px4_autopilot/EKF/ekf.cpp

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/**
 * @file ekf.cpp
 * Core functions for ekf attitude and position estimator.
 *
 * @author Roman Bast <bapstroman@gmail.com>
 *
 */

#include "ekf.h"

Ekf::Ekf():
	_filter_initialised(false),
	_earth_rate_initialised(false),
	_fuse_height(false),
	_fuse_pos(false),
	_fuse_hor_vel(false),
	_fuse_vert_vel(false),
	_time_last_fake_gps(0),
	_time_last_pos_fuse(0),
	_time_last_vel_fuse(0),
	_time_last_hgt_fuse(0),
	_time_last_of_fuse(0),
	_last_disarmed_posD(0.0f),
	_heading_innov(0.0f),
	_heading_innov_var(0.0f),
	_mag_declination(0.0f),
	_gpsDriftVelN(0.0f),
	_gpsDriftVelE(0.0f),
	_gps_drift_velD(0.0f),
	_gps_velD_diff_filt(0.0f),
	_gps_velN_filt(0.0f),
	_gps_velE_filt(0.0f),
	_last_gps_fail_us(0),
	_last_gps_origin_time_us(0),
	_gps_alt_ref(0.0f),
	_baro_counter(0),
	_baro_sum(0.0f),
	_mag_counter(0),
	_baro_at_alignment(0.0f)
{
	_control_status = {};
	_control_status_prev = {};
	_state = {};
	_last_known_posNE.setZero();
	_earth_rate_NED.setZero();
	_R_prev = matrix::Dcm<float>();
	memset(_vel_pos_innov, 0, sizeof(_vel_pos_innov));
	memset(_mag_innov, 0, sizeof(_mag_innov));
	memset(_vel_pos_innov_var, 0, sizeof(_vel_pos_innov_var));
	memset(_mag_innov_var, 0, sizeof(_mag_innov_var));
	_delta_angle_corr.setZero();
	_delta_vel_corr.setZero();
	_vel_corr.setZero();
	_last_known_posNE.setZero();
	_imu_down_sampled = {};
	_q_down_sampled.setZero();
	_mag_sum = {};
	_delVel_sum = {};
}

Ekf::~Ekf()
{
}

bool Ekf::init(uint64_t timestamp)
{
	bool ret = initialise_interface(timestamp);
	_state.ang_error.setZero();
	_state.vel.setZero();
	_state.pos.setZero();
	_state.gyro_bias.setZero();
	_state.gyro_scale(0) = 1.0f;
	_state.gyro_scale(1) = 1.0f;
	_state.gyro_scale(2) = 1.0f;
	_state.accel_z_bias = 0.0f;
	_state.mag_I.setZero();
	_state.mag_B.setZero();
	_state.wind_vel.setZero();
	_state.quat_nominal.setZero();
	_state.quat_nominal(0) = 1.0f;

	_output_new.vel.setZero();
	_output_new.pos.setZero();
	_output_new.quat_nominal = matrix::Quaternion<float>();

	_imu_down_sampled.delta_ang.setZero();
	_imu_down_sampled.delta_vel.setZero();
	_imu_down_sampled.delta_ang_dt = 0.0f;
	_imu_down_sampled.delta_vel_dt = 0.0f;
	_imu_down_sampled.time_us = timestamp;

	_q_down_sampled(0) = 1.0f;
	_q_down_sampled(1) = 0.0f;
	_q_down_sampled(2) = 0.0f;
	_q_down_sampled(3) = 0.0f;

	_imu_updated = false;
	_NED_origin_initialised = false;
	_gps_speed_valid = false;
	_mag_healthy = false;
	return ret;
}

bool Ekf::update()
{
	bool ret = false;	// indicates if there has been an update

	if (!_filter_initialised) {
		_filter_initialised = initialiseFilter();

		if (!_filter_initialised) {
			return false;
		}
	}

	//printStates();
	//printStatesFast();
	// prediction
	if (_imu_updated) {
		ret = true;
		predictState();
		predictCovariance();
	}

	// control logic
	controlFusionModes();

	// measurement updates

	// Fuse magnetometer data using the selected fusion method and only if angular alignment is complete
	if (_mag_buffer.pop_first_older_than(_imu_sample_delayed.time_us, &_mag_sample_delayed)) {
		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_2D && _control_status.flags.yaw_align) {
			fuseMag2D();

		} else if (_control_status.flags.mag_hdg && _control_status.flags.yaw_align) {
			fuseHeading();

		} else {
			// do no fusion at all
		}
	}

	if (_baro_buffer.pop_first_older_than(_imu_sample_delayed.time_us, &_baro_sample_delayed)) {
		_fuse_height = true;
	}

	// If we are using GPS aiding and data has fallen behind the fusion time horizon then fuse it
	// 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 (_gps_buffer.pop_first_older_than(_imu_sample_delayed.time_us, &_gps_sample_delayed) && _control_status.flags.gps) {
		_fuse_pos = true;
		_fuse_vert_vel = true;
		_fuse_hor_vel = true;

