From 171857811f76fb4d8fb3b65329345dd5af0ec9db Mon Sep 17 00:00:00 2001 From: Lorenz Meier Date: Sun, 17 Aug 2014 20:49:46 +0200 Subject: [PATCH] EKF filter update. Now correctly scaling variance (well, if you could call this ever "correct") for repeated fusion of the same data quantity. --- .../ekf_att_pos_estimator_main.cpp | 33 +++++++-- .../estimator_23states.cpp | 72 +++++++++++++++---- .../estimator_23states.h | 17 ++++- 3 files changed, 104 insertions(+), 18 deletions(-) diff --git a/src/modules/ekf_att_pos_estimator/ekf_att_pos_estimator_main.cpp b/src/modules/ekf_att_pos_estimator/ekf_att_pos_estimator_main.cpp index 91d17e787c..6cb68fe779 100644 --- a/src/modules/ekf_att_pos_estimator/ekf_att_pos_estimator_main.cpp +++ b/src/modules/ekf_att_pos_estimator/ekf_att_pos_estimator_main.cpp @@ -96,7 +96,10 @@ extern "C" __EXPORT int ekf_att_pos_estimator_main(int argc, char *argv[]); __EXPORT uint32_t millis(); +__EXPORT uint64_t getMicros(); + static uint64_t IMUmsec = 0; +static uint64_t IMUusec = 0; static const uint64_t FILTER_INIT_DELAY = 1 * 1000 * 1000; uint32_t millis() @@ -104,6 +107,11 @@ uint32_t millis() return IMUmsec; } +uint64_t getMicros() +{ + return IMUusec; +} + class FixedwingEstimator { public: @@ -850,7 +858,8 @@ FixedwingEstimator::task_main() } _last_sensor_timestamp = _gyro.timestamp; - IMUmsec = _gyro.timestamp / 1e3f; + IMUmsec = _gyro.timestamp / 1e3; + IMUusec = _gyro.timestamp; float deltaT = (_gyro.timestamp - _last_run) / 1e6f; _last_run = _gyro.timestamp; @@ -914,7 +923,8 @@ FixedwingEstimator::task_main() // Copy gyro and accel _last_sensor_timestamp = _sensor_combined.timestamp; - IMUmsec = _sensor_combined.timestamp / 1e3f; + IMUmsec = _sensor_combined.timestamp / 1e3; + IMUusec = _sensor_combined.timestamp; float deltaT = (_sensor_combined.timestamp - _last_run) / 1e6f; @@ -994,8 +1004,6 @@ FixedwingEstimator::task_main() if (gps_updated) { - last_gps = _gps.timestamp_position; - orb_copy(ORB_ID(vehicle_gps_position), _gps_sub, &_gps); perf_count(_perf_gps); @@ -1008,11 +1016,17 @@ FixedwingEstimator::task_main() _gps_start_time = hrt_absolute_time(); /* check if we had a GPS outage for a long time */ - if (hrt_elapsed_time(&last_gps) > 5 * 1000 * 1000) { + float gps_elapsed = hrt_elapsed_time(&last_gps) / 1e6f; + + const float pos_reset_threshold = 5.0f; // seconds + + /* timeout of 5 seconds */ + if (gps_elapsed > pos_reset_threshold) { _ekf->ResetPosition(); _ekf->ResetVelocity(); _ekf->ResetStoredStates(); } + _ekf->updateDtGpsFilt(math::constrain((_gps.timestamp_position - last_gps) / 1e6f, 0.01f, pos_reset_threshold)); /* fuse GPS updates */ @@ -1044,6 +1058,8 @@ FixedwingEstimator::task_main() newDataGps = true; + last_gps = _gps.timestamp_position; + } } @@ -1052,8 +1068,15 @@ FixedwingEstimator::task_main() orb_check(_baro_sub, &baro_updated); if (baro_updated) { + + hrt_abstime baro_last = _baro.timestamp; + orb_copy(ORB_ID(sensor_baro0), _baro_sub, &_baro); + float baro_elapsed = (_baro.timestamp - baro_last) / 1e6f; + + _ekf->updateDtHgtFilt(math::constrain(baro_elapsed, 0.001f, 0.1)); + _ekf->baroHgt = _baro.altitude; if (!