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ekf: split accel bias learning in independant xyz components (#817) 

This is a non-functional change required to select accel bias estimation
per axis selection. The intent is then to disable the learning before
takeoff of the components that are poorly observable.
master
Mathieu Bresciani 5 years ago committed by GitHub
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3 changed files with 74 additions and 89 deletions
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  1. 149
      EKF/covariance.cpp
  2. 2
      EKF/ekf.h
  3. 12
      test/test_EKF_initialization.cpp

149
EKF/covariance.cpp
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@ -146,37 +146,42 @@ void Ekf::predictCovariance() @@ -146,37 +146,42 @@ void Ekf::predictCovariance()
const float d_vel_bias_sig = dt * dt * math::constrain(_params.accel_bias_p_noise, 0.0f, 1.0f);
// inhibit learning of imu accel bias if the manoeuvre levels are too high to protect against the effect of sensor nonlinearities or bad accel data is detected
// xy accel bias learning is also disabled on ground as those states are poorly observable when perpendicular to the gravity vector
const float alpha = math::constrain((dt / _params.acc_bias_learn_tc), 0.0f, 1.0f);
const float beta = 1.0f - alpha;
_ang_rate_magnitude_filt = fmaxf(dt_inv * _imu_sample_delayed.delta_ang.norm(), beta * _ang_rate_magnitude_filt);
_accel_magnitude_filt = fmaxf(dt_inv * _imu_sample_delayed.delta_vel.norm(), beta * _accel_magnitude_filt);
_accel_vec_filt = alpha * dt_inv * _imu_sample_delayed.delta_vel + beta * _accel_vec_filt;
if (_ang_rate_magnitude_filt > _params.acc_bias_learn_gyr_lim
|| _accel_magnitude_filt > _params.acc_bias_learn_acc_lim
|| _bad_vert_accel_detected) {
const bool is_manoeuvre_level_high = _ang_rate_magnitude_filt > _params.acc_bias_learn_gyr_lim
|| _accel_magnitude_filt > _params.acc_bias_learn_acc_lim;
// store the bias state variances to be reinstated later
if (!_accel_bias_inhibit) {
_prev_dvel_bias_var = P.slice<3,3>(13,13).diag();
}
const bool do_inhibit_all_axes = (_params.fusion_mode & MASK_INHIBIT_ACC_BIAS)
|| is_manoeuvre_level_high
|| _bad_vert_accel_detected;
_accel_bias_inhibit = true;
for (unsigned stateIndex = 13; stateIndex <= 15; stateIndex++) {
const unsigned index = stateIndex - 13;
} else {
if (_accel_bias_inhibit) {
// reinstate the bias state variances
P(13,13) = _prev_dvel_bias_var(0);
P(14,14) = _prev_dvel_bias_var(1);
P(15,15) = _prev_dvel_bias_var(2);
// TODO: When on ground, only consider an accel bias observable if aligned with the gravity vector
// const bool is_bias_observable = (fabsf(_R_to_earth(2, index)) > 0.8f) || _control_status.flags.in_air;
const bool is_bias_observable = true;
