# PolyDataPointNormals

vtk-examples/Cxx/PolyData/PolyDataPointNormals

### Description¶

This demo adds a normal to each point in a polydata.

Question

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### Code¶

PolyDataPointNormals.cxx

#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;
}


### CMakeLists.txt¶

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}
)


### Download and Build PolyDataPointNormals¶

Click here to download PolyDataPointNormals and its CMakeLists.txt file. Once the tarball PolyDataPointNormals.tar has been downloaded and extracted,

cd PolyDataPointNormals/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:

./PolyDataPointNormals


WINDOWS USERS

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