Bridge elevations should interpolate elevations at the ends

[graue]

Crossing Geneva over 280, the router thinks you're descending and ascending extremely steep hills:

Stretches of road with bridge=* should perhaps treat the elevation as linearly interpolated between the ends.

[karussell]

Should work already: https://github.com/graphhopper/graphhopper/blob/master/core/src/main/java/com/graphhopper/reader/dem/ElevationInterpolator.java

[graue]

Thanks, Peter! Though it apparently doesn't currently work in our fork, based on those grade numbers that we see, but it's helpful to have that pointer on what code we should look at.

[abhumbla]

it's very possible we broke something when we did all that elevation penalty work a while ago

[karussell]

The problem could be the time when you grab the elevation. If you need this already while the OSM import then it is too early as the interpolation is done afterwards in postImportOSM.

[abhumbla]

that's probably it. we now store the calculated grade on the edge at graph creation time so that we can refer to it in the flag encoder step when assigning weights

we use both grade and infrastructure quality to determine the penalty multiplier for each edge. this means grade is double counted, since we also reduce the speed (and increase the time) for high grades. but this seems to be warranted as it's more accurately capturing the effort cost of steep blocks. the relevant PR is #101 . maybe there was a better way to do this, but this works

the router now generally understands hilly San Francisco (here it is correctly navigating the Wiggle around Buena Vista park

the bus provides a nice lift with a more direct route

[abhumbla]

of course, you know this much better than us! so any suggestions are very welcome :)