ardupilot/libraries/AP_NavEKF2/AP_NavEKF2.h

/*
  24 state EKF based on the derivation in https://github.com/priseborough/
  InertialNav/blob/master/derivations/RotationVectorAttitudeParameterisation/
  GenerateNavFilterEquations.m

  Converted from Matlab to C++ by Paul Riseborough

  EKF Tuning parameters refactored by Tom Cauchois

  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/>.
 */
#pragma once

#include <AP_Math/AP_Math.h>
#include <AP_Param/AP_Param.h>
#include <GCS_MAVLink/GCS_MAVLink.h>
#include <AP_NavEKF/AP_Nav_Common.h>
#include <AP_Baro/AP_Baro.h>
#include <AP_Airspeed/AP_Airspeed.h>
#include <AP_Compass/AP_Compass.h>
#include <AP_RangeFinder/AP_RangeFinder.h>

class NavEKF2_core;
class AP_AHRS;

class NavEKF2 {
    friend class NavEKF2_core;

public:
    NavEKF2(const AP_AHRS *ahrs, const RangeFinder &rng);

    /* Do not allow copies */
    NavEKF2(const NavEKF2 &other) = delete;
    NavEKF2 &operator=(const NavEKF2&) = delete;

    static const struct AP_Param::GroupInfo var_info[];

    // allow logging to determine the number of active cores
    uint8_t activeCores(void) const {
        return num_cores;
    }

    // Initialise the filter
    bool InitialiseFilter(void);

    // Update Filter States - this should be called whenever new IMU data is available
    void UpdateFilter(void);

    // check if we should write log messages
    void check_log_write(void);
    
    // Check basic filter health metrics and return a consolidated health status
    bool healthy(void) const;

    // returns the index of the primary core
    // return -1 if no primary core selected
    int8_t getPrimaryCoreIndex(void) const;

    // returns the index of the IMU of the primary core
    // return -1 if no primary core selected
    int8_t getPrimaryCoreIMUIndex(void) const;
    
    // Write the last calculated NE position relative to the reference point (m) for the specified instance.
    // An out of range instance (eg -1) returns data for the the primary instance
    // If a calculated solution is not available, use the best available data and return false
    // If false returned, do not use for flight control
    bool getPosNE(int8_t instance, Vector2f &posNE) const;

    // Write the last calculated D position relative to the reference point (m) for the specified instance.
    // An out of range instance (eg -1) returns data for the the primary instance
    // If a calculated solution is not available, use the best available data and return false
    // If false returned, do not use for flight control
    bool getPosD(int8_t instance, float &posD) const;

    // return NED velocity in m/s for the specified instance
    // An out of range instance (eg -1) returns data for the the primary instance
    void getVelNED(int8_t instance, Vector3f &vel) const;

    // Return the rate of change of vertical position in the down diection (dPosD/dt) in m/s for the specified instance
    // An out of range instance (eg -1) returns data for the the primary instance
    // This can be different to the z component of the EKF velocity state because it will fluctuate with height errors and corrections in the EKF
    // but will always be kinematically consistent with the z component of the EKF position state
    float getPosDownDerivative(int8_t instance) const;

    // This returns the specific forces in the NED frame
    void getAccelNED(Vector3f &accelNED) const;

    // return body axis gyro bias estimates in rad/sec for the specified instance
    // An out of range instance (eg -1) returns data for the the primary instance
    void getGyroBias(int8_t instance, Vector3f &gyroBias) const;

    // return body axis gyro scale factor error as a percentage for the specified instance
    // An out of range instance (eg -1) returns data for the the primary instance
    void getGyroScaleErrorPercentage(int8_t instance, Vector3f &gyroScale) const;

    // return tilt error convergence metric for the specified instance
    // An out of range instance (eg -1) returns data for the the primary instance
    void getTiltError(int8_t instance, float &ang) const;

    // reset body axis gyro bias estimates
    void resetGyroBias(void);

    // Resets the baro so that it reads zero at the current height
    // Resets the EKF height to zero
    // Adjusts the EKf origin height so that the EKF height + origin height is the same as before
    // Returns true if the height datum reset has been performed
    // If using a range finder for height no reset is performed and it returns false
    bool resetHeightDatum(void);

