Why no left turn?
  • Vote Up0Vote Down IU0BMPIU0BMP
    I once wrote that MFN is "afraid" of taking a left turn at intersections (or maybe right turns if you drive in the UK).
    I can provide an example here. Coordinates are 41.73949, 12.26363 (start) - 41.74053, 12.26357 (destination)
    First screenshot is in pedestrian mode.
    Second screenshot is in car mode.
    These screenshot were made with the Windows application, but the problem is just the same with Android. Does it depend on the maps or on the routing algorithm??



  • 19 Comments sorted by
  • Vote Up0Vote Down chattiewomanchattiewoman
    Can you provide the direct link to OSM? I bet a turning restriction (prohibition) on the junction is the cause.
  • Vote Up0Vote Down IU0BMPIU0BMP
    Direct link to OSM http://www.openstreetmap.org/#map=19/41.73951/12.26412

    From Street view, there is only a Stop sign, no other restrinction.. street view
  • Vote Up0Vote Down IU0BMPIU0BMP
    another example, (even worse, as the detour is quite long) from 41°53'39.4"N 12°35'18.8"E to 41°53'36.1"N 12°35'13.6"E


    Coming from via Prenestina from east to west, having to turn left on via Aristide Staderini, heading south
  • Vote Up0Vote Down chattiewomanchattiewoman
    The mapping seems to be correct. My only other explanation: your car profile doesn't allow to drive on streets mapped as unclassified. You can easily test it by creating a route onto south part of Via dell'Appaglitore. It's mapped as unclassified too - which isn't wrong, by the way!
  • Vote Up0Vote Down IU0BMPIU0BMP
    Thanks Chattie,
    :-O I'm using the default car profile. I have tried a route on the southern part of via Appagliatore, starting from via dell'Idroscalo, ending on via delle Azzorre and route is correct.
    Did you see my second example? I don't think it has to do with unclassified roads :
  • Vote Up0Vote Down IU0BMPIU0BMP
    I have enabled 'small local road' and 'other road' and now the route is correct for the first example. But I get a very strange detour for the second example. I will post screenshots after lunch :)
  • Vote Up0Vote Down chattiewomanchattiewoman
    In your second example, there IS a turning restriction on the junction, but sending everybody WEST (not south) when coming from east. Coming from east, this mapping causes nobody may turn left into Via Aristide Staderini although it's the beginning of a oneway street
  • Vote Up0Vote Down TantumTantum
    Yes, that's how I solved it as well...however I set the preference on 15% to the small local roads to ensure that I won't be routed thru them all the time
  • Vote Up0Vote Down IU0BMPIU0BMP
    By the way, this is the 'small local road' of the first example: street view I am not an expert of mapping but I wonder if this is correct..
    Now, going to the second example,here are the screenshots: with small roads enabled image
    with small roads disabled image
  • Vote Up0Vote Down chattiewomanchattiewoman
    Apparently I previously misunderstood you. The first screen shot is showing a correct routing according to OSM.
    Are you sure you are allowed in reality to directly turn left?? Then OSM needs to be corrected.
  • Vote Up0Vote Down IU0BMPIU0BMP
    Chattie, I am not an expert regarding mapping and openstreetmap, so I trust you when say there IS a turning restriction on the junction, altough I cannot see it. And I cannot see it from street view either. There is no sign saying you can't turn left..  8-|
    To answer your last question, I believe it is allowed to turn left. See the dashed line on the street. If it were a continuous line, the left turn would not be allowed.
  • Vote Up0Vote Down chattiewomanchattiewoman
    I just deleted the wrong turning restriction in OSM. Will be considered then in one of next IT maps.
  • Vote Up0Vote Down TantumTantum
    there is an "only straight on" restriction
    you can see it clearly in the JOSN editor - if you haven't played with it yet..then this is the best way how to review junctions
    or
    just click EDIT > Edit with ID and click on the node at the junction ... you'll see "only via" there

    EDIT -- now you will not see it cause Chattie already deleted it :D
  • Vote Up0Vote Down chattiewomanchattiewoman
    @Tantum

    OSM data are too sensitive to be "played" with just for fun ;-)
  • Vote Up0Vote Down IU0BMPIU0BMP
    Tantum, thank you for solving this little mistery ;)
    Chattie, I made a few map corrections in the past and I know this is a serious thing that must be done carefully..
    Now everything seems to be solved, but I still 'confused' by the fact that I had to enable the small local roads in the first example.. There must be something wrong there as well
  • Vote Up0Vote Down TantumTantum
    @chattiewoman - I believe @IU0BMP knows what I meant ;) ... but you are absolutely right


    @IU0BMP - just for your benefit...this is how it look(ed) like in JOSN...nice and clean way to check in case you have any questions re. the data in OSM
    image
  • Vote Up0Vote Down IU0BMPIU0BMP
    Thank you again Tantum. So this is how it looks like with JOSM... That restriction was not there with the browser editor... 
  • Vote Up0Vote Down chattiewomanchattiewoman
    @IU0BMP
    I still edit with Potlach instead of ID as browser editor, and there, turning restrictions are at least indicated too.
  • Vote Up0Vote Down IU0BMPIU0BMP
    Potlach looks good  :)>-
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