px4-firmware/EKF/control.cpp

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/**
 * @file control.cpp
 * Control functions for ekf attitude and position estimator.
 *
 * @author Paul Riseborough <p_riseborough@live.com.au>
 *
 */

#include "ekf.h"

void Ekf::controlFusionModes()
{
	// Determine the vehicle status
	calculateVehicleStatus();

	// optical flow fusion mode selection logic
	_control_status.flags.opt_flow = false;

	// GPS fusion mode selection logic
	// To start use GPS we need angular alignment completed, the local NED origin set and fresh GPS data
	if (!_control_status.flags.gps) {
		if (_control_status.flags.angle_align && (_time_last_imu - _time_last_gps) < 5e5 && _NED_origin_initialised
		    && (_time_last_imu - _last_gps_fail_us > 5e6)) {
			_control_status.flags.gps = true;
			resetPosition();
			resetVelocity();
		}
	}

	// decide when to start using optical flow data
	if (!_control_status.flags.opt_flow) {
		// TODO optical flow start logic
	}

	// handle the case when we are relying on GPS fusion and lose it
	if (_control_status.flags.gps && !_control_status.flags.opt_flow) {
		// We are relying on GPS aiding to constrain attitude drift so after 10 seconds without aiding we need to do something
		if ((_time_last_imu - _time_last_pos_fuse > 10e6) && (_time_last_imu - _time_last_vel_fuse > 10e6)) {
			if (_time_last_imu - _time_last_gps > 5e5) {
				// if we don't have gps then we need to switch to the non-aiding mode, zero the veloity states
				// and set the synthetic GPS position to the current estimate
				_control_status.flags.gps = false;
				_last_known_posNE(0) = _state.pos(0);
				_last_known_posNE(1) = _state.pos(1);
				_state.vel.setZero();

			} else {
				// Reset states to the last GPS measurement
				resetPosition();
				resetVelocity();
			}
		}
	}

	// handle the case when we are relying on optical flow fusion and lose it
	if (_control_status.flags.opt_flow && !_control_status.flags.gps) {
		// TODO
	}

	// 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.armed) {
		// always use simple mag fusion for initial startup
		_control_status.flags.mag_hdg = true;
		_control_status.flags.mag_3D = false;

	} else {
		if (_control_status.flags.in_air) {
			// always use 3-axis mag fusion when airborne
			_control_status.flags.mag_hdg = false;
			_control_status.flags.mag_3D = true;

		} else {
			// always use simple heading fusion when on the ground
			_control_status.flags.mag_hdg = true;
			_control_status.flags.mag_3D = false;
		}
	}

        // if we are using 3-axis magnetometer fusion, but without external aiding, then the declination needs to be fused as an observation to prevent long term heading drift
        if(_control_status.flags.mag_3D && _control_status.flags.gps) {
            _control_status.flags.mag_dec = false;
        } else {
            _control_status.flags.mag_dec = true;
        }
}

void Ekf::calculateVehicleStatus()
{
	// determine if the vehicle is armed
	_control_status.flags.armed = _vehicle_armed;

	// record vertical position whilst disarmed to use as a height change reference
	if (!_control_status.flags.armed) {
		_last_disarmed_posD = _state.pos(2);
	}

	// Transition to in-air occurs when armed and when altitude has increased sufficiently from the altitude at arming
	if (!_control_status.flags.in_air && _control_status.flags.armed && (_state.pos(2) - _last_disarmed_posD) < -1.0f) {
		_control_status.flags.in_air = true;
	}

	// Transition to on-ground occurs when disarmed.
	if (_control_status.flags.in_air && !_control_status.flags.armed) {
		_control_status.flags.in_air = false;
	}
}