[vtkusers] Bug? vtkNormalFilter changes # of points in polydata

[BBerco]

Dear all, 
I have noticed a strange behavior of vtkNormalFilter.

When called, this filter appears to change the number of vtkPolyData ->
GetNumberOfPoints(), as illustrated below:
*
        // returns 4586
*        std::cout << read_polydata_without_id -> GetNumberOfPoints() <<
std::endl;

        // The polydata is fed to an IDFilter.
        vtkSmartPointer<vtkIdFilter>  id_filter =
vtkSmartPointer<vtkIdFilter>::New();
        id_filter -> SetIdsArrayName("ids");
        id_filter -> SetInputData(read_polydata_without_id);
        id_filter -> PointIdsOn();
        id_filter -> CellIdsOn();

        id_filter -> Update();
*        // returns 4586
*        std::cout << id_filter -> GetOutput() -> GetNumberOfPoints() <<
std::endl;

        // The normals are added to the polydata
        vtkSmartPointer<vtkPolyDataNormals> normal_filter =
vtkPolyDataNormals::New();
        normal_filter -> ComputePointNormalsOff();
        normal_filter -> ComputeCellNormalsOn();
        normal_filter -> SetInputConnection(id_filter -> GetOutputPort());
        normal_filter -> Update ();
        
*        // returns 4716
*        std::cout << normal_filter -> GetOutput() -> GetNumberOfPoints() <<
std::endl;


I have noticed this issue with several polydatas created from an input obj
file such as this one (http://echo.jpl.nasa.gov/asteroids/shapes/kw4a.obj).
Polydata generated from VTK seem unchanged.

In any case, I find strange that this property gets modified. Am I missing
something? Why would adding the normals to the polydata change the number of
points it contains?

Best, 
Ben



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