make use of local position height for takeoff in gps denied environment

- When taking off in an gps denied environment, there would be no global
  position. Thus we make use of the local position estimate to check
whether we have met the position setpoint.

- As a side effect: This enables the ModeCompleted Message to be sent to
  an onboard computer for the ModeExecutor to know it can continue

Author: henrykotze

src/modules/navigator/mission_block.cpp

@@ -199,6 +199,12 @@ MissionBlock::is_mission_item_reached_or_completed()
 				_waypoint_position_reached = true;
 			}
 
+			/* in gps denied environment we make use of the local position estimate*/
+			if(_navigator->get_local_position()->z <
+			(-1.0f * takeoff_alt + altitude_acceptance_radius)) {
+				_waypoint_position_reached = true;
+			}
+
 		} else if (_mission_item.nav_cmd == NAV_CMD_TAKEOFF
 			   && _navigator->get_vstatus()->vehicle_type == vehicle_status_s::VEHICLE_TYPE_FIXED_WING) {
 			/* fixed-wing takeoff is reached once the vehicle has exceeded the takeoff altitude */