# PolyDataCellNormals

VTKExamples/Cxx/PolyData/PolyDataCellNormals

### Description¶

This example shows how to add normals to vertices. This is identical to adding normals to any type of cells. The only difference from [Normals to/from a Polydata]]([Add/Get) is

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

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

are changed to

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

and

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

Question

### Code¶

PolyDataCellNormals.cxx

#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 =
dynamic_cast<vtkDoubleArray*>(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;
}


### CMakeLists.txt¶

cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

project(PolyDataCellNormals)

find_package(VTK COMPONENTS
vtkCommonCore
vtkCommonDataModel QUIET)
if (NOT VTK_FOUND)
message("Skipping PolyDataCellNormals: ${VTK_NOT_FOUND_MESSAGE}") return () endif() message (STATUS "VTK_VERSION:${VTK_VERSION}")
if (VTK_VERSION VERSION_LESS "8.90.0")
# old system
include(${VTK_USE_FILE}) add_executable(PolyDataCellNormals MACOSX_BUNDLE PolyDataCellNormals.cxx ) target_link_libraries(PolyDataCellNormals PRIVATE${VTK_LIBRARIES})
else ()
# include all components
target_link_libraries(PolyDataCellNormals PRIVATE ${VTK_LIBRARIES}) # vtk_module_autoinit is needed vtk_module_autoinit( TARGETS PolyDataCellNormals MODULES${VTK_LIBRARIES}
)
endif ()


cd PolyDataCellNormals/build


If VTK is installed:

cmake ..


If VTK is not installed but compiled on your system, you will need to specify the path to your VTK build:

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


Build the project:

make


and run it:

./PolyDataCellNormals


WINDOWS USERS

Be sure to add the VTK bin directory to your path. This will resolve the VTK dll's at run time.