gistfile1.rb

require 'rubygems'
require 'cloudmade'
include CloudMade

class MapService
  
  def initialize(latmin,latmax,lonmin,lonmax,zoommin,zoommax,styleid)
    @latmin = latmin
    @latmax = latmax
    @lonmin = lonmin
    @lonmax = lonmax
    @zoommin = zoommin
    @zoommax = zoommax
    @styleid = styleid
    @apikey = 'YOUR KEY'
  end
  
  def selecttiles

    cm = Client.from_parameters(@apikey)

  	tl = []

    for zoom in @zoommin..@zoommax

      txmin = cm.tiles.xtile(@lonmin,zoom)
      txmax = cm.tiles.xtile(@lonmax,zoom)

      tymin = cm.tiles.ytile(@latmax,zoom)
      tymax = cm.tiles.ytile(@latmin,zoom)

      ntx = txmax - txmin + 1
      nty = tymax - tymin + 1

      tl[zoom] = []

      puts "Schedule #{ntx*nty} tiles for zoom level #{zoom} for downloan .."

      for tx in txmin..txmax
        for ty in tymin..tymax
          tl[zoom].push([tx,ty,zoom])
        end
      end

    end

    return tl

  end

  def downloadtiles(tiles)

    for zoom in tiles
      unless zoom == nil
        puts "Downloadings #{zoom.count} tiles for zoom level #{zoom[0][2]}"
        for tile in zoom
          downloadtile(tile[0],tile[1],tile[2])
        end
      end
    end

  end

  def downloadtile(x,y,z)

    cm = Client.from_parameters(@apikey)
    png = cm.tiles.get_xy_tile(x,y,z,@styleid)

    directory_z = "#{z}"
    directory_x = "#{z}/#{x}"

    if !FileTest::directory?(directory_z)
      Dir::mkdir(directory_z)
    end

    if !FileTest::directory?(directory_x)
      Dir::mkdir(directory_x)
    end

    file = File.new("#{z}/#{x}/#{y}.png", 'w')
    file.write(png)
    file.close
    
  end
  
end

#example usage 
m = MapService.new(51.4264,51.5886,-0.2695,0.0124,3,18,2666)
tiles = m.selecttiles
m.downloadtiles(tiles)