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ardupilot/libraries/AP_NavEKF2/AP_NavEKF2_VehicleStatus.cpp

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#include "AP_NavEKF2_core.h"
#include "AP_NavEKF2.h"
#include <AP_DAL/AP_DAL.h>
/* Monitor GPS data to see if quality is good enough to initialise the EKF
Monitor magnetometer innovations to see if the heading is good enough to use GPS
Return true if all criteria pass for 10 seconds
We also record the failure reason so that pre_arm_check()
can give a good report to the user on why arming is failing
This sets gpsGoodToAlign class variable
*/
void NavEKF2_core::calcGpsGoodToAlign(void)
{
const auto &gps = dal.gps();
if (inFlight && assume_zero_sideslip() && !use_compass()) {
// this is a special case where a plane has launched without magnetometer
// is now in the air and needs to align yaw to the GPS and start navigating as soon as possible
gpsGoodToAlign = true;
return;
}
// User defined multiplier to be applied to check thresholds
ftype checkScaler = 0.01f*(ftype)frontend->_gpsCheckScaler;
if (gpsGoodToAlign) {
/*
if we have already passed GPS alignment checks then raise
the check threshold so that we have some hysterisis and
don't continuously change from able to arm to not able to
arm
*/
checkScaler *= 1.3f;
}
// If we have good magnetometer consistency and bad innovations for longer than 5 seconds then we reset heading and field states
// This enables us to handle large changes to the external magnetic field environment that occur before arming
if ((magTestRatio.x <= 1.0f && magTestRatio.y <= 1.0f && yawTestRatio <= 1.0f) || !consistentMagData) {
magYawResetTimer_ms = imuSampleTime_ms;
}
if ((imuSampleTime_ms - magYawResetTimer_ms > 5000) && !motorsArmed) {
// request reset of heading and magnetic field states
magYawResetRequest = true;
// reset timer to ensure that bad magnetometer data cannot cause a heading reset more often than every 5 seconds
magYawResetTimer_ms = imuSampleTime_ms;
}
// Check for significant change in GPS position if disarmed which indicates bad GPS
// This check can only be used when the vehicle is stationary
const Location &gpsloc = gps.location(); // Current location
const ftype posFiltTimeConst = 10.0f; // time constant used to decay position drift
// calculate time lapsed since last update and limit to prevent numerical errors
ftype deltaTime = constrain_ftype(float(imuDataDelayed.time_ms - lastPreAlignGpsCheckTime_ms)*0.001f,0.01f,posFiltTimeConst);
lastPreAlignGpsCheckTime_ms = imuDataDelayed.time_ms;
// Sum distance moved
gpsDriftNE += gpsloc_prev.get_distance(gpsloc);
gpsloc_prev = gpsloc;
// Decay distance moved exponentially to zero
gpsDriftNE *= (1.0f - deltaTime/posFiltTimeConst);
// Clamp the filter state to prevent excessive persistence of large transients
gpsDriftNE = MIN(gpsDriftNE,10.0f);
// Fail if more than 3 metres drift after filtering whilst on-ground
// This corresponds to a maximum acceptable average drift rate of 0.3 m/s or single glitch event of 3m
bool gpsDriftFail = (gpsDriftNE > 3.0f*checkScaler) && onGround && (frontend->_gpsCheck & MASK_GPS_POS_DRIFT);
// Report check result as a text string and bitmask
if (gpsDriftFail) {
dal.snprintf(prearm_fail_string,
sizeof(prearm_fail_string),
"GPS drift %.1fm (needs %.1f)", (double)gpsDriftNE, (double)(3.0f*checkScaler));
gpsCheckStatus.bad_horiz_drift = true;
} else {
gpsCheckStatus.bad_horiz_drift = false;
}
// Check that the vertical GPS vertical velocity is reasonable after noise filtering
bool gpsVertVelFail;
if (gps.have_vertical_velocity() && onGround) {
// check that the average vertical GPS velocity is close to zero
gpsVertVelFilt = 0.1f * gpsDataNew.vel.z + 0.9f * gpsVertVelFilt;
gpsVertVelFilt = constrain_ftype(gpsVertVelFilt,-10.0f,10.0f);
gpsVertVelFail = (fabsF(gpsVertVelFilt) > 0.3f*checkScaler) && (frontend->_gpsCheck & MASK_GPS_VERT_SPD);
