sfnetwork {sfnetworks}

Create a sfnetwork

Description

sfnetwork is a tidy data structure for geospatial networks. It extends the tbl_graph data structure for relational data into the domain of geospatial networks, with nodes and edges embedded in geographical space, and offers smooth integration with sf for spatial data analysis.

Usage

sfnetwork(
  nodes,
  edges = NULL,
  directed = TRUE,
  node_key = "name",
  edges_as_lines = NULL,
  length_as_weight = FALSE,
  force = FALSE,
  message = TRUE,
  ...
)

Arguments

nodes

The nodes of the network. Should be an object of class sf, or directly convertible to it using st_as_sf. All features should have an associated geometry of type POINT.

edges

The edges of the network. May be an object of class sf, with all features having an associated geometry of type LINESTRING. It may also be a regular data.frame or tbl_df object. In any case, the nodes at the ends of each edge must either be encoded in a to and from column, as integers or characters. Integers should refer to the position of a node in the nodes table, while characters should refer to the name of a node encoded in the column referred to in the node_key argument. Setting edges to NULL will create a network without edges.

directed

Should the constructed network be directed? Defaults to TRUE.

node_key

The name of the column in the nodes table that character represented to and from columns should be matched against. If NA, the first column is always chosen. This setting has no effect if to and from are given as integers. Defaults to 'name'.

edges_as_lines

Should the edges be spatially explicit, i.e. have LINESTRING geometries stored in a geometry list column? If NULL, this will be automatically defined, by setting the argument to TRUE when the edges are given as an object of class sf, and FALSE otherwise. Defaults to NULL.

length_as_weight

Should the length of the edges be stored in a column named weight? If set to TRUE, this will calculate the length of the linestring geometry of the edge in the case of spatially explicit edges, and the straight-line distance between the source and target node in the case of spatially implicit edges. If there is already a column named weight, it will be overwritten. Defaults to FALSE.

force

Should network validity checks be skipped? Defaults to FALSE, meaning that network validity checks are executed when constructing the network. These checks guarantee a valid spatial network structure. For the nodes, this means that they all should have POINT geometries. In the case of spatially explicit edges, it is also checked that all edges have LINESTRING geometries, nodes and edges have the same CRS and boundary points of edges match their corresponding node coordinates. These checks are important, but also time consuming. If you are already sure your input data meet the requirements, the checks are unnecessary and can be turned off to improve performance.

message

Should informational messages (those messages that are neither warnings nor errors) be printed when constructing the network? Defaults to TRUE.

...

Arguments passed on to st_as_sf, if nodes need to be converted into an sf object during construction.

Value

An object of class sfnetwork.

Examples

library(sf, quietly = TRUE)

## Create sfnetwork from sf objects
p1 = st_point(c(7, 51))
p2 = st_point(c(7, 52))
p3 = st_point(c(8, 52))
nodes = st_as_sf(st_sfc(p1, p2, p3, crs = 4326))

e1 = st_cast(st_union(p1, p2), "LINESTRING")
e2 = st_cast(st_union(p1, p3), "LINESTRING")
e3 = st_cast(st_union(p3, p2), "LINESTRING")
edges = st_as_sf(st_sfc(e1, e2, e3, crs = 4326))
edges$from = c(1, 1, 3)
edges$to = c(2, 3, 2)

# Default.
sfnetwork(nodes, edges)

# Undirected network.
sfnetwork(nodes, edges, directed = FALSE)

# Using character encoded from and to columns.
nodes$name = c("city", "village", "farm")
edges$from = c("city", "city", "farm")
edges$to = c("village", "farm", "village")
sfnetwork(nodes, edges, node_key = "name")

# Spatially implicit edges.
sfnetwork(nodes, edges, edges_as_lines = FALSE)

# Store edge lenghts in a weight column.
sfnetwork(nodes, edges, length_as_weight = TRUE)

# Adjust the number of features printed by active and inactive components
oldoptions = options(sfn_max_print_active = 1, sfn_max_print_inactive = 2)
sfnetwork(nodes, edges)
options(oldoptions)