PolyData connectivity filter with mode to specified regions only shows the first region selected

Support
1

Hello,

I have a question about vtkPolyDataConnectivityFilter with SetExtractionModeToSpecifiedRegions . It does it well if I only get one region with label 0 or 1. But if I already specified one, the other returns both labels.

           vtkSmartPointer<vtkPolyDataConnectivityFilter>
          GetConnectedComponents(vtkSmartPointer<vtkPolyData> pol) {
                vtkNew<vtkPolyDataConnectivityFilter> result;
                result->SetInputData(pol);
                result->SetExtractionModeToAllRegions();
               result->Modified();
               result->Update();
               return result;
            }

 
         vtkSmartPointer<vtkPolyDataConnectivityFilter> components_alongX =
          GetConnectedComponents(polydata);


      if (components_alongX->GetNumberOfExtractedRegions() == 2) {
        components_alongX->SetExtractionModeToSpecifiedRegions();
        components_alongX->AddSpecifiedRegion(0); 
        components_alongX->Update();

	cout << "Number of cells : " << components_alongX->GetOutput()-
                    >GetNumberOfCells() << "\n";

            components_alongX->SetExtractionModeToSpecifiedRegions();
            components_alongX->AddSpecifiedRegion(1); 
            components_alongX->Update();

           	cout << "Number of cells : " << components_alongX->GetOutput()-
                    >GetNumberOfCells() << "\n";
              }

I have also tried like this. But it was still worse I got both components in both labels

          components_alongX->InitializeSpecifiedRegionList();
          components_alongX->AddSpecifiedRegion(1); //select the region to extract here
          components_alongX->Update();

Someone had the same problem?. I am using vtk 8. Thanks !!

2

If i do this between region selections:
components_alongX =
GetConnectedComponents(polydata);

and i get the other label It works. But this is not efficient at all. Is it a bug in vtk 8.x?

Thanks

3

Have you tried calling components_alongX->DeleteSpecifiedRegion() to delete one or the other regions you no longer wish to extract?

4

hello, thank you for answering. Yes i also tried this but the same result. the only way to make it work is to apply the connected components again to the same polydata and choose the second label.

5

Hmm, I don’t see a problem in either your code or in the code of the vtkPolyDataConnectvityFilter itself.

6

When i have time i will debug this vtk filter. There must be something wrong in it. I let you know. by now, I will make this trick that it works.