When generating isochrones near Thames some edges are not properly included in the generated isochrone polygon. Initially i used the car profile and got the following result.
Then I thought that this is happening as the paths at the edges are foot paths so cars are not allowed. So i changed the profile to be “foot walking” but I still get the edges excluded (see here)
For comparison it seems the mapbox isochrone service is fairly good at that.
So it seems that nodes at the edges are excluded for some reason. Is there any kind of configuration that could fix that?
this has to do with how the polygon is being created from the actually reachable points on the road network.
This issue has a brief explanation.
This will even lead to different isochrones if different distances with intervals are requested, that result in the same “partial” isochrones. In the following, a 1km, the 1km of a 2km and the 1km of a 4 km isochrone is shown:
I have opened an issue about this, feel free to follow the discussion there.
this is indeed a problem with how the polygon geometries are being calculated, not with the actually reachable points. Unfortunately, this cannot be fixed without allowing dangerous amounts of load to our servers.
Sometime down the line, this will get fixed by switching to a different algorithm, but this is unfortunately not something that will happen soon.
Until then, I feel like this is something you’ll have to fix by issuing smaller queries and stitching together the resulting polygons.