PolyDataPointNormals

#include <vtkCellArray.h>
#include <vtkDoubleArray.h>
#include <vtkNew.h>
#include <vtkPointData.h>
#include <vtkPoints.h>
#include <vtkPolyData.h>

#include <iostream>
#include <string>

int main(int, char*[])
{
  ///////// Set Point Normals ///////////
  // Create 3 points.
  vtkNew<vtkPoints> points;
  points->InsertNextPoint(1.0, 0.0, 0.0);
  points->InsertNextPoint(0.0, 0.0, 0.0);
  points->InsertNextPoint(0.0, 1.0, 0.0);

  // Add the points to a polydata.
  vtkNew<vtkPolyData> polydata;
  polydata->SetPoints(points);

  // Set point normals.
  vtkNew<vtkDoubleArray> pointNormalsArray;
  pointNormalsArray->SetNumberOfComponents(3); // 3d normals (ie x,y,z)
  pointNormalsArray->SetNumberOfTuples(polydata->GetNumberOfPoints());

  // Construct the normal vectors.
  double pN1[3] = {1.0, 0.0, 0.0};
  double pN2[3] = {0.0, 1.0, 0.0};
  double pN3[3] = {0.0, 0.0, 1.0};

  // Add the data to the normals array.
  pointNormalsArray->SetTuple(0, pN1);
  pointNormalsArray->SetTuple(1, pN2);
  pointNormalsArray->SetTuple(2, pN3);

  // Add the normals to the points in the polydata.
  polydata->GetPointData()->SetNormals(pointNormalsArray);

  ///////// Get Point Normals ///////////
  auto pointNormalsRetrieved =
      dynamic_cast<vtkDoubleArray*>(polydata->GetPointData()->GetNormals());
  if (pointNormalsRetrieved)
  {
    std::cout << "There are " << pointNormalsRetrieved->GetNumberOfTuples()
              << " point normals." << std::endl;

    for (vtkIdType i = 0; i < pointNormalsRetrieved->GetNumberOfTuples(); i++)
    {
      double pN[3];
      pointNormalsRetrieved->GetTuple(i, pN);
      std::cout << "Point normal " << i << ": " << pN[0] << " " << pN[1] << " "
                << pN[2] << std::endl;
    }

  } // end if(pointNormalsRetrieved)
  else
  {
    std::cout << "No point normals." << std::endl;
  }

  return EXIT_SUCCESS;
}

cmake_minimum_required(VERSION 3.12 FATAL_ERROR)

project(PolyDataPointNormals)

find_package(VTK COMPONENTS 
  CommonCore
  CommonDataModel
)

if (NOT VTK_FOUND)
  message(FATAL_ERROR "PolyDataPointNormals: Unable to find the VTK build folder.")
endif()

# Prevent a "command line is too long" failure in Windows.
set(CMAKE_NINJA_FORCE_RESPONSE_FILE "ON" CACHE BOOL "Force Ninja to use response files.")
add_executable(PolyDataPointNormals MACOSX_BUNDLE PolyDataPointNormals.cxx )
  target_link_libraries(PolyDataPointNormals PRIVATE ${VTK_LIBRARIES}
)
# vtk_module_autoinit is needed
vtk_module_autoinit(
  TARGETS PolyDataPointNormals
  MODULES ${VTK_LIBRARIES}
)

cd PolyDataPointNormals/build

cmake ..

cmake -DVTK_DIR:PATH=/home/me/vtk_build ..

make

./PolyDataPointNormals