Plane: allow for negative WP_LOITER_RAD for conter-clockwise loiter

this follows the same convention as missions

ArduPlane/GCS_Mavlink.pde

@@ -1301,9 +1301,9 @@ void GCS_MAVLINK::handleMessage(mavlink_message_t* msg)
         case MAV_CMD_NAV_LOITER_TIME:
         case MAV_CMD_NAV_LOITER_TURNS:
             if (tell_command.options & MASK_OPTIONS_LOITER_DIRECTION) {
-                param3 = -g.loiter_radius;
+                param3 = -abs(g.loiter_radius);
             } else {
-                param3 = g.loiter_radius;
+                param3 = abs(g.loiter_radius);
             }
         case MAV_CMD_NAV_TAKEOFF:
         case MAV_CMD_DO_SET_HOME:
@@ -1312,9 +1312,9 @@ void GCS_MAVLINK::handleMessage(mavlink_message_t* msg)
 
         case MAV_CMD_NAV_LOITER_UNLIM:
             if (tell_command.options & MASK_OPTIONS_LOITER_DIRECTION) {
-                param3 = -g.loiter_radius;;
+                param3 = -abs(g.loiter_radius);
             } else {
-                param3 = g.loiter_radius;
+                param3 = abs(g.loiter_radius);
             }
             break;
         case MAV_CMD_CONDITION_CHANGE_ALT:

ArduPlane/Parameters.pde

@@ -184,7 +184,7 @@ const AP_Param::Info var_info[] PROGMEM = {
 
     // @Param: WP_LOITER_RAD
     // @DisplayName: Waypoint Loiter Radius
-    // @Description: Defines the distance from the waypoint center, the plane will maintain during a loiter
+    // @Description: Defines the distance from the waypoint center, the plane will maintain during a loiter. If you set this value to a negative number then the default loiter direction will be counter-clockwise instead of clockwise.
     // @Units: Meters
     // @Range: 1 32767
     // @Increment: 1

ArduPlane/commands_logic.pde

@@ -230,7 +230,12 @@ static void do_RTL(void)
     control_mode    = RTL;
     crash_timer     = 0;
     next_WP                 = home;
-    loiter_direction = 1;
+
+    if (g.loiter_radius < 0) {
+        loiter_direction = -1;
+    } else {
+        loiter_direction = 1;
+    }
 
     // Altitude to hold over home
     // Set by configuration tool
@@ -268,7 +273,7 @@ static void loiter_set_direction_wp(const struct Location *nav_command)
     if (nav_command->options & MASK_OPTIONS_LOITER_DIRECTION) {
         loiter_direction = -1;
     } else {
-        loiter_direction=1;
+        loiter_direction = 1;
     }
 }
 
@@ -507,7 +512,11 @@ static bool verify_within_distance()
 
 static void do_loiter_at_location()
 {
-    loiter_direction = 1;
+    if (g.loiter_radius < 0) {
+        loiter_direction = -1;
+    } else {
+        loiter_direction = 1;
+    }
     next_WP = current_loc;
 }
 

ArduPlane/navigation.pde

@@ -142,6 +142,6 @@ static void calc_altitude_error()
 
 static void update_loiter()
 {
-    nav_controller->update_loiter(next_WP, g.loiter_radius, loiter_direction);
+    nav_controller->update_loiter(next_WP, abs(g.loiter_radius), loiter_direction);
 }