[OSRM-talk] "nearest suitable road segment" Was: Helgoland in St. Peter-Ording

Daniel Patterson daniel at mapbox.com
Wed Aug 17 20:26:44 UTC 2016

Hi Florian,

  This sounds like more of a geocoding problem than a routing problem.  OSRM itself doesn't know anything about addresses, it only works with coordinates and road geometry.  All OSRM has internally are street names, not street numbers or place names.

  In order to route from "Münsterstraße 15a", it must first be turned into a coordinate.  On the OSM website, the Nominatim service is used to do this.  Once the web interface has a coordinate for an address, it gives that to OSRM for routing.  OSRM snaps that point to the nearest road, then finds a route.

  You might want to do some digging into how Nominatim determines address coordinates, and possibly consider adding `building=entrance` nodes - this (I think) will cause Nominatim to return a more specific location rather than the centroid of the building/airport polygon.

  Geocoding is a related, but separate problem.  There are a bunch of tags in OSM that are used by Nominatim, including `building=entrace` on nodes, `addr:*` on ways/nodes/relations/areas, etc.  Determining the best coordinate to return to the user is itself a difficult problem.


> On Aug 17, 2016, at 1:06 PM, Florian Lohoff <f at zz.de> wrote:
> Daniel,
> On Wed, Aug 17, 2016 at 11:56:40AM -0700, Daniel Patterson wrote:
>> Florian,
>>  OSRM simply snaps the coordinate to the nearest road.  If the back
>>  yard "streets" are part of the main road network (i.e. not
>>  `access=private`), then it's simply the closest road segment to your
>>  start point that gets used.  Nominated is returning the building
>>  centroid for Münsterstraße 15a, so it's snapping to the parking lot
>>  roads.
>>  I'm not really sure what we could change in OSRM to fix this -
>>  perhaps excluding `service=parking_aisle` road segments might have
>>  the general effect?  Maybe in this case there should be a
>>  `service=driveway` on the entrance to the parking lot, and we should
>>  exclude driveways?
> Still there are cases where you have a House whose Address is on
> Street A and nearest to Street A but still only accessible through 
> Street B - I have 1-2 of those cases - i cant solve them right now.
> And putting tags on service road to try to turn routing systems
> away from them although the tagging does not reflect reality is broken.
> I'd wish to have a tagging scheme (probably by relation) to manually
> hint/set a point on the routeable network to use for navigation.
> If you wish to reach A you need to go to B
> Currently i try to workaround all those problems by moving
> service/driveways around until the driveway is more close than the other
> street and stuff like that. This is all broken and does not really
> match reality.
> And the case is also for POIs - If you want to navigate to a Zoo or Park 
> you'll find the "area" for the Zoo - not necessary the Entrance. 1) One
> might to put in a relation - "If you want to go to Zoo A you need to
> navigate to Entrance B". POIs built with areas have a problematic
> potential here.
> Flo
> 1) I tried once to navigate to Airport PAD (Paderborn) and endet up in
> the woods on the opposite side of the runway at the fence. It was the
> nearest point on the road network to the POI.
> -- 
> Florian Lohoff                                                 f at zz.de
>             UTF-8 Test: The 🐈 ran after a 🐁, but the 🐁 ran away
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