stplanr (version 0.6.2)

rnet_breakup_vertices: Break up an sf object with LINESTRING geometry.

Description

This function breaks up a single LINESTRING geometry into multiple LINESTRING(s) for preserving routability of an sfNetwork object created by SpatialLinesNetwork() function with Open Street Map data. See details and stplanr/issues/282.

Usage

rnet_breakup_vertices(rnet, breakup_internal_vertex_matches = TRUE)

Arguments

rnet

An sf object with LINESTRING geometry representing a route network.

breakup_internal_vertex_matches

Boolean. Should breaks be made at shared internal points? TRUE by default. Internal points are points that do not lie in the boundary of the LINESTRING.

Value

An sf object with LINESTRING geometry created after breaking up the input object.

Details

A LINESTRING geometry is broken-up when one of the following conditions is met:

1. two or more LINESTRINGS share a POINT that lies in the union of their boundaries (see the rnet_roundabout example);

2. two or more LINESTRINGS share a POINT which is not in the boundary of any LINESTRING (see the rnet_cycleway_intersection example).

The problem with the first example is that, according to algorithm behind SpatialLinesNetwork(), two LINESTRINGS are connected if and only if they share at least one point in their boundaries. The roads and the roundabout are clearly connected in the "real" world but the corresponding LINESTRING objects do not share any boundary point. In fact, by Open Street Map standards, a roundabout is represented as a closed and circular LINESTRING and this implies that the roundabout is not connected to the other roads according to SpatialLinesNetwork() definition. By the same reasoning, the roads in the second example are clearly connected in the "real" world, but they do not share any point in their boundaries. This function is used to solve this type of problem.

See Also

Other rnet: SpatialLinesNetwork, calc_catchment_sum(), calc_catchment(), calc_moving_catchment(), calc_network_catchment(), find_network_nodes(), gsection(), islines(), lineLabels(), overline(), plot,SpatialLinesNetwork,ANY-method, plot,sfNetwork,ANY-method, sln2points(), sum_network_links(), sum_network_routes()

Examples

# NOT RUN {
library(sf)
def_par = par(no.readonly = TRUE)
par(mar = rep(0, 4))

# Check the geometry of the roundabout example. The dots represent the
# boundary points of the LINESTRINGS. The "isolated" red point in the top-left
# is the boundary point of the roundabout, and it is not shared with any
# other street.
plot(st_geometry(rnet_roundabout), lwd = 2, col = rainbow(nrow(rnet_roundabout)))
boundary_points <- st_geometry(line2points(rnet_roundabout))
points_cols <- rep(rainbow(nrow(rnet_roundabout)), each = 2)
plot(boundary_points, pch = 16, add = TRUE, col = points_cols)

# Clean the roundabout example.
rnet_roundabout_clean <- rnet_breakup_vertices(rnet_roundabout)
plot(st_geometry(rnet_roundabout_clean), lwd = 2, col = rainbow(nrow(rnet_roundabout_clean)))
boundary_points <- st_geometry(line2points(rnet_roundabout_clean))
points_cols <- rep(rainbow(nrow(rnet_roundabout_clean)), each = 2)
plot(boundary_points, pch = 16, add = TRUE, col = points_cols)
# The roundabout is now routable since it was divided into multiple pieces
# (one for each colour), which, according to SpatialLinesNetwork() function,
# are connected to the other streets.

# Check the geometry of the overpasses example. This example is used to test
# that this function does not create any spurious intersection.
plot(st_geometry(rnet_overpass), lwd = 2, col = rainbow(nrow(rnet_overpass)))
boundary_points <- st_geometry(line2points(rnet_overpass))
points_cols <- rep(rainbow(nrow(rnet_overpass)), each = 2)
plot(boundary_points, pch = 16, add = TRUE, col = points_cols)
# At the moment the network is not routable since one of the underpasses is
# not connected to the other streets.

# Check interactively.
# mapview::mapview(rnet_overpass)

# Clean the network. It should not create any spurious intersection between
# roads located at different heights.
rnet_overpass_clean <- rnet_breakup_vertices(rnet_overpass)
plot(st_geometry(rnet_overpass_clean), lwd = 2, col = rainbow(nrow(rnet_overpass_clean)))
# Check interactively.
# mapview::mapview(rnet_overpass)

# Check the geometry of the cycleway_intersection example. The black dots
# represent the boundary points and we can see that the two roads are not
# connected according to SpatialLinesNetwork() function.
plot(rnet_cycleway_intersection$geometry, lwd = 2,
     col = rainbow(nrow(rnet_cycleway_intersection)))
plot(st_geometry(line2points(rnet_cycleway_intersection)), pch = 16, add = TRUE)
# Check interactively
# mapview::mapview(rnet_overpass)

# Clean the rnet object and plot the result.
rnet_cycleway_intersection_clean <- rnet_breakup_vertices(rnet_cycleway_intersection)
plot(rnet_cycleway_intersection_clean$geometry,
     lwd = 2, col = rainbow(nrow(rnet_cycleway_intersection_clean)))
plot(st_geometry(line2points(rnet_cycleway_intersection_clean)), pch = 16, add = TRUE)

par(def_par)
# }