Strange routes persist in 8 - possible reasons?

Open Source Routing Engine
1

Hi, Using version 7, I was having strange routes, so I tried version 8. But I still have weird routes. For example: the route here with all the default settings…

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using Google maps, the route looks like this
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Looks like many others also have this problem (e.g., Strange routes at the border of dataset - #7 by Geoman, Strange routing - indirect route and more). What are the reasons that could be behind the weird routes? Sometimes, OSM tags show one-way which restrict direct route. What are the other possible reasons for these routes? How can we explain such routes? And how to solve/avoid these- any generic solution?

2

Your destination isn’t directly reachable according to OSM:

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The road around the facility is tagged with access=no and has additional barrier=gate nodes.

GraphHopper picks the nearest routable street which happens to be the nearby motorway:

GH yields a sensible route with a slightly modified destination:

3

@karussell it would be nice if the snapping would be a bit smarter in that regard.

Instead of simply blocking trunk/motorway like we do it in the SnapPreventionEdgeFilter we could apply a factor to the normDist depending on the EdgeIteratorState.

e.g 2 * normedDist for trunk/motorway

Snap findClosest(double lat, double lon, EdgeFilter edgeFilter, EdgePriority edgePriority);

public interface EdgePriority {
    EdgePriority DEFAULT_PRIORITY = edgeState -> 1d;

    double priority(EdgeIteratorState edgeState);
}
4

Oh… thanks for the explanation.

5

Why GH blocks motorway in SnapPreventionEdgeFilter? What does it actually do?

6

Not by default. But you can tell it to:

https://docs.graphhopper.com/#operation/getRoute!in=query&path=snap_prevention&t=request

7

At the moment I don’t think a “smart” snapping would be an improvement. We have point_hints and snap_preventions for the /route endpoint, which should solve mostly all issues in this regard. For the public GraphHopper Maps I would keep it as it is (maybe in the future we add point_hints) but you can configure it and we e.g. already avoid ferries.