1. 直接使用vtkConnectivityFilter提取连通区域，渲染上没问题，但是打印出polydata中的点数，发现跟原始数据是一致的。

	for (int i = 0; i < numRegions; ++i)
	{
		vtkSmartPointer<vtkConnectivityFilter> connectivityFilter = vtkSmartPointer<vtkConnectivityFilter>::New();
		connectivityFilter->SetInputData(polyData);
		connectivityFilter->SetExtractionModeToSpecifiedRegions();
		connectivityFilter->InitializeSpecifiedRegionList();
		connectivityFilter->AddSpecifiedRegion(i);
		connectivityFilter->Update();
		cout << connectivityFilter->GetOutput()->GetNumberOfPoints() << endl;
	}

2. 正确的做法是后街一个vtkCleanPolyData过滤器

	for (int i = 0; i < numRegions; ++i)
   {
   	vtkSmartPointer<vtkConnectivityFilter> connectivityFilter = vtkSmartPointer<vtkConnectivityFilter>::New();
   	connectivityFilter->SetInputData(polyData);
   	connectivityFilter->SetExtractionModeToSpecifiedRegions();
   	connectivityFilter->InitializeSpecifiedRegionList();
   	connectivityFilter->AddSpecifiedRegion(i);
   	connectivityFilter->Update();
   	
   	// 使用vtkCleanPolyData删除孤立点
   	vtkSmartPointer<vtkCleanPolyData> cleanPolyData = vtkSmartPointer<vtkCleanPolyData>::New();
   	cleanPolyData->SetInputData(connectivityFilter->GetOutput());
   	cleanPolyData->Update();
   	
   	cout << cleanPolyData->GetOutput()->GetNumberOfPoints() << endl;
   }