mirror of https://github.com/ArduPilot/ardupilot
761 lines
34 KiB
C++
761 lines
34 KiB
C++
#include <AP_HAL/AP_HAL.h>
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#if HAL_CPU_CLASS >= HAL_CPU_CLASS_150
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#include "AP_NavEKF2.h"
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#include "AP_NavEKF2_core.h"
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#include <AP_AHRS/AP_AHRS.h>
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#include <AP_Vehicle/AP_Vehicle.h>
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#include <GCS_MAVLink/GCS.h>
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#include <stdio.h>
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extern const AP_HAL::HAL& hal;
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/********************************************************
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* OPT FLOW AND RANGE FINDER *
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********************************************************/
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// Read the range finder and take new measurements if available
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// Apply a median filter
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void NavEKF2_core::readRangeFinder(void)
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{
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uint8_t midIndex;
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uint8_t maxIndex;
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uint8_t minIndex;
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// get theoretical correct range when the vehicle is on the ground
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// don't allow range to go below 5cm becasue this can cause problems with optical flow processing
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rngOnGnd = MAX(frontend->_rng.ground_clearance_cm() * 0.01f, 0.05f);
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// read range finder at 20Hz
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// TODO better way of knowing if it has new data
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if ((imuSampleTime_ms - lastRngMeasTime_ms) > 50) {
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// reset the timer used to control the measurement rate
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lastRngMeasTime_ms = imuSampleTime_ms;
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// store samples and sample time into a ring buffer if valid
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// use data from two range finders if available
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for (uint8_t sensorIndex = 0; sensorIndex <= 1; sensorIndex++) {
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if (frontend->_rng.status(sensorIndex) == RangeFinder::RangeFinder_Good) {
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rngMeasIndex[sensorIndex] ++;
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if (rngMeasIndex[sensorIndex] > 2) {
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rngMeasIndex[sensorIndex] = 0;
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}
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storedRngMeasTime_ms[sensorIndex][rngMeasIndex[sensorIndex]] = imuSampleTime_ms - 25;
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storedRngMeas[sensorIndex][rngMeasIndex[sensorIndex]] = frontend->_rng.distance_cm(sensorIndex) * 0.01f;
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}
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// check for three fresh samples
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bool sampleFresh[2][3] = {};
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for (uint8_t index = 0; index <= 2; index++) {
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sampleFresh[sensorIndex][index] = (imuSampleTime_ms - storedRngMeasTime_ms[sensorIndex][index]) < 500;
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}
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// find the median value if we have three fresh samples
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if (sampleFresh[sensorIndex][0] && sampleFresh[sensorIndex][1] && sampleFresh[sensorIndex][2]) {
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if (storedRngMeas[sensorIndex][0] > storedRngMeas[sensorIndex][1]) {
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minIndex = 1;
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maxIndex = 0;
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} else {
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minIndex = 0;
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maxIndex = 1;
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}
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if (storedRngMeas[sensorIndex][2] > storedRngMeas[sensorIndex][maxIndex]) {
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midIndex = maxIndex;
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} else if (storedRngMeas[sensorIndex][2] < storedRngMeas[sensorIndex][minIndex]) {
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midIndex = minIndex;
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} else {
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midIndex = 2;
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}
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// don't allow time to go backwards
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if (storedRngMeasTime_ms[sensorIndex][midIndex] > rangeDataNew.time_ms) {
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rangeDataNew.time_ms = storedRngMeasTime_ms[sensorIndex][midIndex];
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}
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// limit the measured range to be no less than the on-ground range
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rangeDataNew.rng = MAX(storedRngMeas[sensorIndex][midIndex],rngOnGnd);
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// get position in body frame for the current sensor
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rangeDataNew.sensor_idx = sensorIndex;
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// write data to buffer with time stamp to be fused when the fusion time horizon catches up with it
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storedRange.push(rangeDataNew);
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// indicate we have updated the measurement
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rngValidMeaTime_ms = imuSampleTime_ms;
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} else if (!takeOffDetected && ((imuSampleTime_ms - rngValidMeaTime_ms) > 200)) {
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// before takeoff we assume on-ground range value if there is no data
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rangeDataNew.time_ms = imuSampleTime_ms;
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rangeDataNew.rng = rngOnGnd;
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rangeDataNew.time_ms = imuSampleTime_ms;
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// don't allow time to go backwards
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if (imuSampleTime_ms > rangeDataNew.time_ms) {
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rangeDataNew.time_ms = imuSampleTime_ms;
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}
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// write data to buffer with time stamp to be fused when the fusion time horizon catches up with it
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storedRange.push(rangeDataNew);
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// indicate we have updated the measurement
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rngValidMeaTime_ms = imuSampleTime_ms;
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}
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}
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}
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}
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// write the raw optical flow measurements
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// this needs to be called externally.