} else {
gpsVertVelFail = false;
}
// Report check result as a text string and bitmask
if (gpsVertVelFail) {
dal.snprintf(prearm_fail_string,
sizeof(prearm_fail_string),
"GPS vertical speed %.2fm/s (needs %.2f)", (double)fabsF(gpsVertVelFilt), (double)(0.3f*checkScaler));
gpsCheckStatus.bad_vert_vel = true;
} else {
gpsCheckStatus.bad_vert_vel = false;
}
// Check that the horizontal GPS vertical velocity is reasonable after noise filtering
// This check can only be used if the vehicle is stationary
bool gpsHorizVelFail;
if (onGround) {
gpsHorizVelFilt = 0.1f * gpsDataDelayed.vel.xy().length() + 0.9f * gpsHorizVelFilt;
gpsHorizVelFilt = constrain_ftype(gpsHorizVelFilt,-10.0f,10.0f);
gpsHorizVelFail = (fabsF(gpsHorizVelFilt) > 0.3f*checkScaler) && (frontend->_gpsCheck & MASK_GPS_HORIZ_SPD);
} else {
gpsHorizVelFail = false;
}
// Report check result as a text string and bitmask
if (gpsHorizVelFail) {
dal.snprintf(prearm_fail_string,
sizeof(prearm_fail_string),
"GPS horizontal speed %.2fm/s (needs %.2f)", (double)gpsDriftNE, (double)(0.3f*checkScaler));
gpsCheckStatus.bad_horiz_vel = true;
} else {
gpsCheckStatus.bad_horiz_vel = false;
}
// fail if horiziontal position accuracy not sufficient
float hAcc = 0.0;
bool hAccFail;
if (gps.horizontal_accuracy(hAcc)) {
hAccFail = (hAcc > 5.0f*checkScaler) && (frontend->_gpsCheck & MASK_GPS_POS_ERR);
} else {
hAccFail = false;
}
// Report check result as a text string and bitmask
if (hAccFail) {
dal.snprintf(prearm_fail_string,
sizeof(prearm_fail_string),
"GPS horiz error %.1fm (needs %.1f)", (double)hAcc, (double)(5.0f*checkScaler));
gpsCheckStatus.bad_hAcc = true;
} else {
gpsCheckStatus.bad_hAcc = false;
}
// Check for vertical GPS accuracy
float vAcc = 0.0f;
bool vAccFail = false;
if (gps.vertical_accuracy(vAcc)) {
vAccFail = (vAcc > 7.5f * checkScaler) && (frontend->_gpsCheck & MASK_GPS_POS_ERR);
}
// Report check result as a text string and bitmask
if (vAccFail) {
dal.snprintf(prearm_fail_string,
sizeof(prearm_fail_string),
"GPS vert error %.1fm (needs < %.1f)", (double)vAcc, (double)(7.5f * checkScaler));
gpsCheckStatus.bad_vAcc = true;
} else {
gpsCheckStatus.bad_vAcc = false;
}
// fail if reported speed accuracy greater than threshold
bool gpsSpdAccFail = (gpsSpdAccuracy > 1.0f*checkScaler) && (frontend->_gpsCheck & MASK_GPS_SPD_ERR);
// Report check result as a text string and bitmask
if (gpsSpdAccFail) {
dal.snprintf(prearm_fail_string,
sizeof(prearm_fail_string),
"GPS speed error %.1f (needs < %.1f)", (double)gpsSpdAccuracy, (double)(1.0f*checkScaler));
gpsCheckStatus.bad_sAcc = true;
} else {
gpsCheckStatus.bad_sAcc = false;
}
// fail if satellite geometry is poor
bool hdopFail = (gps.get_hdop() > 250) && (frontend->_gpsCheck & MASK_GPS_HDOP);
// Report check result as a text string and bitmask
if (hdopFail) {
dal.snprintf(prearm_fail_string, sizeof(prearm_fail_string),
"GPS HDOP %.1f (needs 2.5)", (double)(0.01f * gps.get_hdop()));
gpsCheckStatus.bad_hdop = true;
} else {
gpsCheckStatus.bad_hdop = false;
}
// fail if not enough sats
bool numSatsFail = (gps.num_sats() < 6) && (frontend->_gpsCheck & MASK_GPS_NSATS);
// Report check result as a text string and bitmask
if (numSatsFail) {
dal.snprintf(prearm_fail_string, sizeof(prearm_fail_string),
"GPS numsats %u (needs 6)", gps.num_sats());
gpsCheckStatus.bad_sats = true;
} else {
gpsCheckStatus.bad_sats = false;
}
// fail if magnetometer innovations are outside limits indicating bad yaw
// with bad yaw we are unable to use GPS
bool yawFail;
if ((magTestRatio.x > 1.0f || magTestRatio.y > 1.0f || yawTestRatio > 1.0f) && (frontend->_gpsCheck & MASK_GPS_YAW_ERR)) {
yawFail = true;
} else {
yawFail = false;
}
// Report check result as a text string and bitmask
if (yawFail) {
dal.snprintf(prearm_fail_string,
sizeof(prearm_fail_string),
