The post is related to The Example About vtkPolyDataNormals.
If you want to use vtkPolyDataNormals to compute the normals of points, it’s better to set variable Splitting false.

#include <vtkVersion.h>
#include <vtkSmartPointer.h>
#include <vtkSurfaceReconstructionFilter.h>
#include <vtkProgrammableSource.h>
#include <vtkContourFilter.h>
#include <vtkReverseSense.h>
#include <vtkPolyDataMapper.h>
#include <vtkProperty.h>
#include <vtkPolyData.h>
#include <vtkCamera.h>
#include <vtkRenderer.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkSphereSource.h>
#include <vtkXMLPolyDataReader.h>
#include <vtkUnstructuredGrid.h>
#include <vtkDataSetMapper.h>
#include <vtkPolyDataNormals.h>
#include <vtkPointData.h>
#include <vtkCellData.h>
#include <vtkConeSource.h>
#include <vtkTransform.h>
#include <vtkTransformPolyDataFilter.h>
#include <vtkGlyph3D.h>

int main(int argc, char *argv[])
{
    setbuf( stdout, nullptr );

    // There are first four points which z = 0: {0, 0, 0}, {0, 0, 1}, {1, 0, 1}, {1, 0, 0}
    // They form a plane
    // Other points have same scene.
    double coords[8][3] = { {0, 0, 0}, {0, 0, 1}, {1, 0, 1}, {1, 0, 0},
                       {0, 1, 0}, {0, 1, 1}, {1, 1, 1}, {1, 1, 0} };
    vtkSmartPointer<vtkPoints> points =
        vtkSmartPointer<vtkPoints>::New();
    for( int i = 0; i < 8; ++i )
    {
        points->InsertPoint( i, coords[i] );
    }
    vtkSmartPointer<vtkCellArray> polys =
            vtkSmartPointer<vtkCellArray>::New();
    vtkIdType pts[6][4]={ {0,1,2,3}, {4,5,6,7}, {0,1,5,4},
                            {1,2,6,5}, {2,3,7,6}, {3,0,4,7} };
    for( int i = 0; i < 6; ++i )
    {
        polys->InsertNextCell( 4, pts[i] );
    }
    vtkSmartPointer<vtkPolyData> pd =
            vtkSmartPointer<vtkPolyData>::New();
    pd->SetPolys( polys );
    pd->SetPoints( points );
    vtkSmartPointer<vtkPolyDataMapper> mapper =
            vtkSmartPointer<vtkPolyDataMapper>::New();
    mapper->SetInputData( pd );

    vtkSmartPointer<vtkActor> surfaceActor =
        vtkSmartPointer<vtkActor>::New();
    surfaceActor->SetMapper( mapper );

    vtkSmartPointer<vtkPolyDataNormals> pdNormals =
            vtkSmartPointer<vtkPolyDataNormals>::New();
    pdNormals->SetInputData( surfaceActor->GetMapper()->GetInput() );
    pdNormals->SetSplitting( false );
    pdNormals->ComputeCellNormalsOff();
    pdNormals->Update();

    vtkPointData* ptData = pdNormals->GetOutput()->GetPointData();
    vtkDataArray* ptNormals = pdNormals->GetOutput()->GetPointData()->GetNormals();

    printf( "For points in every cell: \n" );
    printf( "GetNumberOfTuples: %d\n", ptNormals->GetNumberOfTuples() );
    for( int i = 0; i < ptNormals->GetNumberOfTuples(); ++i )
    {
        double value[3];
        ptNormals->GetTuple( i, value );
        printf( "Value: (%lf, %lf, %lf)\n", value[0], value[1], value[2] );
    }

    vtkSmartPointer<vtkConeSource> cone =
            vtkSmartPointer<vtkConeSource>::New();
    cone->SetResolution( 6 );
    vtkSmartPointer<vtkTransform> transform =
            vtkSmartPointer<vtkTransform>::New();
    transform->RotateY( 180 ); // make vertex outside
    vtkSmartPointer<vtkTransformPolyDataFilter> transformF =
            vtkSmartPointer<vtkTransformPolyDataFilter>::New();
    transformF->SetInputConnection( cone->GetOutputPort() );
    transformF->SetTransform( transform );

    vtkSmartPointer<vtkGlyph3D> glyph =
            vtkSmartPointer<vtkGlyph3D>::New();
    glyph->SetInputConnection( pdNormals->GetOutputPort() );
    glyph->SetSourceConnection( transformF->GetOutputPort() ); // source => transform => graph3D
    glyph->SetVectorModeToUseNormal();
    glyph->SetScaleModeToScaleByVector();
    glyph->SetScaleFactor( 0.1 );

    vtkSmartPointer<vtkPolyDataMapper> spikeMapper =
            vtkSmartPointer<vtkPolyDataMapper>::New();
    spikeMapper->SetInputConnection( glyph->GetOutputPort() );

    vtkSmartPointer<vtkActor> spikeActor = vtkSmartPointer<vtkActor>::New();
    spikeActor->SetMapper( spikeMapper );
    spikeActor->GetProperty()->SetColor( 0.0, 0.79, 0.34 );

