[agl] use ground_alt from autopilot if no SRTM data available

sw/lib/ocaml/mapWaypoints.ml

@@ -74,6 +74,7 @@ object (self)
   val label = new CL.widget ~name:name ~color:"white" s 0. wpt_group
   val mutable name = name (* FIXME: already in label ! *)
   val mutable alt = alt
+  val mutable ground_alt = 0.
   val mutable moved = None
   val mutable deleted = false
   val mutable commit_cb = None
@@ -145,7 +146,7 @@ object (self)
     ea#set_adjustment adj;
     ea#set_value alt; (* this should be done by set_adjustment but seems to fail on ubuntu 13.10 (at least) *)
 
-    let agl = alt -. float (try Srtm.of_wgs84 initial_wgs84 with _ -> 0) in
+    let agl = alt -. (try float (Srtm.of_wgs84 initial_wgs84) with _ -> ground_alt) in
     let agl_lab  = GMisc.label ~text:(sprintf " AGL: %4.0fm" agl) ~packing:ha#add () in
     let plus10= GButton.button ~label:"+10" ~packing:ha#add () in
     let change_alt = fun x ->
@@ -282,6 +283,7 @@ object (self)
           if update then updated ()
       | (None, false) | (Some _, true) -> ()
       | Some _, false -> self#reset_moved ()
+  method set_ground_alt ga = ground_alt <- ga
   method delete () =
     deleted <- true; (* BOF *)
     wpt_group#destroy ()

sw/lib/ocaml/mapWaypoints.mli

@@ -52,6 +52,7 @@ class waypoint :
     method move : float -> float -> unit
     method name : string
     method set : ?altitude:float -> ?update:bool -> Latlong.geographic -> unit
+    method set_ground_alt : float -> unit
     method set_name : string -> unit
     method xy : float * float
     method zoom : float -> unit