AC_PrecLand: add ACC_P_NSE parameter

libraries/AC_PrecLand/AC_PrecLand.cpp

@@ -57,7 +57,12 @@ const AP_Param::GroupInfo AC_PrecLand::var_info[] = {
     // @User: Advanced
     AP_GROUPINFO("EST_TYPE",    5, AC_PrecLand, _estimator_type, 1),
 
-    // 6 RESERVED for ACC_NSE
+    // @Param: ACC_P_NSE
+    // @DisplayName: Kalman Filter Accelerometer Noise
+    // @Description: Kalman Filter Accelerometer Noise, higher values weight the input from the camera more, accels less
+    // @Range: 0.5 5
+    // @User: Advanceds
+    AP_GROUPINFO("ACC_P_NSE", 6, AC_PrecLand, _accel_noise, 2.5f),
 
     AP_GROUPEND
 };
@@ -249,8 +254,8 @@ void AC_PrecLand::run_estimator(float rangefinder_alt_m, bool rangefinder_alt_va
                 const float& dt = inertial_data_delayed.dt;
                 const Vector3f& vehicleDelVel = inertial_data_delayed.correctedVehicleDeltaVelocityNED;
 
-                _ekf_x.predict(dt, -vehicleDelVel.x, 0.5f*dt);
-                _ekf_y.predict(dt, -vehicleDelVel.y, 0.5f*dt);
+                _ekf_x.predict(dt, -vehicleDelVel.x, _accel_noise*dt);
+                _ekf_y.predict(dt, -vehicleDelVel.y, _accel_noise*dt);
             }
 
             // Update if a new LOS measurement is available

libraries/AC_PrecLand/AC_PrecLand.h

@@ -108,6 +108,7 @@ private:
     AP_Float                    _yaw_align;         // Yaw angle from body x-axis to sensor x-axis.
     AP_Float                    _land_ofs_cm_x;     // Desired landing position of the camera forward of the target in vehicle body frame
     AP_Float                    _land_ofs_cm_y;     // Desired landing position of the camera right of the target in vehicle body frame
+    AP_Float                    _accel_noise;       // accelometer process noise
 
     uint32_t                    _last_update_ms;    // system time in millisecond when update was last called
     bool                        _target_acquired;   // true if target has been seen recently