_baro_init) { diff --git a/src/modules/ekf_att_pos_estimator/estimator_23states.cpp b/src/modules/ekf_att_pos_estimator/estimator_23states.cpp index c7c7305b2a..d1349535d4 100644 --- a/src/modules/ekf_att_pos_estimator/estimator_23states.cpp +++ b/src/modules/ekf_att_pos_estimator/estimator_23states.cpp @@ -2,6 +2,11 @@ #include #include #include +#include + +#ifndef M_PI_F +#define M_PI_F ((float)M_PI) +#endif #define EKF_COVARIANCE_DIVERGED 1.0e8f @@ -38,6 +43,7 @@ AttPosEKF::AttPosEKF() : resetStates{}, storedStates{}, statetimeStamp{}, + lastVelPosFusion(millis()), statesAtVelTime{}, statesAtPosTime{}, statesAtHgtTime{}, @@ -59,7 +65,12 @@ AttPosEKF::AttPosEKF() : accel(), dVelIMU(), dAngIMU(), - dtIMU(0), + dtIMU(0.005f), + dtIMUfilt(0.005f), + dtVelPos(0.01f), + dtVelPosFilt(0.01f), + dtHgtFilt(0.01f), + dtGpsFilt(0.1f), fusionModeGPS(0), innovVelPos{}, varInnovVelPos{}, @@ -260,6 +271,9 @@ void AttPosEKF::UpdateStrapdownEquationsNED() // Constrain states (to protect against filter divergence) ConstrainStates(); + + // update filtered IMU time step length + dtIMUfilt = 0.99f * dtIMUfilt + 0.01f * dtIMU; } void AttPosEKF::CovariancePrediction(float dt) @@ -962,6 +976,21 @@ void AttPosEKF::CovariancePrediction(float dt) ConstrainVariances(); } +void AttPosEKF::updateDtGpsFilt(float dt) +{ + dtGpsFilt = ConstrainFloat(dt, 0.001f, 2.0f) * 0.05f + dtGpsFilt * 0.95f; +} + +void AttPosEKF::updateDtHgtFilt(float dt) +{ + dtHgtFilt = ConstrainFloat(dt, 0.001f, 2.0f) * 0.05f + dtHgtFilt * 0.95f; +} + +void AttPosEKF::updateDtVelPosFilt(float dt) +{ + dtVelPosFilt = ConstrainFloat(dt, 0.0005f, 2.0f) * 0.05f + dtVelPosFilt * 0.95f; +} + void AttPosEKF::FuseVelposNED() { @@ -998,6 +1027,18 @@ void AttPosEKF::FuseVelposNED() // associated with sequential fusion if (fuseVelData || fusePosData || fuseHgtData) { + uint64_t tNow = getMicros(); + updateDtVelPosFilt((tNow - lastVelPosFusion) / 1e6f); + lastVelPosFusion = tNow; + + // scaler according to the number of repetitions of the + // same measurement in one fusion step + float gpsVarianceScaler = dtGpsFilt / dtVelPosFilt; + + // scaler according to the number of repetitions of the + // same measurement in one fusion step + float hgtVarianceScaler = dtHgtFilt / dtVelPosFilt; + // set the GPS data timeout depending on whether airspeed data is present if (useAirspeed) horizRetryTime = gpsRetryTime; else horizRetryTime = gpsRetryTimeNoTAS; @@ -1010,12 +1051,12 @@ void AttPosEKF::FuseVelposNED() // Estimate the GPS Velocity, GPS horiz position and height measurement variances. velErr = 0.2f*accNavMag; // additional error in GPS velocities caused by manoeuvring posErr = 0.2f*accNavMag; // additional error in GPS position caused by manoeuvring - R_OBS[0] = sq(vneSigma) + sq(velErr); + R_OBS[0] = gpsVarianceScaler * sq(vneSigma) + sq(velErr); R_OBS[1] = R_OBS[0]; - R_OBS[2] = sq(vdSigma) + sq(velErr); - R_OBS[3] = sq(posNeSigma) + sq(posErr); + R_OBS[2] = gpsVarianceScaler * sq(vdSigma) + sq(velErr); + R_OBS[3] = gpsVarianceScaler * sq(posNeSigma) + sq(posErr); R_OBS[4] = R_OBS[3]; - R_OBS[5] = sq(posDSigma) + sq(posErr); + R_OBS[5] = hgtVarianceScaler * sq(posDSigma) + sq(posErr); // calculate innovations and check GPS data validity using an innovation consistency check if (fuseVelData) @@ -1995,9 +2036,8 @@ void AttPosEKF::FuseOptFlow() varInnovOptFlow[0] = 1.0f/SK_LOS[0]; innovOptFlow[0] = losPred[0] - losData[0]; - // reset the observation index to 0 (we start by fusing the X - // measurement) - obsIndex = 0; + // set the observation index to 1 to fuse the y component next time round and reset the commence fusion flag + obsIndex = 1; fuseOptFlowData = false; } else if (obsIndex == 1) // we are now fusing the Y measurement @@ -2041,6 +2081,10 @@ void