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=NA, verbose=FALSE)
	getTiles(xlim,ylim,zoom,path,maxTiles = 16,cacheDir=tempdir(),
		timeOut=5*24*60*60,verbose=FALSE)
	osmTiles(name)

Arguments

Either raster, SPDF, matrix corresponding to a bounding box or an Extent.

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 null, 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

cacheDir

A directory for caching tiles retrieved over the web. Not used if tiles are coming from a local directory.

xlim

Length-2 vector of min and max X coordinate (latitude)

ylim

Length-2 vector of min and max Y coordinate (longitude)

timeOut

Tiles in the cache directory older than this (in minutes) are re-retrieved.

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.

Value

openmap returns a RasterBrick brick, with 'red', 'green' and 'blue' layers. getTiles returns a list of RasterBricks

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 0 has one tile that covers the whole world at a resolution of 256x256 pixels. 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.

The function getTiles() retrieves tiles to cover a given latitude and longitude range at a given zoom level. Note that since tiles are generated at a fixed set of lat-long ranges the returned tiles will overlap the requested area. There may be some way of clipping to the requested area in a future revision.

The getTilePaths() function returns information about tiles in a region at a zoom level. The tile source path is given but tiles are not requested. A list is returned with one element per tile giving the path, the I and J coordinates, the zoom level, and the geographic bounds for the tile.

The tileBbox() function returns the bounds of the tiles by simply constructing the bounding box of all the constitutent SpatialGridDataFrame objects.

http://wiki.openstreetmap.org/index.php/Tile_usage_policy

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')