// select the height measurement to be fused from the available baro, range finder and GPS sources
void NavEKF2_core::selectHeightForFusion()
{
// Read range finder data and check for new data in the buffer
// This data is used by both height and optical flow fusion processing
readRangeFinder();
rangeDataToFuse = storedRange.recall(rangeDataDelayed,imuDataDelayed.time_ms);
// read baro height data from the sensor and check for new data in the buffer
readBaroData();
baroDataToFuse = storedBaro.recall(baroDataDelayed, imuDataDelayed.time_ms);
// select height source
if (((frontend->_useRngSwHgt > 0) || (frontend->_altSource == 1)) && (imuSampleTime_ms - rngValidMeaTime_ms < 500)) {
if (frontend->_altSource == 1) {
// always use range finder
activeHgtSource = HGT_SOURCE_RNG;
} else {
// determine if we are above or below the height switch region
float rangeMaxUse = 1e-4f * (float)frontend->_rng.max_distance_cm() * (float)frontend->_useRngSwHgt;
bool aboveUpperSwHgt = (terrainState - stateStruct.position.z) > rangeMaxUse;
bool belowLowerSwHgt = (terrainState - stateStruct.position.z) < 0.7f * rangeMaxUse;
// If the terrain height is consistent and we are moving slowly, then it can be
// used as a height reference in combination with a range finder
float horizSpeed = norm(stateStruct.velocity.x, stateStruct.velocity.y);
bool dontTrustTerrain = (horizSpeed > 2.0f) || !terrainHgtStable;
bool trustTerrain = (horizSpeed < 1.0f) && terrainHgtStable;
/*
* Switch between range finder and primary height source using height above ground and speed thresholds with
* hysteresis to avoid rapid switching. Using range finder for height requires a consistent terrain height
* which cannot be assumed if the vehicle is moving horizontally.
*/
if ((aboveUpperSwHgt || dontTrustTerrain) && (activeHgtSource == HGT_SOURCE_RNG)) {
// cannot trust terrain or range finder so stop using range finder height
if (frontend->_altSource == 0) {
activeHgtSource = HGT_SOURCE_BARO;
} else if (frontend->_altSource == 2) {
activeHgtSource = HGT_SOURCE_GPS;
}
} else if (belowLowerSwHgt && trustTerrain && (activeHgtSource != HGT_SOURCE_RNG)) {
// reliable terrain and range finder so start using range finder height
activeHgtSource = HGT_SOURCE_RNG;
}
}
} else if ((frontend->_altSource == 2) && ((imuSampleTime_ms - lastTimeGpsReceived_ms) < 500) && validOrigin && gpsAccuracyGood) {
activeHgtSource = HGT_SOURCE_GPS;
} else {
activeHgtSource = HGT_SOURCE_BARO;
}
// Use Baro alt as a fallback if we lose range finder or GPS
bool lostRngHgt = ((activeHgtSource == HGT_SOURCE_RNG) && ((imuSampleTime_ms - rngValidMeaTime_ms) > 500));
bool lostGpsHgt = ((activeHgtSource == HGT_SOURCE_GPS) && ((imuSampleTime_ms - lastTimeGpsReceived_ms) > 2000));
if (lostRngHgt || lostGpsHgt) {
activeHgtSource = HGT_SOURCE_BARO;
}
// if there is new baro data to fuse, calculate filtered baro data required by other processes
if (baroDataToFuse) {
// calculate offset to baro data that enables us to switch to Baro height use during operation
if (activeHgtSource != HGT_SOURCE_BARO) {
calcFiltBaroOffset();
}
// filtered baro data used to provide a reference for takeoff
// it is is reset to last height measurement on disarming in performArmingChecks()
if (!getTakeoffExpected()) {
const float gndHgtFiltTC = 0.5f;
const float dtBaro = frontend->hgtAvg_ms*1.0e-3f;
float alpha = constrain_float(dtBaro / (dtBaro+gndHgtFiltTC),0.0f,1.0f);
meaHgtAtTakeOff += (baroDataDelayed.hgt-meaHgtAtTakeOff)*alpha;
}
}
// calculate offset to GPS height data that enables us to switch to GPS height during operation
