[gcs] prevent speech spam with 'approaching'

only triggered when close enough but not too much, and flying a long segment
fix #1833

sw/ground_segment/cockpit/live.ml

@@ -38,6 +38,9 @@ let (//) = Filename.concat
 let gcs_id = "GCS"
 
 let approaching_alert_time = 3.
+let approaching_alert_dmin = 0.5
+let approaching_alert_slmin = 20.
+
 let track_size = ref 500
 
 let _auto_hide_fp = ref false
@@ -961,12 +964,14 @@ let highlight_fp = fun ac b s ->
   end
 
 
-let check_approaching = fun ac geo alert ->
+let check_approaching = fun ac geo1 geo2 alert ->
   match ac.track#last with
       None -> ()
     | Some ac_pos ->
-      let d = LL.wgs84_distance ac_pos geo in
-      if d < ac.speed *. approaching_alert_time then
+      let s_len = LL.wgs84_distance geo1 geo2 in (* length of the segment *)
+      let d = LL.wgs84_distance ac_pos geo2 in (* distance to end of the segment *)
+      (* only log_and_say "approaching" if close enough but not too much and when flying long segments *)
+      if d < ac.speed *. approaching_alert_time && d > approaching_alert_dmin && s_len > approaching_alert_slmin then
         log_and_say alert ac.ac_name (sprintf "%s, approaching" ac.ac_speech_name)
 
 
@@ -1266,7 +1271,7 @@ let listen_flight_params = fun geomap auto_center_new_ac alert alt_graph ->
     ac.track#draw_segment geo1 geo2;
 
     (* Check if approaching the end of the segment *)
-    check_approaching ac geo2 alert
+    check_approaching ac geo1 geo2 alert
   in
   safe_bind "SEGMENT_STATUS" get_segment_status;