调整仅仅在有centerOffset值的时候，使用默认0,0,其他时候采用自动计算下边框中点

lib/ios/AMap3D/maps/AMapMarker.m

@@ -135,8 +135,14 @@
         _annotationView.draggable = _draggable;
         _annotationView.customCalloutView = _calloutView;
         //设置中心点
-        CGPoint point = CGPointMake(0, -_customView.bounds.size.height/2);
-        _annotationView.centerOffset = point;
+        if(_centerOffset.x == 0 && _centerOffset.y == 0)
+        {
+            CGPoint point = CGPointMake(0, -_customView.bounds.size.height/2);
+            _annotationView.centerOffset = point;
+        } else
+        {
+            _annotationView.centerOffset = CGPointMake(0, 0);
+        }
         if (_zIndex) {
             _annotationView.zIndex = _zIndex;
         }