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  /**
   * @file control.cpp
   * Control functions for ekf attitude and position estimator.
   *
   * @author Paul Riseborough <p_riseborough@live.com.au>
   *
   */
  
  #include "../ecl.h"
  #include "ekf.h"
  #include <mathlib/mathlib.h>
  
  void Ekf::controlFusionModes()
  {
  	// Store the status to enable change detection
  	_control_status_prev.value = _control_status.value;
  
  	// Get the magnetic declination
  	calcMagDeclination();
  
  	// monitor the tilt alignment
  	if (!_control_status.flags.tilt_align) {
  		// whilst we are aligning the tilt, monitor the variances
  		Vector3f angle_err_var_vec = calcRotVecVariances();
  
  		// Once the tilt variances have reduced to equivalent of 3deg uncertainty, re-set the yaw and magnetic field states
  		// and declare the tilt alignment complete
  		if ((angle_err_var_vec(0) + angle_err_var_vec(1)) < sq(math::radians(3.0f))) {
  			_control_status.flags.tilt_align = true;
  			_control_status.flags.yaw_align = resetMagHeading(_mag_sample_delayed.mag);
  
  			// send alignment status message to the console
  			if (_control_status.flags.baro_hgt) {
  				ECL_INFO("EKF aligned, (pressure height, IMU buf: %i, OBS buf: %i)", (int)_imu_buffer_length, (int)_obs_buffer_length);
  
  			} else if (_control_status.flags.ev_hgt) {
  				ECL_INFO("EKF aligned, (EV height, IMU buf: %i, OBS buf: %i)", (int)_imu_buffer_length, (int)_obs_buffer_length);
  
  			} else if (_control_status.flags.gps_hgt) {
  				ECL_INFO("EKF aligned, (GPS height, IMU buf: %i, OBS buf: %i)", (int)_imu_buffer_length, (int)_obs_buffer_length);
  
  			} else if (_control_status.flags.rng_hgt) {
  				ECL_INFO("EKF aligned, (range height, IMU buf: %i, OBS buf: %i)", (int)_imu_buffer_length, (int)_obs_buffer_length);
  
  			} else {
  				ECL_ERR("EKF aligned, (unknown height, IMU buf: %i, OBS buf: %i)", (int)_imu_buffer_length, (int)_obs_buffer_length);
  			}
  
  		}
  
  	}
  
  	// check faultiness (before pop_first_older_than) to see if we can change back to original height sensor
  	const baroSample &baro_init = _baro_buffer.get_newest();
  	_baro_hgt_faulty = !((_time_last_imu - baro_init.time_us) < 2 * BARO_MAX_INTERVAL);
  
  	const gpsSample &gps_init = _gps_buffer.get_newest();
  	_gps_hgt_faulty = !((_time_last_imu - gps_init.time_us) < 2 * GPS_MAX_INTERVAL);
  
  	// check for arrival of new sensor data at the fusion time horizon
  	_gps_data_ready = _gps_buffer.pop_first_older_than(_imu_sample_delayed.time_us, &_gps_sample_delayed);
  	_mag_data_ready = _mag_buffer.pop_first_older_than(_imu_sample_delayed.time_us, &_mag_sample_delayed);
  
  	_delta_time_baro_us = _baro_sample_delayed.time_us;
  	_baro_data_ready = _baro_buffer.pop_first_older_than(_imu_sample_delayed.time_us, &_baro_sample_delayed);
  
  	// if we have a new baro sample save the delta time between this sample and the last sample which is
  	// used below for baro offset calculations
  	if (_baro_data_ready) {
  		_delta_time_baro_us = _baro_sample_delayed.time_us - _delta_time_baro_us;
  	}
  
  	// calculate 2,2 element of rotation matrix from sensor frame to earth frame
  	// this is required for use of range finder and flow data
  	_R_rng_to_earth_2_2 = _R_to_earth(2, 0) * _sin_tilt_rng + _R_to_earth(2, 2) * _cos_tilt_rng;
  
  	// Get range data from buffer and check validity
  	_range_data_ready = _range_buffer.pop_first_older_than(_imu_sample_delayed.time_us, &_range_sample_delayed);
  
  	checkRangeDataValidity();
  
  	if (_range_data_ready && !_rng_hgt_faulty) {
  		// correct the range data for position offset relative to the IMU
  		Vector3f pos_offset_body = _params.rng_pos_body - _params.imu_pos_body;
  		Vector3f pos_offset_earth = _R_to_earth * pos_offset_body;
  		_range_sample_delayed.rng += pos_offset_earth(2) / _R_rng_to_earth_2_2;
  	}
  	
  	// We don't fuse flow data immediately because we have to wait for the mid integration point to fall behind the fusion time horizon.
  	// This means we stop looking for new data until the old data has been fused.
  	if (!_flow_data_ready) {
  		_flow_data_ready = _flow_buffer.pop_first_older_than(_imu_sample_delayed.time_us, &_flow_sample_delayed)
  				   && (_R_to_earth(2, 2) > _params.range_cos_max_tilt);
  	}
  
  	_ev_data_ready = _ext_vision_buffer.pop_first_older_than(_imu_sample_delayed.time_us, &_ev_sample_delayed);
  	_tas_data_ready = _airspeed_buffer.pop_first_older_than(_imu_sample_delayed.time_us, &_airspeed_sample_delayed);
  
  	// check for height sensor timeouts and reset and change sensor if necessary
  	controlHeightSensorTimeouts();
  
  	// control use of observations for aiding
  	controlMagFusion();
  	controlOpticalFlowFusion();
  	controlGpsFusion();
  	controlAirDataFusion();
  	controlBetaFusion();
  	controlDragFusion();
  	controlHeightFusion();
  
  	// For efficiency, fusion of direct state observations for position and velocity is performed sequentially
  	// in a single function using sensor data from multiple sources (GPS, baro, range finder, etc)
  	controlVelPosFusion();
  
  	// Additional data from an external vision pose estimator can be fused.
  	controlExternalVisionFusion();
  
  	// Additional NE velocity data from an auxiliary sensor can be fused
  	controlAuxVelFusion();
  
  	// check if we are no longer fusing measurements that directly constrain velocity drift
  	update_deadreckoning_status();
  }
  
  void Ekf::controlExternalVisionFusion()
  {
  	// Check for new exernal vision data
  	if (_ev_data_ready) {
  
  		// if the ev data is not in a NED reference frame, then the transformation between EV and EKF navigation frames
  		// needs to be calculated and the observations rotated into the EKF frame of reference
  		if ((_params.fusion_mode & MASK_ROTATE_EV) && (_params.fusion_mode & MASK_USE_EVPOS) && !_control_status.flags.ev_yaw) {
  			// rotate EV measurements into the EKF Navigation frame
  			calcExtVisRotMat();
  		}
  
  		// external vision position aiding selection logic
  		if ((_params.fusion_mode & MASK_USE_EVPOS) && !_control_status.flags.ev_pos && _control_status.flags.tilt_align
  		    && _control_status.flags.yaw_align) {
  
  			// check for a exernal vision measurement that has fallen behind the fusion time horizon
  			if (_time_last_imu - _time_last_ext_vision < 2 * EV_MAX_INTERVAL) {
  				// turn on use of external vision measurements for position
  				_control_status.flags.ev_pos = true;
  				ECL_INFO("EKF commencing external vision position fusion");
  
  				if ((_params.fusion_mode & MASK_ROTATE_EV) && !(_params.fusion_mode & MASK_USE_EVYAW))  {
  					// Reset transformation between EV and EKF navigation frames when starting fusion
  					resetExtVisRotMat();
  				}
  
  				// reset the position if we are not already aiding using GPS, else use a relative position
  				// method for fusing the position data
  				if (_control_status.flags.gps) {
  					_fuse_hpos_as_odom = true;
  
  				} else {
  					resetPosition();
  					resetVelocity();
  
  				}
  			}
  		}
  
  		// external vision yaw aiding selection logic
  		if (!_control_status.flags.gps && (_params.fusion_mode & MASK_USE_EVYAW) && !_control_status.flags.ev_yaw && _control_status.flags.tilt_align) {
  			// don't start using EV data unless daa is arriving frequently
  			if (_time_last_imu - _time_last_ext_vision < 2 * EV_MAX_INTERVAL) {
  				// reset the yaw angle to the value from the observaton quaternion
  				// get the roll, pitch, yaw estimates from the quaternion states
  				Quatf q_init(_state.quat_nominal);
  				Eulerf euler_init(q_init);
  
  				// get initial yaw from the observation quaternion
  				const extVisionSample &ev_newest = _ext_vision_buffer.get_newest();
  				Quatf q_obs(ev_newest.quat);
  				Eulerf euler_obs(q_obs);
  				euler_init(2) = euler_obs(2);
  
