,
> supplementing but not replacing the existing one, where properties can be tagged
> on the node itself ('no_turn', 'no_right_turn_northbound') avoiding the need
> for relations at all.
>
> Or perhaps editors just need better support for editing ways as a group to cope
> with the reality that things tend to get chopped into smaller and smaller bits
> as the map improves.

I think the latter is probably the most likely solution.  Something
like that using relations wouldn't be too hard to do.

Also it's a solution which solves a lot of other problems, as there
are *lots* of reasons ways already get split (e.g. bridges), and lots
more to come as more information is added to the db (speed limits,
number of lanes, etc.).



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