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"
#include <drivers/drv_hrt.h>

Ekf::Ekf():
	_filter_initialised(false),
	_earth_rate_initialised(false),
	_fuse_height(false),
	_fuse_pos(false),
	_fuse_vel(false),
	_mag_fuse_index(0),
	_time_last_fake_gps(0)
{
	_earth_rate_NED.setZero();
	_R_prev = matrix::Dcm<float>();
	_delta_angle_corr.setZero();
	_delta_vel_corr.setZero();
	_vel_corr.setZero();
}


Ekf::~Ekf()
{

}

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();
	}

	// measurement updates

	if (_mag_buffer.pop_first_older_than(_imu_sample_delayed.time_us, &_mag_sample_delayed)) {
		fuseHeading();
		//fuseMag(_mag_fuse_index);
		//_mag_fuse_index = (_mag_fuse_index + 1) % 3;
	}

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

	if (_gps_buffer.pop_first_older_than(_imu_sample_delayed.time_us, &_gps_sample_delayed)) {
		_fuse_pos = true;
		_fuse_vel = true;
	} else if (_time_last_imu - _time_last_gps > 2000000 && _time_last_imu - _time_last_fake_gps > 70000) {
		_fuse_vel = true;
		_gps_sample_delayed.vel.setZero();
	}


	if (_fuse_height || _fuse_pos || _fuse_vel) {
		fuseVelPosHeight();
		_fuse_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)
{
	_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 accel vector, assuming vehicle is static
	Vector3f accel_init = _imu_down_sampled.delta_vel / _imu_down_sampled.delta_vel_dt;

	float pitch = 0.0f;
	float roll = 0.0f;

	if (accel_init.norm() > 0.001f) {
		accel_init.normalize();

		pitch = asinf(accel_init(0));
		roll = -asinf(accel_init(1) / cosf(pitch));
	}

    matrix::Euler<float> euler_init(roll, pitch, 0.0f);

    // Get the latest magnetic field measurement.
    // If we don't have a measurement then we cannot initialise the filter
    magSample mag_init = _mag_buffer.get_newest();
	if (mag_init.time_us == 0) {
		return false;
	}

    // rotate magnetic field into earth frame assuming zero yaw and estimate yaw angle assuming zero declination
    // TODO use declination if available
    matrix::Dcm<float> R_to_earth_zeroyaw(euler_init);
    Vector3f mag_ef_zeroyaw = R_to_earth_zeroyaw * mag_init.mag;
    float declination = 0.0f;
    euler_init(2) = declination - atan2f(mag_ef_zeroyaw(1), mag_ef_zeroyaw(0));

    // calculate initial quaternion states
    _state.quat_nominal = Quaternion(euler_init);

    // calculate initial earth magnetic field states
    matrix::Dcm<float> R_to_earth(euler_init);
    _state.mag_I = R_to_earth * mag_init.mag;

    resetVelocity();
	resetPosition();

	initialiseCovariance();

	return true;
}

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

	// attitude error state prediciton
	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();
}

void Ekf::calculateOutputStates()
{
	imuSample imu_new = _imu_sample_new;
	Vector3f delta_angle;
	delta_angle(0) = imu_new.delta_ang(0) * _state.gyro_scale(0);
	delta_angle(1) = imu_new.delta_ang(1) * _state.gyro_scale(1);
	delta_angle(2) = imu_new.delta_ang(2) * _state.gyro_scale(2);

	delta_angle -= _state.gyro_bias;

	Vector3f delta_vel = imu_new.delta_vel;
	delta_vel(2) -= _state.accel_z_bias;

	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;
	}

	if (!_output_buffer.pop_first_older_than(_imu_sample_delayed.time_us, &_output_sample_delayed))
	{
		return;
	}

	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()
{

}

void Ekf::printStates()
{
	static int counter = 0;

	if (counter % 50 == 0) {
		printf("quaternion\n");
		for(int i = 0; i < 4; i++) {
			printf("quat %i %.5f\n", i, (double)_state.quat_nominal(i));
		}

		matrix::Euler<float> euler(_state.quat_nominal);
		printf("yaw pitch roll %.5f %.5f %.5f\n", (double)euler(2), (double)euler(1), (double)euler(0));

		printf("vel\n");
		for(int i = 0; i < 3; i++) {
			printf("v %i %.5f\n", i, (double)_state.vel(i));
		}

		printf("pos\n");
		for(int i = 0; i < 3; i++) {
			printf("p %i %.5f\n", i, (double)_state.pos(i));
		}

		printf("gyro_scale\n");
		for(int i = 0; i < 3; i++) {
			printf("gs %i %.5f\n", i, (double)_state.gyro_scale(i));
		}

		printf("mag earth\n");
		for(int i = 0; i < 3; i++) {
			printf("mI %i %.5f\n", i, (double)_state.mag_I(i));
		}

		printf("mag bias\n");
		for(int i = 0; i < 3; i++) {
			printf("mB %i %.5f\n", i, (double)_state.mag_B(i));
		}
		counter = 0;
	}
	counter++;

}

void Ekf::printStatesFast()
{
	static int counter_fast = 0;

	if (counter_fast % 50 == 0) {
		printf("quaternion\n");
		for(int i = 0; i < 4; i++) {
			printf("quat %i %.5f\n", i, (double)_output_new.quat_nominal(i));
		}

		printf("vel\n");
		for(int i = 0; i < 3; i++) {
			printf("v %i %.5f\n", i, (double)_output_new.vel(i));
		}

		printf("pos\n");
		for(int i = 0; i < 3; i++) {
			printf("p %i %.5f\n", i, (double)_output_new.pos(i));
		}

		counter_fast = 0;
	}
	counter_fast++;
}