    // Commands the EKF to not use GPS.
    // This command must be sent prior to arming as it will only be actioned when the filter is in static mode
    // This command is forgotten by the EKF each time it goes back into static mode (eg the vehicle disarms)
    // Returns 0 if command rejected
    // Returns 1 if attitude, vertical velocity and vertical position will be provided
    // Returns 2 if attitude, 3D-velocity, vertical position and relative horizontal position will be provided
    uint8_t setInhibitGPS(void);

    // Set the argument to true to prevent the EKF using the GPS vertical velocity
    // This can be used for situations where GPS velocity errors are causing problems with height accuracy
    void setInhibitGpsVertVelUse(const bool varIn) { inhibitGpsVertVelUse = varIn; };

    // return the horizontal speed limit in m/s set by optical flow sensor limits
    // return the scale factor to be applied to navigation velocity gains to compensate for increase in velocity noise with height when using optical flow
    void getEkfControlLimits(float &ekfGndSpdLimit, float &ekfNavVelGainScaler) const;

    // return the Z-accel bias estimate in m/s^2 for the specified instance
    // An out of range instance (eg -1) returns data for the the primary instance
    void getAccelZBias(int8_t instance, float &zbias) const;

    // return the NED wind speed estimates in m/s (positive is air moving in the direction of the axis)
    // An out of range instance (eg -1) returns data for the the primary instance
    void getWind(int8_t instance, Vector3f &wind) const;

    // return earth magnetic field estimates in measurement units / 1000 for the specified instance
    // An out of range instance (eg -1) returns data for the the primary instance
    void getMagNED(int8_t instance, Vector3f &magNED) const;

    // return body magnetic field estimates in measurement units / 1000 for the specified instance
    // An out of range instance (eg -1) returns data for the the primary instance
    void getMagXYZ(int8_t instance, Vector3f &magXYZ) const;

    // return the magnetometer in use for the specified instance
    // An out of range instance (eg -1) returns data for the the primary instance
    uint8_t getActiveMag(int8_t instance) const;

    // Return estimated magnetometer offsets
    // Return true if magnetometer offsets are valid
    bool getMagOffsets(uint8_t mag_idx, Vector3f &magOffsets) const;

    // Return the last calculated latitude, longitude and height in WGS-84
    // If a calculated location isn't available, return a raw GPS measurement
    // The status will return true if a calculation or raw measurement is available
    // The getFilterStatus() function provides a more detailed description of data health and must be checked if data is to be used for flight control
    bool getLLH(struct Location &loc) const;

    // Return the latitude and longitude and height used to set the NED origin for the specified instance
    // An out of range instance (eg -1) returns data for the the primary instance
    // All NED positions calculated by the filter are relative to this location
    // Returns false if the origin has not been set
    bool getOriginLLH(int8_t instance, struct Location &loc) const;

    // set the latitude and longitude and height used to set the NED origin
    // All NED positions calculated by the filter will be relative to this location
    // The origin cannot be set if the filter is in a flight mode (eg vehicle armed)
    // Returns false if the filter has rejected the attempt to set the origin
    bool setOriginLLH(const Location &loc);

    // return estimated height above ground level
    // return false if ground height is not being estimated.
    bool getHAGL(float &HAGL) const;

    // return the Euler roll, pitch and yaw angle in radians for the specified instance
    // An out of range instance (eg -1) returns data for the the primary instance
    void getEulerAngles(int8_t instance, Vector3f &eulers) const;

    // return the transformation matrix from XYZ (body) to NED axes
    void getRotationBodyToNED(Matrix3f &mat) const;

    // return the quaternions defining the rotation from NED to XYZ (body) axes
    void getQuaternion(int8_t instance, Quaternion &quat) const;

    // return the innovations for the specified instance
    // An out of range instance (eg -1) returns data for the the primary instance
    void  getInnovations(int8_t index, Vector3f &velInnov, Vector3f &posInnov, Vector3f &magInnov, float &tasInnov, float &yawInnov) const;

    // publish output observer angular, velocity and position tracking error
    void getOutputTrackingError(int8_t instance, Vector3f &error) const;

    // return the innovation consistency test ratios for the specified instance
    // An out of range instance (eg -1) returns data for the the primary instance
    void  getVariances(int8_t instance, float &velVar, float &posVar, float &hgtVar, Vector3f &magVar, float &tasVar, Vector2f &offset) const;

