zoom.py 文件源码

def tile(self, lonlat, zoom):
        """
        Returns a Polygon  corresponding to the region represented by a fictional
        Google Tile for the given longitude/latitude pair and zoom level. This
        tile is used to determine the size of a tile at the given point.
        """
        # The given lonlat is the center of the tile.
        delta = self._tilesize / 2

        # Getting the pixel coordinates corresponding to the
        # the longitude/latitude.
        px = self.lonlat_to_pixel(lonlat, zoom)

        # Getting the lower-left and upper-right lat/lon coordinates
        # for the bounding box of the tile.
        ll = self.pixel_to_lonlat((px[0]-delta, px[1]-delta), zoom)
        ur = self.pixel_to_lonlat((px[0]+delta, px[1]+delta), zoom)

        # Constructing the Polygon, representing the tile and returning.
        return Polygon(LinearRing(ll, (ll[0], ur[1]), ur, (ur[0], ll[1]), ll), srid=4326)