  				// save a copy of the quaternion state for later use in calculating the amount of reset change
  				Quatf quat_before_reset = _state.quat_nominal;
  
  				// calculate initial quaternion states for the ekf
  				_state.quat_nominal = Quatf(euler_init);
  
  				// calculate the amount that the quaternion has changed by
  				_state_reset_status.quat_change = quat_before_reset.inversed() * _state.quat_nominal;
  
  				// add the reset amount to the output observer buffered data
  				// Note q1 *= q2 is equivalent to q1 = q2 * q1
  				for (uint8_t i = 0; i < _output_buffer.get_length(); i++) {
  					_output_buffer[i].quat_nominal *= _state_reset_status.quat_change;
  				}
  
  				// apply the change in attitude quaternion to our newest quaternion estimate
  				// which was already taken out from the output buffer
  				_output_new.quat_nominal = _state_reset_status.quat_change * _output_new.quat_nominal;
  
  				// capture the reset event
  				_state_reset_status.quat_counter++;
  
  				// flag the yaw as aligned
  				_control_status.flags.yaw_align = true;
  
  				// turn on fusion of external vision yaw measurements and disable all magnetoemter fusion
  				_control_status.flags.ev_yaw = true;
  				_control_status.flags.mag_hdg = false;
  				_control_status.flags.mag_3D = false;
  				_control_status.flags.mag_dec = false;
  
  				ECL_INFO("EKF commencing external vision yaw fusion");
  			}
  		}
  
  		// determine if we should start using the height observations
  		if (_params.vdist_sensor_type == VDIST_SENSOR_EV) {
  			// don't start using EV data unless data is arriving frequently
  			if (!_control_status.flags.ev_hgt && (_time_last_imu - _time_last_ext_vision < 2 * EV_MAX_INTERVAL)) {
  				setControlEVHeight();
  				resetHeight();
  			}
  		}
  
  		// determine if we should use the vertical position observation
  		if (_control_status.flags.ev_hgt) {
  			_fuse_height = true;
  		}
  
  		// determine if we should use the horizontal position observations
  		if (_control_status.flags.ev_pos) {
  			_fuse_pos = true;
  
  			// correct position and height for offset relative to IMU
  			Vector3f pos_offset_body = _params.ev_pos_body - _params.imu_pos_body;
  			Vector3f pos_offset_earth = _R_to_earth * pos_offset_body;
  			_ev_sample_delayed.posNED(0) -= pos_offset_earth(0);
  			_ev_sample_delayed.posNED(1) -= pos_offset_earth(1);
  			_ev_sample_delayed.posNED(2) -= pos_offset_earth(2);
  
  			// Use an incremental position fusion method for EV data if using GPS or if the observations are not in NED
  			if (_control_status.flags.gps || (_params.fusion_mode & MASK_ROTATE_EV)) {
  				_fuse_hpos_as_odom = true;
  
  			} else {
  				_fuse_hpos_as_odom = false;
  			}
  
  			if (_fuse_hpos_as_odom) {
  				if (!_hpos_prev_available) {
  					// no previous observation available to calculate position change
  					_fuse_pos = false;
  					_hpos_prev_available = true;
  
  				} else {
  					// calculate the change in position since the last measurement
  					Vector3f ev_delta_pos = _ev_sample_delayed.posNED - _pos_meas_prev;
  
  					// rotate measurement into body frame if required
  					if (_params.fusion_mode & MASK_ROTATE_EV) {
  						ev_delta_pos = _ev_rot_mat * ev_delta_pos;
  					}
  
  					// use the change in position since the last measurement
  					_vel_pos_innov[3] = _state.pos(0) - _hpos_pred_prev(0) - ev_delta_pos(0);
  					_vel_pos_innov[4] = _state.pos(1) - _hpos_pred_prev(1) - ev_delta_pos(1);
  
  				}
  
  				// record observation and estimate for use next time
  				_pos_meas_prev = _ev_sample_delayed.posNED;
  				_hpos_pred_prev(0) = _state.pos(0);
  				_hpos_pred_prev(1) = _state.pos(1);
  
  			} else {
  				// use the absolute position
  				_vel_pos_innov[3] = _state.pos(0) - _ev_sample_delayed.posNED(0);
  				_vel_pos_innov[4] = _state.pos(1) - _ev_sample_delayed.posNED(1);
  
  				// check if we have been deadreckoning too long
  				if (_time_last_imu - _time_last_pos_fuse > _params.no_gps_timeout_max) {
  					// don't reset velocity if we have another source of aiding constraining it
  					if (_time_last_imu - _time_last_of_fuse > (uint64_t)1E6) {
  						resetVelocity();
  					}
  
  					resetPosition();
  				}
  			}
  
  			// observation 1-STD error
  			_posObsNoiseNE = fmaxf(_ev_sample_delayed.posErr, 0.01f);
  
  			// innovation gate size
  			_posInnovGateNE = fmaxf(_params.ev_innov_gate, 1.0f);
  		}
  
  		// Fuse available NED position data into the main filter
  		if (_fuse_height || _fuse_pos) {
  			fuseVelPosHeight();
  			_fuse_pos = _fuse_height = false;
  			_fuse_hpos_as_odom = false;
  
  		}
  
  		// determine if we should use the yaw observation
  		if (_control_status.flags.ev_yaw) {
  			fuseHeading();
  
  		}
  
  	} else if (_control_status.flags.ev_pos
  		   && (_time_last_imu >= _time_last_ext_vision)
  		   && (_time_last_imu - _time_last_ext_vision > (uint64_t)_params.no_gps_timeout_max)) {
  
  		// Turn off EV fusion mode if no data has been received
  		_control_status.flags.ev_pos = false;
  		ECL_INFO("EKF External Vision Data Stopped");
  
  	}
  }
  
  void Ekf::controlOpticalFlowFusion()
  {
  	// Check if on ground motion is un-suitable for use of optical flow
  	if (!_control_status.flags.in_air) {
  		// When on ground check if the vehicle is being shaken or moved in a way that could cause a loss of navigation
  		const float accel_norm = _accel_vec_filt.norm();
  
  		const bool motion_is_excessive = ((accel_norm > (CONSTANTS_ONE_G * 1.5f)) // upper g limit
  					    || (accel_norm < (CONSTANTS_ONE_G * 0.5f)) // lower g limit
  					    || (_ang_rate_mag_filt > _flow_max_rate) // angular rate exceeds flow sensor limit
  					    || (_R_to_earth(2,2) < cosf(math::radians(30.0f)))); // tilted excessively
  
  		if (motion_is_excessive) {
  			_time_bad_motion_us = _imu_sample_delayed.time_us;
  
  		} else {
  			_time_good_motion_us = _imu_sample_delayed.time_us;
  		}
  
  	} else {
  		_time_bad_motion_us = 0;
  		_time_good_motion_us = _imu_sample_delayed.time_us;
  	}
  
  	// Accumulate autopilot gyro data across the same time interval as the flow sensor
  	_imu_del_ang_of += _imu_sample_delayed.delta_ang - _state.gyro_bias;
  	_delta_time_of += _imu_sample_delayed.delta_ang_dt;
  
  	// New optical flow data is available and is ready to be fused when the midpoint of the sample falls behind the fusion time horizon
  	if (_flow_data_ready) {
  		// Inhibit flow use if motion is un-suitable or we have good quality GPS
  		// Apply hysteresis to prevent rapid mode switching
  		float gps_err_norm_lim;
  		if (_control_status.flags.opt_flow) {
  			gps_err_norm_lim = 0.7f;
  		} else {
  			gps_err_norm_lim = 1.0f;
  		}
  
  		// Check if we are in-air and require optical flow to control position drift
  		bool flow_required = _control_status.flags.in_air &&
  				(_is_dead_reckoning // is doing inertial dead-reckoning so must constrain drift urgently
  				  || (_control_status.flags.opt_flow && !_control_status.flags.gps && !_control_status.flags.ev_pos) // is completely reliant on optical flow
  				  || (_control_status.flags.gps && (_gps_error_norm > gps_err_norm_lim))); // is using GPS, but GPS is bad
  
  		if (!_inhibit_flow_use && _control_status.flags.opt_flow) {
  			// inhibit use of optical flow if motion is unsuitable and we are not reliant on it for flight navigation
  			bool preflight_motion_not_ok = !_control_status.flags.in_air && ((_imu_sample_delayed.time_us - _time_good_motion_us) > (uint64_t)1E5);
  			bool flight_motion_not_ok = _control_status.flags.in_air && !_range_aid_mode_enabled;
  			if ((preflight_motion_not_ok || flight_motion_not_ok) && !flow_required) {
  				_inhibit_flow_use = true;
  			}
  		} else if (_inhibit_flow_use && !_control_status.flags.opt_flow){
  			// allow use of optical flow if motion is suitable or we are reliant on it for flight navigation
  			bool preflight_motion_ok = !_control_status.flags.in_air && ((_imu_sample_delayed.time_us - _time_bad_motion_us) > (uint64_t)5E6);
  			bool flight_motion_ok = _control_status.flags.in_air && _range_aid_mode_enabled;
  			if (preflight_motion_ok || flight_motion_ok || flow_required) {
  				_inhibit_flow_use = false;
  			}
  		}
  
