[Tagging] The direction=* tag

Daniel Hofmann hofmann at mapbox.com
Fri Mar 17 14:38:19 UTC 2017


On the routing engine side these tags will be translated to turn penalties
for specific turns, so the matching equivalent would probably be
from,via,to relations. Which is not a feasible modelling in OSM
realistically speaking. Simple stop signs could go on ways, but fail to
capture more complex situations.

The problem with traffic lights specifically is their interconnectivity:
you don't want to add turn penalties multiple times if traffic lights are
connected. But you can't tell. This is a bit off-topic, feel free to
cross-post to the osrm-talk or routing mailing list, or open an issue in
osrm-backend.

On Fri, Mar 17, 2017 at 3:29 PM, Tod Fitch <tod at fitchdesign.com> wrote:

> From a data consumer point of view, what type of tagging would be
> reasonable to indicate the, for lack of a better work, direction of travel
> a stop, give way or traffic light has effect?
>
> On Mar 17, 2017, at 3:54 AM, Daniel Hofmann <hofmann at mapbox.com> wrote:
>
> Jumping in here to give a perspective from a routing engine (OSRM,
> https://github.com/Project-OSRM/osrm-backend#open-source-routing-machine).
> We do not handle direction tags on nodes which indicate a property for a
> way or a turn at an intersection. The example with stop signs and give
> yield signs is spot on. Even worse is the assumption that routing engines
> can just infer the direction by checking the distance to the nearest
> intersection. This is in conflict with how parsing and creating a graph
> works.
>
> There is a similar problem with exit_to node tags, indicating the exit way
> destination - you can read about it here
>
> - https://www.openstreetmap.org/user/daniel-j-h/diary/40555 (en)
> - https://www.openstreetmap.org/user/daniel-j-h/diary/40554 (de)
>
> Cheers,
> Daniel J H
>
>
> On Fri, Mar 17, 2017 at 11:25 AM, Martin Koppenhoefer <
> dieterdreist at gmail.com> wrote:
>
>>
>> 2017-03-16 5:13 GMT+01:00 Tod Fitch <tod at fitchdesign.com>:
>>
>>> The “direction” tag [1] has different uses that seem disjoint to me.
>>>
>>>    1. To specify the orientation (compass point or degrees from north)
>>>    of an object (adit or cave entrance, etc.).
>>>
>>>
>> "orientation" would have been a better descriptor IMHO, but the crowd
>> uses this tag differently (see taginfo, also subtags like roof:orientation,
>> ...). Direction is working for me nonetheless.
>>
>>
>> 2. To specify direction (clockwise/counterclockwise) around a roundabout
>>> (not sure why this is needed as it should be apparent from local laws or
>>> specified with a “oneway=yes”).
>>
>>
>>
>> agree with you
>>
>>
>> 3. To indicate the direction (forward/backward) a stop or yield (give
>>> way) sign has effect along a way.
>>
>>
>>
>> broken. From time to time people are coming up with features to tag on
>> nodes that require (or seem to require) the information of a direction.
>> Taking the direction of a different object (e.g. here a way) doesn't seem a
>> healthy way to represent this. Ways might get split, might get reversed,
>> nodes might be (or become) part of several ways, etc. Either use a cardinal
>> direction or a short way stub or a relation, etc., but not "forward" or
>> "backward" tag values on a node, it simply doesn't make sense. Tags should
>> refer to the object they are tagged on.
>>
>>
>>
>>
>>> Oddly, that third use seems only for stop and yield signs but not for
>>> traffic signals where a “traffic_signals:direction=forward | backward”
>>> tag is to be used. However that seems to be the most used form [2].
>>> Apparently some have figured that if we have “traffic_signals:direction”
>>> there should be “stop:direction” [3] and “give_way:direction” [4] tags.
>>>
>>
>>
>> similarly broken
>>
>>
>> I would keep the variant 1 and discourage 2 and 3.
>>
>> Cheers,
>> Martin
>>
>>
>>
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>>
>>
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