def __init__(self, num_zoom=19, tilesize=256):
        # 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 xrange(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
Initializes the Google Zoom object.
dataset/ETHPy150Open AppScale/appscale/AppServer/lib/django-1.4/django/contrib/gis/maps/google/zoom.py/GoogleZoom.__init__