"Mag yaw error x=%.1f y=%.1f",
(double)magTestRatio.x,
(double)magTestRatio.y);
gpsCheckStatus.bad_yaw = true;
} else {
gpsCheckStatus.bad_yaw = false;
}
// assume failed first time through and notify user checks have started
if (lastGpsVelFail_ms == 0) {
dal.snprintf(prearm_fail_string, sizeof(prearm_fail_string), "EKF starting GPS checks");
lastGpsVelFail_ms = imuSampleTime_ms;
}
// record time of fail or pass
if (gpsSpdAccFail || numSatsFail || hdopFail || hAccFail || vAccFail || yawFail || gpsDriftFail || gpsVertVelFail || gpsHorizVelFail) {
lastGpsVelFail_ms = imuSampleTime_ms;
} else {
lastGpsVelPass_ms = imuSampleTime_ms;
}
// continuous period of 10s without fail required to set healthy
// continuous period of 5s without pass required to set unhealthy
if (!gpsGoodToAlign && imuSampleTime_ms - lastGpsVelFail_ms > 10000) {
gpsGoodToAlign = true;
} else if (gpsGoodToAlign && imuSampleTime_ms - lastGpsVelPass_ms > 5000) {
gpsGoodToAlign = false;
}
}
// update inflight calculaton that determines if GPS data is good enough for reliable navigation
void NavEKF2_core::calcGpsGoodForFlight(void)
{
// use a simple criteria based on the GPS receivers claimed speed accuracy and the EKF innovation consistency checks
// set up varaibles and constants used by filter that is applied to GPS speed accuracy
const ftype alpha1 = 0.2f; // coefficient for first stage LPF applied to raw speed accuracy data
const ftype tau = 10.0f; // time constant (sec) of peak hold decay
if (lastGpsCheckTime_ms == 0) {
lastGpsCheckTime_ms = imuSampleTime_ms;
}
ftype dtLPF = (imuSampleTime_ms - lastGpsCheckTime_ms) * 1e-3f;
lastGpsCheckTime_ms = imuSampleTime_ms;
ftype alpha2 = constrain_ftype(dtLPF/tau,0.0f,1.0f);
// get the receivers reported speed accuracy
float gpsSpdAccRaw;
if (!dal.gps().speed_accuracy(gpsSpdAccRaw)) {
gpsSpdAccRaw = 0.0f;
}
// filter the raw speed accuracy using a LPF
sAccFilterState1 = constrain_ftype((alpha1 * gpsSpdAccRaw + (1.0f - alpha1) * sAccFilterState1),0.0f,10.0f);
// apply a peak hold filter to the LPF output
sAccFilterState2 = MAX(sAccFilterState1,((1.0f - alpha2) * sAccFilterState2));
// Apply a threshold test with hysteresis to the filtered GPS speed accuracy data
if (sAccFilterState2 > 1.5f ) {
gpsSpdAccPass = false;
} else if(sAccFilterState2 < 1.0f) {
gpsSpdAccPass = true;
}
// Apply a threshold test with hysteresis to the normalised position and velocity innovations
// Require a fail for one second and a pass for 10 seconds to transition
if (lastInnovFailTime_ms == 0) {
lastInnovFailTime_ms = imuSampleTime_ms;
lastInnovPassTime_ms = imuSampleTime_ms;
}
if (velTestRatio < 1.0f && posTestRatio < 1.0f) {
lastInnovPassTime_ms = imuSampleTime_ms;
} else if (velTestRatio > 0.7f || posTestRatio > 0.7f) {
lastInnovFailTime_ms = imuSampleTime_ms;
}
if ((imuSampleTime_ms - lastInnovPassTime_ms) > 1000) {
ekfInnovationsPass = false;
} else if ((imuSampleTime_ms - lastInnovFailTime_ms) > 10000) {
ekfInnovationsPass = true;
}
// both GPS speed accuracy and EKF innovations must pass
gpsAccuracyGood = gpsSpdAccPass && ekfInnovationsPass;
}
// Detect if we are in flight or on ground
void NavEKF2_core::detectFlight()
{
/*
If we are a fly forward type vehicle (eg plane), then in-air status can be determined through a combination of speed and height criteria.
Because of the differing certainty requirements of algorithms that need the in-flight / on-ground status we use two booleans where
onGround indicates a high certainty we are not flying and inFlight indicates a high certainty we are flying. It is possible for
both onGround and inFlight to be false if the status is uncertain, but they cannot both be true.
If we are a plane as indicated by the assume_zero_sideslip() status, then different logic is used
TODO - this logic should be moved out of the EKF and into the flight vehicle code.
