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[EKF2] Tilt estimate improvements #24247

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[EKF2] Tilt estimate improvements #24247

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d29fd26
ekf2-decl: do not always update tilt
bresch Jan 21, 2025
beb7e7d
ekf2-gravity: start based on accel LPF instead of peak hold
bresch Jan 23, 2025
b1b6810
ekf2-gravity: do not estimate accel bias when gravity fusion is active
bresch Jan 23, 2025
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5 changes: 3 additions & 2 deletions src/modules/ekf2/EKF/aid_sources/gravity/gravity_fusion.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -54,8 +54,9 @@ void Ekf::controlGravityFusion(const imuSample &imu)

const float upper_accel_limit = CONSTANTS_ONE_G * 1.1f;
const float lower_accel_limit = CONSTANTS_ONE_G * 0.9f;
const bool accel_lpf_norm_good = (_accel_magnitude_filt > lower_accel_limit)
&& (_accel_magnitude_filt < upper_accel_limit);
const float accel_lpf_norm_sq = _accel_lpf.getState().norm_squared();
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_accel_lpf is only being updated during init, but I was thinking we should move it regardless.

PX4-Autopilot/src/modules/ekf2/EKF/ekf.cpp

Lines 180 to 198 in beb7e7d

bool Ekf::initialiseFilter()
{
// Filter accel for tilt initialization
const imuSample &imu_init = _imu_buffer.get_newest();
// protect against zero data
if (imu_init.delta_vel_dt < 1e-4f || imu_init.delta_ang_dt < 1e-4f) {
return false;
}
if (_is_first_imu_sample) {
_accel_lpf.reset(imu_init.delta_vel / imu_init.delta_vel_dt);
_gyro_lpf.reset(imu_init.delta_ang / imu_init.delta_ang_dt);
_is_first_imu_sample = false;
} else {
_accel_lpf.update(imu_init.delta_vel / imu_init.delta_vel_dt);
_gyro_lpf.update(imu_init.delta_ang / imu_init.delta_ang_dt);
}

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I was moving it here, but got a little sidetracked. #24046

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Ouch, I didn't realize that; thanks

const bool accel_lpf_norm_good = (accel_lpf_norm_sq > sq(lower_accel_limit))
&& (accel_lpf_norm_sq < sq(upper_accel_limit));

// fuse gravity observation if our overall acceleration isn't too big
_control_status.flags.gravity_vector = (_params.imu_ctrl & static_cast<int32_t>(ImuCtrl::GravityVector))
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4 changes: 2 additions & 2 deletions src/modules/ekf2/EKF/aid_sources/magnetometer/mag_control.cpp
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Expand Up @@ -236,13 +236,13 @@ void Ekf::controlMagFusion(const imuSample &imu_sample)
&& PX4_ISFINITE(_wmm_declination_rad)
) {
// using declination from the world magnetic model
fuseDeclination(_wmm_declination_rad, 0.5f, update_all_states);
fuseDeclination(_wmm_declination_rad, 0.5f, update_all_states, update_tilt);

} else if ((_params.mag_declination_source & GeoDeclinationMask::SAVE_GEO_DECL)
&& PX4_ISFINITE(_params.mag_declination_deg) && (fabsf(_params.mag_declination_deg) > 0.f)
) {
// using previously saved declination
fuseDeclination(math::radians(_params.mag_declination_deg), R_DECL, update_all_states);
fuseDeclination(math::radians(_params.mag_declination_deg), R_DECL, update_all_states, update_tilt);

} else {
// if there is no aiding coming from an inertial frame we need to fuse some declination
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10 changes: 8 additions & 2 deletions src/modules/ekf2/EKF/aid_sources/magnetometer/mag_fusion.cpp
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Expand Up @@ -140,7 +140,7 @@ bool Ekf::fuseMag(const Vector3f &mag, const float R_MAG, VectorState &H, estima
return true;
}

bool Ekf::fuseDeclination(float decl_measurement_rad, float R, bool update_all_states)
bool Ekf::fuseDeclination(float decl_measurement_rad, float R, bool update_all_states, bool update_tilt)
{
VectorState H;
float decl_pred;
Expand All @@ -160,7 +160,13 @@ bool Ekf::fuseDeclination(float decl_measurement_rad, float R, bool update_all_s
// Calculate the Kalman gains
VectorState Kfusion = P * H / innovation_variance;

if (!update_all_states) {
if (update_all_states) {
if (!update_tilt) {
Kfusion(State::quat_nominal.idx + 0) = 0.f;
Kfusion(State::quat_nominal.idx + 1) = 0.f;
}

} else {
// zero non-mag Kalman gains if not updating all states

// copy mag_I and mag_B Kalman gains
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3 changes: 2 additions & 1 deletion src/modules/ekf2/EKF/ekf.h
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Expand Up @@ -669,7 +669,8 @@ class Ekf final : public EstimatorInterface

// fuse magnetometer declination measurement
// R: declination observation variance (rad**2)
bool fuseDeclination(const float decl_measurement_rad, const float R, bool update_all_states = false);
bool fuseDeclination(const float decl_measurement_rad, const float R, bool update_all_states = false,
bool update_tilt = false);

#endif // CONFIG_EKF2_MAGNETOMETER

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4 changes: 2 additions & 2 deletions src/modules/ekf2/EKF/ekf_helper.cpp
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Expand Up @@ -1013,8 +1013,8 @@ void Ekf::updateIMUBiasInhibit(const imuSample &imu_delayed)
} else if (_control_status.flags.fake_hgt) {
is_bias_observable = false;

} else if (_control_status.flags.fake_pos) {
// when using fake position (but not fake height) only consider an accel bias observable if aligned with the gravity vector
} else if (_control_status.flags.fake_pos || _control_status.flags.gravity_vector) {
// only consider an accel bias observable if aligned with the gravity vector
is_bias_observable = (fabsf(_R_to_earth(2, index)) > 0.966f); // cos 15 degrees ~= 0.966
}

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