st_network_blend: Blend spatial points into a spatial network

In luukvdmeer/sfnetworks: Tidy Geospatial Networks

Blend spatial points into a spatial network

Description

Blending a point into a network is the combined process of first projecting the point onto its nearest point on its nearest edge in the network, then subdividing that edge at the location of the projected point, and finally adding the projected point as node to the network. If the location of the projected point is equal an existing node in the network, the attributes of the point will be joined to that node, instead of adding a new node.

Usage

st_network_blend(x, y, tolerance = Inf, ignore_duplicates = TRUE)

Arguments

x	An object of class sfnetwork.
y	The spatial features to be blended, either as object of class sf or sfc, with POINT geometries.
tolerance	The tolerance distance to be used. Only features that are at least as close to the network as the tolerance distance will be blended. Should be a non-negative number preferably given as an object of class units. Otherwise, it will be assumed that the unit is meters. If set to Inf all features will be blended. Defaults to Inf.
ignore_duplicates	If there are multiple points in y that have the same projected location, only the first one of them is blended into the network. But what should happen with the others? If this argument is set to TRUE, they will be ignored. If this argument is set to FALSE, they will be added as isolated nodes to the returned network. Nodes at equal locations can then be merged using the spatial morpher to_spatial_unique. Defaults to TRUE.

Details

When the projected location of a given point intersects with more than one edge, it is only blended into the first of these edges. Edges are not connected at blending locations. Use the spatial morpher to_spatial_subdivision for that.

To determine if a projected point is equal to an existing node, and to determine if multiple projected points are equal to each other, sfnetworks by default rounds coordinates to 12 decimal places. You can influence this behavior by explicitly setting the precision of the network using st_set_precision.

Value

The blended network as an object of class sfnetwork.

Note

Due to internal rounding of rational numbers, it may occur that the intersection point between a line and a point is not evaluated as actually intersecting that line by the designated algorithm. Instead, the intersection point lies a tiny-bit away from the edge. Therefore, it is recommended to set the tolerance to a very small number (for example 1e-5) even if you only want to blend points that intersect an edge.

Examples

library(sf, quietly = TRUE)

oldpar = par(no.readonly = TRUE)
par(mar = c(1,1,1,1), mfrow = c(1,2))

# Create a spatial network.
n1 = st_point(c(0, 0))
n2 = st_point(c(1, 0))
n3 = st_point(c(2, 0))

e1 = st_sfc(st_linestring(c(n1, n2)), crs = 3857)
e2 = st_sfc(st_linestring(c(n2, n3)), crs = 3857)

net = as_sfnetwork(c(e1, e2))

# Create spatial points to blend in.
p1 = st_sfc(st_point(c(0.5, 0.1)))
p2 = st_sfc(st_point(c(0.5, -0.2)))
p3 = st_sfc(st_point(c(1, 0.2)))
p4 = st_sfc(st_point(c(1.75, 0.2)))
p5 = st_sfc(st_point(c(1.25, 0.1)))

pts = st_sf(foo = letters[1:5], geometry = c(p1, p2, p3, p4, p5), crs = 3857)

# Blend all points into the network.
b1 = st_network_blend(net, pts)
b1

plot(net)
plot(st_geometry(pts), pch = 20, col = "orange", add = TRUE)
plot(b1)
plot(st_geometry(pts), pch = 20, col = "orange", add = TRUE)

# Blend points within a tolerance distance.
tol = units::set_units(0.1, "m")
b2 = st_network_blend(net, pts, tolerance = tol)
b2

plot(net)
plot(st_geometry(pts), pch = 20, col = "orange", add = TRUE)
plot(b2)
plot(st_geometry(pts), pch = 20, col = "orange", add = TRUE)

# Add points with duplicated projected location as isolated nodes.
b3 = st_network_blend(net, pts, ignore_duplicates = FALSE)
b3

par(oldpar)

luukvdmeer/sfnetworks documentation built on Nov. 21, 2024, 4:54 a.m.