zoom.py 文件源码

def __init__(self, num_zoom=19, tilesize=256):
        "Initializes the Google Zoom object."
        # Google's tilesize is 256x256, square tiles are assumed.
        self._tilesize = tilesize

        # The number of zoom levels
        self._nzoom = num_zoom

        # Initializing arrays to hold the parameters for each one of the
        # zoom levels.
        self._degpp = []  # Degrees per pixel
        self._radpp = []  # Radians per pixel
        self._npix = []  # 1/2 the number of pixels for a tile at the given zoom level

        # Incrementing through the zoom levels and populating the parameter arrays.
        z = tilesize  # The number of pixels per zoom level.
        for i in range(num_zoom):
            # Getting the degrees and radians per pixel, and the 1/2 the number of
            # for every zoom level.
            self._degpp.append(z / 360.)  # degrees per pixel
            self._radpp.append(z / (2 * pi))  # radians per pixel
            self._npix.append(z / 2)  # number of pixels to center of tile

            # Multiplying `z` by 2 for the next iteration.
            z *= 2