const bool do_inhibit_axis = do_inhibit_all_axes || !is_bias_observable;
} else {
if (do_inhibit_axis) {
// store the bias state variances to be reinstated later
_prev_dvel_bias_var = P.slice<3,3>(13,13).diag();
if (!_accel_bias_inhibit[index]) {
_prev_dvel_bias_var(index) = P(stateIndex, stateIndex);
_accel_bias_inhibit[index] = true;
}
} else {
if (_accel_bias_inhibit[index]) {
// reinstate the bias state variances
P(stateIndex, stateIndex) = _prev_dvel_bias_var(index);
_accel_bias_inhibit[index] = false;
}
}
_accel_bias_inhibit = false;
}
// Don't continue to grow the earth field variances if they are becoming too large or we are not doing 3-axis fusion as this can make the covariance matrix badly conditioned
@ -431,68 +436,43 @@ void Ekf::predictCovariance() @@ -431,68 +436,43 @@ void Ekf::predictCovariance()
nextP(i,i) = kahanSummation(nextP(i,i), process_noise(i), _delta_angle_bias_var_accum(index));
}
// Don't calculate these covariance terms if IMU delta velocity bias estimation is inhibited
if (!(_params.fusion_mode & MASK_INHIBIT_ACC_BIAS) && !_accel_bias_inhibit) {
// calculate variances and upper diagonal covariances for IMU delta velocity bias states
nextP(0,13) = P(0,13) + P(1,13)*SF[9] + P(2,13)*SF[11] + P(3,13)*SF[10] + P(10,13)*SF[14] + P(11,13)*SF[15] + P(12,13)*SPP[10];
nextP(1,13) = P(1,13) + P(0,13)*SF[8] + P(2,13)*SF[7] + P(3,13)*SF[11] - P(12,13)*SF[15] + P(11,13)*SPP[10] - (P(10,13)*q0)/2;
nextP(2,13) = P(2,13) + P(0,13)*SF[6] + P(1,13)*SF[10] + P(3,13)*SF[8] + P(12,13)*SF[14] - P(10,13)*SPP[10] - (P(11,13)*q0)/2;
nextP(3,13) = P(3,13) + P(0,13)*SF[7] + P(1,13)*SF[6] + P(2,13)*SF[9] + P(10,13)*SF[15] - P(11,13)*SF[14] - (P(12,13)*q0)/2;
nextP(4,13) = P(4,13) + P(0,13)*SF[5] + P(1,13)*SF[3] - P(3,13)*SF[4] + P(2,13)*SPP[0] + P(13,13)*SPP[3] + P(14,13)*SPP[6] - P(15,13)*SPP[9];
nextP(5,13) = P(5,13) + P(0,13)*SF[4] + P(2,13)*SF[3] + P(3,13)*SF[5] - P(1,13)*SPP[0] - P(13,13)*SPP[8] + P(14,13)*SPP[2] + P(15,13)*SPP[5];
nextP(6,13) = P(6,13) + P(1,13)*SF[4] - P(2,13)*SF[5] + P(3,13)*SF[3] + P(0,13)*SPP[0] + P(13,13)*SPP[4] - P(14,13)*SPP[7] - P(15,13)*SPP[1];
nextP(7,13) = P(7,13) + P(4,13)*dt;
nextP(8,13) = P(8,13) + P(5,13)*dt;
nextP(9,13) = P(9,13) + P(6,13)*dt;
nextP(10,13) = P(10,13);
nextP(11,13) = P(11,13);
nextP(12,13) = P(12,13);
nextP(13,13) = P(13,13);
nextP(0,14) = P(0,14) + P(1,14)*SF[9] + P(2,14)*SF[11] + P(3,14)*SF[10] + P(10,14)*SF[14] + P(11,14)*SF[15] + P(12,14)*SPP[10];
nextP(1,14) = P(1,14) + P(0,14)*SF[8] + P(2,14)*SF[7] + P(3,14)*SF[11] - P(12,14)*SF[15] + P(11,14)*SPP[10] - (P(10,14)*q0)/2;
nextP(2,14) = P(2,14) + P(0,14)*SF[6] + P(1,14)*SF[10] + P(3,14)*SF[8] + P(12,14)*SF[14] - P(10,14)*SPP[10] - (P(11,14)*q0)/2;
