AP_NavEKF3: Enable use of yaw fusion before external yaw sensor starts

libraries/AP_NavEKF3/AP_NavEKF3_MagFusion.cpp

@@ -273,11 +273,29 @@ void NavEKF3_core::SelectMagFusion()
                 alignYawAngle();
             } else if (tiltAlignComplete && yawAlignComplete) {
                 fuseEulerYaw(false, true);
-            } else {
-                fuseEulerYaw(true, true);
             }
             have_fused_gps_yaw = true;
             last_gps_yaw_fusion_ms = now;
+        } else if (tiltAlignComplete && !yawAlignComplete && (imuSampleTime_ms > lastSynthYawTime_ms + 140)) {
+            yawAngDataDelayed.yawAngErr = MAX(frontend->_yawNoise, 0.05f);
+            if (onGroundNotMoving) {
+                // fuse last known good yaw angle before we stopped moving to allow yaw bias learning when on ground before flight
+                fuseEulerYaw(false, true);
+            } else {
+                // update the yaw angle using the last estimate which will be used as a static yaw reference when movement stops
+                if (fabsf(prevTnb[0][2]) < fabsf(prevTnb[1][2])) {
+                    // A 321 rotation order is best conditioned because the X axis is closer to horizontal than the Y axis
+                    yawAngDataDelayed.yawAng = atan2f(prevTnb[0][1], prevTnb[0][0]);
+                    yawAngDataDelayed.type = 2;
+                } else if (yawAngDataDelayed.type == 1) {
+                    // A 312 rotation order is best conditioned because the Y axis is closer to horizontal than the X axis
+                    yawAngDataDelayed.yawAng = atan2f(-prevTnb[0][1], prevTnb[1][1]);
+                    yawAngDataDelayed.type = 1;
+                }
+                // prevent uncontrolled yaw variance growth by fusing a zero innovation
+                fuseEulerYaw(true, true);
+            }
+            lastSynthYawTime_ms = imuSampleTime_ms;
         }
         if (magcal == MagCal::EXTERNAL_YAW) {
             // no fallback
@@ -381,7 +399,7 @@ void NavEKF3_core::SelectMagFusion()
     // from becoming badly conditioned. For planes we only do this on-ground because they can align the yaw from GPS when
     // airborne. For other platform types we do this all the time.
     if (!use_compass()) {
-        if ((onGround || !assume_zero_sideslip()) && (imuSampleTime_ms - lastSynthYawTime_ms > 140)) {
+        if ((onGround || !assume_zero_sideslip()) && (imuSampleTime_ms > lastSynthYawTime_ms + 140)) {
             fuseEulerYaw(true, false);
             magTestRatio.zero();
             yawTestRatio = 0.0f;

libraries/AP_NavEKF3/AP_NavEKF3_Measurements.cpp

@@ -393,9 +393,8 @@ void NavEKF3_core::readIMUData()
     // update the inactive bias states
     learnInactiveBiases();
 
-    if (!yawAlignComplete && effective_magCal() == MagCal::EXTERNAL_YAW_FALLBACK && !inFlight) {
-        updateZGyroBias();
-    }
+    // run movement check using IMU data
+    updateMovementCheck();
 
     readDeltaVelocity(accel_index_active, imuDataNew.delVel, imuDataNew.delVelDT);
     accelPosOffset = ins.get_imu_pos_offset(accel_index_active);
@@ -1054,35 +1053,77 @@ float NavEKF3_core::MagDeclination(void) const
 }
 
