return current location

def location(self, relative_alt=False):
        '''return current location'''
        self.wait_gps_fix()
        # wait for another VFR_HUD, to ensure we have correct altitude
        self.recv_match(type='VFR_HUD', blocking=True)
        self.recv_match(type='GLOBAL_POSITION_INT', blocking=True)
        if relative_alt:
            alt = self.messages['GLOBAL_POSITION_INT'].relative_alt*0.001
        else:
            alt = self.messages['VFR_HUD'].alt
        return location(self.messages['GPS_RAW_INT'].lat*1.0e-7,
                        self.messages['GPS_RAW_INT'].lon*1.0e-7,
                        alt,
                        self.messages['VFR_HUD'].heading)