openmap: Download map tiles

Description

Downloads map tiles from Openstreetmap.org and other servers.

Usage

openmap(x, zoom, 
	path="http://tile.openstreetmap.org/",
	maxTiles = 9,
	crs=projection(x),   extend=0, verbose=FALSE)
	osmTiles(name)
	openmapAttribution(name, type=c('text','latex','markdown','html'), short=FALSE)

Arguments

An extent or any spatial object (raster, Spatial*) from which an extent can be obtained.

zoom

the zoom level, when missing it will be determined by maxTiles.

path

the tile server from which to get the map, see http://wiki.openstreetmap.org/wiki/Tiles#Servers.

maxTiles

If zoom is missing, zoom will be chosen such that the number of map tiles is less than or equl to this number.

crs

Projection for the output, defaulting to the same projection as x. If x has no projection, for instance when x is a matrix or extent, crs is also used as the projection of x. If cr

extend

Extend the extent for which the map is requested, in units of x. Can be negative, or a vector of length 2 for different x and y extensions

verbose

If TRUE, give information on where tiles are coming from, cache hits, etc

name

name of a tile path, if missing a vector of all available tile paths is returned. name can be any of the names of the vector returned when name is unspecified.

type

format for the attribution

short

short or long attribution

Value

openmap returns a RasterBrick brick, with 'red', 'green' and 'blue' layers.

Details

These functions download, display, and manipulate map tiles stored in a standard way either on a web server or a local folder.

Map tiles are a set of PNG images that span the world at a set of zoom levels. Zoom level 1 has four 256x256 pixel tiles in a 2x2 pattern over the whole world. In general, zoom level n has 2^n by 2^n tiles. Zoom levels go up to about 17 or 18 depending on the tile server.

Be sure to attribute any maps you publish, the osmAttribution function will assist.

Examples

Run this code

myraster = raster(matrix(0,10,10),xmn=8,xmx=18,ymn=0,ymx=10, 
  crs="+proj=longlat +datum=WGS84 +no_defs +ellps=WGS84 +towgs84=0,0,0")
values(myraster) = seq(0,1,len=ncell(myraster))

myPoints = SpatialPoints(myraster, proj4string=CRS(proj4string(myraster)))[
	seq(1,ncell(myraster),len=5)]

names(osmTiles())

mytiles = openmap(myraster)

	map.new(myraster)
	plot(mytiles, add=TRUE)
	points(myPoints,col='red')



	mytiles = openmap(myPoints,
		path=osmTiles("mapquest-sat"), verbose=TRUE)
	map.new(myPoints)
	plotRGB(mytiles, add=TRUE)
	points(myPoints,col='red')
	openmapAttribution(mytiles)

openmapAttribution("osm", type='markdown')