Wrong route choices

[Mark Howard]

Newbie question:

I have a new re-install of OsmAnd+ V3.8.4   on Android 8.1.0

Standard New Zealand map loaded.

If I try to travel from Petrie St, Rotorua to Esplanade, Kinloch, OsmAnd tries to route me down Tirohanga Rd (off State Highway 1 just south of the Waikato river) rather than than down Oruanui Rd (off State Highway 1 about 15km further south).  Via Oruanui Rd is 3 kms shorter and 4 minutes quicker.

Do I have a setting wrong?

I initially tried editing some of the routing options, but it then took me WAY out of my way - by about 60km.  I couldn't fix that (even after dismissing the route) and retrying without uninstalling and reinstalling the app.

Any help would be greatly appreciated.

BTW I love the clean look of the maps - please help me be able to use this app.

[Poutnik Fornntp]

Check, if the roads and their connections are mapped OK in OSM.

The easiest way is probably generating the route by other software using OSM data. You may try e.g. http://brouter.de/BRouter-web/

Dne 23. listopadu 2020 5:47:38 Mark Howard <m.km....@gmail.com> napsal:

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[Mark Howard]

Thanks for that Poutnik.

If I try the same trip using OpenStreetMap on my computer, it takes me the correct way.

Does that indicate a problem within OsmAnd?

[Poutnik Fornntp]

It may be a problem, if there is a bug in the algorithm. Or, it may be the result of different algorithm priorities, comparing OSM routing and OsmAnd routing. Or, difference between algorithm and human priorities. 

Another factor is that OSM data do not reflect all aspects leading to real route driving time. Algorithms may for the given route push the estimation toward real value or away from it. For other route the successfulness may be switched.

What is the relative difference in distance and time, between the provided route and the optimal one.  Or what are absolute distances and times for both routes ?

Dne 23. listopadu 2020 7:24:27 Mark Howard <m.km....@gmail.com> napsal:

To view this discussion on the web visit https://groups.google.com/d/msgid/osmand/85d03cac-45a8-403a-9c81-8d7c04aae001n%40googlegroups.com.

[Greg Troxel]

Poutnik Fornntp <poutni...@gmail.com> writes:

> It may be a problem, if there is a bug in the algorithm. Or, it may be
> the result of different algorithm priorities, comparing OSM routing
> and OsmAnd routing. Or, difference between algorithm and human
> priorities.

Agreeing and saying part of this a little louder:

Talking about what the right answer is for routing is very difficult.
Given a map database there are issues:

what are the assumptions about travel time vs road speed

what are the assumptions about turns, stop signs, lights

what is the goal? shortest time, shortest distance, a blend, "eco
routing"?

Besides an estimate of the time and the distance, are there or should
there be "penalties" applied that express the human concept of "taking
this left turn is scary, so I would rather have a 43m route that does
not include that left turn than a 40m route that does".

Generally, for something like osmand, it is considered to be doing well
if the calculated route is reasonable, relative to someone who does not
know the area. That's different from the best route with local expert
knowledge, but it's great for a non-local compared to being lost.

The advice to use other routing engines is also excellent. Besides
brouter, there are multiple engines available for foot, bicycle and car.

https://www.openstreetmap.org/directions?engine=graphhopper_car&route=-38.1530%2C176.2230%3B-38.6609%2C175.9215

Mark Howard writes:

> Via Oruanui Rd is 3 kms shorter and 4 minutes quicker.

Do you mean that it is *actually* shorter and quicker, on average, if
you drive each way 5 times and record the data?


You are talking about a route that ORSM and graphhopper both come out
as:

82km 1:07
82km 0:56

but they seem to pick the same route. If osmand chooses a route which
is 3km and 4 minutes longer *in actuality* than some route that another
engine finds, that's really not so bad.

Digging into this is likely going to be some combination of

checking the representation in OSM of the roads chosen and not chosen
to be sure they are accurate. (Proably you know this, but *do not*
adjust OSM to have data that is not accurate to make routing come out
better.)

looking at the routing code to see what assumptions it makes about
turns, lights, and so on

computing two routes, one to an intermediate point you like and then
from there (just route to intermedidate, then again, and choose "add
as subsequent destination). If the total route as displayed is
shorter/faster than the original route, you have found a route
computation suboptimality.

and steps on the path to really addressing this are:

setting up osmand's router to meet the same interface as the OSM web
page

modifying osmand on android to export computed routes in the same
format

writing some code to compare routes, and to make the various routers
evaluted the other routers' choices

surely some more hard work after thtat


Looking more at your particular routes, I wonder if there is something
in the OSM data that one engine interprets very differently.

You can also help make progress by calculating shorter routes, basically
starting a bit before the divergence.

Look at this route:

https://www.openstreetmap.org/directions?engine=fossgis_osrm_car&route=-38.3476%2C176.0065%3B-38.6370%2C175.9212

then move the red marker SW just barely. The two paths are both 44km
0:34. If I move to Kinloch Road, it's 43k 0:33 for one, and presumably
45km 0:35 for the other.

So basically I am concluding the difference in OsmAnd and osrm's
opinions about the total cost of one of these routes is on the order of
2km 2 minutes.

Until you drive both and actually find out what happens (maybe you have
and that's what you mean), it's hard to say this is wrong for sure.