if (gpsDataToFuse && (activeHgtSource != HGT_SOURCE_GPS)) {
calcFiltGpsHgtOffset();
}
// Select the height measurement source
if (rangeDataToFuse && (activeHgtSource == HGT_SOURCE_RNG)) {
// using range finder data
// correct for tilt using a flat earth model
if (prevTnb.c.z >= 0.7) {
// calculate height above ground
hgtMea = MAX(rangeDataDelayed.rng * prevTnb.c.z, rngOnGnd);
// correct for terrain position relative to datum
hgtMea -= terrainState;
// enable fusion
fuseHgtData = true;
// set the observation noise
posDownObsNoise = sq(constrain_float(frontend->_rngNoise, 0.1f, 10.0f));
// add uncertainty created by terrain gradient and vehicle tilt
posDownObsNoise += sq(rangeDataDelayed.rng * frontend->_terrGradMax) * MAX(0.0f , (1.0f - sq(prevTnb.c.z)));
} else {
// disable fusion if tilted too far
fuseHgtData = false;
}
} else if (gpsDataToFuse && (activeHgtSource == HGT_SOURCE_GPS)) {
// using GPS data
hgtMea = gpsDataDelayed.hgt;
// enable fusion
fuseHgtData = true;
// set the observation noise using receiver reported accuracy or the horizontal noise scaled for typical VDOP/HDOP ratio
if (gpsHgtAccuracy > 0.0f) {
posDownObsNoise = sq(constrain_float(gpsHgtAccuracy, 1.5f * frontend->_gpsHorizPosNoise, 100.0f));
} else {
posDownObsNoise = sq(constrain_float(1.5f * frontend->_gpsHorizPosNoise, 0.1f, 10.0f));
}
} else if (baroDataToFuse && (activeHgtSource == HGT_SOURCE_BARO)) {
// using Baro data
hgtMea = baroDataDelayed.hgt - baroHgtOffset;
// enable fusion
fuseHgtData = true;
// set the observation noise
posDownObsNoise = sq(constrain_float(frontend->_baroAltNoise, 0.1f, 10.0f));
// reduce weighting (increase observation noise) on baro if we are likely to be in ground effect
if (getTakeoffExpected() || getTouchdownExpected()) {
posDownObsNoise *= frontend->gndEffectBaroScaler;
}
// If we are in takeoff mode, the height measurement is limited to be no less than the measurement at start of takeoff
// This prevents negative baro disturbances due to copter downwash corrupting the EKF altitude during initial ascent
if (motorsArmed && getTakeoffExpected()) {
hgtMea = MAX(hgtMea, meaHgtAtTakeOff);
}
} else {
fuseHgtData = false;
}
// If we haven't fused height data for a while, then declare the height data as being timed out
// set timeout period based on whether we have vertical GPS velocity available to constrain drift
hgtRetryTime_ms = (useGpsVertVel && !velTimeout) ? frontend->hgtRetryTimeMode0_ms : frontend->hgtRetryTimeMode12_ms;
if (imuSampleTime_ms - lastHgtPassTime_ms > hgtRetryTime_ms) {
hgtTimeout = true;
} else {
hgtTimeout = false;
}
}
// select the height measurement to be fused from the available baro, range finder and GPS sources
void NavEKF2_core::selectHeightForFusion()
{
// Read range finder data and check for new data in the buffer
// This data is used by both height and optical flow fusion processing
readRangeFinder();
rangeDataToFuse = RecallRange();
// read baro height data from the sensor and check for new data in the buffer
readBaroData();
baroDataToFuse = RecallBaro();
// determine if we should be using a height source other than baro
bool usingRangeForHgt = (frontend->_altSource == 1 && imuSampleTime_ms - rngValidMeaTime_ms < 500 && frontend->_fusionModeGPS == 3);
bool usingGpsForHgt = (frontend->_altSource == 2 && imuSampleTime_ms - lastTimeGpsReceived_ms < 500 && validOrigin);
// if there is new baro data to fuse, calculate filterred baro data required by other processes
if (baroDataToFuse) {
