FW land detector: only use LNDFW_ROT_MAX if speeds are not valid

The rotational speed threshold on fixed-wing vehicles is triggering easily
if the plane is lifted prior to takeoff (hand-launch), and can cause issues
for the auto takeoff state machine. Thus if either airspeed or groundspeed is valid,
it's better to rely on these for land detection, and only use the rotational
speed if they're invalid.

Signed-off-by: Silvan <silvan@auterion.com>

Author: sfuhrer

src/modules/land_detector/FixedwingLandDetector.cpp

@@ -121,7 +121,9 @@ bool FixedwingLandDetector::_get_landed_state()
 		const float vel_xy_max_threshold   = airspeed_invalid ? 0.7f * _param_lndfw_vel_xy_max.get() :
 						     _param_lndfw_vel_xy_max.get();
 
-		const float max_rotation_threshold = math::radians(_param_lndfw_rot_max.get()) ;
+		// only use the max rotational threshold if neither airspeed nor groundspeed can be used for landing detection
+		const float max_rotation_threshold = (!_vehicle_local_position.v_xy_valid
+						      && airspeed_invalid) ? math::radians(_param_lndfw_rot_max.get()) : INFINITY;
 
 		// Crude land detector for fixedwing.
 		landDetected = _airspeed_filtered         < _param_lndfw_airspd.get()

src/modules/land_detector/land_detector_params_fw.c

@@ -107,6 +107,7 @@ PARAM_DEFINE_FLOAT(LNDFW_TRIG_TIME, 2.f);
  * Fixed-wing land detector: max rotational speed
  *
  * Maximum allowed norm of the angular velocity in the landed state.
+ * Only used if neither airspeed nor groundspeed can be used for landing detection.
  *
  * @unit deg/s
  * @decimal 1