closestNode: Find the closest node to a given location
In thibautjombart/geograph: Walking through the geographic space using graphs

closestNode

R Documentation

Find the closest node to a given location

Description

The function closestNode searches for the closest node in a gGraph or a gData object to a given location. It is possible to restrain the research to given values of a node attribute. For instance, one can search the closest node on land to a given location.

Usage

closestNode(x, ...)

## S4 method for signature 'gGraph'
closestNode(x, loc, zoneSize = 5, attr.name = NULL, attr.values = NULL)

## S4 method for signature 'gData'
closestNode(x, zoneSize = 5, attr.name = NULL, attr.values = NULL)

Arguments

`x`	a valid gGraph or gData object. In the latter case, the gGraph to which the gData is linked has to be in the current environment.
`...`	further arguments passed to specific methods.
`loc`	locations, specified as a list with two components indicating longitude and latitude of locations. Alternatively, this can be a data.frame or a matrix with longitude and latitude in columns, in this order. Note that `locator()` can be used to specify interactively the locations.
`zoneSize`	a numeric value indicating the size of the zone (in latitude/longitude units) where the closest node is searched for. Note that this only matters for speed purpose: if no closest node is found inside a given zone, the zone is expanded until nodes are found.
`attr.name`	the optional name of a node attribute. See details.
`attr.values`	an optional vector giving values for `attr.names`. See details.

Details

This function is also used to match locations of a gData object with nodes of the gGraph object to which it is linked.

When creating a gData object, if the gGraph.name argument is provided, then locations are matched with the gGraph object automatically, by an internal call to closestNode. Note, however, that it is not possible to specify node attributes (attr.names and attr.values) this way.

Value

If x is a gGraph object: a vector of node names.

If x is a gData object: a gData object with matching nodes stored in the @nodes.id slot. Note that previous content of @nodes.id will be erased.

Functions

closestNode(gGraph): Method for gGraph
closestNode(gData): Method for gData

Examples

## Not run: 
## interactive example ##
plot(worldgraph.10k, reset = TRUE)

## zooming in
geo.zoomin(list(x = c(-6, 38), y = c(35, 73)))
title("Europe")

## click some locations
myNodes <- closestNode(worldgraph.10k, locator(), attr.name = "habitat", attr.value = "land")
myNodes

## here are the closestNodes
points(getCoords(worldgraph.10k)[myNodes, ], col = "red")

## End(Not run)

## example with a gData object ##
myLoc <- list(x = c(3, -8, 11, 28), y = c(50, 57, 71, 67)) # some locations
obj <- new("gData", coords = myLoc) # new gData object
obj

obj@gGraph.name <- "worldgraph.10k" # this could be done when creating obj
obj <- closestNode(obj, attr.name = "habitat", attr.value = "land")

## plot the result (original location -> assigned node)
plot(obj, method = "both", reset = TRUE)
title("'x'=location, 'o'=assigned node")

thibautjombart/geograph documentation built on Jan. 27, 2024, 10 p.m.