code: def latlon2tilenums(lat, lon, zoom)
        factor = 2**(zoom - 1)
        lat = radians(lat)
        lon = radians(lon)
        xtile = 1 + lon / Math::PI
        ytile = 1 - Math.log(Math.tan(lat) + (1 / Math.cos(lat))) / Math::PI
        return Point.new((xtile * factor).to_i, (ytile * factor).to_i)
      end
docs: Convert latitude, longitude pair to tile coordinates. Returns tile coordinates as a CloudMade::Point object
   * +lat+ Latitude
   * +lon+ Longitude
   * +zoom+ Zoom level