    // should we use the compass? This is public so it can be used for
    // reporting via ahrs.use_compass()
    bool use_compass(void) const;

    // write the raw optical flow measurements
    // rawFlowQuality is a measured of quality between 0 and 255, with 255 being the best quality
    // rawFlowRates are the optical flow rates in rad/sec about the X and Y sensor axes.
    // rawGyroRates are the sensor rotation rates in rad/sec measured by the sensors internal gyro
    // The sign convention is that a RH physical rotation of the sensor about an axis produces both a positive flow and gyro rate
    // msecFlowMeas is the scheduler time in msec when the optical flow data was received from the sensor.
    // posOffset is the XYZ flow sensor position in the body frame in m
    void  writeOptFlowMeas(const uint8_t rawFlowQuality, const Vector2f &rawFlowRates, const Vector2f &rawGyroRates, const uint32_t msecFlowMeas, const Vector3f &posOffset);

    // return data for debugging optical flow fusion for the specified instance
    // An out of range instance (eg -1) returns data for the the primary instance
    void getFlowDebug(int8_t instance, float &varFlow, float &gndOffset, float &flowInnovX, float &flowInnovY, float &auxInnov, float &HAGL, float &rngInnov, float &range, float &gndOffsetErr) const;

    /*
        Returns the following data for debugging range beacon fusion from the specified instance
        An out of range instance (eg -1) returns data for the the primary instance
        ID : beacon identifier
        rng : measured range to beacon (m)
        innov : range innovation (m)
        innovVar : innovation variance (m^2)
        testRatio : innovation consistency test ratio
        beaconPosNED : beacon NED position (m)
        returns true if data could be found, false if it could not
    */
    bool getRangeBeaconDebug(int8_t instance, uint8_t &ID, float &rng, float &innov, float &innovVar, float &testRatio, Vector3f &beaconPosNED, float &offsetHigh, float &offsetLow) const;

    // called by vehicle code to specify that a takeoff is happening
    // causes the EKF to compensate for expected barometer errors due to ground effect
    void setTakeoffExpected(bool val);

    // called by vehicle code to specify that a touchdown is expected to happen
    // causes the EKF to compensate for expected barometer errors due to ground effect
    void setTouchdownExpected(bool val);

    // Set to true if the terrain underneath is stable enough to be used as a height reference
    // in combination with a range finder. Set to false if the terrain underneath the vehicle
    // cannot be used as a height reference
    void setTerrainHgtStable(bool val);

    /*
    return the filter fault status as a bitmasked integer for the specified instance
    An out of range instance (eg -1) returns data for the the primary instance
     0 = quaternions are NaN
     1 = velocities are NaN
     2 = badly conditioned X magnetometer fusion
     3 = badly conditioned Y magnetometer fusion
     5 = badly conditioned Z magnetometer fusion
     6 = badly conditioned airspeed fusion
     7 = badly conditioned synthetic sideslip fusion
     7 = filter is not initialised
    */
    void  getFilterFaults(int8_t instance, uint16_t &faults) const;

    /*
    return filter timeout status as a bitmasked integer for the specified instance
    An out of range instance (eg -1) returns data for the the primary instance
     0 = position measurement timeout
     1 = velocity measurement timeout
     2 = height measurement timeout
     3 = magnetometer measurement timeout
     5 = unassigned
     6 = unassigned
     7 = unassigned
     7 = unassigned
    */
    void  getFilterTimeouts(int8_t instance, uint8_t &timeouts) const;

    /*
    return filter gps quality check status for the specified instance
    An out of range instance (eg -1) returns data for the the primary instance
    */
    void  getFilterGpsStatus(int8_t instance, nav_gps_status &faults) const;

    /*
    return filter status flags for the specified instance
    An out of range instance (eg -1) returns data for the the primary instance
    */
    void  getFilterStatus(int8_t instance, nav_filter_status &status) const;

    // send an EKF_STATUS_REPORT message to GCS
    void send_status_report(mavlink_channel_t chan);

    // provides the height limit to be observed by the control loops
    // returns false if no height limiting is required
    // this is needed to ensure the vehicle does not fly too high when using optical flow navigation
    bool getHeightControlLimit(float &height) const;