  		// Handle cases where we are using optical flow but are no longer able to because data is old
  		// or its use has been inhibited.
  		if (_control_status.flags.opt_flow) {
  		       if (_inhibit_flow_use) {
  			       _control_status.flags.opt_flow = false;
  			       _time_last_of_fuse = 0;
  
  			} else if (_time_last_imu - _flow_sample_delayed.time_us > (uint64_t)_params.no_gps_timeout_max) {
  				_control_status.flags.opt_flow = false;
  
  			}
  		}
  
  		// optical flow fusion mode selection logic
  		printf("params fusion mode %d\n",_params.fusion_mode);
  		printf("opt_flow %d \n",_control_status.flags.opt_flow);
  		printf("control status flags tilt %d\n", _control_status.flags.tilt_align);
  		if ((_params.fusion_mode & MASK_USE_OF) // optical flow has been selected by the user
  			&& !_control_status.flags.opt_flow // we are not yet using flow data
  			&& _control_status.flags.tilt_align // we know our tilt attitude
  			&& !_inhibit_flow_use
  			&& get_terrain_valid()) // we have a valid distance to ground estimate
  		{
  			// If the heading is not aligned, reset the yaw and magnetic field states
  			if (!_control_status.flags.yaw_align) {
  				_control_status.flags.yaw_align = resetMagHeading(_mag_sample_delayed.mag);
  			}
  
  			// If the heading is valid and use is not inhibited , start using optical flow aiding
  			if (_control_status.flags.yaw_align) {
  				// set the flag and reset the fusion timeout
  				_control_status.flags.opt_flow = true;
  				printf("Here!");
  				_time_last_of_fuse = _time_last_imu;
  
  				// if we are not using GPS then the velocity and position states and covariances need to be set
  				if (!_control_status.flags.gps || !_control_status.flags.ev_pos) {
  					resetVelocity();
  					resetPosition();
  
  					// align the output observer to the EKF states
  					alignOutputFilter();
  
  				}
  			}
  
  		} else if (!(_params.fusion_mode & MASK_USE_OF)) {
  			_control_status.flags.opt_flow = false;
  
  		}
  
  		// handle the case when we have optical flow, are reliant on it, but have not been using it for an extended period
  		if (_control_status.flags.opt_flow
  		    && !_control_status.flags.gps
  		    && !_control_status.flags.ev_pos) {
  
  			bool do_reset = _time_last_imu - _time_last_of_fuse > _params.no_gps_timeout_max;
  
  			if (do_reset) {
  				resetVelocity();
  				resetPosition();
  			}
  		}
  
  		// Only fuse optical flow if valid body rate compensation data is available
  		if (calcOptFlowBodyRateComp()) {
  
  			bool flow_quality_good = (_flow_sample_delayed.quality >= _params.flow_qual_min);
  
  			if (!flow_quality_good && !_control_status.flags.in_air) {
  				// when on the ground with poor flow quality, assume zero ground relative velocity and LOS rate
  				_flowRadXYcomp.zero();
  			} else {
  				// compensate for body motion to give a LOS rate
  				_flowRadXYcomp(0) = _flow_sample_delayed.flowRadXY(0) - _flow_sample_delayed.gyroXYZ(0);
  				_flowRadXYcomp(1) = _flow_sample_delayed.flowRadXY(1) - _flow_sample_delayed.gyroXYZ(1);
  			}
  		} else {
  			// don't use this flow data and wait for the next data to arrive
  			_flow_data_ready = false;
  		}
  	}
  
  	// Wait until the midpoint of the flow sample has fallen behind the fusion time horizon
  	if (_flow_data_ready && (_imu_sample_delayed.time_us > _flow_sample_delayed.time_us - uint32_t(1e6f * _flow_sample_delayed.dt) / 2)) {
  		// Fuse optical flow LOS rate observations into the main filter only if height above ground has been updated recently
  		// but use a relaxed time criteria to enable it to coast through bad range finder data
  		if (_control_status.flags.opt_flow && (_time_last_imu - _time_last_hagl_fuse < (uint64_t)10e6)) {
  			fuseOptFlow();
  			_last_known_posNE(0) = _state.pos(0);
  			_last_known_posNE(1) = _state.pos(1);
  		}
  
  		_flow_data_ready = false;
  	}
  }
  
  void Ekf::controlGpsFusion()
  {
  	// Check for new GPS data that has fallen behind the fusion time horizon
  	if (_gps_data_ready) {
  
  		// Determine if we should use GPS aiding for velocity and horizontal position
  		// To start using GPS we need angular alignment completed, the local NED origin set and GPS data that has not failed checks recently
  		bool gps_checks_passing = (_time_last_imu - _last_gps_fail_us > (uint64_t)5e6);
  		bool gps_checks_failing = (_time_last_imu - _last_gps_pass_us > (uint64_t)5e6);
  		if ((_params.fusion_mode & MASK_USE_GPS) && !_control_status.flags.gps) {
  			if (_control_status.flags.tilt_align && _NED_origin_initialised && gps_checks_passing) {
  				// If the heading is not aligned, reset the yaw and magnetic field states
  				// Do not use external vision for yaw if using GPS because yaw needs to be
  				// defined relative to an NED reference frame
  				if (!_control_status.flags.yaw_align || _control_status.flags.ev_yaw || _mag_inhibit_yaw_reset_req) {
  					_control_status.flags.yaw_align = false;
  					_control_status.flags.ev_yaw = false;
  					_control_status.flags.yaw_align = resetMagHeading(_mag_sample_delayed.mag);
  					// Handle the special case where we have not been constraining yaw drift or learning yaw bias due
  					// to assumed invalid mag field associated with indoor operation with a downwards looking flow sensor.
  					if (_mag_inhibit_yaw_reset_req) {
  						_mag_inhibit_yaw_reset_req = false;
  						// Zero the yaw bias covariance and set the variance to the initial alignment uncertainty
  						setDiag(P, 12, 12, sq(_params.switch_on_gyro_bias * FILTER_UPDATE_PERIOD_S));
  					}
  				}
  
  				// If the heading is valid start using gps aiding
  				if (_control_status.flags.yaw_align) {
  					// if we are not already aiding with optical flow, then we need to reset the position and velocity
  					// otherwise we only need to reset the position
  					_control_status.flags.gps = true;
  
  					if (!_control_status.flags.opt_flow) {
  						if (!resetPosition() || !resetVelocity()) {
  							_control_status.flags.gps = false;
  
  						}
  
  					} else if (!resetPosition()) {
  						_control_status.flags.gps = false;
  
  					}
  
  					if (_control_status.flags.gps) {
  						ECL_INFO("EKF commencing GPS fusion");
  						_time_last_gps = _time_last_imu;
  					}
  				}
  			}
  
  		}  else if (!(_params.fusion_mode & MASK_USE_GPS)) {
  			_control_status.flags.gps = false;
  
  		}
  
  		// Handle the case where we are using GPS and another source of aiding and GPS is failing checks
  		if (_control_status.flags.gps  && gps_checks_failing && (_control_status.flags.opt_flow || _control_status.flags.ev_pos)) {
  			_control_status.flags.gps = false;
  			ECL_WARN("EKF GPS data quality poor - stopping use");
  		}
  
  		// handle the case when we now have GPS, but have not been using it for an extended period
  		if (_control_status.flags.gps) {
  			// We are relying on aiding to constrain drift so after a specified time
  			// with no aiding we need to do something
  			bool do_reset = (_time_last_imu - _time_last_pos_fuse > _params.no_gps_timeout_max)
  					&& (_time_last_imu - _time_last_delpos_fuse > _params.no_gps_timeout_max)
  					&& (_time_last_imu - _time_last_vel_fuse > _params.no_gps_timeout_max)
  					&& (_time_last_imu - _time_last_of_fuse > _params.no_gps_timeout_max);
  
  			// We haven't had an absolute position fix for a longer time so need to do something
  			do_reset = do_reset || (_time_last_imu - _time_last_pos_fuse > 2 * _params.no_gps_timeout_max);
  
  			if (do_reset) {
  				// use GPS velocity data to check and correct yaw angle if a FW vehicle
  				if (_control_status.flags.fixed_wing && _control_status.flags.in_air) {
  					// if flying a fixed wing aircraft, do a complete reset that includes yaw
  					realignYawGPS();
  				}
  
  				resetVelocity();
  				resetPosition();
  				_velpos_reset_request = false;
  				ECL_WARN("EKF GPS fusion timeout - reset to GPS");
  