// calculate offset to baro data that enables baro to be used as a backup if we are using other height sources
if (usingRangeForHgt || usingGpsForHgt) {
calcFiltBaroOffset();
}
// filtered baro data used to provide a reference for takeoff
// it is is reset to last height measurement on disarming in performArmingChecks()
if (!getTakeoffExpected()) {
const float gndHgtFiltTC = 0.5f;
const float dtBaro = frontend->hgtAvg_ms*1.0e-3f;
float alpha = constrain_float(dtBaro / (dtBaro+gndHgtFiltTC),0.0f,1.0f);
meaHgtAtTakeOff += (baroDataDelayed.hgt-meaHgtAtTakeOff)*alpha;
}
}
// Select the height measurement source
if (rangeDataToFuse && usingRangeForHgt) {
// using range finder data
// correct for tilt using a flat earth model
if (prevTnb.c.z >= 0.7) {
hgtMea = max(rangeDataDelayed.rng * prevTnb.c.z, rngOnGnd);
// enable fusion
fuseHgtData = true;
// set the observation noise
posDownObsNoise = sq(constrain_float(frontend->_rngNoise, 0.1f, 10.0f));
} else {
// disable fusion if tilted too far
fuseHgtData = false;
}
} else if (gpsDataToFuse && usingGpsForHgt) {
// using GPS data
hgtMea = gpsDataDelayed.hgt;
// enable fusion
fuseHgtData = true;
// set the observation noise to the horizontal GPS noise plus a scaler becasue GPS vertical position is usually less accurate
// TODO use VDOP/HDOP, reported accuracy or a separate parameter
posDownObsNoise = sq(constrain_float(frontend->_gpsHorizPosNoise * 1.5f, 0.1f, 10.0f));
} else if (baroDataToFuse && !usingRangeForHgt && !usingGpsForHgt) {
// using Baro data
hgtMea = baroDataDelayed.hgt - baroHgtOffset;
// enable fusion
fuseHgtData = true;
// set the observation noise
posDownObsNoise = sq(constrain_float(frontend->_baroAltNoise, 0.1f, 10.0f));
// reduce weighting (increase observation noise) on baro if we are likely to be in ground effect
if (getTakeoffExpected() || getTouchdownExpected()) {
posDownObsNoise *= frontend->gndEffectBaroScaler;
}
} else {
fuseHgtData = false;
}
// If we haven't fused height data for a while, then declare the height data as being timed out
// set timeout period based on whether we have vertical GPS velocity available to constrain drift
hgtRetryTime_ms = (useGpsVertVel && !velTimeout) ? frontend->hgtRetryTimeMode0_ms : frontend->hgtRetryTimeMode12_ms;
if (imuSampleTime_ms - lastHgtPassTime_ms > hgtRetryTime_ms) {
hgtTimeout = true;
} else {
hgtTimeout = false;
}
}
// select the height measurement to be fused from the available baro, range finder and GPS sources
void NavEKF2_core::selectHeightForFusion()
{
// Read range finder data and check for new data in the buffer
// This data is used by both height and optical flow fusion processing
readRangeFinder();
rangeDataToFuse = storedRange.recall(rangeDataDelayed,imuDataDelayed.time_ms);
// correct range data for the body frame position offset relative to the IMU
// the corrected reading is the reading that would have been taken if the sensor was
// co-located with the IMU
if (rangeDataToFuse) {
AP_RangeFinder_Backend *sensor = frontend->_rng.get_backend(rangeDataDelayed.sensor_idx);
if (sensor != nullptr) {
Vector3f posOffsetBody = sensor->get_pos_offset() - accelPosOffset;
if (!posOffsetBody.is_zero()) {
Vector3f posOffsetEarth = prevTnb.mul_transpose(posOffsetBody);
rangeDataDelayed.rng += posOffsetEarth.z / prevTnb.c.z;
}
}
}
// read baro height data from the sensor and check for new data in the buffer
readBaroData();
baroDataToFuse = storedBaro.recall(baroDataDelayed, imuDataDelayed.time_ms);
// select height source
if (extNavUsedForPos) {
// always use external vision as the hight source if using for position.