    // return the amount of yaw angle change (in radians) due to the last yaw angle reset or core selection switch
    // returns the time of the last yaw angle reset or 0 if no reset has ever occurred
    uint32_t getLastYawResetAngle(float &yawAngDelta);

    // return the amount of NE position change due to the last position reset in metres
    // returns the time of the last reset or 0 if no reset has ever occurred
    uint32_t getLastPosNorthEastReset(Vector2f &posDelta);

    // return the amount of NE velocity change due to the last velocity reset in metres/sec
    // returns the time of the last reset or 0 if no reset has ever occurred
    uint32_t getLastVelNorthEastReset(Vector2f &vel) const;

    // return the amount of vertical position change due to the last reset in metres
    // returns the time of the last reset or 0 if no reset has ever occurred
    uint32_t getLastPosDownReset(float &posDelta);

    // report any reason for why the backend is refusing to initialise
    const char *prearm_failure_reason(void) const;

    // set and save the _baroAltNoise parameter
    void set_baro_alt_noise(float noise) { _baroAltNoise.set_and_save(noise); };

    // allow the enable flag to be set by Replay
    void set_enable(bool enable) { _enable.set(enable); }

    // are we doing sensor logging inside the EKF?
    bool have_ekf_logging(void) const { return logging.enabled && _logging_mask != 0; }

    // get timing statistics structure
    void getTimingStatistics(int8_t instance, struct ekf_timing &timing) const;

    /*
     * Write position and quaternion data from an external navigation system
     *
     * pos        : position in the RH navigation frame. Frame is assumed to be NED if frameIsNED is true. (m)
     * quat       : quaternion desribing the the rotation from navigation frame to body frame
     * posErr     : 1-sigma spherical position error (m)
     * angErr     : 1-sigma spherical angle error (rad)
     * timeStamp_ms : system time the measurement was taken, not the time it was received (mSec)
     * resetTime_ms : system time of the last position reset request (mSec)
     *
    */
    void writeExtNavData(const Vector3f &sensOffset, const Vector3f &pos, const Quaternion &quat, float posErr, float angErr, uint32_t timeStamp_ms, uint32_t resetTime_ms);

private:
    uint8_t num_cores; // number of allocated cores
    uint8_t primary;   // current primary core
    NavEKF2_core *core = nullptr;
    const AP_AHRS *_ahrs;
    const RangeFinder &_rng;

    uint32_t _frameTimeUsec;        // time per IMU frame
    uint8_t  _framesPerPrediction;  // expected number of IMU frames per prediction

