ardupilot: added MAV_CMD_SET_HAGL

allows for height above ground from external sources

message_definitions/v1.0/ardupilotmega.xml

@@ -340,6 +340,16 @@
         <param index="6" label="Longitude">Longitude</param>
         <param index="7" label="Altitude" units="m">Altitude, not used. Should be sent as NaN. May be supported in a future version of this message.</param>
       </entry>
+      <entry value="43005" name="MAV_CMD_SET_HAGL" hasLocation="false" isDestination="false">
+        <description>Provide a value for height above ground level. This can be used for things like fixed wing and VTOL landing.</description>
+        <param index="1" label="hagl" units="m">Height above ground level.</param>
+        <param index="2" label="accuracy" units="m">estimated one standard deviation accuracy of the measurement. Set to NaN if not known.</param>
+        <param index="3" label="timeout" units="s">Timeout for this data. The flight controller should only consider this data valid within the timeout window.</param>
+        <param index="4">Empty</param>
+        <param index="5">Empty</param>
+        <param index="6">Empty</param>
+        <param index="7">Empty</param>
+      </entry>
     </enum>
     <enum name="SCRIPTING_CMD">
       <entry value="0" name="SCRIPTING_CMD_REPL_START">