FW land detector: tighten thresholds in airspeed-less case

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

src/modules/land_detector/FixedwingLandDetector.cpp

@@ -1,6 +1,6 @@
 /****************************************************************************
  *
- *   Copyright (c) 2013-2016 PX4 Development Team. All rights reserved.
+ *   Copyright (c) 2013-2021 PX4 Development Team. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -80,9 +80,12 @@ bool FixedwingLandDetector::_get_landed_state()
 		airspeed_validated_s airspeed_validated{};
 		_airspeed_validated_sub.copy(&airspeed_validated);
 
+		bool airspeed_invalid = false;
+
 		// set _airspeed_filtered to 0 if airspeed data is invalid
 		if (!PX4_ISFINITE(airspeed_validated.true_airspeed_m_s) || hrt_elapsed_time(&airspeed_validated.timestamp) > 1_s) {
 			_airspeed_filtered = 0.0f;
+			airspeed_invalid = true;
 
 		} else {
 			_airspeed_filtered = 0.95f * _airspeed_filtered + 0.05f * airspeed_validated.true_airspeed_m_s;
@@ -93,10 +96,16 @@ bool FixedwingLandDetector::_get_landed_state()
 		const float acc_hor = matrix::Vector2f(_acceleration).norm();
 		_xy_accel_filtered = _xy_accel_filtered * 0.8f + acc_hor * 0.18f;
 
+		// make thresholds tighter if airspeed is invalid
+		const float vel_xy_max_threshold = airspeed_invalid ? 0.7f * _param_lndfw_vel_xy_max.get() :
+						   _param_lndfw_vel_xy_max.get();
+		const float vel_z_max_threshold = airspeed_invalid ? 0.7f * _param_lndfw_vel_z_max.get() :
+						  _param_lndfw_vel_z_max.get();
+
 		// Crude land detector for fixedwing.
 		landDetected = _airspeed_filtered       < _param_lndfw_airspd.get()
-			       && _velocity_xy_filtered < _param_lndfw_vel_xy_max.get()
-			       && _velocity_z_filtered  < _param_lndfw_vel_z_max.get()
+			       && _velocity_xy_filtered < vel_xy_max_threshold
+			       && _velocity_z_filtered  < vel_z_max_threshold
 			       && _xy_accel_filtered    < _param_lndfw_xyaccel_max.get();
 
 	} else {

src/modules/land_detector/land_detector_params_fw.c

@@ -1,6 +1,6 @@
 /****************************************************************************
  *
- *   Copyright (c) 2014-2017 PX4 Development Team. All rights reserved.
+ *   Copyright (c) 2014-2021 PX4 Development Team. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -32,9 +32,11 @@
  ****************************************************************************/
 
 /**
- * Fixedwing max horizontal velocity
+ * Fixed-wing land detector: Max horizontal velocity threshold
  *
- * Maximum horizontal velocity allowed in the landed state
+ * Maximum horizontal velocity allowed in the landed state.
+ * A factor of 0.7 is applied in case of airspeed-less flying
+ * (either because no sensor is present or sensor data got invalid in flight).
  *
  * @unit m/s
  * @min 0.5
@@ -46,9 +48,11 @@
 PARAM_DEFINE_FLOAT(LNDFW_VEL_XY_MAX, 5.0f);
 
 /**
- * Fixedwing max climb rate
+ * Fixed-wing land detector: Max vertiacal velocity threshold
  *
- * Maximum vertical velocity allowed in the landed state
+ * Maximum vertical velocity allowed in the landed state.
+ * A factor of 0.7 is applied in case of airspeed-less flying
+ * (either because no sensor is present or sensor data got invalid in flight).
  *
  * @unit m/s
  * @min 0.1
@@ -57,10 +61,10 @@ PARAM_DEFINE_FLOAT(LNDFW_VEL_XY_MAX, 5.0f);
  *
  * @group Land Detector
  */
-PARAM_DEFINE_FLOAT(LNDFW_VEL_Z_MAX, 3.0f);
+PARAM_DEFINE_FLOAT(LNDFW_VEL_Z_MAX, 2.0f);
 
 /**
- * Fixedwing max horizontal acceleration
+ * Fixed-wing land detector: Max horizontal acceleration
  *
  * Maximum horizontal (x,y body axes) acceleration allowed in the landed state
  *
@@ -74,12 +78,12 @@ PARAM_DEFINE_FLOAT(LNDFW_VEL_Z_MAX, 3.0f);
 PARAM_DEFINE_FLOAT(LNDFW_XYACC_MAX, 8.0f);
 
 /**
- * Airspeed max
+ * Fixed-wing land detector: Max airspeed
  *
  * Maximum airspeed allowed in the landed state
  *
  * @unit m/s
- * @min 4
+ * @min 2
  * @max 20
  * @decimal 1
  *