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void NavEKF2_core::writeOptFlowMeas(uint8_t &rawFlowQuality, Vector2f &rawFlowRates, Vector2f &rawGyroRates, uint32_t &msecFlowMeas, const Vector3f &posOffset)
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{
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// The raw measurements need to be optical flow rates in radians/second averaged across the time since the last update
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// The PX4Flow sensor outputs flow rates with the following axis and sign conventions:
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// A positive X rate is produced by a positive sensor rotation about the X axis
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// A positive Y rate is produced by a positive sensor rotation about the Y axis
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// This filter uses a different definition of optical flow rates to the sensor with a positive optical flow rate produced by a
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// negative rotation about that axis. For example a positive rotation of the flight vehicle about its X (roll) axis would produce a negative X flow rate
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flowMeaTime_ms = imuSampleTime_ms;
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// calculate bias errors on flow sensor gyro rates, but protect against spikes in data
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// reset the accumulated body delta angle and time
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// don't do the calculation if not enough time lapsed for a reliable body rate measurement
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if (delTimeOF > 0.01f) {
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flowGyroBias.x = 0.99f * flowGyroBias.x + 0.01f * constrain_float((rawGyroRates.x - delAngBodyOF.x/delTimeOF),-0.1f,0.1f);
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flowGyroBias.y = 0.99f * flowGyroBias.y + 0.01f * constrain_float((rawGyroRates.y - delAngBodyOF.y/delTimeOF),-0.1f,0.1f);
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delAngBodyOF.zero();
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delTimeOF = 0.0f;
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}
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// by definition if this function is called, then flow measurements have been provided so we
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// need to run the optical flow takeoff detection
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detectOptFlowTakeoff();
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// calculate rotation matrices at mid sample time for flow observations
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stateStruct.quat.rotation_matrix(Tbn_flow);
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// don't use data with a low quality indicator or extreme rates (helps catch corrupt sensor data)
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if ((rawFlowQuality > 0) && rawFlowRates.length() < 4.2f && rawGyroRates.length() < 4.2f) {
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// correct flow sensor body rates for bias and write
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ofDataNew.bodyRadXYZ.x = rawGyroRates.x - flowGyroBias.x;
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ofDataNew.bodyRadXYZ.y = rawGyroRates.y - flowGyroBias.y;
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// the sensor interface doesn't provide a z axis rate so use the rate from the nav sensor instead
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if (delTimeOF > 0.001f) {
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// first preference is to use the rate averaged over the same sampling period as the flow sensor
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ofDataNew.bodyRadXYZ.z = delAngBodyOF.z / delTimeOF;
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} else if (imuDataNew.delAngDT > 0.001f){
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// second preference is to use most recent IMU data
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ofDataNew.bodyRadXYZ.z = imuDataNew.delAng.z / imuDataNew.delAngDT;
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} else {
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// third preference is use zero
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ofDataNew.bodyRadXYZ.z = 0.0f;
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}
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// write uncorrected flow rate measurements
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// note correction for different axis and sign conventions used by the px4flow sensor
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ofDataNew.flowRadXY = - rawFlowRates; // raw (non motion compensated) optical flow angular rate about the X axis (rad/sec)
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// write the flow sensor position in body frame
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ofDataNew.body_offset = &posOffset;
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// write flow rate measurements corrected for body rates
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ofDataNew.flowRadXYcomp.x = ofDataNew.flowRadXY.x + ofDataNew.bodyRadXYZ.x;
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ofDataNew.flowRadXYcomp.y = ofDataNew.flowRadXY.y + ofDataNew.bodyRadXYZ.y;
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// record time last observation was received so we can detect loss of data elsewhere
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flowValidMeaTime_ms = imuSampleTime_ms;
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// estimate sample time of the measurement
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ofDataNew.time_ms = imuSampleTime_ms - frontend->_flowDelay_ms - frontend->flowTimeDeltaAvg_ms/2;
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// Correct for the average intersampling delay due to the filter updaterate
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ofDataNew.time_ms -= localFilterTimeStep_ms/2;
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// Prevent time delay exceeding age of oldest IMU data in the buffer
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ofDataNew.time_ms = MAX(ofDataNew.time_ms,imuDataDelayed.time_ms);
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// Save data to buffer
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storedOF.push(ofDataNew);
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// Check for data at the fusion time horizon
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flowDataToFuse = storedOF.recall(ofDataDelayed, imuDataDelayed.time_ms);
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}
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}
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/********************************************************
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* MAGNETOMETER *
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********************************************************/
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// check for new magnetometer data and update store measurements if available
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void NavEKF2_core::readMagData()
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{
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if (!_ahrs->get_compass()) {
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allMagSensorsFailed = true;
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return;
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}
