Insert new nodes into a graph, breaking edges at point of nearest intersection.

Note that this routine presumes graphs to be dodgr_streetnet object, with geographical coordinates.

Usage

add_nodes_to_graph(graph, xy, dist_tol = 0.000001, intersections_only = FALSE)

Arguments

graph: A dodgr graph with spatial coordinates, such as a dodgr_streetnet object.
xy: coordinates of points to be matched to the vertices, either as matrix or sf-formatted data.frame.
dist_tol: Only insert new nodes if they are further from existing nodes than this distance, expressed in units of the distance column of graph.
intersections_only: If FALSE

Value

A modified version of graph, with additional edges formed by breaking previous edges at nearest perpendicular intersections with the points, xy.

Details

This inserts new nodes by extending lines from each input point to the edge with the closest point of perpendicular intersection. That edge is then split at that point of intersection, creating two new edges (or four for directed edges). If intersections_only = FALSE (default), then additional edges are inserted from those intersection points to the input points. If intersections_only = TRUE, then nodes are added by splitting graph edges at points of nearest perpendicular intersection, without adding additional edges out to the actual input points.

In the former case, the properties of those new edges, such as distance and time weightings, are inherited from the edges which are intersected, and may need to be manually modified after calling this function.

Examples

graph <- weight_streetnet (hampi, wt_profile = "foot")
dim (graph)
#> [1] 6813   15

verts <- dodgr_vertices (graph)
set.seed (2)
npts <- 10
xy <- data.frame (
    x = min (verts$x) + runif (npts) * diff (range (verts$x)),
    y = min (verts$y) + runif (npts) * diff (range (verts$y))
)

graph <- add_nodes_to_graph (graph, xy)
dim (graph) # more edges than original
#> [1] 6863   15