	} else if (!_control_status.flags.gps && !_control_status.flags.opt_flow
		   && ((_time_last_imu - _time_last_fake_gps > 2e5) || _fuse_height)) {
		_fuse_pos = true;
		_gps_sample_delayed.pos(0) = _last_known_posNE(0);
		_gps_sample_delayed.pos(1) = _last_known_posNE(1);
		_time_last_fake_gps = _time_last_imu;
	}

	if (_fuse_height || _fuse_pos || _fuse_hor_vel || _fuse_vert_vel) {
		fuseVelPosHeight();
		_fuse_hor_vel = _fuse_vert_vel = _fuse_pos = _fuse_height = false;
	}

	if (_range_buffer.pop_first_older_than(_imu_sample_delayed.time_us, &_range_sample_delayed)) {
		fuseRange();
	}

	if (_airspeed_buffer.pop_first_older_than(_imu_sample_delayed.time_us, &_airspeed_sample_delayed)) {
		fuseAirspeed();
	}

	calculateOutputStates();

	return ret;
}

bool Ekf::initialiseFilter(void)
{
	// Keep accumulating measurements until we have a minimum of 10 samples for the baro and magnetoemter

	// Sum the IMU delta angle measurements
	_delVel_sum += _imu_down_sampled.delta_vel;

	// Sum the magnetometer measurements
	magSample mag_init = _mag_buffer.get_newest();

	if (mag_init.time_us != 0) {
		_mag_counter ++;
		_mag_sum += mag_init.mag;
	}

	// Sum the barometer measurements
	// initialize vertical position with newest baro measurement
	baroSample baro_init = _baro_buffer.get_newest();

	if (baro_init.time_us != 0) {
		_baro_counter ++;
		_baro_sum += baro_init.hgt;
	}

	// check to see if we have enough measurements and return false if not
	if (_baro_counter < 10 || _mag_counter < 10) {
		return false;

	} else {
		// Zero all of the states
		_state.ang_error.setZero();
		_state.vel.setZero();
		_state.pos.setZero();
		_state.gyro_bias.setZero();
		_state.gyro_scale(0) = _state.gyro_scale(1) = _state.gyro_scale(2) = 1.0f;
		_state.accel_z_bias = 0.0f;
		_state.mag_I.setZero();
		_state.mag_B.setZero();
		_state.wind_vel.setZero();

		// get initial roll and pitch estimate from delta velocity vector, assuming vehicle is static
		float pitch = 0.0f;
		float roll = 0.0f;

		if (_delVel_sum.norm() > 0.001f) {
			_delVel_sum.normalize();
			pitch = asinf(_delVel_sum(0));
			roll = -asinf(_delVel_sum(1) / cosf(pitch));

		} else {
			return false;
		}

		// calculate initial tilt alignment
		matrix::Euler<float> euler_init(roll, pitch, 0.0f);
		_state.quat_nominal = Quaternion(euler_init);
		_output_new.quat_nominal = _state.quat_nominal;
		_control_status.flags.tilt_align = true;

		// calculate the averaged magnetometer reading
		Vector3f mag_init = _mag_sum * (1.0f / (float(_mag_counter)));

		// calculate the initial magnetic field and yaw alignment
		_control_status.flags.yaw_align = resetMagHeading(mag_init);

		// calculate the averaged barometer reading
		_baro_at_alignment = _baro_sum / (float)_baro_counter;

		// set the velocity to the GPS measurement (by definition, the initial position and height is at the origin)
		resetVelocity();

		// initialise the state covariance matrix
		initialiseCovariance();

		return true;
	}
}

void Ekf::predictState()
{
	if (!_earth_rate_initialised) {
		if (_NED_origin_initialised) {
			calcEarthRateNED(_earth_rate_NED, _pos_ref.lat_rad);
			_earth_rate_initialised = true;
		}
	}

	// attitude error state prediction
	matrix::Dcm<float> R_to_earth(_state.quat_nominal);	// transformation matrix from body to world frame
	Vector3f corrected_delta_ang = _imu_sample_delayed.delta_ang - _R_prev * _earth_rate_NED *
				       _imu_sample_delayed.delta_ang_dt;
	Quaternion dq;	// delta quaternion since last update
	dq.from_axis_angle(corrected_delta_ang);
	_state.quat_nominal = dq * _state.quat_nominal;
	_state.quat_nominal.normalize();

	_R_prev = R_to_earth.transpose();

	Vector3f vel_last = _state.vel;

	// predict velocity states
	_state.vel += R_to_earth * _imu_sample_delayed.delta_vel;
	_state.vel(2) += 9.81f * _imu_sample_delayed.delta_vel_dt;