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// If we are a vehicle with a sideslip constraint to aid yaw estimation and we have timed out on our last avialable
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// magnetometer, then declare the magnetometers as failed for this flight
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uint8_t maxCount = _ahrs->get_compass()->get_count();
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if (allMagSensorsFailed || (magTimeout && assume_zero_sideslip() && magSelectIndex >= maxCount-1 && inFlight)) {
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allMagSensorsFailed = true;
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return;
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}
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// do not accept new compass data faster than 14Hz (nominal rate is 10Hz) to prevent high processor loading
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// because magnetometer fusion is an expensive step and we could overflow the FIFO buffer
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if (use_compass() && _ahrs->get_compass()->last_update_usec() - lastMagUpdate_us > 70000) {
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frontend->logging.log_compass = true;
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// If the magnetometer has timed out (been rejected too long) we find another magnetometer to use if available
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// Don't do this if we are on the ground because there can be magnetic interference and we need to know if there is a problem
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// before taking off. Don't do this within the first 30 seconds from startup because the yaw error could be due to large yaw gyro bias affsets
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if (magTimeout && (maxCount > 1) && !onGround && imuSampleTime_ms - ekfStartTime_ms > 30000) {
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// search through the list of magnetometers
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for (uint8_t i=1; i<maxCount; i++) {
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uint8_t tempIndex = magSelectIndex + i;
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// loop back to the start index if we have exceeded the bounds
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if (tempIndex >= maxCount) {
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tempIndex -= maxCount;
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}
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// if the magnetometer is allowed to be used for yaw and has a different index, we start using it
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if (_ahrs->get_compass()->use_for_yaw(tempIndex) && tempIndex != magSelectIndex) {
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magSelectIndex = tempIndex;
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GCS_MAVLINK::send_statustext_all(MAV_SEVERITY_INFO, "EKF2 IMU%u switching to compass %u",(unsigned)imu_index,magSelectIndex);
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// reset the timeout flag and timer
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magTimeout = false;
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lastHealthyMagTime_ms = imuSampleTime_ms;
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// zero the learned magnetometer bias states
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stateStruct.body_magfield.zero();
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// clear the measurement buffer
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storedMag.reset();
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// clear the data waiting flag so that we do not use any data pending from the previous sensor
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magDataToFuse = false;
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// request a reset of the magnetic field states
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magStateResetRequest = true;
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// declare the field unlearned so that the reset request will be obeyed
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magFieldLearned = false;
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}
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}
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}
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// detect changes to magnetometer offset parameters and reset states
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Vector3f nowMagOffsets = _ahrs->get_compass()->get_offsets(magSelectIndex);
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bool changeDetected = lastMagOffsetsValid && (nowMagOffsets != lastMagOffsets);
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if (changeDetected) {
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// zero the learned magnetometer bias states
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stateStruct.body_magfield.zero();
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// clear the measurement buffer
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storedMag.reset();
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}
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lastMagOffsets = nowMagOffsets;
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lastMagOffsetsValid = true;
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// store time of last measurement update
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lastMagUpdate_us = _ahrs->get_compass()->last_update_usec(magSelectIndex);
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// estimate of time magnetometer measurement was taken, allowing for delays
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magDataNew.time_ms = imuSampleTime_ms - frontend->magDelay_ms;
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// Correct for the average intersampling delay due to the filter updaterate
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magDataNew.time_ms -= localFilterTimeStep_ms/2;
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// read compass data and scale to improve numerical conditioning
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magDataNew.mag = _ahrs->get_compass()->get_field(magSelectIndex) * 0.001f;
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// check for consistent data between magnetometers
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consistentMagData = _ahrs->get_compass()->consistent();
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// save magnetometer measurement to buffer to be fused later
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storedMag.push(magDataNew);
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}
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}
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/********************************************************
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* Inertial Measurements *
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********************************************************/
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/*
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* Read IMU delta angle and delta velocity measurements and downsample to 100Hz
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* for storage in the data buffers used by the EKF. If the IMU data arrives at
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* lower rate than 100Hz, then no downsampling or upsampling will be performed.
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* Downsampling is done using a method that does not introduce coning or sculling
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* errors.
