build_streetnet: Build a routable graph from a set of linestrings

In triply-at/gtfsmulti: Creating, storing and analyzing multi-modal transportation networks

Description

Build a routable graph from a set of linestrings

Usage

build_streetnet(x, protect = NULL)

Arguments

x

An object of class sf with LINESTRING or MULTILINESTRING geometries.

protect

Set of points that protect their nearest linestring vertex from being smoothed (see Details). That is, the closest linestring vertices to these points are guaranteed to be a node in the resulting graph, even if they are neither a pendant node nor a junction node. May be given either as an object of class sf or sfc with POINT geometries, or as a two-column numeric matrix containing respectively the longitude and latitude coordinates of the points.

Details

Graph building is implemented as a step-wise process. The graph will be directed, so first all linestring geometries of x that are not marked as being a oneway street (through the oneway attribute column if present) are duplicated and reversed. Then, all the linestring geometries are split such that their segments become separate linestring geometries on their own. These serve as the edges in the initial graph, and their endpoints become the nodes. Endpoints that are shared between multiple edges become a single node, such that these edges are connected. Only the largest connected component of the initial graph is preserved. Finally, the initial graph is smoothed by removing all nodes that are neither a pendant node (i.e. a node at the end of an edge without a connection to any other edge) nor a junction node (i.e. a node that connects more than two edges) nor a nearest node to any of the points passed to the protect parameter.

Value

An object of class sfnetwork.

Note

Coordinates should be expressed in coordinate reference system EPSG:4326. The function assumes this to be true, and does not check for it.

triply-at/gtfsmulti documentation built on Dec. 24, 2021, 1:21 a.m.