  				// Reset the timeout counters
  				_time_last_pos_fuse = _time_last_imu;
  				_time_last_vel_fuse = _time_last_imu;
  
  			}
  		}
  
  		// Only use GPS data for position and velocity aiding if enabled
  		if (_control_status.flags.gps) {
  			_fuse_pos = true;
  			_fuse_vert_vel = true;
  			_fuse_hor_vel = true;
  
  			// correct velocity for offset relative to IMU
  			Vector3f ang_rate = _imu_sample_delayed.delta_ang * (1.0f / _imu_sample_delayed.delta_ang_dt);
  			Vector3f pos_offset_body = _params.gps_pos_body - _params.imu_pos_body;
  			Vector3f vel_offset_body = cross_product(ang_rate, pos_offset_body);
  			Vector3f vel_offset_earth = _R_to_earth * vel_offset_body;
  			_gps_sample_delayed.vel -= vel_offset_earth;
  
  			// correct position and height for offset relative to IMU
  			Vector3f pos_offset_earth = _R_to_earth * pos_offset_body;
  			_gps_sample_delayed.pos(0) -= pos_offset_earth(0);
  			_gps_sample_delayed.pos(1) -= pos_offset_earth(1);
  			_gps_sample_delayed.hgt += pos_offset_earth(2);
  
  			// calculate observation process noise
  			float lower_limit = fmaxf(_params.gps_pos_noise, 0.01f);
  
  			if (_control_status.flags.opt_flow || _control_status.flags.ev_pos) {
  				// if we are using other sources of aiding, then relax the upper observation
  				// noise limit which prevents bad GPS perturbing the position estimate
  				_posObsNoiseNE = fmaxf(_gps_sample_delayed.hacc, lower_limit);
  
  			} else {
  				// if we are not using another source of aiding, then we are reliant on the GPS
  				// observations to constrain attitude errors and must limit the observation noise value.
  				float upper_limit = fmaxf(_params.pos_noaid_noise, lower_limit);
  				_posObsNoiseNE = math::constrain(_gps_sample_delayed.hacc, lower_limit, upper_limit);
  			}
  
  			_velObsVarNE(1) = _velObsVarNE(0) = sq(fmaxf(_gps_sample_delayed.sacc, _params.gps_vel_noise));
  
  			// calculate innovations
  			_vel_pos_innov[0] = _state.vel(0) - _gps_sample_delayed.vel(0);
  			_vel_pos_innov[1] = _state.vel(1) - _gps_sample_delayed.vel(1);
  			_vel_pos_innov[2] = _state.vel(2) - _gps_sample_delayed.vel(2);
  			_vel_pos_innov[3] = _state.pos(0) - _gps_sample_delayed.pos(0);
  			_vel_pos_innov[4] = _state.pos(1) - _gps_sample_delayed.pos(1);
  
  			// set innovation gate size
  			_posInnovGateNE = fmaxf(_params.posNE_innov_gate, 1.0f);
  			_hvelInnovGate = fmaxf(_params.vel_innov_gate, 1.0f);
  		}
  
  	} else if (_control_status.flags.gps && (_imu_sample_delayed.time_us - _gps_sample_delayed.time_us > (uint64_t)10e6)) {
  		_control_status.flags.gps = false;
  		ECL_WARN("EKF GPS data stopped");
  	}
  }
  
  void Ekf::controlHeightSensorTimeouts()
  {
  	/*
  	 * Handle the case where we have not fused height measurements recently and
  	 * uncertainty exceeds the max allowable. Reset using the best available height
  	 * measurement source, continue using it after the reset and declare the current
  	 * source failed if we have switched.
  	*/
  
  	// Check for IMU accelerometer vibration induced clipping as evidenced by the vertical innovations being positive and not stale.
  	// Clipping causes the average accel reading to move towards zero which makes the INS think it is falling and produces positive vertical innovations
  	float var_product_lim = sq(_params.vert_innov_test_lim) * sq(_params.vert_innov_test_lim);
  	bool bad_vert_accel = (_control_status.flags.baro_hgt && // we can only run this check if vertical position and velocity observations are indepedant
  			(sq(_vel_pos_innov[5] * _vel_pos_innov[2]) > var_product_lim * (_vel_pos_innov_var[5] * _vel_pos_innov_var[2])) && // vertical position and velocity sensors are in agreement that we have a significant error
  			(_vel_pos_innov[2] > 0.0f) && // positive innovation indicates that the inertial nav thinks it is falling
  			((_imu_sample_delayed.time_us - _baro_sample_delayed.time_us) < 2 * BARO_MAX_INTERVAL) && // vertical position data is fresh
  			((_imu_sample_delayed.time_us - _gps_sample_delayed.time_us) < 2 * GPS_MAX_INTERVAL)); // vertical velocity data is fresh
  
  	// record time of last bad vert accel
  	if (bad_vert_accel) {
  		_time_bad_vert_accel =  _time_last_imu;
  
  	} else {
  		_time_good_vert_accel = _time_last_imu;
  	}
  
  	// declare a bad vertical acceleration measurement and make the declaration persist
  	// for a minimum of 10 seconds
  	if (_bad_vert_accel_detected) {
  		_bad_vert_accel_detected = (_time_last_imu - _time_bad_vert_accel < BADACC_PROBATION);
  
  	} else {
  		_bad_vert_accel_detected = bad_vert_accel;
  	}
  
  	// check if height is continuously failing becasue of accel errors
  	bool continuous_bad_accel_hgt = ((_time_last_imu - _time_good_vert_accel) > (unsigned)_params.bad_acc_reset_delay_us);
  
  	// check if height has been inertial deadreckoning for too long
  	bool hgt_fusion_timeout = ((_time_last_imu - _time_last_hgt_fuse) > (uint64_t)5e6);
  
  	// reset the vertical position and velocity states
  	if (hgt_fusion_timeout || continuous_bad_accel_hgt) {
  		// boolean that indicates we will do a height reset
  		bool reset_height = false;
  
  		// handle the case where we are using baro for height
  		if (_control_status.flags.baro_hgt) {
  			// check if GPS height is available
  			const gpsSample &gps_init = _gps_buffer.get_newest();
  			bool gps_hgt_available = ((_time_last_imu - gps_init.time_us) < 2 * GPS_MAX_INTERVAL);
  			bool gps_hgt_accurate = (gps_init.vacc < _params.req_vacc);
  
  			const baroSample &baro_init = _baro_buffer.get_newest();
  			bool baro_hgt_available = ((_time_last_imu - baro_init.time_us) < 2 * BARO_MAX_INTERVAL);
  
  			// check for inertial sensing errors in the last 10 seconds
  			bool prev_bad_vert_accel = (_time_last_imu - _time_bad_vert_accel < BADACC_PROBATION);
  
  			// reset to GPS if adequate GPS data is available and the timeout cannot be blamed on IMU data
  			bool reset_to_gps = gps_hgt_available && gps_hgt_accurate && !_gps_hgt_faulty && !prev_bad_vert_accel;
  
  			// reset to GPS if GPS data is available and there is no Baro data
  			reset_to_gps = reset_to_gps || (gps_hgt_available && !baro_hgt_available);
  
  			// reset to Baro if we are not doing a GPS reset and baro data is available
  			bool reset_to_baro = !reset_to_gps && baro_hgt_available;
  
  			if (reset_to_gps) {
  				// set height sensor health
  				_baro_hgt_faulty = true;
  
  				// declare the GPS height healthy
  				_gps_hgt_faulty = false;
  
  				// reset the height mode
  				setControlGPSHeight();
  
  				// request a reset
  				reset_height = true;
  				ECL_WARN("EKF baro hgt timeout - reset to GPS");
  
  			} else if (reset_to_baro) {
  				// set height sensor health
  				_baro_hgt_faulty = false;
  
  				// reset the height mode
  				setControlBaroHeight();
  
  				// request a reset
  				reset_height = true;
  				ECL_WARN("EKF baro hgt timeout - reset to baro");
  
  			} else {
  				// we have nothing we can reset to
  				// deny a reset
  				reset_height = false;
  
  			}
  		}
  
  		// handle the case we are using GPS for height
  		if (_control_status.flags.gps_hgt) {
  			// check if GPS height is available
  			const gpsSample &gps_init = _gps_buffer.get_newest();
  			bool gps_hgt_available = ((_time_last_imu - gps_init.time_us) < 2 * GPS_MAX_INTERVAL);
  			bool gps_hgt_accurate = (gps_init.vacc < _params.req_vacc);
  
  			// check the baro height source for consistency and freshness
  			const baroSample &baro_init = _baro_buffer.get_newest();
  			bool baro_data_fresh = ((_time_last_imu - baro_init.time_us) < 2 * BARO_MAX_INTERVAL);
  			float baro_innov = _state.pos(2) - (_hgt_sensor_offset - baro_init.hgt + _baro_hgt_offset);
  			bool baro_data_consistent = fabsf(baro_innov) < (sq(_params.baro_noise) + P[9][9]) * sq(_params.baro_innov_gate);
  