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*/
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void NavEKF2_core::readIMUData()
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{
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const AP_InertialSensor &ins = _ahrs->get_ins();
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// average IMU sampling rate
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dtIMUavg = ins.get_loop_delta_t();
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// the imu sample time is used as a common time reference throughout the filter
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imuSampleTime_ms = AP_HAL::millis();
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// use the nominated imu or primary if not available
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if (ins.use_accel(imu_index)) {
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readDeltaVelocity(imu_index, imuDataNew.delVel, imuDataNew.delVelDT);
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accelPosOffset = ins.get_imu_pos_offset(imu_index);
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} else {
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readDeltaVelocity(ins.get_primary_accel(), imuDataNew.delVel, imuDataNew.delVelDT);
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accelPosOffset = ins.get_imu_pos_offset(ins.get_primary_accel());
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}
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// Get delta angle data from primary gyro or primary if not available
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if (ins.use_gyro(imu_index)) {
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readDeltaAngle(imu_index, imuDataNew.delAng);
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} else {
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readDeltaAngle(ins.get_primary_gyro(), imuDataNew.delAng);
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}
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imuDataNew.delAngDT = MAX(ins.get_delta_angle_dt(imu_index),1.0e-4f);
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// Get current time stamp
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imuDataNew.time_ms = imuSampleTime_ms;
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// Accumulate the measurement time interval for the delta velocity and angle data
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imuDataDownSampledNew.delAngDT += imuDataNew.delAngDT;
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imuDataDownSampledNew.delVelDT += imuDataNew.delVelDT;
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// Rotate quaternon atitude from previous to new and normalise.
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// Accumulation using quaternions prevents introduction of coning errors due to downsampling
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imuQuatDownSampleNew.rotate(imuDataNew.delAng);
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imuQuatDownSampleNew.normalize();
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// Rotate the latest delta velocity into body frame at the start of accumulation
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Matrix3f deltaRotMat;
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imuQuatDownSampleNew.rotation_matrix(deltaRotMat);
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// Apply the delta velocity to the delta velocity accumulator
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imuDataDownSampledNew.delVel += deltaRotMat*imuDataNew.delVel;
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// Keep track of the number of IMU frames since the last state prediction
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framesSincePredict++;
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// If 10msec has elapsed, and the frontend has allowed us to start a new predict cycle, then store the accumulated IMU data
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// to be used by the state prediction, ignoring the frontend permission if more than 20msec has lapsed
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if ((dtIMUavg*(float)framesSincePredict >= EKF_TARGET_DT && startPredictEnabled) || (dtIMUavg*(float)framesSincePredict >= 2.0f*EKF_TARGET_DT)) {
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// convert the accumulated quaternion to an equivalent delta angle
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imuQuatDownSampleNew.to_axis_angle(imuDataDownSampledNew.delAng);
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// Time stamp the data
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imuDataDownSampledNew.time_ms = imuSampleTime_ms;
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// Write data to the FIFO IMU buffer
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storedIMU.push_youngest_element(imuDataDownSampledNew);
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// calculate the achieved average time step rate for the EKF
