buffer: Compute buffers around locations for gGraph and gData objects

In thibautjombart/geograph: Walking through the geographic space using graphs

Compute buffers around locations for gGraph and gData objects

Description

The generic function buffer finds buffers around specified locations of a gGraph or a gData object. Different format for the output are available.

Usage

## S4 method for signature 'gGraph'
buffer(x, nodes, d, res.type = c("nodes", "gGraph"), ...)

## S4 method for signature 'gData'
buffer(x, d, res.type = c("nodes", "gData", "gGraph"), ...)

Arguments

x	a valid gGraph or gData object.
nodes	a character vector identifying the nodes aournd which buffers should be computed.
d	the radius of the buffer, in km.
res.type	the type of result that should be returned (see section value.
...	further arguments passed to specific methods.

Details

The computed buffers are sets of nodes lying within a given distance of specified locations. All nodes of a buffer need to be connected to the location they surround.

Value

The output depends on the value of the argument res.type:

• nodes: a vector of characters identifying the nodes of the buffers.
  

• gGraph: a gGraph object with a new attribute "buffer" (TRUE: within buffers; FALSE: outside buffers), and new color rules for this attribute in @meta$buf.colors.
  

• gData: a gData object including all the nodes of the buffers.
  

Examples

#### gGraph example ####
## zoom in to an area
plot(worldgraph.10k, reset = TRUE)
geo.zoomin(list(x = c(-6, 38), y = c(35, 73)))

## identify one node
oneNodeXY <- c(getCoords(worldgraph.10k)[9299, 1], getCoords(worldgraph.10k)[9299, 2])
points(oneNodeXY[1], oneNodeXY[2], col = "red")

## find some buffers
buffer(worldgraph.10k, "9299", 100) # nothing around 100km
buffer(worldgraph.10k, "9299", 500)
buf500km <- buffer(worldgraph.10k, "9299", 500, res = "gGraph")
plot(buf500km, col.rules = buf500km@meta$buf.colors)
buf1000km <- buffer(worldgraph.10k, "9299", 1000, res = "gGraph")
plot(buf1000km, col.rules = buf1000km@meta$buf.colors)


#### gData example ####
x <- hgdp[27:30] # retain a subset of hgdp
plot(x, reset = TRUE, col.g = "lightgrey", pch.node = 20)
buf.200 <- buffer(x, 200, res = "gData")
buf.400 <- buffer(x, 400, res = "gData")
buf.600 <- buffer(x, 600, res = "gData")
buf.1000 <- buffer(x, 1000, res = "gData")
points(buf.1000, col.node = "black")
points(buf.600, col.node = "yellow")
points(buf.400, col.node = "gold")
points(buf.200, col.node = "orange")
title("Different buffers for a gData \n(100km, 200km, 500km)")

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