PX4-Autopilot/EKF/ekf.h

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/**
 * @file ekf.h
 * Class for core functions for ekf attitude and position estimator.
 *
 * @author Roman Bast <bapstroman@gmail.com>
 * @author Paul Riseborough <p_riseborough@live.com.au>
 *
 */

#include "estimator_interface.h"

class Ekf : public EstimatorInterface
{
public:

	Ekf();
	~Ekf();

	bool init(uint64_t timestamp);
	bool update();

	// gets the innovations of velocity and position measurements
	// 0-2 vel, 3-5 pos
	void get_vel_pos_innov(float vel_pos_innov[6]);

	// gets the innovations of the earth magnetic field measurements
	void get_mag_innov(float mag_innov[3]);

	// gets the innovations of the heading measurement
	void get_heading_innov(float *heading_innov);

	// gets the innovation variances of velocity and position measurements
	// 0-2 vel, 3-5 pos
	void get_vel_pos_innov_var(float vel_pos_innov_var[6]);

	// gets the innovation variances of the earth magnetic field measurements
	void get_mag_innov_var(float mag_innov_var[3]);

	// gets the innovation variance of the heading measurement
	void get_heading_innov_var(float *heading_innov_var);

	// get the state vector at the delayed time horizon
	void get_state_delayed(float *state);

	// get the diagonal elements of the covariance matrix
	void get_covariances(float *covariances);

	// ask estimator for sensor data collection decision and do any preprocessing if required, returns true if not defined
	bool collect_gps(uint64_t time_usec, struct gps_message *gps);
	bool collect_imu(imuSample &imu);

	filter_control_status_u _control_status = {};

	// get the ekf WGS-84 origin position and height and the system time it was last set
	void get_ekf_origin(uint64_t *origin_time, map_projection_reference_s *origin_pos, float *origin_alt);

private:

	static const uint8_t _k_num_states = 24;
	static constexpr float _k_earth_rate = 0.000072921f;

	stateSample _state;

	bool _filter_initialised;
	bool _earth_rate_initialised;

	bool _fuse_height;	// baro height data should be fused
	bool _fuse_pos;		// gps position data should be fused
	bool _fuse_hor_vel;		// gps horizontal velocity measurement should be fused
	bool _fuse_vert_vel;	// gps vertical velocity measurement should be fused

	uint64_t _time_last_fake_gps;

	uint64_t _time_last_pos_fuse;   // time the last fusion of horizotal position measurements was performed (usec)
	uint64_t _time_last_vel_fuse;   // time the last fusion of velocity measurements was performed (usec)
	uint64_t _time_last_hgt_fuse;   // time the last fusion of height measurements was performed (usec)
	uint64_t _time_last_of_fuse;    // time the last fusion of optical flow measurements were performed (usec)
	Vector2f _last_known_posNE;     // last known local NE position vector (m)
	float _last_disarmed_posD;      // vertical position recorded at arming (m)

	Vector3f _earth_rate_NED;

	matrix::Dcm<float> _R_prev;

	float P[_k_num_states][_k_num_states];	// state covariance matrix

	float _vel_pos_innov[6];	// innovations: 0-2 vel,  3-5 pos
	float _mag_innov[3];		// earth magnetic field innovations
	float _heading_innov;		// heading measurement innovation

	float _vel_pos_innov_var[6]; // innovation variances: 0-2 vel, 3-5 pos
	float _mag_innov_var[3]; // earth magnetic field innovation variance
	float _heading_innov_var; // heading measurement innovation variance

	// complementary filter states
	Vector3f _delta_angle_corr;
	Vector3f _delta_vel_corr;
	Vector3f _vel_corr;
	imuSample _imu_down_sampled;
	Quaternion _q_down_sampled;

	// variables used for the GPS quality checks
	float _gpsDriftVelN = 0.0f;     // GPS north position derivative (m/s)
	float _gpsDriftVelE = 0.0f;     // GPS east position derivative (m/s)
	float _gps_drift_velD = 0.0f;     // GPS down position derivative (m/s)
	float _gps_velD_diff_filt = 0.0f;   // GPS filtered Down velocity (m/s)
	float _gps_velN_filt = 0.0f;  // GPS filtered North velocity (m/s)
	float _gps_velE_filt = 0.0f;   // GPS filtered East velocity (m/s)
	uint64_t _last_gps_fail_us = 0;   // last system time in usec that the GPS failed it's checks

	// Variables used to publish the WGS-84 location of the EKF local NED origin
	uint64_t _last_gps_origin_time_us = 0;              // time the origin was last set (uSec)
	float _gps_alt_ref = 0.0f;                          // WGS-84 height (m)

	// Variables used to initialise the filter states
	uint8_t _baro_counter = 0;      // number of baro samples averaged
	float _baro_sum = 0.0f;         // summed baro measurement
	uint8_t _mag_counter = 0;       // number of magnetometer samples averaged
	Vector3f _mag_sum = {};         // summed magnetometer measurement
	Vector3f _delVel_sum = {};      // summed delta velocity
	float _baro_at_alignment;       // baro offset relative to alignment position

	gps_check_fail_status_u _gps_check_fail_status;

	void calculateOutputStates();

	bool initialiseFilter(void);

	void initialiseCovariance();

	void predictState();

	void predictCovariance();

	void fuseMag();

	void fuseHeading();

	void fuseDeclination();

	void fuseAirspeed();

	void fuseRange();

	void fuseVelPosHeight();

	void resetVelocity();

	void resetPosition();

	void resetHeight();

	void makeCovSymetrical();

	void limitCov();

	void printCovToFile(char const *filename);

	void assertCovNiceness();

	void makeSymmetrical();

	void constrainStates();

	void fuse(float *K, float innovation);

	void printStates();

	void printStatesFast();

	void calcEarthRateNED(Vector3f &omega, double lat_rad) const;

	// return true id the GPS quality is good enough to set an origin and start aiding
	bool gps_is_good(struct gps_message *gps);

	// Control the filter fusion modes
	void controlFusionModes();

	// Determine if we are airborne or motors are armed
	void calculateVehicleStatus();

	// return the square of two foating point numbers - used in autocoded sections
	inline float sq(float var)
	{
		return var * var;
	}
};