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float dtNow = constrain_float(0.5f*(imuDataDownSampledNew.delAngDT+imuDataDownSampledNew.delVelDT),0.0f,10.0f*EKF_TARGET_DT);
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dtEkfAvg = 0.98f * dtEkfAvg + 0.02f * dtNow;
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// zero the accumulated IMU data and quaternion
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imuDataDownSampledNew.delAng.zero();
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imuDataDownSampledNew.delVel.zero();
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imuDataDownSampledNew.delAngDT = 0.0f;
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imuDataDownSampledNew.delVelDT = 0.0f;
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imuQuatDownSampleNew[0] = 1.0f;
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imuQuatDownSampleNew[3] = imuQuatDownSampleNew[2] = imuQuatDownSampleNew[1] = 0.0f;
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// reset the counter used to let the frontend know how many frames have elapsed since we started a new update cycle
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framesSincePredict = 0;
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// set the flag to let the filter know it has new IMU data nad needs to run
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runUpdates = true;
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// extract the oldest available data from the FIFO buffer
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imuDataDelayed = storedIMU.pop_oldest_element();
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// protect against delta time going to zero
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// TODO - check if calculations can tolerate 0
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float minDT = 0.1f*dtEkfAvg;
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imuDataDelayed.delAngDT = MAX(imuDataDelayed.delAngDT,minDT);
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imuDataDelayed.delVelDT = MAX(imuDataDelayed.delVelDT,minDT);
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// correct the extracted IMU data for sensor errors
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delAngCorrected = imuDataDelayed.delAng;
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delVelCorrected = imuDataDelayed.delVel;
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correctDeltaAngle(delAngCorrected, imuDataDelayed.delAngDT);
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correctDeltaVelocity(delVelCorrected, imuDataDelayed.delVelDT);
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} else {
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// we don't have new IMU data in the buffer so don't run filter updates on this time step
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runUpdates = false;
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}
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}
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// read the delta velocity and corresponding time interval from the IMU
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// return false if data is not available
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bool NavEKF2_core::readDeltaVelocity(uint8_t ins_index, Vector3f &dVel, float &dVel_dt) {
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const AP_InertialSensor &ins = _ahrs->get_ins();
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if (ins_index < ins.get_accel_count()) {
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ins.get_delta_velocity(ins_index,dVel);
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dVel_dt = MAX(ins.get_delta_velocity_dt(ins_index),1.0e-4f);
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return true;
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}
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return false;
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}
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/********************************************************
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* Global Position Measurement *
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********************************************************/
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// check for new valid GPS data and update stored measurement if available
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void NavEKF2_core::readGpsData()
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{
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// check for new GPS data
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// do not accept data at a faster rate than 14Hz to avoid overflowing the FIFO buffer
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if (_ahrs->get_gps().last_message_time_ms() - lastTimeGpsReceived_ms > 70) {
