[GraphHopper] Issues detecting driving paths along one way streets?

[Rodney O'Donnell]

Thanks Peter,

That makes sense, I didn't think to modify the graph.
We are using a planet graph, so we do have the islands issue, but finding a
sensible threshold should (hopefully!) be straightforward.

Cheers!

Rod.


On 14 May 2014 20:03, Peter K <peathal at yahoo.de> wrote:

>  Hey Rod,
>
> The problem you have is relative easy to fix if don't mind 100% accuracy
> (and if you use only one vehicle per graph it is rather easy): in a
> preprocessing stage on import you remove unreachable points. As you already
> found the problem is mainly due to oneways. So, if you traverse the graph
> via an outgoing EdgeExplorer and remove all unvisited nodes then other
> nearby points will be used instead (the same you have to do with an
> 'ingoing' explorer).
>
> This works rather well for smaller areas - for the world wide case you
> have to handle that there are many valid 'islands' and you have to decide
> when to remove them. But probably you can use a fixed parameter of
> subnetwork size like we already do in PrepareRoutingSubnetworks. See also
> issue 86 for more details especially in the case of multiple vehicles per
> graph (if you use CH this does not apply):
> https://github.com/graphhopper/graphhopper/issues/86
>
> For our API we think of a more accurate solution where we can keep the
> oneways and make this "lookup-nearby" behaviour default but configurable.
> E.g. sometimes it would be important to know the problematic cases like for
> finding map issues.
>
> Regards,
> Peter.
>
>
>   Hi,
>
>  Congrats on releasing v0.3!
>
>  I'm looking at replacing the car/foot routing component we use at
> rome2rio.com with the graphhopper web API.
>  It looks great so far, however graphhopper is unable to find a route for
> 4-5% of our queries.
>
> A lot of these failures involve one way streets ... particularly around
> trains stations and airports (which we see a lot of).
>  I've hacked up a change which naively tries routing from positions near
> the origin/destination/waypoint, which works ok, but isn't particularly
> elegant.
>
> I'm happy to trade off some accuracy with the origin/destination points to
> increase the "recall" of finding routes.
> Treating one-way roads as two way could also work for our use case.
> Any thought on the best way to achieve this in graphhopper?
>
>
>  Examples:
>
> http://graphhopper.com/maps/?point=45.461820,9.278362&point=45.48472,9.236413# No route
>
>
> http://graphhopper.com/maps/?point=45.461884,9.276520&point=45.48472,9.236413
> # Works fine
>
>
>
>
> http://graphhopper.com/maps/?point=40.734454,-74.163026&point=40.73722,-74.17129
> # No route
>
>
> http://graphhopper.com/maps/?point=40.734519,-74.16294&point=40.73722,-74.17129
> # Works
>
>
>  Cheers!
>
>  Rod.
>
>
>
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