called when user selects "Set Home" on map

def cmd_set_home(self, args):
        '''called when user selects "Set Home" on map'''
        (lat, lon) = (self.click_position[0], self.click_position[1])
        alt = self.ElevationMap.GetElevation(lat, lon)
        print("Setting home to: ", lat, lon, alt)
        self.master.mav.command_long_send(
            self.settings.target_system, self.settings.target_component,
            mavutil.mavlink.MAV_CMD_DO_SET_HOME,
            1, # set position
            0, # param1
            0, # param2
            0, # param3
            0, # param4
            lat, # lat
            lon, # lon
            alt)