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if (_ahrs->get_gps().status() >= AP_GPS::GPS_OK_FIX_3D) {
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// report GPS fix status
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gpsCheckStatus.bad_fix = false;
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// store fix time from previous read
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secondLastGpsTime_ms = lastTimeGpsReceived_ms;
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// get current fix time
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lastTimeGpsReceived_ms = _ahrs->get_gps().last_message_time_ms();
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// estimate when the GPS fix was valid, allowing for GPS processing and other delays
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// ideally we should be using a timing signal from the GPS receiver to set this time
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gpsDataNew.time_ms = lastTimeGpsReceived_ms - frontend->_gpsDelay_ms;
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// Correct for the average intersampling delay due to the filter updaterate
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gpsDataNew.time_ms -= localFilterTimeStep_ms/2;
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||
// Prevent time delay exceeding age of oldest IMU data in the buffer
|
||
gpsDataNew.time_ms = MAX(gpsDataNew.time_ms,imuDataDelayed.time_ms);
|
||
|
||
// Get which GPS we are using for position information
|
||
gpsDataNew.sensor_idx = _ahrs->get_gps().primary_sensor();
|
||
|
||
// read the NED velocity from the GPS
|
||
gpsDataNew.vel = _ahrs->get_gps().velocity();
|
||
|
||
// Use the speed and position accuracy from the GPS if available, otherwise set it to zero.
|
||
// Apply a decaying envelope filter with a 5 second time constant to the raw accuracy data
|
||
float alpha = constrain_float(0.0002f * (lastTimeGpsReceived_ms - secondLastGpsTime_ms),0.0f,1.0f);
|
||
gpsSpdAccuracy *= (1.0f - alpha);
|
||
float gpsSpdAccRaw;
|
||
if (!_ahrs->get_gps().speed_accuracy(gpsSpdAccRaw)) {
|
||
gpsSpdAccuracy = 0.0f;
|
||
} else {
|
||
gpsSpdAccuracy = MAX(gpsSpdAccuracy,gpsSpdAccRaw);
|
||
gpsSpdAccuracy = MIN(gpsSpdAccuracy,50.0f);
|
||
}
|
||
gpsPosAccuracy *= (1.0f - alpha);
|
||
float gpsPosAccRaw;
|
||
if (!_ahrs->get_gps().horizontal_accuracy(gpsPosAccRaw)) {
|
||
gpsPosAccuracy = 0.0f;
|
||
} else {
|
||
gpsPosAccuracy = MAX(gpsPosAccuracy,gpsPosAccRaw);
|
||
gpsPosAccuracy = MIN(gpsPosAccuracy,100.0f);
|
||
}
|
||
gpsHgtAccuracy *= (1.0f - alpha);
|
||
float gpsHgtAccRaw;
|
||
if (!_ahrs->get_gps().vertical_accuracy(gpsHgtAccRaw)) {
|
||
gpsHgtAccuracy = 0.0f;
|
||
} else {
|
||
gpsHgtAccuracy = MAX(gpsHgtAccuracy,gpsHgtAccRaw);
|
||
gpsHgtAccuracy = MIN(gpsHgtAccuracy,100.0f);
|
||
}
|
||
|
||
// check if we have enough GPS satellites and increase the gps noise scaler if we don't
|
||
if (_ahrs->get_gps().num_sats() >= 6 && (PV_AidingMode == AID_ABSOLUTE)) {
|
||
gpsNoiseScaler = 1.0f;
|
||
} else if (_ahrs->get_gps().num_sats() == 5 && (PV_AidingMode == AID_ABSOLUTE)) {
|
||
gpsNoiseScaler = 1.4f;
|
||
} else { // <= 4 satellites or in constant position mode
|
||
gpsNoiseScaler = 2.0f;
|
||
}
|
||
|
||
// Check if GPS can output vertical velocity and set GPS fusion mode accordingly
|
||
if (_ahrs->get_gps().have_vertical_velocity() && frontend->_fusionModeGPS == 0) {
|
||
useGpsVertVel = true;
|
||
} else {
|
||
useGpsVertVel = false;
|
||
}
|
||
|
||
// Monitor quality of the GPS velocity data before and after alignment using separate checks
|
||
if (PV_AidingMode != AID_ABSOLUTE) {
|
||
// Pre-alignment checks
|
||
gpsGoodToAlign = calcGpsGoodToAlign();
|
||
} else {
|
||
gpsGoodToAlign = false;
|
||
}
|
||
|
||
// Post-alignment checks
|
||
calcGpsGoodForFlight();
|
||
|
||
// Read the GPS locaton in WGS-84 lat,long,height coordinates
|
||
const struct Location &gpsloc = _ahrs->get_gps().location();
|
||
|
||
// Set the EKF origin and magnetic field declination if not previously set and GPS checks have passed
|
||
if (gpsGoodToAlign && !validOrigin) {
|
||
setOrigin();
|
||
|
||
// set the NE earth magnetic field states using the published declination
|
||
// and set the corresponding variances and covariances
|
||
alignMagStateDeclination();
|
||
|
||
// Set the height of the NED origin to ‘height of baro height datum relative to GPS height datum'
|
||
EKF_origin.alt = gpsloc.alt - baroDataNew.hgt;
|
||
|
||
// Set the uncertinty of the GPS origin height
|
||
ekfOriginHgtVar = sq(gpsHgtAccuracy);
|
||
|
||
}
|
||
|
||
// 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);
|
||
gpsDataNew.hgt = 0.01f * (gpsloc.alt - EKF_origin.alt);
|
||
storedGPS.push(gpsDataNew);
|
||
// declare GPS available for use
|
||
gpsNotAvailable = false;
|
||
}
|
||
|
||
frontend->logging.log_gps = true;
|
||
|
||
} else {
|
||
// report GPS fix status
|
||
gpsCheckStatus.bad_fix = true;
|
||
}
|
||
}
|
||
}
|
||
|
||
// read the delta angle and corresponding time interval from the IMU
|
||
// return false if data is not available
