MCLandDetector: clean up logic for ground effect

Before: in_ground_effect was always true with the default settings (LNDMC_ALT_GND =-1)
 and when a distance sensor was present with valid data.
Now: default of LNDMC_ALT_GND is set to 2m by default, and if set to a negative value
then in_ground_effect is never set to true

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

src/modules/land_detector/MulticopterLandDetector.cpp

@@ -187,8 +187,8 @@ bool MulticopterLandDetector::_get_ground_contact_state()
 		_horizontal_movement = false; // not known
 	}
 
-	if (lpos_available && _vehicle_local_position.dist_bottom_valid) {
-		_below_gnd_effect_hgt = _vehicle_local_position.dist_bottom < _get_gnd_effect_altitude();
+	if (lpos_available && _vehicle_local_position.dist_bottom_valid && _param_lndmc_alt_gnd_effect.get() > 0) {
+		_below_gnd_effect_hgt = _vehicle_local_position.dist_bottom < _param_lndmc_alt_gnd_effect.get();
 
 	} else {
 		_below_gnd_effect_hgt = false;
@@ -323,16 +323,6 @@ bool MulticopterLandDetector::_get_landed_state()
 	return _maybe_landed_hysteresis.get_state();
 }
 
-float MulticopterLandDetector::_get_gnd_effect_altitude()
-{
-	if (_param_lndmc_alt_gnd_effect.get() < 0.0f) {
-		return INFINITY;
-
-	} else {
-		return _param_lndmc_alt_gnd_effect.get();
-	}
-}
-
 bool MulticopterLandDetector::_get_ground_effect_state()
 {
 	return (_in_descend && !_horizontal_movement) ||

src/modules/land_detector/MulticopterLandDetector.h

@@ -79,8 +79,6 @@ protected:
 
 	void _set_hysteresis_factor(const int factor) override;
 private:
-
-	float _get_gnd_effect_altitude();
 	bool _is_close_to_ground();
 
 	/** Time in us that freefall has to hold before triggering freefall */

src/modules/land_detector/land_detector_params_mc.c

@@ -113,4 +113,4 @@ PARAM_DEFINE_FLOAT(LNDMC_ALT_MAX, -1.0f);
  * @group Land Detector
  *
  */
-PARAM_DEFINE_FLOAT(LNDMC_ALT_GND, -1.0f);
+PARAM_DEFINE_FLOAT(LNDMC_ALT_GND, 2.f);