nextP(3,14) = P(3,14) + P(0,14)*SF[7] + P(1,14)*SF[6] + P(2,14)*SF[9] + P(10,14)*SF[15] - P(11,14)*SF[14] - (P(12,14)*q0)/2;
nextP(4,14) = P(4,14) + P(0,14)*SF[5] + P(1,14)*SF[3] - P(3,14)*SF[4] + P(2,14)*SPP[0] + P(13,14)*SPP[3] + P(14,14)*SPP[6] - P(15,14)*SPP[9];
nextP(5,14) = P(5,14) + P(0,14)*SF[4] + P(2,14)*SF[3] + P(3,14)*SF[5] - P(1,14)*SPP[0] - P(13,14)*SPP[8] + P(14,14)*SPP[2] + P(15,14)*SPP[5];
nextP(6,14) = P(6,14) + P(1,14)*SF[4] - P(2,14)*SF[5] + P(3,14)*SF[3] + P(0,14)*SPP[0] + P(13,14)*SPP[4] - P(14,14)*SPP[7] - P(15,14)*SPP[1];
nextP(7,14) = P(7,14) + P(4,14)*dt;
nextP(8,14) = P(8,14) + P(5,14)*dt;
nextP(9,14) = P(9,14) + P(6,14)*dt;
nextP(10,14) = P(10,14);
nextP(11,14) = P(11,14);
nextP(12,14) = P(12,14);
nextP(13,14) = P(13,14);
nextP(14,14) = P(14,14);
nextP(0,15) = P(0,15) + P(1,15)*SF[9] + P(2,15)*SF[11] + P(3,15)*SF[10] + P(10,15)*SF[14] + P(11,15)*SF[15] + P(12,15)*SPP[10];
nextP(1,15) = P(1,15) + P(0,15)*SF[8] + P(2,15)*SF[7] + P(3,15)*SF[11] - P(12,15)*SF[15] + P(11,15)*SPP[10] - (P(10,15)*q0)/2;
nextP(2,15) = P(2,15) + P(0,15)*SF[6] + P(1,15)*SF[10] + P(3,15)*SF[8] + P(12,15)*SF[14] - P(10,15)*SPP[10] - (P(11,15)*q0)/2;
nextP(3,15) = P(3,15) + P(0,15)*SF[7] + P(1,15)*SF[6] + P(2,15)*SF[9] + P(10,15)*SF[15] - P(11,15)*SF[14] - (P(12,15)*q0)/2;
nextP(4,15) = P(4,15) + P(0,15)*SF[5] + P(1,15)*SF[3] - P(3,15)*SF[4] + P(2,15)*SPP[0] + P(13,15)*SPP[3] + P(14,15)*SPP[6] - P(15,15)*SPP[9];
nextP(5,15) = P(5,15) + P(0,15)*SF[4] + P(2,15)*SF[3] + P(3,15)*SF[5] - P(1,15)*SPP[0] - P(13,15)*SPP[8] + P(14,15)*SPP[2] + P(15,15)*SPP[5];
nextP(6,15) = P(6,15) + P(1,15)*SF[4] - P(2,15)*SF[5] + P(3,15)*SF[3] + P(0,15)*SPP[0] + P(13,15)*SPP[4] - P(14,15)*SPP[7] - P(15,15)*SPP[1];
nextP(7,15) = P(7,15) + P(4,15)*dt;
nextP(8,15) = P(8,15) + P(5,15)*dt;
nextP(9,15) = P(9,15) + P(6,15)*dt;
nextP(10,15) = P(10,15);
nextP(11,15) = P(11,15);
nextP(12,15) = P(12,15);
nextP(13,15) = P(13,15);
nextP(14,15) = P(14,15);
nextP(15,15) = P(15,15);
for (unsigned i = 13; i <= 15; i++) {
const unsigned index = i - 13;
if (!_accel_bias_inhibit[index]) {
// calculate variances and upper diagonal covariances for IMU delta velocity bias states
nextP(0,i) = P(0,i) + P(1,i)*SF[9] + P(2,i)*SF[11] + P(3,i)*SF[10] + P(10,i)*SF[14] + P(11,i)*SF[15] + P(12,i)*SPP[10];
nextP(1,i) = P(1,i) + P(0,i)*SF[8] + P(2,i)*SF[7] + P(3,i)*SF[11] - P(12,i)*SF[15] + P(11,i)*SPP[10] - (P(10,i)*q0)/2;
nextP(2,i) = P(2,i) + P(0,i)*SF[6] + P(1,i)*SF[10] + P(3,i)*SF[8] + P(12,i)*SF[14] - P(10,i)*SPP[10] - (P(11,i)*q0)/2;
nextP(3,i) = P(3,i) + P(0,i)*SF[7] + P(1,i)*SF[6] + P(2,i)*SF[9] + P(10,i)*SF[15] - P(11,i)*SF[14] - (P(12,i)*q0)/2;
nextP(4,i) = P(4,i) + P(0,i)*SF[5] + P(1,i)*SF[3] - P(3,i)*SF[4] + P(2,i)*SPP[0] + P(13,i)*SPP[3] + P(14,i)*SPP[6] - P(15,i)*SPP[9];