|
||
bool NavEKF2_core::readDeltaAngle(uint8_t ins_index, Vector3f &dAng) {
|
||
const AP_InertialSensor &ins = _ahrs->get_ins();
|
||
|
||
if (ins_index < ins.get_gyro_count()) {
|
||
ins.get_delta_angle(ins_index,dAng);
|
||
frontend->logging.log_imu = true;
|
||
return true;
|
||
}
|
||
return false;
|
||
}
|
||
|
||
|
||
/********************************************************
|
||
* Height Measurements *
|
||
********************************************************/
|
||
|
||
// check for new pressure altitude measurement data and update stored measurement if available
|
||
void NavEKF2_core::readBaroData()
|
||
{
|
||
// check to see if baro measurement has changed so we know if a new measurement has arrived
|
||
// do not accept data at a faster rate than 14Hz to avoid overflowing the FIFO buffer
|
||
if (frontend->_baro.get_last_update() - lastBaroReceived_ms > 70) {
|
||
frontend->logging.log_baro = true;
|
||
|
||
baroDataNew.hgt = frontend->_baro.get_altitude();
|
||
|
||
// 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 (getTakeoffExpected()) {
|
||
baroDataNew.hgt = MAX(baroDataNew.hgt, meaHgtAtTakeOff);
|
||
}
|
||
|
||
// time stamp used to check for new measurement
|
||
lastBaroReceived_ms = frontend->_baro.get_last_update();
|
||
|
||
// estimate of time height measurement was taken, allowing for delays
|
||
baroDataNew.time_ms = lastBaroReceived_ms - frontend->_hgtDelay_ms;
|
||
|
||
// Correct for the average intersampling delay due to the filter updaterate
|
||
baroDataNew.time_ms -= localFilterTimeStep_ms/2;
|
||
|
||
// Prevent time delay exceeding age of oldest IMU data in the buffer
|
||
baroDataNew.time_ms = MAX(baroDataNew.time_ms,imuDataDelayed.time_ms);
|
||
|
||
// save baro measurement to buffer to be fused later
|
||
storedBaro.push(baroDataNew);
|
||
}
|
||
}
|
||
|
||
// calculate filtered offset between baro height measurement and EKF height estimate
|
||
// offset should be subtracted from baro measurement to match filter estimate
|
||
// offset is used to enable reversion to baro from alternate height data source
|
||
void NavEKF2_core::calcFiltBaroOffset()
|
||
{
|
||
// Apply a first order LPF with spike protection
|
||
baroHgtOffset += 0.1f * constrain_float(baroDataDelayed.hgt + stateStruct.position.z - baroHgtOffset, -5.0f, 5.0f);
|
||
}
|
||
|
||
// calculate filtered offset between GPS height measurement and EKF height estimate
|
||
// offset should be subtracted from GPS measurement to match filter estimate
|
||
// offset is used to switch reversion to GPS from alternate height data source
|
||
void NavEKF2_core::calcFiltGpsHgtOffset()
|
||
{
|
||
// Estimate the WGS-84 height of the EKF's origin using a Bayes filter
|
||
|
||
// calculate the variance of our a-priori estimate of the ekf origin height
|
||
float deltaTime = constrain_float(0.001f * (imuDataDelayed.time_ms - lastOriginHgtTime_ms), 0.0f, 1.0f);
|
||
if (activeHgtSource == HGT_SOURCE_BARO) {
|
||
// Use the baro drift rate
|
||
const float baroDriftRate = 0.05f;
|
||
ekfOriginHgtVar += sq(baroDriftRate * deltaTime);
|
||
} else if (activeHgtSource == HGT_SOURCE_RNG) {
|
||
// use the worse case expected terrain gradient and vehicle horizontal speed
|
||
const float maxTerrGrad = 0.25f;
|
||
ekfOriginHgtVar += sq(maxTerrGrad * norm(stateStruct.velocity.x , stateStruct.velocity.y) * deltaTime);
|
||
} else if (activeHgtSource == HGT_SOURCE_GPS) {
|
||
// by definition we are using GPS height as the EKF datum in this mode
|
||
// so cannot run this filter
|
||
return;
|
||
}
|
||
lastOriginHgtTime_ms = imuDataDelayed.time_ms;
|
||
|
||
// calculate the observation variance assuming EKF error relative to datum is independant of GPS observation error
|
||
// when not using GPS as height source
|
||
float originHgtObsVar = sq(gpsHgtAccuracy) + P[8][8];
|
||
|
||
// calculate the correction gain
|
||
float gain = ekfOriginHgtVar / (ekfOriginHgtVar + originHgtObsVar);
|
||
|
||
// calculate the innovation
|
||
float innovation = - stateStruct.position.z - gpsDataDelayed.hgt;
|
||
|
||
// check the innovation variance ratio
|
||
float ratio = sq(innovation) / (ekfOriginHgtVar + originHgtObsVar);
|
||
|
||
// correct the EKF origin and variance estimate if the innovation variance ratio is < 5-sigma
|
||
if (ratio < 5.0f) {
|
||
EKF_origin.alt -= (int)(100.0f * gain * innovation);
|
||
ekfOriginHgtVar -= fmaxf(gain * ekfOriginHgtVar , 0.0f);
|
||
}
|
||
}
|
||
|
||
/********************************************************
|
||
* Air Speed Measurements *
|
||
********************************************************/
|
||
|
||
// check for new airspeed data and update stored measurements if available
|
||
void NavEKF2_core::readAirSpdData()
|
||
{
|
||
// if airspeed reading is valid and is set by the user to be used and has been updated then
|
||
// we take a new reading, convert from EAS to TAS and set the flag letting other functions
|
||
// know a new measurement is available
|
||
const AP_Airspeed *aspeed = _ahrs->get_airspeed();
|
||
if (aspeed &&
|
||
aspeed->use() &&
