code: function modelCenter(view, magnet) {
  
          var model = view.model;
          var bbox = model.getBBox();
          var center = bbox.center();
          var angle = model.angle();
  
          var portId = view.findAttribute('port', magnet);
          if (portId) {
              var portGroup = model.portProp(portId, 'group');
              var portsPositions = model.getPortsPositions(portGroup);
              var anchor = new g.Point(portsPositions[portId]).offset(bbox.origin());
              anchor.rotate(center, -angle);
              return anchor;
          }
  
          return center;
      }
docs: Can find anchor from model, when there is no selector or the link end is connected to a port