Get Normals Of Points By vtkPolyDataNormals

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)