|
||
aspeed->last_update_ms() != timeTasReceived_ms) {
|
||
tasDataNew.tas = aspeed->get_airspeed() * aspeed->get_EAS2TAS();
|
||
timeTasReceived_ms = aspeed->last_update_ms();
|
||
tasDataNew.time_ms = timeTasReceived_ms - frontend->tasDelay_ms;
|
||
|
||
// Correct for the average intersampling delay due to the filter update rate
|
||
tasDataNew.time_ms -= localFilterTimeStep_ms/2;
|
||
|
||
// Save data into the buffer to be fused when the fusion time horizon catches up with it
|
||
storedTAS.push(tasDataNew);
|
||
}
|
||
// Check the buffer for measurements that have been overtaken by the fusion time horizon and need to be fused
|
||
tasDataToFuse = storedTAS.recall(tasDataDelayed,imuDataDelayed.time_ms);
|
||
}
|
||
|
||
/********************************************************
|
||
* Range Beacon Measurements *
|
||
********************************************************/
|
||
|
||
// check for new airspeed data and update stored measurements if available
|
||
void NavEKF2_core::readRngBcnData()
|
||
{
|
||
// get the location of the beacon data
|
||
const AP_Beacon *beacon = _ahrs->get_beacon();
|
||
|
||
// exit immediately if no beacon object
|
||
if (beacon == nullptr) {
|
||
return;
|
||
}
|
||
|
||
// get the number of beacons in use
|
||
N_beacons = beacon->count();
|
||
|
||
// search through all the beacons for new data and if we find it stop searching and push the data into the observation buffer
|
||
bool newDataToPush = false;
|
||
uint8_t numRngBcnsChecked = 0;
|
||
// start the search one index up from where we left it last time
|
||
uint8_t index = lastRngBcnChecked;
|
||
while (!newDataToPush && numRngBcnsChecked < N_beacons) {
|
||
// track the number of beacons checked
|
||
numRngBcnsChecked++;
|
||
|
||
// move to next beacon, wrap index if necessary
|
||
index++;
|
||
if (index >= N_beacons) {
|
||
index = 0;
|
||
}
|
||
|
||
// check that the beacon is healthy and has new data
|
||
if (beacon->beacon_healthy(index) &&
|
||
beacon->beacon_last_update_ms(index) != lastTimeRngBcn_ms[index])
|
||
{
|
||
// set the timestamp, correcting for measurement delay and average intersampling delay due to the filter update rate
|
||
lastTimeRngBcn_ms[index] = beacon->beacon_last_update_ms(index);
|
||
rngBcnDataNew.time_ms = lastTimeRngBcn_ms[index] - frontend->_rngBcnDelay_ms - localFilterTimeStep_ms/2;
|
||
|
||
// set the range noise
|
||
// TODO the range library should provide the noise/accuracy estimate for each beacon
|
||
rngBcnDataNew.rngErr = frontend->_rngBcnNoise;
|
||
|
||
// set the range measurement
|
||
rngBcnDataNew.rng = beacon->beacon_distance(index);
|
||
|
||
// set the beacon position
|
||
rngBcnDataNew.beacon_posNED = beacon->beacon_position(index);
|
||
|
||
// identify the beacon identifier
|
||
rngBcnDataNew.beacon_ID = index;
|
||
|
||
// indicate we have new data to push to the buffer
|
||
newDataToPush = true;
|
||
|
||
// update the last checked index
|
||
lastRngBcnChecked = index;
|
||
}
|
||
}
|
||
|
||
// Check if the beacon system has returned a 3D fix
|
||
if (beacon->get_vehicle_position_ned(beaconVehiclePosNED, beaconVehiclePosErr)) {
|
||
rngBcnLast3DmeasTime_ms = imuSampleTime_ms;
|
||
}
|
||
|
||
// Check if the range beacon data can be used to align the vehicle position
|
||
if (imuSampleTime_ms - rngBcnLast3DmeasTime_ms < 250 && beaconVehiclePosErr < 1.0f && rngBcnAlignmentCompleted) {
|
||
// check for consistency between the position reported by the beacon and the position from the 3-State alignment filter
|
||
float posDiffSq = sq(receiverPos.x - beaconVehiclePosNED.x) + sq(receiverPos.y - beaconVehiclePosNED.y);
|
||
float posDiffVar = sq(beaconVehiclePosErr) + receiverPosCov[0][0] + receiverPosCov[1][1];
|
||
if (posDiffSq < 9.0f*posDiffVar) {
|
||
rngBcnGoodToAlign = true;
|
||
// Set the EKF origin and magnetic field declination if not previously set
|
||
if (!validOrigin && PV_AidingMode != AID_ABSOLUTE) {
|
||
// get origin from beacon system
|
||
Location origin_loc;
|
||
if (beacon->get_origin(origin_loc)) {
|
||
setOriginLLH(origin_loc);
|
||
|
||
// set the NE earth magnetic field states using the published declination
|
||
// and set the corresponding variances and covariances
|
||
alignMagStateDeclination();
|
||
|
||
// Set the height of the NED origin to ‘height of baro height datum relative to GPS height datum'
|
||
EKF_origin.alt = origin_loc.alt - baroDataNew.hgt;
|
||
|
||
// Set the uncertainty of the origin height
|
||
ekfOriginHgtVar = sq(beaconVehiclePosErr);
|
||
}
|
||
}
|
||
} else {
|
||
rngBcnGoodToAlign = false;
|
||
}
|
||
} else {
|
||
rngBcnGoodToAlign = false;
|
||
}
|
||
|
||
// Save data into the buffer to be fused when the fusion time horizon catches up with it
|
||
if (newDataToPush) {
|
||
storedRangeBeacon.push(rngBcnDataNew);
|
||
}
|
||
|
||
// Check the buffer for measurements that have been overtaken by the fusion time horizon and need to be fused
|
||
rngBcnDataToFuse = storedRangeBeacon.recall(rngBcnDataDelayed,imuDataDelayed.time_ms);
|
||
|
||
}
|
||
#endif // HAL_CPU_CLASS
|