nextP(5,i) = P(5,i) + P(0,i)*SF[4] + P(2,i)*SF[3] + P(3,i)*SF[5] - P(1,i)*SPP[0] - P(13,i)*SPP[8] + P(14,i)*SPP[2] + P(15,i)*SPP[5];
nextP(6,i) = P(6,i) + P(1,i)*SF[4] - P(2,i)*SF[5] + P(3,i)*SF[3] + P(0,i)*SPP[0] + P(13,i)*SPP[4] - P(14,i)*SPP[7] - P(15,i)*SPP[1];
nextP(7,i) = P(7,i) + P(4,i)*dt;
nextP(8,i) = P(8,i) + P(5,i)*dt;
nextP(9,i) = P(9,i) + P(6,i)*dt;
nextP(10,i) = P(10,i);
nextP(11,i) = P(11,i);
nextP(12,i) = P(12,i);
nextP(13,i) = P(13,i);
if (i > 13) {
nextP(14,i) = P(14,i);
}
// add process noise that is not from the IMU
// process noise contributiton for delta velocity states can be very small compared to
// the variances, therefore use algorithm to minimise numerical error
for (unsigned i = 13; i <= 15; i++) {
const int index = i-13;
if (i > 14) {
nextP(15,i) = P(15,i);
}
// add process noise that is not from the IMU
// process noise contributiton for delta velocity states can be very small compared to
// the variances, therefore use algorithm to minimise numerical error
nextP(i,i) = kahanSummation(nextP(i,i), process_noise(i), _delta_vel_bias_var_accum(index));
}
} else {
// Inhibit delta velocity bias learning by zeroing the covariance terms
nextP.uncorrelateCovarianceSetVariance<3>(13, 0.0f);
_delta_vel_bias_var_accum.setZero();
} else {
nextP.uncorrelateCovarianceSetVariance<1>(i, 0.f);
_delta_vel_bias_var_accum(index) = 0.f;
}
}
// Don't do covariance prediction on magnetic field states unless we are using 3-axis fusion
@ -757,16 +737,17 @@ void Ekf::fixCovarianceErrors(bool force_symmetry) @@ -757,16 +737,17 @@ void Ekf::fixCovarianceErrors(bool force_symmetry)
// by ensuring the corresponding covariance matrix values are kept at zero
// accelerometer bias states
if ((_params.fusion_mode & MASK_INHIBIT_ACC_BIAS) || _accel_bias_inhibit) {
P.uncorrelateCovarianceSetVariance<3>(13, 0.0f);
} else {
if (!_accel_bias_inhibit[0] || !_accel_bias_inhibit[1] || !_accel_bias_inhibit[2]) {
// Find the maximum delta velocity bias state variance and request a covariance reset if any variance is below the safe minimum
const float minSafeStateVar = 1e-9f;
float maxStateVar = minSafeStateVar;
bool resetRequired = false;
for (uint8_t stateIndex = 13; stateIndex <= 15; stateIndex++) {
if (_accel_bias_inhibit[stateIndex - 13]) {
// Skip the check for the inhibited axis
continue;
}
if (P(stateIndex,stateIndex) > maxStateVar) {
maxStateVar = P(stateIndex,stateIndex);
@ -782,6 +763,10 @@ void Ekf::fixCovarianceErrors(bool force_symmetry) @@ -782,6 +763,10 @@ void Ekf::fixCovarianceErrors(bool force_symmetry)
float minAllowedStateVar = fmaxf(0.01f * maxStateVar, minStateVarTarget);
for (uint8_t stateIndex = 13; stateIndex <= 15; stateIndex++) {
if (_accel_bias_inhibit[stateIndex - 13]) {
// Skip the check for the inhibited axis
continue;
}
