I’m not sure how to correct / fix this issue and didn’t want to screw it up. I have attached a couple of screen shots, one of Map Source and the other in OSM.
In Map Source when routing it does a detour around the Intersection. Checking it out it does show some turns but doesn’t show any at the intersection.
Can someone in the community correct / fix it? I’ll then review the changes so I know what to do in the future if I come across this type of issue again.
I don’t see any issues routing here using routers available on OSM.org, see for example Valhalla: OpenStreetMap
Is Map Source router perhaps configured to avoid left turns onto a main road (here Putnam Road southbound onto Hamilton Road), or to avoid sharp turns?
Alternatively there might have been a data problem in the past but has since been resolved? Do you know if Map Source is using latest data?
No, Map Source is not configured to avoid left turns on a main road.
This is from the OSM from Oct 19, 2024 which is very recent.
Map Source doesn’t do it with the map from Garmin,
Since the map is first split and then made using mkgmap (using the latest versions) to be compatible with Garmin it might be the way it is being handled in mkgmap. Since it is local and I know turns can be made I just ignore the instructions from the gps to make the turn down the side street. I just thought it would be nice to correct if it was something in OSM causing the routing issue
I’ve attached screen shots showing Map Source with OSM and the Map from Garmin…
I had a look at the data in josm, no strange things that could explain things.
You did not specify the profile (car/bicycle/foot) you are using. For a pedestrian route I think the detour is not bad although the routers on osm still take the shorter route. brouter with the Safety profile takes the detour.
The profile used is vehicle such as car or motorcycle. The detour is only in OSM not the map from Garmin. I download the north-america-latest.osm.pbf file. I then use the splitter and mkgmap programs to split and convert it into a gmap file to work with Garmin GPS’s. https://www.mkgmap.org.uk/
I would suspect that if there are no strange things in the data in josm it happens during the creation of the Garmin map file for some reason.
I looked at the turns for the intersections in OSM and also didn’t see any reason for it cause a detour.
Another option is that Map Source handles the data incorrectly. You could try Basecamp instead of Map Source or an actual GPS device.
I could imagine, that the left route is less costly for the routing algorithm (therefore shorter time).
Reasons could be that turning left on a primary road has a high penalty and/or that it makes wrong assumptions about the speed limit on Marshall St since there isn’t one explicitly tagged.
If you happen to be in that area again, you could check for a speed limit on that small road and see if adding it fixes things.
Besides you wrote that it seems not to allow turns. I think you migtht be able to figure out if that is the case, if you bring the end point closer to the junction
Actually the detour would be slower since going on to a side street with a slower speed limit and further distance. Detour is 578m and no detour is 468m to same spot to spot.
Which end point are you referring to about being closer to the junction? If doing a route that is say 100 km from one spot to another spot the routing is automatic.
If I pick a start point near the intersection the route actually goes the other way to take the side street. The only time I have encountered something similar is where a road is closed or bridge is out.
Thats what I was referring to when I said try an change the end point. Strange behavior indeed.
The only routing engine I could somewhat reproduce this with was Graphhopper in pedestrian mode
But it doesn’t avoid the junction quite as much as MapSource (when you put the end point closer it will use the shorter route) .
Here the reason most likely is that Putnam Road has sidewalk=no and Graphhopper tries to avoid using those.
But of course that doesn’t explain the issue you have with a vehicle profile in MapSource.
I’m out of ideas. There are no tags on the ways or relations that would keep it from using that junction.
Likely not surprising, the software uses the same libraries. I think there is a 50% chance an actual GPS uses another library.
Ideally you would like to get debug output from the routing algorithm or dump the .img file.
For seeing what a routing algorithm does I think brouter-web is the best and maybe the only one that gives direct graphical access, just try the spreadsheet icon or press T. Unfortunately brouter can not work based on a .img file.
I think your best option is to create a very small cut out of the area, create an .img file for that, test if the problem is there and if so debug mkgmap.
Edit: Maybe also good to find out if there is maybe some “tile boundary” here.
