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AP_NavEKF2: added EK2_MAG_EF_LIM parameter 

this sets a limit on the difference between the earth field from the
WMM tables and the learned earth field inside the EKF. Setting it to
zero disables the feature. A positive value sets the limit in mGauss.
This commit is contained in:
Andrew Tridgell 2019-07-06 08:49:00 +10:00
parent 74805870b8
commit 6f5d0fa3f0
6 changed files with 72 additions and 7 deletions
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8
libraries/AP_NavEKF2/AP_NavEKF2.cpp
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@ -552,6 +552,14 @@ const AP_Param::GroupInfo NavEKF2::var_info[] = {
// @RebootRequired: True
AP_GROUPINFO("OGN_HGT_MASK", 49, NavEKF2, _originHgtMode, 0),
// @Param: MAG_EF_LIM
// @DisplayName: EarthField error limit
// @Description: This limits the difference between the learned earth magnetic field and the earth field from the world magnetic model tables. A value of zero means to disable the use of the WMM tables.
// @User: Advanced
// @Range: 0 500
// @Units: mGauss
AP_GROUPINFO("MAG_EF_LIM", 52, NavEKF2, _mag_ef_limit, 0),
AP_GROUPEND
};

1
libraries/AP_NavEKF2/AP_NavEKF2.h
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@ -396,6 +396,7 @@ private:
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.
AP_Int16 _mag_ef_limit; // limit on difference between WMM tables and learned earth field.
// Tuning parameters
const float gpsNEVelVarAccScale = 0.05f; // Scale factor applied to NE velocity measurement variance due to manoeuvre acceleration

12
libraries/AP_NavEKF2/AP_NavEKF2_MagFusion.cpp
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@ -269,7 +269,9 @@ void NavEKF2_core::SelectMagFusion()
} else {
// if we are not doing aiding with earth relative observations (eg GPS) then the declination is
// maintained by fusing declination as a synthesised observation
if (PV_AidingMode != AID_ABSOLUTE) {
// We also fuse declination if we are using the WMM tables
if (PV_AidingMode != AID_ABSOLUTE ||
(frontend->_mag_ef_limit > 0 && have_table_earth_field)) {
FuseDeclination(0.34f);
}
// fuse the three magnetometer componenents sequentially
@ -813,7 +815,7 @@ void NavEKF2_core::fuseEulerYaw()
// Use measured mag components rotated into earth frame to measure yaw
Tbn_zeroYaw.from_euler(euler321.x, euler321.y, 0.0f);
Vector3f magMeasNED = Tbn_zeroYaw*magDataDelayed.mag;
measured_yaw = wrap_PI(-atan2f(magMeasNED.y, magMeasNED.x) + _ahrs->get_compass()->get_declination());
measured_yaw = wrap_PI(-atan2f(magMeasNED.y, magMeasNED.x) + MagDeclination());
} else if (extNavUsedForYaw) {
// Get the yaw angle from the external vision data
extNavDataDelayed.quat.to_euler(euler321.x, euler321.y, euler321.z);
@ -859,7 +861,7 @@ void NavEKF2_core::fuseEulerYaw()
// Use measured mag components rotated into earth frame to measure yaw
Tbn_zeroYaw.from_euler312(euler312.x, euler312.y, 0.0f);
Vector3f magMeasNED = Tbn_zeroYaw*magDataDelayed.mag;
measured_yaw = wrap_PI(-atan2f(magMeasNED.y, magMeasNED.x) + _ahrs->get_compass()->get_declination());
measured_yaw = wrap_PI(-atan2f(magMeasNED.y, magMeasNED.x) + MagDeclination());
} else if (extNavUsedForYaw) {
// Get the yaw angle from the external vision data
euler312 = extNavDataDelayed.quat.to_vector312();
@ -1045,7 +1047,7 @@ void NavEKF2_core::FuseDeclination(float declErr)
}
// get the magnetic declination
float magDecAng = use_compass() ? _ahrs->get_compass()->get_declination() : 0;
float magDecAng = MagDeclination();
// Calculate the innovation
float innovation = atan2f(magE , magN) - magDecAng;
@ -1129,7 +1131,7 @@ void NavEKF2_core::alignMagStateDeclination()
}
// get the magnetic declination
float magDecAng = use_compass() ? _ahrs->get_compass()->get_declination() : 0;
float magDecAng = MagDeclination();
// rotate the NE values so that the declination matches the published value
Vector3f initMagNED = stateStruct.earth_magfield;