    // Create the RenderWindow, Renderer and both Actors
    vtkSmartPointer<vtkRenderer> ren =
        vtkSmartPointer<vtkRenderer>::New();
    vtkSmartPointer<vtkRenderWindow> renWin =
        vtkSmartPointer<vtkRenderWindow>::New();
    renWin->AddRenderer(ren);
    vtkSmartPointer<vtkRenderWindowInteractor> iren =
        vtkSmartPointer<vtkRenderWindowInteractor>::New();
    iren->SetRenderWindow(renWin);

    // Add the actors to the renderer, set the background and size
    ren->AddActor( surfaceActor );
    ren->AddActor( spikeActor );
    ren->SetBackground(.2, .3, .4);

    renWin->Render();
    iren->Start();

    return EXIT_SUCCESS;
}

Output:

GetNumberOfTuples: 8
Value: (0.577350, 0.577350, 0.577350)
Value: (0.577350, 0.577350, -0.577350)
Value: (-0.577350, 0.577350, -0.577350)
Value: (-0.577350, 0.577350, 0.577350)
Value: (0.577350, -0.577350, 0.577350)
Value: (0.577350, -0.577350, -0.577350)
Value: (-0.577350, -0.577350, -0.577350)
Value: (-0.577350, -0.577350, 0.577350)

The vtkPolyDataNormals object will split edge and add points if don’t set Splitting false. The number of points of new polyData from vtkPolyDataNormals become 24.

    vtkSmartPointer<vtkPolyDataNormals> pdNormals =
            vtkSmartPointer<vtkPolyDataNormals>::New();
    pdNormals->SetInputData( pd );
    pdNormals->ComputeCellNormalsOff();
    pdNormals->Update();


    vtkSmartPointer<vtkPolyDataMapper> mapper =
            vtkSmartPointer<vtkPolyDataMapper>::New();
    mapper->SetInputData( pdNormals->GetOutput() );

    auto newPts = pdNormals->GetOutput()->GetPoints();
    printf( "GetNumberOfPoints: %d\n", newPts->GetNumberOfPoints() );

    vtkSmartPointer<vtkActor> surfaceActor =
        vtkSmartPointer<vtkActor>::New();
    surfaceActor->SetMapper( mapper );

    vtkPointData* ptData = pdNormals->GetOutput()->GetPointData();
    vtkDataArray* ptNormals = pdNormals->GetOutput()->GetPointData()->GetNormals();

    printf( "GetNumberOfTuples: %d\n", ptNormals->GetNumberOfTuples() );
    for( int i = 0; i < ptNormals->GetNumberOfTuples(); ++i )
    {
        double value[3];
        ptNormals->GetTuple( i, value );
        printf( "Value: (%lf, %lf, %lf)\n", value[0], value[1], value[2] );
    }

Output:

GetNumberOfPoints: 24
GetNumberOfTuples: 24
Value: (0.000000, 1.000000, 0.000000)
Value: (0.000000, 1.000000, 0.000000)
Value: (0.000000, 1.000000, 0.000000)
Value: (0.000000, 1.000000, 0.000000)
Value: (0.000000, -1.000000, 0.000000)
Value: (0.000000, -1.000000, 0.000000)
Value: (0.000000, -1.000000, 0.000000)
Value: (0.000000, -1.000000, 0.000000)
Value: (1.000000, 0.000000, 0.000000)
Value: (0.000000, 0.000000, 1.000000)
Value: (1.000000, 0.000000, 0.000000)
Value: (0.000000, 0.000000, -1.000000)
Value: (0.000000, 0.000000, -1.000000)
Value: (-1.000000, 0.000000, 0.000000)
Value: (-1.000000, 0.000000, 0.000000)
Value: (0.000000, 0.000000, 1.000000)
Value: (1.000000, 0.000000, 0.000000)
Value: (0.000000, 0.000000, 1.000000)
Value: (1.000000, 0.000000, 0.000000)
Value: (0.000000, 0.000000, -1.000000)
Value: (0.000000, 0.000000, -1.000000)
Value: (-1.000000, 0.000000, 0.000000)
Value: (-1.000000, 0.000000, 0.000000)
Value: (0.000000, 0.000000, 1.000000)


Categories: VTK

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