EARTH_RADIUS_IN_METERS = 6371010
TILE_SIZE = 256
SCREEN_PIXEL_HEIGHT = 768
RADIUS_X_PIXEL_HEIGHT = 27.3611 * EARTH_RADIUS_IN_METERS * SCREEN_PIXEL_HEIGHT

def altitude(zoom, latitude)
  (RADIUS_X_PIXEL_HEIGHT * Math.cos((latitude * Math::PI) / 180)) / ((2 ** zoom) * TILE_SIZE)
end