Manually adjusting the routing output

[BjoernRave]

Sometimes valhalla doesnt give optimal routes back. I want to build a feature where the user can edit the directions manually. Now I am unsure how to deal with the instructions from valhalla, as they are are going to be off. Has anyone done something similar before? How would I ideally go about this?

[kevinkreiser]

the api allows you to have more than 2 locations, and the locations have different types which determines if a uturn or a maneuver could or should (respectively) happen at those extra locations. i would suggest you simply allow a user to "add" extra way points with the via or through location.type just like you can do with googles web gui. another option would be to let the user draw a bunch of points like with the paint brush tool in a typical image editor and pass all of those to the map matching api. in both cases you will paths that more closely follow your users prefered route and the generated directions will match as well.

[BjoernRave]

Okay, seems I wasnt 100% clear. What I mean is, that I want to adjust the route to go like this, but there is no "path" in the osm/valhalla data there, so it always takes this weird detour. How I would incorporate suche a change, but I guess its not really possible and I would just do two navigations, from the start of the "detour" and from the end of it and in between, maybe calculate my own instructions or just not have any

[chrstnbwnkl]

Looks like a mapping error in osm to me. "Surgical" edits to a Valhalla graph are not really possible (you can try, but I would strongly advise against going down that rabbit hole), so your only real options is to rebuild the entire graph every time.

[BjoernRave]

rebuilding the graph sounds much more difficult to me, tbh as I dont have a lot of experience with the innner workings of valhalla and it sounds like I need to spend quite some compute everytime a user wants to adjust a route, also probably coming with a lot of latency. Thanks for the warning, but I think the "surgical" edit seems more reachable and performant to me. As it will mostly only be small parts I guess I just dont have any navigation instructions for those parts. I will only be using these edits in the context of a walking tour where the guide dictates the directions, so I dont need to access my "surgical edits" everytime I do a route calculation with valhalla