Tracker: add DISTANCE_MIN parameter

Vehicles will only be tracked if they are at least DISTANCE_MIN meters
away from the tracker

AntennaTracker/Parameters.h

@@ -89,7 +89,8 @@ public:
         k_param_yaw_trim,
         k_param_pitch_trim,
         k_param_yaw_range,
-        k_param_pitch_range,            // 136
+        k_param_pitch_range,
+        k_param_distance_min,       // 137
 
         //
         // 150: Telemetry control
@@ -138,6 +139,7 @@ public:
     AP_Float pitch_trim;
     AP_Int16 yaw_range;             // yaw axis total range of motion in degrees
     AP_Int16 pitch_range;           // pitch axis total range of motion in degrees
+    AP_Int16 distance_min;          // target's must be at least this distance from tracker to be tracked
 
     // Waypoints
     //

AntennaTracker/Parameters.pde

@@ -178,6 +178,15 @@ const AP_Param::Info var_info[] PROGMEM = {
     // @User: Standard
     GSCALAR(pitch_range,            "PITCH_RANGE", PITCH_RANGE_DEFAULT),
 
+    // @Param: DISTANCE_MIN
+    // @DisplayName: Distance minimum to target
+    // @Description: Tracker will track targets at least this distance away
+    // @Units: meters
+    // @Increment: 1
+    // @Range: 0 100
+    // @User: Standard
+    GSCALAR(distance_min,           "DISTANCE_MIN", DISTANCE_MIN_DEFAULT),
+
     // barometer ground calibration. The GND_ prefix is chosen for
     // compatibility with previous releases of ArduPlane
     // @Group: GND_

AntennaTracker/config.h

@@ -53,6 +53,9 @@
 #ifndef TRACKING_TIMEOUT_SEC
  # define TRACKING_TIMEOUT_SEC              5.0f    // consider we've lost track of vehicle after 5 seconds with no position update.
 #endif
+#ifndef DISTANCE_MIN_DEFAULT
+ # define DISTANCE_MIN_DEFAULT              5.0f    // do not track targets within 5 meters
+#endif
 
 //////////////////////////////////////////////////////////////////////////////
 // Developer Items

AntennaTracker/control_auto.pde

@@ -17,6 +17,10 @@ static void update_auto(void)
 
     float yaw = wrap_180_cd((nav_status.bearing+g.yaw_trim)*100) * 0.01f;
     float pitch = constrain_float(nav_status.pitch+g.pitch_trim, -90, 90);
-    update_pitch_servo(pitch);
-    update_yaw_servo(yaw);
+
+    // only move servos if target is at least distance_min away
+    if ((g.distance_min <= 0) || (nav_status.distance >= g.distance_min)) {
+        update_pitch_servo(pitch);
+        update_yaw_servo(yaw);
+    }
 }