[OSM-talk] Divided/Non-Divided Intersection

Dylan Semler dylan.semler at gmail.com
Thu Jul 22 16:25:41 BST 2010


On Thu, Jul 22, 2010 at 11:08 AM, Dylan Semler <dylan.semler at gmail.com>wrote:

>
>
> On Thu, Jul 22, 2010 at 5:57 AM, andrzej zaborowski <balrogg at gmail.com>wrote:
>
>> On 11 July 2010 10:23, Maarten Deen <mdeen at xs4all.nl> wrote:
>> > If you have a layout like this (use a fixed-width font):
>> >
>> >     | |
>> > A----+-+
>> >     | +----B
>> > C----+-+
>> >     | |
>> >
>> > And you want to go from B to A, why would routing software say "go
>> straight
>> > on" and not "go right, then go left"?
>>
>> My opinion is that it is a routing software issue after all.  When a
>> road segment is just about 5m long, the software should just skip it
>> in the driving directions and look at the angle between the A and the
>> B roads.  It can go as far as doing what Alan said, i.e. join all of
>> the nodes in a junction (a concentration of nodes where roads meet)
>> into a single node, possibly in the preprocessing phase.  I don't
>> agree that this should be done in OSM data, it will prevent more
>> clever routing direction being given when more clever routing software
>> is written (e.g. software telling your car where to stop to wait for
>> green light, which lane to take etc).
>>
>> The lengths need to be chosen carefully because in e.g. pedestrian
>> routing, 5m may be significant (say you're looking for an exit from a
>> maze).  A car can't even make turns that tight, and you're interested
>> in the bigger picture when you reach a junction, the routing is not
>> clever enough to get you through a junction anyway.
>>
>> >
>> > And option is to map it like this:
>> >     | |
>> > A----+ |
>> >     |\|
>> >     | +----B
>> >     |/|
>> > C----+ |
>> >     | |
>>
>>
> How about grouping all of the nodes of the intersection into a relation?
>  Routing software can treat it as a single intersection and the map can
> reflect how the roads are actually laid.
>

Actually, I see there already is a proposed feature to use relations to
handle routing instructions for complicated turns[1]

[1]http://wiki.openstreetmap.org/wiki/Relations/Proposed/Turn_hints
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