P(stateIndex,stateIndex) = math::constrain(P(stateIndex,stateIndex), minAllowedStateVar, sq(0.1f * CONSTANTS_ONE_G * _dt_ekf_avg));
}
@ -792,7 +777,7 @@ void Ekf::fixCovarianceErrors(bool force_symmetry) @@ -792,7 +777,7 @@ void Ekf::fixCovarianceErrors(bool force_symmetry)
// Run additional checks to see if the delta velocity bias has hit limits in a direction that is clearly wrong
// calculate accel bias term aligned with the gravity vector
float dVel_bias_lim = 0.9f * _params.acc_bias_lim * _dt_ekf_avg;
const float dVel_bias_lim = 0.9f * _params.acc_bias_lim * _dt_ekf_avg;
float down_dvel_bias = 0.0f;
for (uint8_t axis_index = 0; axis_index < 3; axis_index++) {

2
EKF/ekf.h
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@ -477,7 +477,7 @@ private: @@ -477,7 +477,7 @@ private:
gps_check_fail_status_u _gps_check_fail_status{};
// variables used to inhibit accel bias learning
bool _accel_bias_inhibit{false}; ///< true when the accel bias learning is being inhibited
bool _accel_bias_inhibit[3]{}; ///< true when the accel bias learning is being inhibited for the specified axis
Vector3f _accel_vec_filt; ///< acceleration vector after application of a low pass filter (m/sec**2)
float _accel_magnitude_filt{0.0f}; ///< acceleration magnitude after application of a decaying envelope filter (rad/sec)
float _ang_rate_magnitude_filt{0.0f}; ///< angular rate magnitude after application of a decaying envelope filter (rad/sec)

12
test/test_EKF_initialization.cpp
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@ -99,14 +99,14 @@ class EkfInitializationTest : public ::testing::Test { @@ -99,14 +99,14 @@ class EkfInitializationTest : public ::testing::Test {
const Vector3f vel_var = _ekf->getVelocityVariance();
const float pos_variance_limit = 0.2f;
EXPECT_TRUE(pos_var(0) > pos_variance_limit) << "pos_var(1)" << pos_var(0);
EXPECT_TRUE(pos_var(1) > pos_variance_limit) << "pos_var(2)" << pos_var(1);
EXPECT_TRUE(pos_var(2) > pos_variance_limit) << "pos_var(3)" << pos_var(2);
EXPECT_TRUE(pos_var(0) > pos_variance_limit) << "pos_var(0)" << pos_var(0);
EXPECT_TRUE(pos_var(1) > pos_variance_limit) << "pos_var(1)" << pos_var(1);
EXPECT_TRUE(pos_var(2) > pos_variance_limit) << "pos_var(2)" << pos_var(2);
const float vel_variance_limit = 0.4f;
EXPECT_TRUE(vel_var(0) > vel_variance_limit) << "vel_var(1)" << vel_var(0);
EXPECT_TRUE(vel_var(1) > vel_variance_limit) << "vel_var(2)" << vel_var(1);
EXPECT_TRUE(vel_var(2) > vel_variance_limit) << "vel_var(3)" << vel_var(2);
EXPECT_TRUE(vel_var(0) > vel_variance_limit) << "vel_var(0)" << vel_var(0);
EXPECT_TRUE(vel_var(1) > vel_variance_limit) << "vel_var(1)" << vel_var(1);
EXPECT_TRUE(vel_var(2) > vel_variance_limit) << "vel_var(2)" << vel_var(2);
}
};

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