[OSRM-talk] calculation of jump distances

[Daniel Patterson]

Hi Bryan,

  OSRM stores the road network in memory.  When you supply a coordinate to
start/finish a route, the first thing that happens is that the nearest
point on the road network is found.  Routing then happens from those
"snapped" points.

  If you've got big rural areas, and you're using large regional centroids,
then I suspect the snapping is starting or finishing your routes on roads
you don't expect.

  Several hundred KM is pretty weird though, unless your road network is
*really* sparse.  Do you have your coordinate the correct way around in
your requests?  The order should be <longitude>,<latitude> for every pair -
getting this wrong is often the source of really weird results.

  Try making a single request with `overview=full&geometries=geojson`, then
plot the full route geometry on http://geojson.io/ or something to see if
it even looks reasonable.

daniel

On Tue, Jan 16, 2018 at 1:43 PM, Sayer, Bryan <BSayer at s-3.com> wrote:

> Hi,
>
>
> We are calculating distances between an U.S. census tract centroid and
> hospitals. A tract averages about 4,000 people, but can vary in area.
> Obviously, the centroid is likely to not be on a street, and thus a jump
> distance has to be calculated to get to a street.
>
>
> Our question is what is the general algorithm for getting to the starting
> point? We definitely end up with some very large numbers (several hundred
> kilometers) on some jump distances, which seems incorrect.
>
>
> Bryan Sayer
>
> ****WARNING**** This information may be confidential. It is intended only
> for the addressee(s) identified above. If you are not the addressee(s), or
> an employee or agent of the addressee(s), please note that any
> dissemination, distribution, or copying of this communication is strictly
> prohibited. If you have received this information in error, please destroy
> the information and notify the sender of the error. Thank you.
>
> _______________________________________________
> OSRM-talk mailing list
> OSRM-talk at openstreetmap.org
> https://lists.openstreetmap.org/listinfo/osrm-talk
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openstreetmap.org/pipermail/osrm-talk/attachments/20180116/7595240f/attachment.html>