[OSRM-talk] 'penalty' for snapping

Daniel Patterson daniel at mapbox.com
Tue Apr 19 20:44:40 UTC 2016

Hi Steve,

  I was thinking about exactly this just the other day when considering

  What I came up with was roughly:

    Find N nearest neighbours, and calculate the walking duration to each
    Insert all neighbours into the search heap, and set the initial cost to
the walk duration
    Route as normal, but include the walk duration in the total time at the

  The question is, how big do we make N, and how do we determine the
overland speed?  Overland speed I suppose could be a profile parameter, and
it feels like walking speed would usually be the most appropriate thing.
But I'm not sure how many possible start points we should reasonably
consider.  Everything within a radius?  Closest N points?


On Tue, Apr 19, 2016 at 12:39 PM, Steven M. Ottens <steven at minst.net> wrote:

> Hi all,
> I am working on a tool that will calculate the travel time from villages
> to for instance the nearest hospital for rural accessibility analysis. So
> far I have build a tool which will calculate this for 215.000 villages in a
> few minutes, thanks to the help of Daniel P. However I realized that not
> all villages are on a road, actually quite a few are at least an hour walk
> from the nearest drivable road see:
> http://stvno.github.io/img/OSRM-snapping.png
> The villages are typically connected to the roads by informal trails,
> which I do not have as a road network. So I was wondering if it would be
> possible to add a basic penalty to the distance of the point to the nearest
> road.
> I am aware that the nearest service will provide me with the distance:
> https://github.com/Project-OSRM/osrm-backend/wiki/New-Server-api#service-nearest
> but before I am going to calculate the extra traveltime for each village, I
> was wondering if it is possible to integrate this with an osrm.table
> request. I am aware this opens quite a can of worms: if there is a penalty
> to snapping, it might be worth it to snap to a road which is further away,
> but in the end quicker to get to the destination. But for the moment I'm
> happy with just the added traveltime for nearest road snapping.
> Any suggestions on how to handle this?
> Steven
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