zoom.py 文件源码

def lonlat_to_pixel(self, lonlat, zoom):
        "Converts a longitude, latitude coordinate pair for the given zoom level."
        # Setting up, unpacking the longitude, latitude values and getting the
        # number of pixels for the given zoom level.
        lon, lat = self.get_lon_lat(lonlat)
        npix = self._npix[zoom]

        # Calculating the pixel x coordinate by multiplying the longitude value
        # with the number of degrees/pixel at the given zoom level.
        px_x = round(npix + (lon * self._degpp[zoom]))

        # Creating the factor, and ensuring that 1 or -1 is not passed in as the
        # base to the logarithm.  Here's why:
        #  if fac = -1, we'll get log(0) which is undefined;
        #  if fac =  1, our logarithm base will be divided by 0, also undefined.
        fac = min(max(sin(DTOR * lat), -0.9999), 0.9999)

        # Calculating the pixel y coordinate.
        px_y = round(npix + (0.5 * log((1 + fac) / (1 - fac)) * (-1.0 * self._radpp[zoom])))

        # Returning the pixel x, y to the caller of the function.
        return (px_x, px_y)