 /*
-  update earth frame yaw gyro bias. This is only used for
-  MagCal::EXTERNAL_YAW_FALLBACK, when not flying and when we have not
-  yet done a yaw alignment. It prevents a buildup of a large gyro bias
-  for gyro axes that can't be corrected using the accelerometers while
-  waiting for GPS yaw
- */
-void NavEKF3_core::updateZGyroBias(void)
+  Update the on ground and not moving check.
+  Should be called once per IMU update.
+  Only updates when on ground and when operating with an external yaw sensor
+*/
+void NavEKF3_core::updateMovementCheck(void)
 {
-    const float zgyro_learn_limit = radians(3);
+    MagCal magcal = effective_magCal();
+    if (!(magcal == MagCal::EXTERNAL_YAW || magcal == MagCal::EXTERNAL_YAW_FALLBACK) && !onGround) {
+        onGroundNotMoving = false;
+        return;
+    }
+
+    const float gyro_limit = radians(3.0f);
+    const float gyro_diff_limit = 0.1;;
+    const float accel_limit = 1.0f;
+    const float accel_diff_limit = 1.0f;
+    const float hysteresis_ratio = 0.7f;
+    const float dtEkfAvgInv = 1.0f / dtEkfAvg;
+
+    // get current bias corrected gyro and accelerometer
     const AP_InertialSensor &ins = AP::ins();
-    /*
-      get corrected gyro
-     */
-    Vector3f gyro = ins.get_gyro(gyro_index_active) - (stateStruct.gyro_bias / dtEkfAvg);
-    /*
-      we want to push the corrected gyro towards zero, but only in the
-      Z earth axis. Rotate the gyro to earth frame, then zero x,y
-      components then rotate back
-     */
-    Matrix3f rot;
-    stateStruct.quat.rotation_matrix(rot);
-    gyro = rot.transposed() * gyro;
-    gyro.x = 0;
-    gyro.y = 0;
-    gyro = rot * gyro;
-    if (gyro.length_squared() > sq(zgyro_learn_limit)) {
-        // more than 3 degrees/second rotation, don't update. We
-        // assume the vehicle really is moving
+    Vector3f gyro = ins.get_gyro(gyro_index_active) - stateStruct.gyro_bias * dtEkfAvgInv;
+    Vector3f accel = ins.get_accel(accel_index_active) - stateStruct.accel_bias * dtEkfAvgInv;
+
+    if (!prevOnGround) {
+        gyro_prev = gyro;
+        accel_prev = accel;
+        onGroundNotMoving = false;
+        gyro_diff = gyro_diff_limit;
+        accel_diff = accel_diff_limit;
         return;
     }
-    stateStruct.gyro_bias += gyro * 1.0e-4 * dtEkfAvg;
+
+	// calculate a gyro rate of change metric
+	Vector3f temp = (gyro - gyro_prev) * dtEkfAvgInv;
+    gyro_prev = gyro;
+	gyro_diff = 0.99f * gyro_diff + 0.01f * temp.length();
+
+	// calculate a acceleration rate of change metric
+	temp = (accel - accel_prev) * dtEkfAvgInv;
+    accel_prev = accel;
+	accel_diff = 0.99f * accel_diff + 0.01f * temp.length();
+
+    const float gyro_length = gyro.length();
+    const float accel_length_error = accel.length() - GRAVITY_MSS;
+    if (onGroundNotMoving) {
+        if (gyro_length > gyro_limit ||
+            fabsf(accel_length_error) > accel_limit ||
+            gyro_diff > gyro_diff_limit ||
+            accel_diff > accel_diff_limit) {
+                onGroundNotMoving = false;
+            }
+    } else if (gyro.length() < hysteresis_ratio * gyro_limit &&
+               fabsf(accel_length_error) < hysteresis_ratio * accel_limit &&
+               gyro_diff < hysteresis_ratio * gyro_diff_limit &&
+               accel_diff < hysteresis_ratio * accel_diff_limit) {
+        onGroundNotMoving = true;
+    }
+
+    if (imuSampleTime_ms - lastMoveCheckLogTime_ms > 100) {
+        lastMoveCheckLogTime_ms = imuSampleTime_ms;
+        AP::logger().Write("XKFM",
+                        "TimeUS,OGNM,GL,ALE,GD,AD",
+                        "s-----",
+                        "F-----",
+                        "QBffff",
+                        AP_HAL::micros64(),
+                        uint8_t(onGroundNotMoving),
+                        float(gyro_length),
+                        float(accel_length_error),
+                        float(gyro_diff),
+                        float(accel_diff));
+    }
 }

libraries/AP_NavEKF3/AP_NavEKF3_core.h

@@ -1239,6 +1239,14 @@ private:
     float yawInnovAtLastMagReset;   // magnetic yaw innovation last time the yaw and mag field states were reset (rad)
     Quaternion quatAtLastMagReset;  // quaternion states last time the mag states were reset
 
+    // Used by on ground movement check required when operating on ground without a yaw reference
+    float gyro_diff;                    // filtered gyro difference (rad/s)
+    float accel_diff;                   // filtered acceerometer difference (m/s/s)
+    Vector3f gyro_prev;                 // gyro vector from previous time step (rad/s)
+    Vector3f accel_prev;                // accelerometer vector from previous time step (m/s/s)
+    bool onGroundNotMoving;             // true when on the ground and not moving
+    uint32_t lastMoveCheckLogTime_ms;   // last time the movement check data was logged (msec)
+
     // flags indicating severe numerical errors in innovation variance calculation for different fusion operations
     struct {
         bool bad_xmag:1;
@@ -1340,8 +1348,10 @@ private:
     uint8_t gps_yaw_fallback_good_counter;
 
     /*
-      learn Z gyro bias when not flying and when no yaw alignment has
-      been done with EXTERNAL_YAW_FALLBACK
-     */
-    void updateZGyroBias(void);
+    Update the on ground and not moving check.
+    Should be called once per IMU update.
+    Only updates when on ground and when operating with an external yaw sensor
+    */
+    void updateMovementCheck(void);
+
 };