function to insert new vertices

[mpadge]

Following on from @rafapereirabr's SO question, it would be very useful for dodgr to incorporate the ability to insert new points in a network. Current routing can accept arbitrary points, but these are simply mapped to nearest network points and then forgotten. Incorporation of new points would involve modification of the underlying network, so a network with an edge between A and B would be modified through calling

insert_point (network, x, y)

to

A -> (new point with hashed id) -> B

or,

> insert_point (network, x, y, "C")
# A -> C -> B

The points A and B could be automatically identified as the nearest two points, yet this may not necessarily be what is desired. It will likely be necessary to have an option to override this default behaviour that would then graphically show the default, yet enable other options to be specified.

@rafapereirabr: this might take a while to implement, because it will be more appropriately incorporated within the soon-to-appear-on-cran silicate, and associated sc, rather than sf or sp representations. This whole issue is therefore likely to first be shifted to silicate and ultimately resolved there. cc @mdsumner

[rafapereirabr]

The idea is to add a new node somewhere along an existing edge. One element to consider in this task is the location of the new node, whether it should be placed halfway the edge or whether it should be placed at a specific location set by the user. In the case of my SO question, it's the second case, where the user sets a pair of lat long of the new node.

Thanks for taking this task on board !

[JimShady]

For reference, the answer to this stack exchange question provides code which seems to be useful for this extra functionality:

https://gis.stackexchange.com/questions/288445/split-polyline-by-point-using-sf-package-in-r

[JimShady]

The idea is to add a new node somewhere along an existing edge. One element to consider in this task is the location of the new node, whether it should be placed halfway the edge or whether it should be placed at a specific location set by the user. In the case of my SO question, it's the second case, where the user sets a pair of lat long of the new node.

Thanks for taking this task on board !

Just reading this ... the new node should be created at the closest point to the lat long specified by the user I would think. That's what I'd expect anyway. Process would be something like this I think:

1. take the origin latitude and longitudes supplied by a user
2. If requested, start the node insertion process
   a. snap origins to nearest edges
   b. snap destinations to nearest edges
   c. split lines and create new lines
   d. rebuild the graph
3. Perform routing

Maybe the insert_point enhancement would be an option within the routing functions? Something like route_dodgr(start_point,end_point, net, create_nodes = TRUE)

[mpadge]

That commit adds a new function dodgr_insert_vertex(), which does most of what was discussed above. The one thing is does not do is enable a vertex to be inserted at the intersection of two existing lines, because the new vertices are always assumed to be genuinely new, and bear no relation with pre-existing network structures. But at least it's a good start - Please feel free to give it a try, and comment here.

[rafapereirabr]

thanks for the follow up !

[mpadge]

Yeah, sorry it took sooooo long! It's still not ideal, but there are a number of alternative paths from here on, so I think it's just best to first spin out this initial version and see what kind of feedback it might generate before moving further with it. Thanks for the impetus! Please give any feedback, insight, suggestions you might have either here, or in new issues.