New polygon center calc

src/MissionManager/QGCMapPolygon.cc

@@ -253,6 +253,8 @@ void QGCMapPolygon::removeVertex(int vertexIndex)
 
     _polygonPath.removeAt(vertexIndex);
     emit pathChanged();
+
+    _updateCenter();
 }
 
 void QGCMapPolygon::_polygonModelCountChanged(int count)
@@ -266,8 +268,12 @@ void QGCMapPolygon::_updateCenter(void)
         QGeoCoordinate center;
 
         if (_polygonPath.count() > 2) {            
-            QPointF centerPoint = _toPolygonF().boundingRect().center();
-            center = _coordFromPointF(centerPoint);
+            QPointF centroid(0, 0);
+            QPolygonF polygonF = _toPolygonF();
+            for (int i=0; i<polygonF.count(); i++) {
+                centroid += polygonF[i];
+            }
+            center = _coordFromPointF(QPointF(centroid.x() / polygonF.count(), centroid.y() / polygonF.count()));
         }
 
         _center = center;

src/MissionManager/QGCMapPolygonVisuals.qml

@@ -35,8 +35,9 @@ Item {
     property var _splitHandlesComponent
     property var _centerDragHandleComponent
 
-    property real _zorderDragHandle:    QGroundControl.zOrderMapItems + 2
-    property real _zorderSplitHandle:   QGroundControl.zOrderMapItems + 1
+    property real _zorderDragHandle:    QGroundControl.zOrderMapItems + 3   // Highest to prevent splitting when items overlap
+    property real _zorderSplitHandle:   QGroundControl.zOrderMapItems + 2
+    property real _zorderCenterHandle:  QGroundControl.zOrderMapItems + 1   // Lowest such that drag or split takes precedence
 
     function addVisuals() {
         _polygonComponent = polygonComponent.createObject(mapControl)
@@ -281,7 +282,7 @@ Item {
         id: centerDragAreaComponent
 
         MissionItemIndicatorDrag {
-            z:                          _zorderDragHandle
+            z:                          _zorderCenterHandle
             onItemCoordinateChanged:    mapPolygon.center = itemCoordinate
             onDragStart:                mapPolygon.centerDrag = true
             onDragStop:                 mapPolygon.centerDrag = false