Snap to anywhere along an edge

[dabreegster]

In an earlier UX study, Will expected to be able to start snapping in the middle of a road

[dabreegster]

How should we implement this? Now we use https://github.com/georust/rstar to find the closest node to the cursor. Maybe a two-phase approach, first find the closest node, then look at all the incident edges and use https://docs.rs/geo/latest/geo/algorithm/closest_point/trait.ClosestPoint.html?

[Robinlovelace]

This sounds hard!

[dabreegster]

CC @tordans

[Robinlovelace]

Random thought after getting a notification on this: based on a parameter snap_distance break any straight lines longer than that into n pieces where n ensures that there are 'virtual vertices' every snap_distance meters or less and then snap to those?

I imagine you've already thought of that, didn't put that out there before as it seems like a brute force approach that involves a lot of largely unnecessary processing. Could that 'virtual vertex' creation on the fly?

randomideas

[dabreegster]

Virtual nodes introduced every few meters would be one approach, definitely. Depending how it's done, it might bloat memory usage and make the final output much more verbose on curved roads. Reasoning how to do this is not so bad for the simple A-to-B routing case, but with draggable intermediate waypoints and also the area snapping, it'll take some focus to figure it out properly. Not likely to prioritize soon, but contributions welcome

[tordans]

Some thoughts on how to compensate:

• I will experiment with adding a "last mile arc" that connects the snapped node with the selected marker position; that will clarify the "this is how far we can route, the last bit is up to you"
• However, this will not solve the issue where a very long road is not snapped at all.
  • I think the main issues was fixed in https://github.com/dabreegster/route_snapper/pull/54, so I will see how often it comes up in a city.
  • For rural areas, maybe a second file of split points is a solution which could be selected POI/addresses that would be snapped to a road and the road split there?
  • It might also be helpful to make the snap radius a config so one can increase it to improve those situations?
  • Maybe if no snap point was found, the script returns a list of snap points that are further away so the UI can show a list "did not find anything nearby, which do you want to pick: LIST" and then change the maps bbox to include the selected snap point which might be out of view