28
libraries/AP_NavEKF2/AP_NavEKF2_Measurements.cpp
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@ -553,6 +553,17 @@ void NavEKF2_core::readGpsData()
}
if (gpsGoodToAlign && !have_table_earth_field) {
table_earth_field_ga = AP_Declination::get_earth_field_ga(gpsloc);
table_declination = radians(AP_Declination::get_declination(gpsloc.lat*1.0e-7,
gpsloc.lng*1.0e-7));
have_table_earth_field = true;
if (frontend->_mag_ef_limit > 0) {
// initialise earth field from tables
stateStruct.earth_magfield = table_earth_field_ga;
}
}
// convert GPS measurements to local NED and save to buffer to be fused later if we have a valid origin
if (validOrigin) {
gpsDataNew.pos = location_diff(EKF_origin, gpsloc);
@ -871,6 +882,23 @@ void NavEKF2_core::writeExtNavData(const Vector3f &sensOffset, const Vector3f &p
}
/*
return declination in radians
*/
float NavEKF2_core::MagDeclination(void) const
{
// if we are using the WMM tables then use the table declination
// to ensure consistency with the table mag field. Otherwise use
// the declination from the compass library
if (have_table_earth_field && frontend->_mag_ef_limit > 0) {
return table_declination;
}
if (!use_compass()) {
return 0;
}
return _ahrs->get_compass()->get_declination();
}
/*
update estimates of inactive bias states. This keeps inactive IMUs
as hot-spares so we can switch to them without causing a jump in the

20
libraries/AP_NavEKF2/AP_NavEKF2_core.cpp
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@ -339,6 +339,7 @@ void NavEKF2_core::InitialiseVariables()
storedOutput.reset();
storedRangeBeacon.reset();
storedExtNav.reset();
have_table_earth_field = false;
}
// Initialise the states from accelerometer and magnetometer data (if present)
@ -1434,8 +1435,25 @@ void NavEKF2_core::ConstrainStates()
for (uint8_t i=12; i<=14; i++) statesArray[i] = constrain_float(statesArray[i],0.95f,1.05f);
// Z accel bias limit 1.0 m/s^2 (this needs to be finalised from test data)
stateStruct.accel_zbias = constrain_float(stateStruct.accel_zbias,-1.0f*dtEkfAvg,1.0f*dtEkfAvg);
// earth magnetic field limit
if (frontend->_mag_ef_limit <= 0 || !have_table_earth_field) {
// constrain to +/-1Ga
for (uint8_t i=16; i<=18; i++) statesArray[i] = constrain_float(statesArray[i],-1.0f,1.0f);
} else {
// constrain to error from table earth field
float limit_ga = frontend->_mag_ef_limit * 0.001f;
stateStruct.earth_magfield.x = constrain_float(stateStruct.earth_magfield.x,
table_earth_field_ga.x-limit_ga,
table_earth_field_ga.x+limit_ga);
stateStruct.earth_magfield.y = constrain_float(stateStruct.earth_magfield.y,
table_earth_field_ga.y-limit_ga,
table_earth_field_ga.y+limit_ga);
stateStruct.earth_magfield.z = constrain_float(stateStruct.earth_magfield.z,
table_earth_field_ga.z-limit_ga,
table_earth_field_ga.z+limit_ga);
}
// body magnetic field limit
for (uint8_t i=19; i<=21; i++) statesArray[i] = constrain_float(statesArray[i],-0.5f,0.5f);
// wind velocity limit 100 m/s (could be based on some multiple of max airspeed * EAS2TAS) - TODO apply circular limit
@ -1479,7 +1497,7 @@ Quaternion NavEKF2_core::calcQuatAndFieldStates(float roll, float pitch)
float magHeading = atan2f(initMagNED.y, initMagNED.x);
// get the magnetic declination
float magDecAng = use_compass() ? _ahrs->get_compass()->get_declination() : 0;
float magDecAng = MagDeclination();
// calculate yaw angle rel to true north
yaw = magDecAng - magHeading;

8
libraries/AP_NavEKF2/AP_NavEKF2_core.h
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@ -734,6 +734,9 @@ private:
// Input is 1-sigma uncertainty in published declination
void FuseDeclination(float declErr);
// return magnetic declination in radians
float MagDeclination(void) const;
// Propagate PVA solution forward from the fusion time horizon to the current time horizon
// using a simple observer
void calcOutputStates();
@ -1181,6 +1184,11 @@ private:
AP_HAL::Util::perf_counter_t _perf_FuseOptFlow;
AP_HAL::Util::perf_counter_t _perf_test[10];
// earth field from WMM tables
bool have_table_earth_field; // true when we have initialised table_earth_field_ga
Vector3f table_earth_field_ga; // earth field from WMM tables
float table_declination; // declination in radians from the tables
// timing statistics
struct ekf_timing timing;