Get the image boundary

        Returns:
            A tupple composed by the westernmost_longitude,
            the westernmost_longitude, the minimum_latitude and
            the maximum_latitude.

def boundary(self):
        """ Get the image boundary

        Returns:
            A tupple composed by the westernmost_longitude,
            the westernmost_longitude, the minimum_latitude and
            the maximum_latitude.

        """

        return (int(self.WESTERNMOST_LONGITUDE),
                int(self.EASTERNMOST_LONGITUDE),
                int(self.MINIMUM_LATITUDE),
                int(self.MAXIMUM_LATITUDE))