  			// if baro data is acceptable and GPS data is inaccurate, reset height to baro
  			bool reset_to_baro = baro_data_consistent && baro_data_fresh && !_baro_hgt_faulty && !gps_hgt_accurate;
  
  			// if GPS height is unavailable and baro data is available, reset height to baro
  			reset_to_baro = reset_to_baro || (!gps_hgt_available && baro_data_fresh);
  
  			// if we cannot switch to baro and GPS data is available, reset height to GPS
  			bool reset_to_gps = !reset_to_baro && gps_hgt_available;
  
  			if (reset_to_baro) {
  				// set height sensor health
  				_gps_hgt_faulty = true;
  				_baro_hgt_faulty = false;
  
  				// reset the height mode
  				setControlBaroHeight();
  
  				// request a reset
  				reset_height = true;
  				ECL_WARN("EKF gps hgt timeout - reset to baro");
  
  			} else if (reset_to_gps) {
  				// set height sensor health
  				_gps_hgt_faulty = false;
  
  				// reset the height mode
  				setControlGPSHeight();
  
  				// request a reset
  				reset_height = true;
  				ECL_WARN("EKF gps hgt timeout - reset to GPS");
  
  			} else {
  				// we have nothing to reset to
  				reset_height = false;
  
  			}
  		}
  
  		// handle the case we are using range finder for height
  		if (_control_status.flags.rng_hgt) {
  			// check if range finder data is available
  			const rangeSample &rng_init = _range_buffer.get_newest();
  			bool rng_data_available = ((_time_last_imu - rng_init.time_us) < 2 * RNG_MAX_INTERVAL);
  
  			// check if baro data is available
  			const baroSample &baro_init = _baro_buffer.get_newest();
  			bool baro_data_available = ((_time_last_imu - baro_init.time_us) < 2 * BARO_MAX_INTERVAL);
  
  			// reset to baro if we have no range data and baro data is available
  			bool reset_to_baro = !rng_data_available && baro_data_available;
  
  			// reset to range data if it is available
  			bool reset_to_rng = rng_data_available;
  
  			if (reset_to_baro) {
  				// set height sensor health
  				_rng_hgt_faulty = true;
  				_baro_hgt_faulty = false;
  
  				// reset the height mode
  				setControlBaroHeight();
  
  				// request a reset
  				reset_height = true;
  				ECL_WARN("EKF rng hgt timeout - reset to baro");
  
  			} else if (reset_to_rng) {
  				// set height sensor health
  				_rng_hgt_faulty = false;
  
  				// reset the height mode
  				setControlRangeHeight();
  
  				// request a reset
  				reset_height = true;
  				ECL_WARN("EKF rng hgt timeout - reset to rng hgt");
  
  			} else {
  				// we have nothing to reset to
  				reset_height = false;
  
  			}
  		}
  
  		// handle the case where we are using external vision data for height
  		if (_control_status.flags.ev_hgt) {
  			// check if vision data is available
  			const extVisionSample &ev_init = _ext_vision_buffer.get_newest();
  			bool ev_data_available = ((_time_last_imu - ev_init.time_us) < 2 * EV_MAX_INTERVAL);
  
  			// check if baro data is available
  			const baroSample &baro_init = _baro_buffer.get_newest();
  			bool baro_data_available = ((_time_last_imu - baro_init.time_us) < 2 * BARO_MAX_INTERVAL);
  
  			// reset to baro if we have no vision data and baro data is available
  			bool reset_to_baro = !ev_data_available && baro_data_available;
  
  			// reset to ev data if it is available
  			bool reset_to_ev = ev_data_available;
  
  			if (reset_to_baro) {
  				// set height sensor health
  				_baro_hgt_faulty = false;
  
  				// reset the height mode
  				setControlBaroHeight();
  
  				// request a reset
  				reset_height = true;
  				ECL_WARN("EKF ev hgt timeout - reset to baro");
  
  			} else if (reset_to_ev) {
  				// reset the height mode
  				setControlEVHeight();
  
  				// request a reset
  				reset_height = true;
  				ECL_WARN("EKF ev hgt timeout - reset to ev hgt");
  
  			} else {
  				// we have nothing to reset to
  				reset_height = false;
  
  			}
  		}
  
  		// Reset vertical position and velocity states to the last measurement
  		if (reset_height) {
  			resetHeight();
  			// Reset the timout timer
  			_time_last_hgt_fuse = _time_last_imu;
  
  		}
  
  	}
  }
  
  void Ekf::controlHeightFusion()
  {
  	// set control flags for the desired primary height source
  
  	rangeAidConditionsMet();
  
  	_range_aid_mode_selected = (_params.range_aid == 1) && _range_aid_mode_enabled;
  
  	if (_params.vdist_sensor_type == VDIST_SENSOR_BARO) {
  
  		if (_range_aid_mode_selected && _range_data_ready && !_rng_hgt_faulty) {
  			setControlRangeHeight();
  			_fuse_height = true;
  
  			// we have just switched to using range finder, calculate height sensor offset such that current
  			// measurment matches our current height estimate
  			if (_control_status_prev.flags.rng_hgt != _control_status.flags.rng_hgt) {
  				if (get_terrain_valid()) {
  					_hgt_sensor_offset = _terrain_vpos;
  
  				} else {
  					_hgt_sensor_offset = _R_rng_to_earth_2_2 * _range_sample_delayed.rng + _state.pos(2);
  				}
  			}
  
  		} else if (!_range_aid_mode_selected && _baro_data_ready && !_baro_hgt_faulty) {
  			setControlBaroHeight();
  			_fuse_height = true;
  
  			// we have just switched to using baro height, we don't need to set a height sensor offset
  			// since we track a separate _baro_hgt_offset
  			if (_control_status_prev.flags.baro_hgt != _control_status.flags.baro_hgt) {
  				_hgt_sensor_offset = 0.0f;
  			}
  
  			// Turn off ground effect compensation if it times out or sufficient height has been gained
  			// since takeoff.
  			if (_control_status.flags.gnd_effect) {
  				if ((_time_last_imu - _time_last_gnd_effect_on > GNDEFFECT_TIMEOUT) ||
  				    (((_last_on_ground_posD - _state.pos(2)) > _params.gnd_effect_max_hgt) &&
  				     _control_status.flags.in_air)) {
  
  					_control_status.flags.gnd_effect = false;
  				}
  			}
  
  		} else if (_control_status.flags.gps_hgt && _gps_data_ready && !_gps_hgt_faulty) {
  			// switch to gps if there was a reset to gps
  			_fuse_height = true;
  
  			// we have just switched to using gps height, calculate height sensor offset such that current
  			// measurment matches our current height estimate
  			if (_control_status_prev.flags.gps_hgt != _control_status.flags.gps_hgt) {
  				_hgt_sensor_offset = _gps_sample_delayed.hgt - _gps_alt_ref + _state.pos(2);
  			}
  		}
  	}
  
  	// set the height data source to range if requested
  	if ((_params.vdist_sensor_type == VDIST_SENSOR_RANGE) && !_rng_hgt_faulty) {
  		setControlRangeHeight();
  		_fuse_height = _range_data_ready;
  
  		// we have just switched to using range finder, calculate height sensor offset such that current
  		// measurment matches our current height estimate
  		if (_control_status_prev.flags.rng_hgt != _control_status.flags.rng_hgt) {
  			// use the parameter rng_gnd_clearance if on ground to avoid a noisy offset initialization (e.g. sonar)
  			if (_control_status.flags.in_air && get_terrain_valid()) {
  
  				_hgt_sensor_offset = _terrain_vpos;
  
  			} else if (_control_status.flags.in_air) {
  
  				_hgt_sensor_offset = _R_rng_to_earth_2_2 * _range_sample_delayed.rng + _state.pos(2);
  
  			} else {
  
  				_hgt_sensor_offset = _params.rng_gnd_clearance;
  			}
  		}
  
  	} else if ((_params.vdist_sensor_type == VDIST_SENSOR_RANGE) && _baro_data_ready && !_baro_hgt_faulty) {
  		setControlBaroHeight();
  		_fuse_height = true;
  
  		// we have just switched to using baro height, we don't need to set a height sensor offset
  		// since we track a separate _baro_hgt_offset
  		if (_control_status_prev.flags.baro_hgt != _control_status.flags.baro_hgt) {
  			_hgt_sensor_offset = 0.0f;
  		}
  	}
  
  	// Determine if GPS should be used as the height source
  	if (_params.vdist_sensor_type == VDIST_SENSOR_GPS) {
  
  		if (_range_aid_mode_selected && _range_data_ready && !_rng_hgt_faulty) {
  			setControlRangeHeight();
  			_fuse_height = true;
  