activeHgtSource = HGT_SOURCE_EV;
} else if (((frontend->_useRngSwHgt > 0) || (frontend->_altSource == 1)) && (imuSampleTime_ms - rngValidMeaTime_ms < 500)) {
if (frontend->_altSource == 1) {
// always use range finder
activeHgtSource = HGT_SOURCE_RNG;
} else {
// determine if we are above or below the height switch region
float rangeMaxUse = 1e-4f * (float)frontend->_rng.max_distance_cm_orient(ROTATION_PITCH_270) * (float)frontend->_useRngSwHgt;
bool aboveUpperSwHgt = (terrainState - stateStruct.position.z) > rangeMaxUse;
bool belowLowerSwHgt = (terrainState - stateStruct.position.z) < 0.7f * rangeMaxUse;
// If the terrain height is consistent and we are moving slowly, then it can be
// used as a height reference in combination with a range finder
// apply a hysteresis to the speed check to prevent rapid switching
float horizSpeed = norm(stateStruct.velocity.x, stateStruct.velocity.y);
bool dontTrustTerrain = ((horizSpeed > frontend->_useRngSwSpd) && filterStatus.flags.horiz_vel) || !terrainHgtStable;
float trust_spd_trigger = MAX((frontend->_useRngSwSpd - 1.0f),(frontend->_useRngSwSpd * 0.5f));
bool trustTerrain = (horizSpeed < trust_spd_trigger) && terrainHgtStable;
/*
* Switch between range finder and primary height source using height above ground and speed thresholds with
* hysteresis to avoid rapid switching. Using range finder for height requires a consistent terrain height
* which cannot be assumed if the vehicle is moving horizontally.
*/
if ((aboveUpperSwHgt || dontTrustTerrain) && (activeHgtSource == HGT_SOURCE_RNG)) {
// cannot trust terrain or range finder so stop using range finder height
if (frontend->_altSource == 0) {
activeHgtSource = HGT_SOURCE_BARO;
} else if (frontend->_altSource == 2) {
activeHgtSource = HGT_SOURCE_GPS;
}
} else if (belowLowerSwHgt && trustTerrain && (activeHgtSource != HGT_SOURCE_RNG)) {
// reliable terrain and range finder so start using range finder height
activeHgtSource = HGT_SOURCE_RNG;
}
}
} else if ((frontend->_altSource == 2) && ((imuSampleTime_ms - lastTimeGpsReceived_ms) < 500) && validOrigin && gpsAccuracyGood) {
activeHgtSource = HGT_SOURCE_GPS;
} else if ((frontend->_altSource == 3) && validOrigin && rngBcnGoodToAlign) {
activeHgtSource = HGT_SOURCE_BCN;
} else {
activeHgtSource = HGT_SOURCE_BARO;
}
// Use Baro alt as a fallback if we lose range finder, GPS or external nav
bool lostRngHgt = ((activeHgtSource == HGT_SOURCE_RNG) && ((imuSampleTime_ms - rngValidMeaTime_ms) > 500));
bool lostGpsHgt = ((activeHgtSource == HGT_SOURCE_GPS) && ((imuSampleTime_ms - lastTimeGpsReceived_ms) > 2000));
bool lostExtNavHgt = ((activeHgtSource == HGT_SOURCE_EV) && ((imuSampleTime_ms - extNavMeasTime_ms) > 2000));
if (lostRngHgt || lostGpsHgt || lostExtNavHgt) {
activeHgtSource = HGT_SOURCE_BARO;
}
// if there is new baro data to fuse, calculate filtered baro data required by other processes
if (baroDataToFuse) {
// calculate offset to baro data that enables us to switch to Baro height use during operation
if (activeHgtSource != HGT_SOURCE_BARO) {
calcFiltBaroOffset();
}
// filtered baro data used to provide a reference for takeoff
// it is is reset to last height measurement on disarming in performArmingChecks()
if (!getTakeoffExpected()) {
const float gndHgtFiltTC = 0.5f;
const float dtBaro = frontend->hgtAvg_ms*1.0e-3f;
