[OSRM-talk] Route flapping / osrm-prepare adds randomness?

[Florian Lohoff]

Hi,

i am doing QA based on calculating routes. For this i have a defined
set of points (couple hundret) which i calc routes between. On length
change i get a notification by email that the route has changed.

Now i see routes which regularly flap between 2 different geometries and
lengths without the OSM data beeing changed so i started investigating.

The route flap happens irregular when osrm-prepare'ing the same
germany.osm.pbf over an over. I see route flaps on same OSM data input.

What i typically do (pseudo code) every 30-60 Minutes:

while true; do
	update-germany-file-with-osmupdate
	osrm-extract -p car.lua germany.osm.pbf
	osrm-prepare -p car.lua germany.osrm
	restart-osrm-routed

	calculate-routes-and-compare-lengths
done

Now i disabled the step of updateing the germany.osm file and i still
do see the route flaps. It seems osrm-prepare adds some randomness to 
graph weights. 

Here you can see a visual change in route. The route flapped from red
to green and back just be re-preparing the very same osm.pbf file:

http://osm.zz.de/routeqa/?rid=59464,59492
http://osm.zz.de/routeqa/?rid=59492,59571

Is this a known issue/side effect of the contracted hierarchies or
is this expected behaviour e.g. a real bug?

Flo
-- 
Florian Lohoff                                                 f at zz.de
     We need to self-defense - GnuPG/PGP enable your email today!
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