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Strange routing of u-turns

7 Jun 2017
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The routing can do strange things if you want to, say, go up a side road for a cafe stop then retrace your steps back to the main route. Here is an example - I was trying to plot a GPS route for an organised ride this coming weekend.

Here is the "direct" route for a small section - the points are on the route being used into & out of the village.

If I try to add in the location of where the organisers have kindly laid on refreshments, at point 1, I get

Instead of taking me straight back to the original route it takes me some way further on, then onto a footpath to another road, does a u-turn there, back along the footpath before finally putting me back on the road and past where I just stopped.

I've noticed previously that trying to add in a small detour the route will sometimes take me up to a mile further up the road before doing the turn-around. (It is usually at this sort of point I just use the route for reference & manually replot it on to get a usable GPS file :-S)


Wed 7 Jun 2017, 15:45

The core routing engine (OSRM) disallows U-turns at via points by default. It is possible to get it to allow them, but doing that universally would make dragging the route harder in normal circumstances – much of the time it’d just create a ‘spur’.

So I guess the trick would be to add an option for “allow U-turns at this via point”. I’ll put it on the list – won’t be immediate but should be doable, and it dovetails with something else I'm planning to do.

Thu 8 Jun 2017, 20:29

That sounds great. Thanks!