VTK/Examples/Cxx/PolyData/PolyDataCellNormals

polydata->GetPointData()->SetNormals(PointNormalsArray);

vtkSmartPointer<vtkDoubleArray> PointNormalsRetrieved = vtkDoubleArray::SafeDownCast(polydata->GetPointData()->GetNormals());

polydata->GetCellData()->SetNormals(CellNormalsArray);

vtkSmartPointer<vtkDoubleArray> CellNormalsRetrieved = vtkDoubleArray::SafeDownCast(polydata->GetCellData()->GetNormals());

#include <vtkCellData.h>
#include <vtkCellArray.h>
#include <vtkDoubleArray.h>
#include <vtkPoints.h>
#include <vtkPolyData.h>
#include <vtkPointData.h>
#include <vtkSmartPointer.h>
 
int main(int, char *[])
{
 
  ///////// Set Point Normals ///////////
 
  //Setup point coordinates
  double x[3] = {1.0, 0.0, 0.0};
  double y[3] = {0.0, 0.0, 1.0};
  double z[3] = {0.0, 0.0, 0.0};
 
  //create 3 points and add a vertex at each point
  vtkSmartPointer<vtkPoints> points = 
      vtkSmartPointer<vtkPoints>::New();
  vtkSmartPointer<vtkCellArray> vertices = 
      vtkSmartPointer<vtkCellArray>::New();
 
  for ( unsigned int i = 0; i < 3; ++i )
    {
    //Declare a variable to store the index of the point that gets added. This behaves just like an unsigned int.
    vtkIdType pid[1];
 
    //Add a point to the polydata and save its index, which we will use to create the vertex on that point.
    pid[0] = points->InsertNextPoint ( x[i], y[i], z[i] );
 
    //create a vertex cell on the point that was just added.
    vertices->InsertNextCell ( 1,pid );
    }
 
  //add the points and vertices to a polydata
  vtkSmartPointer<vtkPolyData> polydata = 
      vtkSmartPointer<vtkPolyData>::New();
  polydata->SetPoints(points);
  polydata->SetVerts(vertices);
 
  //set vertex (cell) normals
  vtkSmartPointer<vtkDoubleArray> normalsArray = 
      vtkSmartPointer<vtkDoubleArray>::New();
  normalsArray->SetNumberOfComponents(3); //3d normals (ie x,y,z)
  normalsArray->SetNumberOfTuples(polydata->GetNumberOfPoints());
 
  //construct the normal vectors
  double cN1[3] = {1.0, 0.0, 0.0};
  double cN2[3] = {0.0, 1.0, 0.0};
  double cN3[3] = {0.0, 0.0, 1.0};
 
  //add the data to the normals array
  normalsArray->SetTuple(0, cN1) ;
  normalsArray->SetTuple(1, cN2) ;
  normalsArray->SetTuple(2, cN3) ;
 
  //add the normals to the cells in the polydata
  polydata->GetCellData()->SetNormals(normalsArray);
 
  ///////// Get cell normals ///////////
  vtkSmartPointer<vtkDoubleArray> cellNormalsRetrieved = 
      vtkDoubleArray::SafeDownCast(polydata->GetCellData()->GetNormals());
  if(cellNormalsRetrieved)
    { 
    cout << "There are " << cellNormalsRetrieved->GetNumberOfTuples() << " cell normals." << endl;
 
    for(vtkIdType i = 0; i < cellNormalsRetrieved->GetNumberOfTuples(); i++)
      {
      double cN[3];
      cellNormalsRetrieved->GetTuple(i, cN);
      cout << "Cell normal " << i << ": " << cN[0] << " " << cN[1] << " " << cN[2] << endl;
      }
    }
  else
    {
    cout << "No cell normals." << endl;
    }
 
  return EXIT_SUCCESS;
}