	// predict position states via trapezoidal integration of velocity
	_state.pos += (vel_last + _state.vel) * _imu_sample_delayed.delta_vel_dt * 0.5f;

	constrainStates();
}

bool Ekf::collect_imu(imuSample &imu)
{
	imu.delta_ang(0) = imu.delta_ang(0) * _state.gyro_scale(0);
	imu.delta_ang(1) = imu.delta_ang(1) * _state.gyro_scale(1);
	imu.delta_ang(2) = imu.delta_ang(2) * _state.gyro_scale(2);

	imu.delta_ang -= _state.gyro_bias * imu.delta_ang_dt / (_dt_imu_avg > 0 ? _dt_imu_avg : 0.01f);
	imu.delta_vel(2) -= _state.accel_z_bias * imu.delta_vel_dt / (_dt_imu_avg > 0 ? _dt_imu_avg : 0.01f);;

	_imu_sample_new.delta_ang	= imu.delta_ang;
	_imu_sample_new.delta_vel	= imu.delta_vel;
	_imu_sample_new.delta_ang_dt	= imu.delta_ang_dt;
	_imu_sample_new.delta_vel_dt	= imu.delta_vel_dt;
	_imu_sample_new.time_us	= imu.time_us;

	_imu_down_sampled.delta_ang_dt += imu.delta_ang_dt;
	_imu_down_sampled.delta_vel_dt += imu.delta_vel_dt;


	Quaternion delta_q;
	delta_q.rotate(imu.delta_ang);
	_q_down_sampled =  _q_down_sampled * delta_q;
	_q_down_sampled.normalize();

	matrix::Dcm<float> delta_R(delta_q.inversed());
	_imu_down_sampled.delta_vel = delta_R * _imu_down_sampled.delta_vel;
	_imu_down_sampled.delta_vel += imu.delta_vel;

	if ((_dt_imu_avg * _imu_ticks >= (float)(FILTER_UPDATE_PERRIOD_MS) / 1000) ||
	    _dt_imu_avg * _imu_ticks >= 0.02f) {

		imu.delta_ang     = _q_down_sampled.to_axis_angle();
		imu.delta_vel     = _imu_down_sampled.delta_vel;
		imu.delta_ang_dt  = _imu_down_sampled.delta_ang_dt;
		imu.delta_vel_dt  = _imu_down_sampled.delta_vel_dt;
		imu.time_us       = imu.time_us;

		_imu_down_sampled.delta_ang.setZero();
		_imu_down_sampled.delta_vel.setZero();
		_imu_down_sampled.delta_ang_dt = 0.0f;
		_imu_down_sampled.delta_vel_dt = 0.0f;
		_q_down_sampled(0) = 1.0f;
		_q_down_sampled(1) = _q_down_sampled(2) = _q_down_sampled(3) = 0.0f;
		return true;
	}

	return false;
}

void Ekf::calculateOutputStates()
{
	imuSample imu_new = _imu_sample_new;
	Vector3f delta_angle;

	// Note: We do no not need to consider any bias or scale correction here
	// since the base class has already corrected the imu sample
	delta_angle(0) = imu_new.delta_ang(0);
	delta_angle(1) = imu_new.delta_ang(1);
	delta_angle(2) = imu_new.delta_ang(2);

	Vector3f delta_vel = imu_new.delta_vel;

	delta_angle += _delta_angle_corr;
	Quaternion dq;
	dq.from_axis_angle(delta_angle);

	_output_new.time_us = imu_new.time_us;
	_output_new.quat_nominal = dq * _output_new.quat_nominal;
	_output_new.quat_nominal.normalize();

	matrix::Dcm<float> R_to_earth(_output_new.quat_nominal);

	Vector3f delta_vel_NED = R_to_earth * delta_vel + _delta_vel_corr;
	delta_vel_NED(2) += 9.81f * imu_new.delta_vel_dt;

	Vector3f vel_last = _output_new.vel;

	_output_new.vel += delta_vel_NED;

	_output_new.pos += (_output_new.vel + vel_last) * (imu_new.delta_vel_dt * 0.5f) + _vel_corr * imu_new.delta_vel_dt;

	if (_imu_updated) {
		_output_buffer.push(_output_new);
		_imu_updated = false;
	}

	_output_sample_delayed = _output_buffer.get_oldest();

	Quaternion quat_inv = _state.quat_nominal.inversed();
	Quaternion q_error =  _output_sample_delayed.quat_nominal * quat_inv;
	q_error.normalize();
	Vector3f delta_ang_error;

	float scalar;

	if (q_error(0) >= 0.0f) {
		scalar = -2.0f;

	} else {
		scalar = 2.0f;
	}

	delta_ang_error(0) = scalar * q_error(1);
	delta_ang_error(1) = scalar * q_error(2);
	delta_ang_error(2) = scalar * q_error(3);

	_delta_angle_corr = delta_ang_error * imu_new.delta_ang_dt;

	_delta_vel_corr = (_state.vel - _output_sample_delayed.vel) * imu_new.delta_vel_dt;

	_vel_corr = (_state.pos - _output_sample_delayed.pos);
}

void Ekf::fuseAirspeed()
{

}

void Ekf::fuseRange()
{

}