    // EKF Mavlink Tuneable Parameters
    AP_Int8  _enable;               // zero to disable EKF2
    AP_Float _gpsHorizVelNoise;     // GPS horizontal velocity measurement noise : m/s
    AP_Float _gpsVertVelNoise;      // GPS vertical velocity measurement noise : m/s
    AP_Float _gpsHorizPosNoise;     // GPS horizontal position measurement noise m
    AP_Float _baroAltNoise;         // Baro height measurement noise : m
    AP_Float _magNoise;             // magnetometer measurement noise : gauss
    AP_Float _easNoise;             // equivalent airspeed measurement noise : m/s
    AP_Float _windVelProcessNoise;  // wind velocity state process noise : m/s^2
    AP_Float _wndVarHgtRateScale;   // scale factor applied to wind process noise due to height rate
    AP_Float _magEarthProcessNoise; // Earth magnetic field process noise : gauss/sec
    AP_Float _magBodyProcessNoise;  // Body magnetic field process noise : gauss/sec
    AP_Float _gyrNoise;             // gyro process noise : rad/s
    AP_Float _accNoise;             // accelerometer process noise : m/s^2
    AP_Float _gyroBiasProcessNoise; // gyro bias state process noise : rad/s
    AP_Float _accelBiasProcessNoise;// accel bias state process noise : m/s^2
    AP_Int16 _hgtDelay_ms;          // effective average delay of Height measurements relative to inertial measurements (msec)
    AP_Int8  _fusionModeGPS;        // 0 = use 3D velocity, 1 = use 2D velocity, 2 = use no velocity
    AP_Int16  _gpsVelInnovGate;     // Percentage number of standard deviations applied to GPS velocity innovation consistency check
    AP_Int16  _gpsPosInnovGate;     // Percentage number of standard deviations applied to GPS position innovation consistency check
    AP_Int16  _hgtInnovGate;        // Percentage number of standard deviations applied to height innovation consistency check
    AP_Int16  _magInnovGate;        // Percentage number of standard deviations applied to magnetometer innovation consistency check
    AP_Int16  _tasInnovGate;        // Percentage number of standard deviations applied to true airspeed innovation consistency check
    AP_Int8  _magCal;               // Sets activation condition for in-flight magnetometer calibration
    AP_Int8 _gpsGlitchRadiusMax;    // Maximum allowed discrepancy between inertial and GPS Horizontal position before GPS glitch is declared : m
    AP_Float _flowNoise;            // optical flow rate measurement noise
    AP_Int16  _flowInnovGate;       // Percentage number of standard deviations applied to optical flow innovation consistency check
    AP_Int8  _flowDelay_ms;         // effective average delay of optical flow measurements rel to IMU (msec)
    AP_Int16  _rngInnovGate;        // Percentage number of standard deviations applied to range finder innovation consistency check
    AP_Float _maxFlowRate;          // Maximum flow rate magnitude that will be accepted by the filter
    AP_Int8 _altSource;             // Primary alt source during optical flow navigation. 0 = use Baro, 1 = use range finder.
    AP_Float _gyroScaleProcessNoise;// gyro scale factor state process noise : 1/s
    AP_Float _rngNoise;             // Range finder noise : m
    AP_Int8 _gpsCheck;              // Bitmask controlling which preflight GPS checks are bypassed
    AP_Int8 _imuMask;               // Bitmask of IMUs to instantiate EKF2 for
    AP_Int16 _gpsCheckScaler;       // Percentage increase to be applied to GPS pre-flight accuracy and drift thresholds
    AP_Float _noaidHorizNoise;      // horizontal position measurement noise assumed when synthesised zero position measurements are used to constrain attitude drift : m
    AP_Int8 _logging_mask;          // mask of IMUs to log
    AP_Float _yawNoise;             // magnetic yaw measurement noise : rad
    AP_Int16 _yawInnovGate;         // Percentage number of standard deviations applied to magnetic yaw innovation consistency check
    AP_Int8 _tauVelPosOutput;       // Time constant of output complementary filter : csec (centi-seconds)
    AP_Int8 _useRngSwHgt;           // Maximum valid range of the range finder as a percentage of the maximum range specified by the sensor driver
    AP_Float _terrGradMax;          // Maximum terrain gradient below the vehicle
    AP_Float _rngBcnNoise;          // Range beacon measurement noise (m)
    AP_Int16 _rngBcnInnovGate;      // Percentage number of standard deviations applied to range beacon innovation consistency check
    AP_Int8  _rngBcnDelay_ms;       // effective average delay of range beacon measurements rel to IMU (msec)
    AP_Float _useRngSwSpd;          // Maximum horizontal ground speed to use range finder as the primary height source (m/s)
    AP_Int8 _magMask;               // Bitmask forcng specific EKF core instances to use simple heading magnetometer fusion.
    AP_Int8 _originHgtMode;         // Bitmask controlling post alignment correction and reporting of the EKF origin height.

