AP_AHRS: add getLastPosDownReset accessor

libraries/AP_AHRS/AP_AHRS.h

@@ -438,6 +438,12 @@ public:
         return 0;
     };
 
+    // return the amount of vertical position change due to the last reset in meters
+    // returns the time of the last reset or 0 if no reset has ever occurred
+    virtual uint32_t getLastPosDownReset(float &posDelta) const {
+        return 0;
+    };
+
     // Resets the baro so that it reads zero at the current height
     // Resets the EKF height to zero
     // Adjusts the EKf origin height so that the EKF height + origin height is the same as before

libraries/AP_AHRS/AP_AHRS_NavEKF.cpp

@@ -1191,6 +1191,24 @@ uint32_t AP_AHRS_NavEKF::getLastVelNorthEastReset(Vector2f &vel) const
     return 0;
 }
 
+
+// return the amount of vertical position change due to the last reset in meters
+// returns the time of the last reset or 0 if no reset has ever occurred
+uint32_t AP_AHRS_NavEKF::getLastPosDownReset(float &posDelta) const
+{
+    switch (ekf_type()) {
+    case 1:
+        return 0;
+    case 2:
+        return EKF2.getLastPosDownReset(posDelta);
+#if CONFIG_HAL_BOARD == HAL_BOARD_SITL
+    case EKF_TYPE_SITL:
+        return 0;
+#endif
+    }
+    return 0;
+}
+
 // Resets the baro so that it reads zero at the current height
 // Resets the EKF height to zero
 // Adjusts the EKf origin height so that the EKF height + origin height is the same as before

libraries/AP_AHRS/AP_AHRS_NavEKF.h

@@ -193,6 +193,10 @@ public:
     // returns the time of the last reset or 0 if no reset has ever occurred
     uint32_t getLastVelNorthEastReset(Vector2f &vel) const;
 
+    // return the amount of vertical position change due to the last reset in meters
+    // returns the time of the last reset or 0 if no reset has ever occurred
+    uint32_t getLastPosDownReset(float &posDelta) const;
+
     // Resets the baro so that it reads zero at the current height
     // Resets the EKF height to zero
     // Adjusts the EKf origin height so that the EKF height + origin height is the same as before