  			// we have just switched to using range finder, calculate height sensor offset such that current
  			// measurment matches our current height estimate
  			if (_control_status_prev.flags.rng_hgt != _control_status.flags.rng_hgt) {
  				if (get_terrain_valid()) {
  					_hgt_sensor_offset = _terrain_vpos;
  
  				} else {
  					_hgt_sensor_offset = _R_rng_to_earth_2_2 * _range_sample_delayed.rng + _state.pos(2);
  				}
  			}
  
  		} else if (!_range_aid_mode_selected && _gps_data_ready && !_gps_hgt_faulty) {
  			setControlGPSHeight();
  			_fuse_height = true;
  
  			// we have just switched to using gps height, calculate height sensor offset such that current
  			// measurment matches our current height estimate
  			if (_control_status_prev.flags.gps_hgt != _control_status.flags.gps_hgt) {
  				_hgt_sensor_offset = _gps_sample_delayed.hgt - _gps_alt_ref + _state.pos(2);
  			}
  
  		} else if (_control_status.flags.baro_hgt && _baro_data_ready && !_baro_hgt_faulty) {
  			// switch to baro if there was a reset to baro
  			_fuse_height = true;
  
  			// we have just switched to using baro height, we don't need to set a height sensor offset
  			// since we track a separate _baro_hgt_offset
  			if (_control_status_prev.flags.baro_hgt != _control_status.flags.baro_hgt) {
  				_hgt_sensor_offset = 0.0f;
  			}
  		}
  	}
  
  	// Determine if we rely on EV height but switched to baro
  	if (_params.vdist_sensor_type == VDIST_SENSOR_EV) {
  		if (_control_status.flags.baro_hgt && _baro_data_ready && !_baro_hgt_faulty) {
  			// switch to baro if there was a reset to baro
  			_fuse_height = true;
  
  			// we have just switched to using baro height, we don't need to set a height sensor offset
  			// since we track a separate _baro_hgt_offset
  			if (_control_status_prev.flags.baro_hgt != _control_status.flags.baro_hgt) {
  				_hgt_sensor_offset = 0.0f;
  			}
  		}
  	}
  
  	// calculate a filtered offset between the baro origin and local NED origin if we are not using the baro as a height reference
  	if (!_control_status.flags.baro_hgt && _baro_data_ready) {
  		float local_time_step = 1e-6f * _delta_time_baro_us;
  		local_time_step = math::constrain(local_time_step, 0.0f, 1.0f);
  
  		// apply a 10 second first order low pass filter to baro offset
  		float offset_rate_correction =  0.1f * (_baro_sample_delayed.hgt + _state.pos(
  				2) - _baro_hgt_offset);
  		_baro_hgt_offset += local_time_step * math::constrain(offset_rate_correction, -0.1f, 0.1f);
  	}
  
  	if ((_time_last_imu - _time_last_hgt_fuse) > 2 * RNG_MAX_INTERVAL && _control_status.flags.rng_hgt
  	    && (!_range_data_ready || _rng_hgt_faulty)) {
  
  		// If we are supposed to be using range finder data as the primary height sensor, have missed or rejected measurements
  		// and are on the ground, then synthesise a measurement at the expected on ground value
  		if (!_control_status.flags.in_air) {
  			_range_sample_delayed.rng = _params.rng_gnd_clearance;
  			_range_sample_delayed.time_us = _imu_sample_delayed.time_us;
  
  		}
  
  		_fuse_height = true;
  	}
  
  
  }
  
  void Ekf::rangeAidConditionsMet()
  {
  	// if the parameter for range aid is enabled we allow to switch from using the primary height source to using range finder as height source
  	// under the following conditions
  	// 1) Vehicle is in-air
  	// 2) Range data is valid
  	// 3) Vehicle is no further than max_hagl_for_range_aid away from the ground
  	// 4) Ground speed is not higher than max_vel_for_range_aid
  	// 5) Terrain estimate is stable (needs better checks)
  	if (_control_status.flags.in_air && !_rng_hgt_faulty) {
  		// check if we can use range finder measurements to estimate height, use hysteresis to avoid rapid switching
  		bool can_use_range_finder;
  		if (_range_aid_mode_enabled) {
  			can_use_range_finder = (_terrain_vpos - _state.pos(2) < _params.max_hagl_for_range_aid) && get_terrain_valid();
  
  		} else {
  			// if we were not using range aid in the previous iteration then require the current height above terrain to be
  			// smaller than 70 % of the maximum allowed ground distance for range aid
  			can_use_range_finder = (_terrain_vpos - _state.pos(2) < 0.7f * _params.max_hagl_for_range_aid) && get_terrain_valid();
  		}
  
  		bool horz_vel_valid = (_control_status.flags.gps || _control_status.flags.ev_pos || _control_status.flags.opt_flow)
  				      && (_fault_status.value == 0);
  
  		if (horz_vel_valid) {
  			float ground_vel = sqrtf(_state.vel(0) * _state.vel(0) + _state.vel(1) * _state.vel(1));
  
  			if (_range_aid_mode_enabled) {
  				can_use_range_finder &= ground_vel < _params.max_vel_for_range_aid;
  
  			} else {
  				// if we were not using range aid in the previous iteration then require the ground velocity to be
  				// smaller than 70 % of the maximum allowed ground velocity for range aid
  				can_use_range_finder &= ground_vel < 0.7f * _params.max_vel_for_range_aid;
  			}
  
  		} else {
  			can_use_range_finder = false;
  		}
  
  		// use hysteresis to check for hagl
  		if (_range_aid_mode_enabled) {
  			can_use_range_finder &= ((_hagl_innov * _hagl_innov / (sq(_params.range_aid_innov_gate) * _hagl_innov_var)) < 1.0f);
  
  		} else {
  			// if we were not using range aid in the previous iteration then use a much lower (1/100) threshold to avoid
  			// switching to range finder too soon (wait for terrain to update).
  			can_use_range_finder &= ((_hagl_innov * _hagl_innov / (sq(_params.range_aid_innov_gate) * _hagl_innov_var)) < 0.01f);
  		}
  
  		_range_aid_mode_enabled = can_use_range_finder;
  
  	} else {
  		_range_aid_mode_enabled = false;
  	}
  }
  
  void Ekf::checkRangeDataValidity()
  {
  	// check if out of date
  	if ((_imu_sample_delayed.time_us - _range_sample_delayed .time_us) > 2 * RNG_MAX_INTERVAL) {
  		_rng_hgt_faulty = true;
  		return;
  	}
  
  	// Don't allow faulty flag to clear unless range data is continuous
  	if (_rng_hgt_faulty && !_range_data_continuous) {
  		return;
  	}
  
  	// Don't run the checks after this unless we have retrieved new data from the buffer
  	if (!_range_data_ready) {
  		return;
  	} else {
  		// reset fault status when we get new data
  		_rng_hgt_faulty = false;
  	}
  
  	// Check if excessively tilted
  	if (_R_rng_to_earth_2_2 < _params.range_cos_max_tilt) {
  		_rng_hgt_faulty = true;
  		return;
  	}
  
  	// Check if out of range
  	if ((_range_sample_delayed.rng > _rng_valid_max_val)
  	|| (_range_sample_delayed.rng < _rng_valid_min_val)) {
  		if (_control_status.flags.in_air) {
  			_rng_hgt_faulty = true;
  			return;
  		} else {
  			// Range finders can fail to provide valid readings when resting on the ground
  			// or being handled by the user, which prevents use of as a primary height sensor.
  			// To work around this issue, we replace out of range data with the expected on ground value.
  			_range_sample_delayed.rng = _params.rng_gnd_clearance;
  			return;
  		}
  	}
  
  	// Check for "stuck" range finder measurements when range was not valid for certain period
  	// This handles a failure mode observed with some lidar sensors
  	if (_range_sample_delayed.time_us - _time_last_rng_ready > (uint64_t)10e6 &&
  	    _control_status.flags.in_air) {
  
  		// require a variance of rangefinder values to check for "stuck" measurements
  		if (_rng_stuck_max_val - _rng_stuck_min_val > _params.range_stuck_threshold) {
  			_time_last_rng_ready = _range_sample_delayed.time_us;
  			_rng_stuck_min_val = 0.0f;
  			_rng_stuck_max_val = 0.0f;
  			_control_status.flags.rng_stuck = false;
  
  		} else {
  			if (_range_sample_delayed.rng > _rng_stuck_max_val) {
  				_rng_stuck_max_val = _range_sample_delayed.rng;
  			}
  
  			if (_rng_stuck_min_val < 0.1f || _range_sample_delayed.rng < _rng_stuck_min_val) {
  				_rng_stuck_min_val = _range_sample_delayed.rng;
  			}
  
