Mismatch between the center of the isochrone and requested location


#1

Hi everyone,

First, I would like to thank a lot the OpenRouteService Team for providing this amazing service :slight_smile: !

I have noticed that the center of the isochrone/isodistance returned by OpenRouteService is very often located at different WGS84 coordinates than the requested location.

Here are a few examples:

Center of the returned isochrone: 43.27163 / 6.578473
Requested Latitude / Longitude: 43.270307/6.576772
Type of isochrone: distance-500meters-foot-walking
Distance between the two points: Around 200meters

Center of the returned isochrone: 47.659557/1.942097
Requested Latitude / Longitude: 47.663106/1.929938
Type of isochrone: distance-500meters-foot-walking
Distance between the two points: Almost 1km

Center of the returned isochrone: 43.533575/1.402716
Requested Latitude / Longitude: 43.5336104/1.4031718
Type of isochrone: time-30minutes-driving-car
Distance between the two points: Around 37meters

Why is it the case ?

Thanks in advance and keep up the great work,

M


#2

Hi @MattL and welcome,

the reason is on purpose: the isochrone center is snapped to the “road” which is why the returned center is mostly a little different. In the response you can find the requested center also if you need it.

Cheers, Tim


#3

Hi @timothy,

Thanks a lot for your quick answer. If I understand correctly the isochroning process of ORS, it works as follows:
(1) ORS locates the nearest point from the requested point that belongs to a road suited to the requested profile (driving, walking…)
(2) From this new point, ORS draws the isochrone

Is that correct ? In step 1, does ORS take into account the requested profile ?

And last question : which road network does ORS use to draw the isochrone ? At which frequency is the source network being updated ?

Thanks again,

M


#4

@MattL both correct 1) & 2)

It uses OpenStreetMap data only and is updated every 2-4 weeks -

Cheers, Tim