float alpha = constrain_float(dtBaro / (dtBaro+gndHgtFiltTC),0.0f,1.0f);
meaHgtAtTakeOff += (baroDataDelayed.hgt-meaHgtAtTakeOff)*alpha;
}
}
// If we are not using GPS as the primary height sensor, correct EKF origin height so that
// combined local NED position height and origin height remains consistent with the GPS altitude
// This also enables the GPS height to be used as a backup height source
if (gpsDataToFuse &&
(((frontend->_originHgtMode & (1 << 0)) && (activeHgtSource == HGT_SOURCE_BARO)) ||
((frontend->_originHgtMode & (1 << 1)) && (activeHgtSource == HGT_SOURCE_RNG)))
) {
correctEkfOriginHeight();
}
// Select the height measurement source
if (extNavDataToFuse && (activeHgtSource == HGT_SOURCE_EV)) {
hgtMea = -extNavDataDelayed.pos.z;
posDownObsNoise = sq(constrain_float(extNavDataDelayed.posErr, 0.1f, 10.0f));
} else if (rangeDataToFuse && (activeHgtSource == HGT_SOURCE_RNG)) {
// using range finder data
// correct for tilt using a flat earth model
if (prevTnb.c.z >= 0.7) {
// calculate height above ground
hgtMea = MAX(rangeDataDelayed.rng * prevTnb.c.z, rngOnGnd);
// correct for terrain position relative to datum
hgtMea -= terrainState;
// enable fusion
fuseHgtData = true;
velPosObs[5] = -hgtMea;
// set the observation noise
posDownObsNoise = sq(constrain_float(frontend->_rngNoise, 0.1f, 10.0f));
// add uncertainty created by terrain gradient and vehicle tilt
posDownObsNoise += sq(rangeDataDelayed.rng * frontend->_terrGradMax) * MAX(0.0f , (1.0f - sq(prevTnb.c.z)));
} else {
// disable fusion if tilted too far
fuseHgtData = false;
}
} else if (gpsDataToFuse && (activeHgtSource == HGT_SOURCE_GPS)) {
// using GPS data
hgtMea = gpsDataDelayed.hgt;
// enable fusion
velPosObs[5] = -hgtMea;
fuseHgtData = true;
// set the observation noise using receiver reported accuracy or the horizontal noise scaled for typical VDOP/HDOP ratio
if (gpsHgtAccuracy > 0.0f) {
posDownObsNoise = sq(constrain_float(gpsHgtAccuracy, 1.5f * frontend->_gpsHorizPosNoise, 100.0f));
} else {
posDownObsNoise = sq(constrain_float(1.5f * frontend->_gpsHorizPosNoise, 0.1f, 10.0f));
}
} else if (baroDataToFuse && (activeHgtSource == HGT_SOURCE_BARO)) {
// using Baro data
hgtMea = baroDataDelayed.hgt - baroHgtOffset;
// enable fusion
velPosObs[5] = -hgtMea;
fuseHgtData = true;
// set the observation noise
posDownObsNoise = sq(constrain_float(frontend->_baroAltNoise, 0.1f, 10.0f));
// reduce weighting (increase observation noise) on baro if we are likely to be in ground effect
if (getTakeoffExpected() || getTouchdownExpected()) {
posDownObsNoise *= frontend->gndEffectBaroScaler;
}
// If we are in takeoff mode, the height measurement is limited to be no less than the measurement at start of takeoff
// This prevents negative baro disturbances due to copter downwash corrupting the EKF altitude during initial ascent
if (motorsArmed && getTakeoffExpected()) {
hgtMea = MAX(hgtMea, meaHgtAtTakeOff);
}
} else {
fuseHgtData = false;
}
// If we haven't fused height data for a while, then declare the height data as being timed out
// set timeout period based on whether we have vertical GPS velocity available to constrain drift
hgtRetryTime_ms = (useGpsVertVel && !velTimeout) ? frontend->hgtRetryTimeMode0_ms : frontend->hgtRetryTimeMode12_ms;
if (imuSampleTime_ms - lastHgtPassTime_ms > hgtRetryTime_ms) {
hgtTimeout = true;
} else {
hgtTimeout = false;
}
}
