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