ardupilot/libraries/AP_AHRS/AP_AHRS_DCM.h

#pragma once

/*
   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

/*
 *  DCM based AHRS (Attitude Heading Reference System) interface for
 *  ArduPilot
 *
 */

class AP_AHRS_DCM : public AP_AHRS {
public:
    AP_AHRS_DCM()
        : AP_AHRS()
        , _error_rp(1.0f)
        , _error_yaw(1.0f)
        , _mag_earth(1, 0)
        , _imu1_weight(0.5f)
    {
        _dcm_matrix.identity();

        // these are experimentally derived from the simulator
        // with large drift levels
        _ki = 0.0087f;
        _ki_yaw = 0.01f;
    }

    /* Do not allow copies */
    AP_AHRS_DCM(const AP_AHRS_DCM &other) = delete;
    AP_AHRS_DCM &operator=(const AP_AHRS_DCM&) = delete;


    // return the smoothed gyro vector corrected for drift
    const Vector3f &get_gyro() const override {
        return _omega;
    }

    // return rotation matrix representing rotaton from body to earth axes
    const Matrix3f &get_rotation_body_to_ned() const override {
        return _body_dcm_matrix;
    }

    // get rotation matrix specifically from DCM backend (used for compass calibrator)
    const Matrix3f &get_DCM_rotation_body_to_ned(void) const override { return _body_dcm_matrix; }
    
    // return the current drift correction integrator value
    const Vector3f &get_gyro_drift() const override {
        return _omega_I;
    }

    // reset the current gyro drift estimate
    //  should be called if gyro offsets are recalculated
    void reset_gyro_drift() override;

    // Methods
    void            update(bool skip_ins_update=false) override;
    void            reset(bool recover_eulers = false) override;

    // reset the current attitude, used on new IMU calibration
    void reset_attitude(const float &roll, const float &pitch, const float &yaw) override;

    // dead-reckoning support
    virtual bool get_position(struct Location &loc) const override;

    // status reporting
    float           get_error_rp() const override {
        return _error_rp;
    }
    float           get_error_yaw() const override {
        return _error_yaw;
    }

    // return a wind estimation vector, in m/s
    Vector3f wind_estimate() const override {
        return _wind;
    }

    void get_relative_position_D_home(float &posD) const override;

    // return an airspeed estimate if available. return true
    // if we have an estimate
    bool airspeed_estimate(float *airspeed_ret) const override;

    bool            use_compass() override;

    void set_home(const Location &loc) override;
    void estimate_wind(void);

    // is the AHRS subsystem healthy?
    bool healthy() const override;

    // time that the AHRS has been up
    uint32_t uptime_ms() const override;

private:
    float _ki;
    float _ki_yaw;

    // Methods
    void            matrix_update(float _G_Dt);
    void            normalize(void);
    void            check_matrix(void);
    bool            renorm(Vector3f const &a, Vector3f &result);
    void            drift_correction(float deltat);
    void            drift_correction_yaw(void);
    float           yaw_error_compass();
    void            euler_angles(void);
    bool            have_gps(void) const;
    bool            use_fast_gains(void) const;

    // primary representation of attitude of board used for all inertial calculations
    Matrix3f _dcm_matrix;

    // primary representation of attitude of flight vehicle body
    Matrix3f _body_dcm_matrix;

    Vector3f _omega_P;                          // accel Omega proportional correction
    Vector3f _omega_yaw_P;                      // proportional yaw correction
    Vector3f _omega_I;                          // Omega Integrator correction
    Vector3f _omega_I_sum;
    float _omega_I_sum_time;
    Vector3f _omega;                            // Corrected Gyro_Vector data

    // variables to cope with delaying the GA sum to match GPS lag
    Vector3f ra_delayed(uint8_t instance, const Vector3f &ra);
    Vector3f _ra_delay_buffer[INS_MAX_INSTANCES];

    // P term gain based on spin rate
    float           _P_gain(float spin_rate);

    // P term yaw gain based on rate of change of horiz velocity
    float           _yaw_gain(void) const;

    // state to support status reporting
    float _renorm_val_sum;
    uint16_t _renorm_val_count;
    float _error_rp;
    float _error_yaw;

    // time in millis when we last got a GPS heading
    uint32_t _gps_last_update;

    // state of accel drift correction
    Vector3f _ra_sum[INS_MAX_INSTANCES];
    Vector3f _last_velocity;
    float _ra_deltat;
    uint32_t _ra_sum_start;

    // the earths magnetic field
    float _last_declination;
    Vector2f _mag_earth;

    // whether we have GPS lock
    bool _have_gps_lock;

    // the lat/lng where we last had GPS lock
    int32_t _last_lat;
    int32_t _last_lng;

    // position offset from last GPS lock
    float _position_offset_north;
    float _position_offset_east;

    // whether we have a position estimate
    bool _have_position;

    // support for wind estimation
    Vector3f _last_fuse;
    Vector3f _last_vel;
    uint32_t _last_wind_time;
    float _last_airspeed;
    uint32_t _last_consistent_heading;

    // estimated wind in m/s
    Vector3f _wind;

    float _imu1_weight;

    // last time AHRS failed in milliseconds
    uint32_t _last_failure_ms;

    // time when DCM was last reset
    uint32_t _last_startup_ms;
};