FixedwingPositionControl: Add support for figure 8 loitering.

The command is sent by a dedicated mavlink command and forwarded to the fixed wing position controller.

The pattern is defined by the radius of the major axis, the radius of the minor axis and the orientation. The pattern is then defined by:
The upper part of the pattern consist of a clockwise circle with radius defined by the minor axis. The center of the circle is defined by the major axis minus the minor axis away from the pattern center.
The lower part of the pattern consist of a counter-clockwise circle with the same definitions as above.
In between, the circles are connected with straight lines in a cross configuration. The lines are always tangetial to the circles.
The orientation rotates the major axis around the NED down axis.

The loitering logic is defined inside its own class used by the fixed wing position control module. It defines which segment (one of the circles or lines) is active and uses the path controller (npfg or l1-control) to determine the desired roll angle.

A feedback mavlink message is send with the executed pattern parameters.

msg/CMakeLists.txt

@@ -85,6 +85,7 @@ set(msg_files
 	EstimatorStatus.msg
 	EstimatorStatusFlags.msg
 	Event.msg
+	FigureEightStatus.msg
 	FailsafeFlags.msg
 	FailureDetectorStatus.msg
 	FollowTarget.msg

msg/FigureEightStatus.msg

@@ -0,0 +1,8 @@
+uint64 timestamp # time since system start (microseconds)
+float32 major_radius 	# Major axis radius of the figure eight [m]. Positive values orbit clockwise, negative values orbit counter-clockwise.
+float32 minor_radius 	# Minor axis radius of the figure eight [m].
+float32 orientation 	# Orientation of the major axis of the figure eight [rad].
+uint8 frame      # The coordinate system of the fields: x, y, z.
+int32 x          # X coordinate of center point. Coordinate system depends on frame field: local = x position in meters * 1e4, global = latitude in degrees * 1e7.
+int32 y        	 # Y coordinate of center point. Coordinate system depends on frame field: local = y position in meters * 1e4, global = latitude in degrees * 1e7.
+float32 z        # Altitude of center point. Coordinate system depends on frame field.

msg/PositionSetpoint.msg

@@ -9,6 +9,9 @@ uint8 SETPOINT_TYPE_TAKEOFF=3	# takeoff setpoint
 uint8 SETPOINT_TYPE_LAND=4	# land setpoint, altitude must be ignored, descend until landing
 uint8 SETPOINT_TYPE_IDLE=5	# do nothing, switch off motors or keep at idle speed (MC)
 
+uint8 LOITER_TYPE_ORBIT=0 	# Circular pattern
+uint8 LOITER_TYPE_FIGUREEIGHT=1 # Pattern resembling an 8
+
 bool valid			# true if setpoint is valid
 uint8 type			# setpoint type to adjust behavior of position controller
 
@@ -25,8 +28,11 @@ bool yaw_valid			# true if yaw setpoint valid
 float32 yawspeed		# yawspeed (only for multirotors, in rad/s)
 bool yawspeed_valid		# true if yawspeed setpoint valid
 
-float32 loiter_radius		# loiter radius (only for fixed wing), in m
+float32 loiter_radius		# loiter major axis radius in m
+float32 loiter_minor_radius	# loiter minor axis radius (used for non-circular loiter shapes) in m
 bool loiter_direction_counter_clockwise # loiter direction is clockwise by default and can be changed using this field
+float32 loiter_orientation 	# Orientation of the major axis with respect to true north in rad [-pi,pi)
+uint8 	loiter_pattern		# loitern pattern to follow
 
 float32 acceptance_radius   # navigation acceptance_radius if we're doing waypoint navigation
 

msg/VehicleCommand.msg

@@ -15,6 +15,7 @@ uint16 VEHICLE_CMD_NAV_LAND = 21			# Land at location |Empty| Empty| Empty| Desi
 uint16 VEHICLE_CMD_NAV_TAKEOFF = 22			# Takeoff from ground / hand |Minimum pitch (if airspeed sensor present), desired pitch without sensor| Empty| Empty| Yaw angle (if magnetometer present), ignored without magnetometer| Latitude| Longitude| Altitude|
 uint16 VEHICLE_CMD_NAV_PRECLAND = 23			# Attempt a precision landing
 uint16 VEHICLE_CMD_DO_ORBIT = 34			# Start orbiting on the circumference of a circle defined by the parameters. |Radius [m] |Velocity [m/s] |Yaw behaviour |Empty |Latitude/X |Longitude/Y |Altitude/Z |
+uint16 VEHICLE_CMD_DO_FIGUREEIGHT = 35        		# Start flying on the outline of a figure eight defined by the parameters. |Major Radius [m] |Minor Radius [m] |Velocity [m/s] |Orientation |Latitude/X |Longitude/Y |Altitude/Z |
 uint16 VEHICLE_CMD_NAV_ROI = 80				# Sets the region of interest (ROI) for a sensor set or the vehicle itself. This can then be used by the vehicles control system to control the vehicle attitude and the attitude of various sensors such as cameras. |Region of interest mode. (see MAV_ROI enum)| MISSION index/ target ID. (see MAV_ROI enum)| ROI index (allows a vehicle to manage multiple ROI's)| Empty| x the location of the fixed ROI (see MAV_FRAME)| y| z|
 uint16 VEHICLE_CMD_NAV_PATHPLANNING = 81		# Control autonomous path planning on the MAV. |0: Disable local obstacle avoidance / local path planning (without resetting map), 1: Enable local path planning, 2: Enable and reset local path planning| 0: Disable full path planning (without resetting map), 1: Enable, 2: Enable and reset map/occupancy grid, 3: Enable and reset planned route, but not occupancy grid| Empty| Yaw angle at goal, in compass degrees, [0..360]| Latitude/X of goal| Longitude/Y of goal| Altitude/Z of goal|
 uint16 VEHICLE_CMD_NAV_VTOL_TAKEOFF = 84		# Takeoff from ground / hand and transition to fixed wing |Minimum pitch (if airspeed sensor present), desired pitch without sensor| Empty| Empty| Yaw angle (if magnetometer present), ignored without magnetometer| Latitude| Longitude| Altitude|