delete the polydata noises with connectivity filter

Hi!
I want to delete noises from my polydata with connectivity filter.I think first I should specify all regions and then delete undesired regions, and finally, just have the largest region. But I don’t know how I can access to the regions’ ids to use DeleteSpecifiedRegion(int id). could you help me?
(my code and my sample polydata is shown below)

vtkNew<vtkPolyDataConnectivityFilter> connectivityFilter;
connectivityFilter->SetInputData(polydata);
connectivityFilter->ColorRegionsOn();
connectivityFilter->SetExtractionModeToSpecifiedRegions();
for (int j=0; j<connectivityFilter-> GetNumberOfExtractedRegions()-1 ; j++){
    connectivityFilter->AddSpecifiedRegion(j); 
 }

connectivityFilter->DeleteSpecifiedRegion(int id);

@mwestphal