  			_control_status.flags.rng_stuck = true;
  			_rng_hgt_faulty = true;
  		}
  
  	} else {
  		_time_last_rng_ready = _range_sample_delayed.time_us;
  	}
  }
  
  void Ekf::controlAirDataFusion()
  {
  	// control activation and initialisation/reset of wind states required for airspeed fusion
  
  	// If both airspeed and sideslip fusion have timed out and we are not using a drag observation model then we no longer have valid wind estimates
  	bool airspeed_timed_out = _time_last_imu - _time_last_arsp_fuse > (uint64_t)10e6;
  	bool sideslip_timed_out = _time_last_imu - _time_last_beta_fuse > (uint64_t)10e6;
  
  	if (_control_status.flags.wind && airspeed_timed_out && sideslip_timed_out && !(_params.fusion_mode & MASK_USE_DRAG)) {
  		_control_status.flags.wind = false;
  
  	}
  
  	if (_control_status.flags.fuse_aspd && airspeed_timed_out) {
  		_control_status.flags.fuse_aspd = false;
  
  	}
  
  	// Always try to fuse airspeed data if available and we are in flight
  	if (_tas_data_ready && _control_status.flags.in_air) {
  		// always fuse airsped data if we are flying and data is present
  		if (!_control_status.flags.fuse_aspd) {
  			_control_status.flags.fuse_aspd = true;
  		}
  
  		// If starting wind state estimation, reset the wind states and covariances before fusing any data
  		if (!_control_status.flags.wind) {
  			// activate the wind states
  			_control_status.flags.wind = true;
  			// reset the timout timer to prevent repeated resets
  			_time_last_arsp_fuse = _time_last_imu;
  			_time_last_beta_fuse = _time_last_imu;
  			// reset the wind speed states and corresponding covariances
  			resetWindStates();
  			resetWindCovariance();
  
  		}
  
  		fuseAirspeed();
  
  	}
  }
  
  void Ekf::controlBetaFusion()
  {
  	// control activation and initialisation/reset of wind states required for synthetic sideslip fusion fusion
  
  	// If both airspeed and sideslip fusion have timed out and we are not using a drag observation model then we no longer have valid wind estimates
  	bool sideslip_timed_out = _time_last_imu - _time_last_beta_fuse > (uint64_t)10e6;
  	bool airspeed_timed_out = _time_last_imu - _time_last_arsp_fuse > (uint64_t)10e6;
  
  	if (_control_status.flags.wind && airspeed_timed_out && sideslip_timed_out && !(_params.fusion_mode & MASK_USE_DRAG)) {
  		_control_status.flags.wind = false;
  	}
  
  	// Perform synthetic sideslip fusion when in-air and sideslip fuson had been enabled externally in addition to the following criteria:
  
  	// Suffient time has lapsed sice the last fusion
  	bool beta_fusion_time_triggered = _time_last_imu - _time_last_beta_fuse > _params.beta_avg_ft_us;
  
  	if (beta_fusion_time_triggered && _control_status.flags.fuse_beta && _control_status.flags.in_air) {
  		// If starting wind state estimation, reset the wind states and covariances before fusing any data
  		if (!_control_status.flags.wind) {
  			// activate the wind states
  			_control_status.flags.wind = true;
  			// reset the timeout timers to prevent repeated resets
  			_time_last_beta_fuse = _time_last_imu;
  			_time_last_arsp_fuse = _time_last_imu;
  			// reset the wind speed states and corresponding covariances
  			resetWindStates();
  			resetWindCovariance();
  		}
  
  		fuseSideslip();
  	}
  }
  
  void Ekf::controlDragFusion()
  {
  	if (_params.fusion_mode & MASK_USE_DRAG) {
  		if (_control_status.flags.in_air
  				&& !_mag_inhibit_yaw_reset_req) {
  			if (!_control_status.flags.wind) {
  				// reset the wind states and covariances when starting drag accel fusion
  				_control_status.flags.wind = true;
  				resetWindStates();
  				resetWindCovariance();
  
  			} else if (_drag_buffer.pop_first_older_than(_imu_sample_delayed.time_us, &_drag_sample_delayed)) {
  				fuseDrag();
  
  			}
  
  		} else {
  			_control_status.flags.wind = false;
  
  		}
  	}
  }
  
  void Ekf::controlMagFusion()
  {
  	// If we are on ground, store the local position and time to use as a reference
  	// Also reset the flight alignment flag so that the mag fields will be re-initialised next time we achieve flight altitude
  	if (!_control_status.flags.in_air) {
  		_last_on_ground_posD = _state.pos(2);
  		_flt_mag_align_complete = false;
  		_num_bad_flight_yaw_events = 0;
  	}
  
  	// check for new magnetometer data that has fallen behind the fusion time horizon
  	// If we are using external vision data for heading then no magnetometer fusion is used
  	if (!_control_status.flags.ev_yaw && _mag_data_ready) {
  
  		// Determine if we should use simple magnetic heading fusion which works better when there are large external disturbances
  		// or the more accurate 3-axis fusion
  		if (_control_status.flags.mag_fault) {
  			// do no magnetometer fusion at all
  			_control_status.flags.mag_hdg = false;
  			_control_status.flags.mag_3D = false;
  
  		} else if (_params.mag_fusion_type == MAG_FUSE_TYPE_AUTO || _params.mag_fusion_type == MAG_FUSE_TYPE_AUTOFW) {
  			// Check if height has increased sufficiently to be away from ground magnetic anomalies
  			bool height_achieved = (_last_on_ground_posD - _state.pos(2)) > 1.5f;
  
  			// Check if there has been enough change in horizontal velocity to make yaw observable
  			// Apply hysteresis to check to avoid rapid toggling
  			if (_yaw_angle_observable) {
  				_yaw_angle_observable = _accel_lpf_NE.norm() > _params.mag_acc_gate;
  
  			} else {
  				_yaw_angle_observable = _accel_lpf_NE.norm() > 2.0f * _params.mag_acc_gate;
  			}
  
  			_yaw_angle_observable = _yaw_angle_observable && (_control_status.flags.gps || _control_status.flags.ev_pos);
  
  			// check if there is enough yaw rotation to make the mag bias states observable
  			if (!_mag_bias_observable && (fabsf(_yaw_rate_lpf_ef) > _params.mag_yaw_rate_gate)) {
  				// initial yaw motion is detected
  				_mag_bias_observable = true;
  				_yaw_delta_ef = 0.0f;
  				_time_yaw_started = _imu_sample_delayed.time_us;
  
  			} else if (_mag_bias_observable) {
  				// monitor yaw rotation in 45 deg sections.
  				// a rotation of 45 deg is sufficient to make the mag bias observable
  				if (fabsf(_yaw_delta_ef) > math::radians(45.0f)) {
  					_time_yaw_started = _imu_sample_delayed.time_us;
  					_yaw_delta_ef = 0.0f;
  				}
  
  				// require sustained yaw motion of 50% the initial yaw rate threshold
  				float min_yaw_change_req =  0.5f * _params.mag_yaw_rate_gate * (1e-6f * (float)(_imu_sample_delayed.time_us - _time_yaw_started));
  				_mag_bias_observable = fabsf(_yaw_delta_ef) > min_yaw_change_req;
  
  			} else {
  				_mag_bias_observable = false;
  			}
  
  			// record the last time that movement was suitable for use of 3-axis magnetometer fusion
  			if (_mag_bias_observable || _yaw_angle_observable) {
  				_time_last_movement = _imu_sample_delayed.time_us;
  			}
  
  			// decide whether 3-axis magnetomer fusion can be used
  			bool use_3D_fusion = _control_status.flags.tilt_align && // Use of 3D fusion requires valid tilt estimates
  					_control_status.flags.in_air && // don't use when on the ground becasue of magnetic anomalies
  					(_flt_mag_align_complete || height_achieved) && // once in-flight field alignment has been performed, ignore relative height
  					((_imu_sample_delayed.time_us - _time_last_movement) < 2 * 1000 * 1000); // Using 3-axis fusion for a minimum period after to allow for false negatives
  
  			// perform switch-over
  			if (use_3D_fusion) {
  				if (!_control_status.flags.mag_3D) {
  					if (!_flt_mag_align_complete) {
  						// If we are flying a vehicle that flies forward, eg plane, then we can use the GPS course to check and correct the heading
  						if (_control_status.flags.fixed_wing && _control_status.flags.in_air) {
  							_flt_mag_align_complete = realignYawGPS();
  
  							if (_velpos_reset_request) {
  								resetVelocity();
  								resetPosition();
  								_velpos_reset_request = false;
  							}
  
  						} else {
  							_flt_mag_align_complete = resetMagHeading(_mag_sample_delayed.mag);
  						}
  
  						_control_status.flags.yaw_align = _control_status.flags.yaw_align || _flt_mag_align_complete;
  
  					} else {
  						// reset the mag field covariances
  						zeroRows(P, 16, 21);
  						zeroCols(P, 16, 21);
  
