AP_InertialNav: Add method to return EKF height above ground estimate

AP_InertialNav: Add validity flag to height above ground estimate

libraries/AP_InertialNav/AP_InertialNav_NavEKF.cpp

@@ -120,6 +120,20 @@ float AP_InertialNav_NavEKF::get_altitude() const
     return _relpos_cm.z;
 }
 
+/**
+ * getHgtAboveGnd - get latest height above ground level estimate in cm and a validity flag
+ *
+ * @return
+ */
+bool AP_InertialNav_NavEKF::get_hagl(float height) const
+{
+    // true when estimate is valid
+    bool valid = _ahrs_ekf.get_NavEKF().getHAGL(height);
+    // convert height from m to cm
+    height *= 100.0f;
+    return valid;
+}
+
 /**
  * get_velocity_z - returns the current climbrate.
  *

libraries/AP_InertialNav/AP_InertialNav_NavEKF.h

@@ -88,6 +88,12 @@ public:
      */
     float       get_altitude() const;
 
+    /**
+     * getHgtAboveGnd - get latest altitude estimate above ground level in centimetres and validity flag
+     * @return
+     */
+    bool       get_hagl(float hagl) const;
+
     /**
      * get_velocity_z - returns the current climbrate.
      *