gistfile1.txt

  def self.tiles_for(lat, lng, search_radius)
    adj_lat = (lat + 90).floor
    adj_lng = (lng + 180).floor

    lat_interval = 110_574 # this is at the poles, its around 111km at the equator so we're using the shorter one - not worth calculating a more accurate value based on lat
    # this one is from here: http://en.wikipedia.org/wiki/Longitude
    # specifically: PI / 180 cos(theta) * N(theta), and we're using a fixed value
    #               of N(theta) because its close enough. Basically it is 0 at the poles
    #               and 68 miles at the equator. We'll allow a minimum of 10km though, which is
    #               basically at the poles, because I dont want to use a ton of tiles in
    #               the search
    lng_interval = (Math.cos(lat * Math::PI / 180) * 6_378_137 * Math::PI / 180)
    lng_interval = 10_000 if lng_interval < 10_000

    lat_deg_radius = (search_radius / lat_interval).ceil
    lng_deg_radius = (search_radius / lng_interval).ceil

    tiles = []
    (adj_lng - lng_deg_radius).upto(adj_lng + lng_deg_radius) do |x|
      (adj_lat - lat_deg_radius).upto(adj_lat + lat_deg_radius) do |y|
        tiles << "#{x}x#{y}"
      end
    end
    tiles
  end