EKF2: move handling of invalid range into ECL (#12988)

* ekf2: Move handling of invalid range finder data inside ecl library

The ecl library EKF is able to use vehicle motion and in-air status to better determine when the default on-ground range finder reading can be used.
The description for the EKF2_MIN_RNG parameter has been updated to make its use clearer.

src/modules/ekf2/ekf2_main.cpp

@@ -1118,28 +1118,12 @@ void Ekf2::run()
 		}
 
 		if (_range_finder_sub_index >= 0) {
-			bool range_finder_updated = _range_finder_subs[_range_finder_sub_index].updated();
 
-			if (range_finder_updated) {
+			if (_range_finder_subs[_range_finder_sub_index].updated()) {
 				distance_sensor_s range_finder;
 
 				if (_range_finder_subs[_range_finder_sub_index].copy(&range_finder)) {
-					// check distance sensor data quality
-					// TODO - move this check inside the ecl library
-					if (range_finder.signal_quality == 0) {
-						// use rng_gnd_clearance if on ground
-						if (_ekf.get_in_air_status()) {
-							range_finder_updated = false;
-
-						} else {
-							range_finder.current_distance = _param_ekf2_min_rng.get();
-						}
-					}
-
-					if (range_finder_updated) {
-						// TODO: Nico's pr will add proper quality handling, for now we put it to unkown
-						_ekf.setRangeData(range_finder.timestamp, range_finder.current_distance, -1.f);
-					}
+					_ekf.setRangeData(range_finder.timestamp, range_finder.current_distance, range_finder.signal_quality);
 
 					// Save sensor limits reported by the rangefinder
 					_ekf.set_rangefinder_limits(range_finder.min_distance, range_finder.max_distance);

src/modules/ekf2/ekf2_params.c

@@ -689,7 +689,9 @@ PARAM_DEFINE_FLOAT(EKF2_RNG_SFE, 0.05f);
 PARAM_DEFINE_FLOAT(EKF2_RNG_GATE, 5.0f);
 
 /**
- * Minimum valid range for the range finder
+ * Expected range finder reading when on ground.
+ *
+ * If the vehicle is on ground, is not moving as determined by the motion test controlled by EKF2_MOVE_TEST and the range finder is returning invalid or no data, then an assumed range value of EKF2_MIN_RNG will be used by the terrain estimator so that a terrain height estimate is avilable at the start of flight in situations where the range finder may be inside its minimum measurements distance when on ground.
  *
  * @group EKF2
  * @min 0.01