*/
if (assume_zero_sideslip()) {
// To be confident we are in the air we use a criteria which combines arm status, ground speed, airspeed and height change
ftype gndSpdSq = sq(gpsDataDelayed.vel.x) + sq(gpsDataDelayed.vel.y);
bool highGndSpd = false;
bool highAirSpd = false;
bool largeHgtChange = false;
// trigger at 8 m/s airspeed
if (dal.airspeed_sensor_enabled()) {
const auto *airspeed = dal.airspeed();
if (airspeed->get_airspeed() * dal.get_EAS2TAS() > 10.0f) {
highAirSpd = true;
}
}
// trigger at 10 m/s GPS velocity, but not if GPS is reporting bad velocity errors
if (gndSpdSq > 100.0f && gpsSpdAccuracy < 1.0f) {
highGndSpd = true;
}
// trigger if more than 10m away from initial height
if (fabsF(hgtMea) > 10.0f) {
largeHgtChange = true;
}
// Determine to a high certainty we are flying
if (motorsArmed && highGndSpd && (highAirSpd || largeHgtChange)) {
onGround = false;
inFlight = true;
}
// if is possible we are in flight, set the time this condition was last detected
if (motorsArmed && (highGndSpd || highAirSpd || largeHgtChange)) {
airborneDetectTime_ms = imuSampleTime_ms;
onGround = false;
}
// Determine to a high certainty we are not flying
// after 5 seconds of not detecting a possible flight condition or we are disarmed, we transition to on-ground mode
if(!motorsArmed || ((imuSampleTime_ms - airborneDetectTime_ms) > 5000)) {
onGround = true;
inFlight = false;
}
} else {
// Non fly forward vehicle, so can only use height and motor arm status
// If the motors are armed then we could be flying and if they are not armed then we are definitely not flying
if (motorsArmed) {
onGround = false;
} else {
inFlight = false;
onGround = true;
}
if (!onGround) {
// If height has increased since exiting on-ground, then we definitely are flying
if ((stateStruct.position.z - posDownAtTakeoff) < -1.5f) {
inFlight = true;
}
// If rangefinder has increased since exiting on-ground, then we definitely are flying
if ((rangeDataNew.rng - rngAtStartOfFlight) > 0.5f) {
inFlight = true;
}
// If more than 5 seconds since likely_flying was set
// true, then set inFlight true
if (dal.get_time_flying_ms() > 5000) {
inFlight = true;
}
}
}
// handle reset of counters used to control how many times we will try to reset the yaw to the EKF-GSF value per flight
if ((!prevOnGround && onGround) || !gpsSpdAccPass) {
// disable filter bank
EKFGSF_run_filterbank = false;
} else if (yawEstimator != nullptr && !EKFGSF_run_filterbank && inFlight && gpsSpdAccPass) {
// flying so reset counters and enable filter bank when GPS is good
EKFGSF_yaw_reset_ms = 0;
EKFGSF_yaw_reset_request_ms = 0;
EKFGSF_yaw_reset_count = 0;
EKFGSF_run_filterbank = true;
Vector3f gyroBias;
getGyroBias(gyroBias);
yawEstimator->setGyroBias(gyroBias);
}
// store current on-ground and in-air status for next time
prevOnGround = onGround;
prevInFlight = inFlight;
// Store vehicle height and range prior to takeoff for use in post takeoff checks
if (onGround) {
// store vertical position at start of flight to use as a reference for ground relative checks
posDownAtTakeoff = stateStruct.position.z;
// store the range finder measurement which will be used as a reference to detect when we have taken off
rngAtStartOfFlight = rangeDataNew.rng;
// if the magnetic field states have been set, then continue to update the vertical position
// quaternion and yaw innovation snapshots to use as a reference when we start to fly.
if (magStateInitComplete) {
posDownAtLastMagReset = stateStruct.position.z;
quatAtLastMagReset = stateStruct.quat;
yawInnovAtLastMagReset = innovYaw;
}
}
}
// 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. Use to prevent range finder operation otherwise
// enabled by the combination of EK2_RNG_AID_HGT and EK2_RNG_USE_SPD parameters.
void NavEKF2_core::setTerrainHgtStable(bool val)
{
terrainHgtStable = val;
}
// Detect takeoff for optical flow navigation
void NavEKF2_core::detectOptFlowTakeoff(void)
{
if (!onGround && !takeOffDetected && (imuSampleTime_ms - timeAtArming_ms) > 1000) {
// we are no longer confidently on the ground so check the range finder and gyro for signs of takeoff
const auto &ins = dal.ins();
Vector3f angRateVec;
Vector3f gyroBias;
getGyroBias(gyroBias);
angRateVec = ins.get_gyro(gyro_index_active) - gyroBias;
takeOffDetected = (takeOffDetected || (angRateVec.length() > 0.1f) || (rangeDataNew.rng > (rngAtStartOfFlight + 0.1f)));
} else if (onGround) {
// we are confidently on the ground so set the takeoff detected status to false
takeOffDetected = false;
}
}
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