    // Tuning parameters
    const float gpsNEVelVarAccScale = 0.05f;       // Scale factor applied to NE velocity measurement variance due to manoeuvre acceleration
    const float gpsDVelVarAccScale = 0.07f;        // Scale factor applied to vertical velocity measurement variance due to manoeuvre acceleration
    const float gpsPosVarAccScale = 0.05f;         // Scale factor applied to horizontal position measurement variance due to manoeuvre acceleration
    const uint8_t magDelay_ms = 60;               // Magnetometer measurement delay (msec)
    const uint8_t tasDelay_ms = 240;              // Airspeed measurement delay (msec)
    const uint16_t tiltDriftTimeMax_ms = 15000;    // Maximum number of ms allowed without any form of tilt aiding (GPS, flow, TAS, etc)
    const uint16_t posRetryTimeUseVel_ms = 10000;  // Position aiding retry time with velocity measurements (msec)
    const uint16_t posRetryTimeNoVel_ms = 7000;    // Position aiding retry time without velocity measurements (msec)
    const uint16_t hgtRetryTimeMode0_ms = 10000;   // Height retry time with vertical velocity measurement (msec)
    const uint16_t hgtRetryTimeMode12_ms = 5000;   // Height retry time without vertical velocity measurement (msec)
    const uint16_t tasRetryTime_ms = 5000;         // True airspeed timeout and retry interval (msec)
    const uint16_t magFailTimeLimit_ms = 10000;    // number of msec before a magnetometer failing innovation consistency checks is declared failed (msec)
    const float magVarRateScale = 0.005f;          // scale factor applied to magnetometer variance due to angular rate
    const float gyroBiasNoiseScaler = 2.0f;        // scale factor applied to gyro bias state process noise when on ground
    const uint8_t hgtAvg_ms = 100;                // average number of msec between height measurements
    const uint8_t betaAvg_ms = 100;               // average number of msec between synthetic sideslip measurements
    const float covTimeStepMax = 0.1f;             // maximum time (sec) between covariance prediction updates
    const float covDelAngMax = 0.05f;              // maximum delta angle between covariance prediction updates
    const float DCM33FlowMin = 0.71f;              // If Tbn(3,3) is less than this number, optical flow measurements will not be fused as tilt is too high.
    const float fScaleFactorPnoise = 1e-10f;       // Process noise added to focal length scale factor state variance at each time step
    const uint8_t flowTimeDeltaAvg_ms = 100;       // average interval between optical flow measurements (msec)
    const uint8_t flowIntervalMax_ms = 100;       // maximum allowable time between flow fusion events
    const uint16_t gndEffectTimeout_ms = 1000;     // time in msec that ground effect mode is active after being activated
    const float gndEffectBaroScaler = 4.0f;        // scaler applied to the barometer observation variance when ground effect mode is active
    const uint8_t gndGradientSigma = 50;           // RMS terrain gradient percentage assumed by the terrain height estimation
    const uint8_t fusionTimeStep_ms = 10;          // The minimum time interval between covariance predictions and measurement fusions in msec

    struct {
        bool enabled:1;
        bool log_compass:1;
        bool log_gps:1;
        bool log_baro:1;
        bool log_imu:1;
    } logging;

    // time at start of current filter update
    uint64_t imuSampleTime_us;
    
    struct {
        uint32_t last_function_call;  // last time getLastYawYawResetAngle was called
        bool core_changed;            // true when a core change happened and hasn't been consumed, false otherwise
        uint32_t last_primary_change; // last time a primary has changed
        float core_delta;             // the amount of yaw change between cores when a change happened
    } yaw_reset_data;

    struct {
        uint32_t last_function_call;  // last time getLastPosNorthEastReset was called
        bool core_changed;            // true when a core change happened and hasn't been consumed, false otherwise
        uint32_t last_primary_change; // last time a primary has changed
        Vector2f core_delta;          // the amount of NE position change between cores when a change happened
    } pos_reset_data;

    struct {
        uint32_t last_function_call;  // last time getLastPosDownReset was called
        bool core_changed;            // true when a core change happened and hasn't been consumed, false otherwise
        uint32_t last_primary_change; // last time a primary has changed
        float core_delta;             // the amount of D position change between cores when a change happened
    } pos_down_reset_data;

    bool runCoreSelection; // true when the primary core has stabilised and the core selection logic can be started

    bool inhibitGpsVertVelUse;  // true when GPS vertical velocity use is prohibited

    // update the yaw reset data to capture changes due to a lane switch
    // new_primary - index of the ekf instance that we are about to switch to as the primary
    // old_primary - index of the ekf instance that we are currently using as the primary
    void updateLaneSwitchYawResetData(uint8_t new_primary, uint8_t old_primary);

    // update the position reset data to capture changes due to a lane switch
    // new_primary - index of the ekf instance that we are about to switch to as the primary
    // old_primary - index of the ekf instance that we are currently using as the primary
    void updateLaneSwitchPosResetData(uint8_t new_primary, uint8_t old_primary);

    // update the position down reset data to capture changes due to a lane switch
    // new_primary - index of the ekf instance that we are about to switch to as the primary
    // old_primary - index of the ekf instance that we are currently using as the primary
    void updateLaneSwitchPosDownResetData(uint8_t new_primary, uint8_t old_primary);
};