  						// re-instate the last used variances
  						for (uint8_t index = 0; index <= 5; index ++) {
  							P[index + 16][index + 16] = _saved_mag_variance[index];
  						}
  					}
  				}
  
  				// only use one type of mag fusion at the same time
  				_control_status.flags.mag_3D = _flt_mag_align_complete;
  				_control_status.flags.mag_hdg = !_control_status.flags.mag_3D;
  
  			} else {
  				// save magnetic field state variances for next time
  				if (_control_status.flags.mag_3D) {
  					for (uint8_t index = 0; index <= 5; index ++) {
  						_saved_mag_variance[index] = P[index + 16][index + 16];
  					}
  
  					_control_status.flags.mag_3D = false;
  				}
  
  				_control_status.flags.mag_hdg = true;
  			}
  
  			/*
  			Control switch-over between only updating the mag states to updating all states
  			When flying as a fixed wing aircraft, a misaligned magnetometer can cause an error in pitch/roll and accel bias estimates.
  			When MAG_FUSE_TYPE_AUTOFW is selected and the vehicle is flying as a fixed wing, then magnetometer fusion is only allowed
  			to access the magnetic field states.
  			*/
  			_control_status.flags.update_mag_states_only = (_params.mag_fusion_type == MAG_FUSE_TYPE_AUTOFW)
  					&& _control_status.flags.fixed_wing;
  
  			// For the first 5 seconds after switching to 3-axis fusion we allow the magnetic field state estimates to stabilise
  			// before they are used to constrain heading drift
  			_flt_mag_align_converging = ((_imu_sample_delayed.time_us - _flt_mag_align_start_time) < (uint64_t)5e6);
  
  			if (!_control_status.flags.update_mag_states_only && _control_status_prev.flags.update_mag_states_only) {
  				// When re-commencing use of magnetometer to correct vehicle states
  				// set the field state variance to the observation variance and zero
  				// the covariance terms to allow the field states re-learn rapidly
  				zeroRows(P, 16, 21);
  				zeroCols(P, 16, 21);
  
  				for (uint8_t index = 0; index <= 5; index ++) {
  					P[index + 16][index + 16] = sq(_params.mag_noise);
  				}
  			}
  
  		} else if (_params.mag_fusion_type == MAG_FUSE_TYPE_HEADING) {
  			// always use heading fusion
  			_control_status.flags.mag_hdg = true;
  			_control_status.flags.mag_3D = false;
  
  		} else if (_params.mag_fusion_type == MAG_FUSE_TYPE_3D) {
  			// if transitioning into 3-axis fusion mode, we need to initialise the yaw angle and field states
  			if (!_control_status.flags.mag_3D) {
  				_control_status.flags.yaw_align = resetMagHeading(_mag_sample_delayed.mag) || _control_status.flags.yaw_align;
  			}
  
  			// always use 3-axis mag fusion
  			_control_status.flags.mag_hdg = false;
  			_control_status.flags.mag_3D = true;
  
  		} else {
  			// do no magnetometer fusion at all
  			_control_status.flags.mag_hdg = false;
  			_control_status.flags.mag_3D = false;
  		}
  
  		// if we are using 3-axis magnetometer fusion, but without external aiding, then the declination must be fused as an observation to prevent long term heading drift
  		// fusing declination when gps aiding is available is optional, but recommended to prevent problem if the vehicle is static for extended periods of time
  		if (_control_status.flags.mag_3D && (!_control_status.flags.gps || (_params.mag_declination_source & MASK_FUSE_DECL))) {
  			_control_status.flags.mag_dec = true;
  
  		} else {
  			_control_status.flags.mag_dec = false;
  		}
  
  		// If the user has selected auto protection against indoor magnetic field errors, only use the magnetomer
  		// if a yaw angle relative to true North is required for navigation. If no GPS or other earth frame aiding
  		// is available, assume that we are operating indoors and the magnetometer should not be used.
  		bool user_selected = (_params.mag_fusion_type == MAG_FUSE_TYPE_INDOOR);
  		bool not_using_gps = !(_params.fusion_mode & MASK_USE_GPS) || !_control_status.flags.gps;
  		bool not_using_evpos = !(_params.fusion_mode & MASK_USE_EVPOS) || !_control_status.flags.ev_pos;
  		bool not_selected_evyaw =  !(_params.fusion_mode & MASK_USE_EVYAW);
  		if (user_selected && not_using_gps && not_using_evpos && not_selected_evyaw) {
  			_mag_use_inhibit = true;
  		} else {
  			_mag_use_inhibit = false;
  			_mag_use_not_inhibit_us = _imu_sample_delayed.time_us;
  		}
  
  		// If magnetomer use has been inhibited continuously then a yaw reset is required for a valid heading
  		if (uint32_t(_imu_sample_delayed.time_us - _mag_use_not_inhibit_us) > (uint32_t)5e6) {
  			_mag_inhibit_yaw_reset_req = true;
  		}
  
  		// fuse magnetometer data using the selected methods
  		if (_control_status.flags.mag_3D && _control_status.flags.yaw_align) {
  			fuseMag();
  
  			if (_control_status.flags.mag_dec) {
  				fuseDeclination();
  			}
  
  		} else if (_control_status.flags.mag_hdg && _control_status.flags.yaw_align) {
  			// fusion of an Euler yaw angle from either a 321 or 312 rotation sequence
  			fuseHeading();
  
  		} else {
  			// do no fusion at all
  		}
  	}
  }
  
  void Ekf::controlVelPosFusion()
  {
  	// if we aren't doing any aiding, fake GPS measurements at the last known position to constrain drift
  	// Coincide fake measurements with baro data for efficiency with a minimum fusion rate of 5Hz
  	if (!(_params.fusion_mode & MASK_USE_GPS)) {
  		_control_status.flags.gps = false;
  	}
  
  	if (!_control_status.flags.gps &&
  	    !_control_status.flags.opt_flow &&
  	    !_control_status.flags.ev_pos &&
  	    !(_control_status.flags.fuse_aspd && _control_status.flags.fuse_beta)) {
  
  		// We now need to use a synthetic positon observation to prevent unconstrained drift of the INS states.
  		_using_synthetic_position = true;
  
  		// Fuse synthetic position observations every 200msec
  		if ((_time_last_imu - _time_last_fake_gps > (uint64_t)2e5) || _fuse_height) {
  			// Reset position and velocity states if we re-commence this aiding method
  			if ((_time_last_imu - _time_last_fake_gps) > (uint64_t)4e5) {
  				resetPosition();
  				resetVelocity();
  				_fuse_hpos_as_odom = false;
  
  				if (_time_last_fake_gps != 0) {
  					ECL_WARN("EKF stopping navigation");
  				}
  
  			}
  
  			_fuse_pos = true;
  			_fuse_hor_vel = false;
  			_fuse_vert_vel = false;
  			_time_last_fake_gps = _time_last_imu;
  
  			if (_control_status.flags.in_air && _control_status.flags.tilt_align) {
  				_posObsNoiseNE = fmaxf(_params.pos_noaid_noise, _params.gps_pos_noise);
  
  			} else {
  				_posObsNoiseNE = 0.5f;
  			}
  
  			_vel_pos_innov[0] = 0.0f;
  			_vel_pos_innov[1] = 0.0f;
  			_vel_pos_innov[2] = 0.0f;
  			_vel_pos_innov[3] = _state.pos(0) - _last_known_posNE(0);
  			_vel_pos_innov[4] = _state.pos(1) - _last_known_posNE(1);
  
  			// glitch protection is not required so set gate to a large value
  			_posInnovGateNE = 100.0f;
  
  		}
  
  	} else {
  		_using_synthetic_position = false;
  	}
  
  	// Fuse available NED velocity and position data into the main filter
  	if (_fuse_height || _fuse_pos || _fuse_hor_vel || _fuse_vert_vel) {
  		fuseVelPosHeight();
  
  	}
  }
  
  void Ekf::controlAuxVelFusion()
  {
  	bool data_ready = _auxvel_buffer.pop_first_older_than(_imu_sample_delayed.time_us, &_auxvel_sample_delayed);
  	bool primary_aiding = _control_status.flags.gps || _control_status.flags.ev_pos || _control_status.flags.opt_flow;
  
  	if (data_ready && primary_aiding) {
  		_fuse_hor_vel = _fuse_vert_vel = _fuse_pos = _fuse_height = false;
  		_fuse_hor_vel_aux = true;
  		_aux_vel_innov[0] = _state.vel(0) - _auxvel_sample_delayed.velNE(0);
  		_aux_vel_innov[1] = _state.vel(1) - _auxvel_sample_delayed.velNE(1);
  		_velObsVarNE = _auxvel_sample_delayed.velVarNE;
  		_hvelInnovGate = _params.auxvel_gate;
  		fuseVelPosHeight();
  	}
  }
  