AttPosEKF::FuseOptFlow() Kfusion[22] = SK_LOS[1]*(P[22][0]*SKK_LOS[10] - P[22][3]*SKK_LOS[13] + P[22][1]*SKK_LOS[11] + P[22][2]*SKK_LOS[12] - P[22][9]*SH_LOS[1]*SH_LOS[7]*SKK_LOS[14] + P[22][22]*SH_LOS[1]*SH_LOS[7]*SKK_LOS[14] + P[22][6]*SH_LOS[3]*SKK_LOS[0]*SKK_LOS[14] + P[22][4]*SH_LOS[3]*SKK_LOS[2]*SKK_LOS[14] - P[22][5]*SH_LOS[3]*SKK_LOS[1]*SKK_LOS[14]); varInnovOptFlow[1] = 1.0f/SK_LOS[1]; innovOptFlow[1] = losPred[1] - losData[1]; + + // reset the observation index + obsIndex = 0; + fuseOptFlowData = false; } // Check the innovation for consistency and don't fuse if > 3Sigma @@ -2102,10 +2146,9 @@ void AttPosEKF::FuseOptFlow() P[i][j] = P[i][j] - KHP[i][j]; } } + ForceSymmetry(); + ConstrainVariances(); } - obsIndex = obsIndex + 1; - ForceSymmetry(); - ConstrainVariances(); } void AttPosEKF::zeroCols(float (&covMat)[n_states][n_states], uint8_t first, uint8_t last) @@ -3006,9 +3049,14 @@ void AttPosEKF::ZeroVariables() { // Initialize on-init initialized variables - + dtIMUfilt = ConstrainFloat(dtIMU, 0.001f, 0.02f); + dtVelPosFilt = ConstrainFloat(dtVelPos, 0.04f, 0.5f); + dtGpsFilt = 1.0f / 5.0f; + dtHgtFilt = 1.0f / 100.0f; storeIndex = 0; + lastVelPosFusion = millis(); + // Do the data structure init for (unsigned i = 0; i < n_states; i++) { for (unsigned j = 0; j < n_states; j++) { diff --git a/src/modules/ekf_att_pos_estimator/estimator_23states.h b/src/modules/ekf_att_pos_estimator/estimator_23states.h index faa6735caa..12cbc53b8d 100644 --- a/src/modules/ekf_att_pos_estimator/estimator_23states.h +++ b/src/modules/ekf_att_pos_estimator/estimator_23states.h @@ -116,6 +116,9 @@ public: float storedStates[n_states][data_buffer_size]; // state vectors stored for the last 50 time steps uint32_t statetimeStamp[data_buffer_size]; // time stamp for each state vector stored + // Times + uint64_t lastVelPosFusion; // the time of the last velocity fusion, in the standard time unit of the filter + float statesAtVelTime[n_states]; // States at the effective measurement time for posNE and velNED measurements float statesAtPosTime[n_states]; // States at the effective measurement time for posNE and velNED measurements float statesAtHgtTime[n_states]; // States at the effective measurement time for the hgtMea measurement @@ -140,7 +143,12 @@ public: Vector3f accel; // acceleration vector in XYZ body axes measured by the IMU (m/s^2) Vector3f dVelIMU; Vector3f dAngIMU; - float dtIMU; // time lapsed since the last IMU measurement or covariance update (sec) + float dtIMU; // time lapsed since the last IMU measurement or covariance update (sec), this may have significant jitter + float dtIMUfilt; // average time between IMU measurements (sec) + float dtVelPos; // time lapsed since the last position / velocity fusion (seconds), this may have significant jitter + float dtVelPosFilt; // average time between position / velocity fusion steps + float dtHgtFilt; // average time between height measurement updates + float dtGpsFilt; // average time between gps measurement updates uint8_t fusionModeGPS; // 0 = GPS outputs 3D velocity, 1 = GPS outputs 2D velocity, 2 = GPS outputs no velocity float innovVelPos[6]; // innovation output float varInnovVelPos[6]; // innovation variance output @@ -211,6 +219,9 @@ public: unsigned storeIndex; +void updateDtGpsFilt(float dt); + +void updateDtHgtFilt(float dt); void UpdateStrapdownEquationsNED(); @@ -300,6 +311,8 @@ void InitializeDynamic(float (&initvelNED)[3], float declination); protected: +void updateDtVelPosFilt(float dt); + bool FilterHealthy(); bool GyroOffsetsDiverged(); @@ -314,3 +327,5 @@ void AttitudeInit(float ax, float ay, float az, float mx, float my, float mz, fl uint32_t millis(); +uint64_t getMicros(); +