# Casting

VTKExamples/Cxx/PolyData/Casting

### Description

This example creates a polydata object with 3 points and attaches a distance value to each point. To retrieve the array from the polydata, we have to use a SafeDownCast to the type that we want. This is necessary because to keep things as general as possible the polydata will return an abstract array class.

### Code

Casting.cxx

    #include <vtkSmartPointer.h>
    #include <vtkDoubleArray.h>
    #include <vtkIntArray.h>
    #include <vtkPoints.h>
    #include <vtkPolyData.h>
    #include <vtkPointData.h>

    int main(int, char *[])
    {
      // Create points
      vtkSmartPointer<vtkPoints> points =
        vtkSmartPointer<vtkPoints>::New();

      unsigned int numberOfPoints = 3;
      points->InsertNextPoint ( 0.0, 0.0, 0.0 );
      points->InsertNextPoint ( 1.0, 0.0, 0.0 );
      points->InsertNextPoint ( 0.0, 1.0, 0.0 );

      // Add the points to a polydata
      vtkSmartPointer<vtkPolyData> polydata =
        vtkSmartPointer<vtkPolyData>::New();
      polydata->SetPoints ( points );

      // Add distances to each point
      vtkSmartPointer<vtkDoubleArray> distances =
        vtkSmartPointer<vtkDoubleArray>::New();
      distances->SetNumberOfComponents(1);
      distances->SetName("Distances");

      distances->InsertNextValue(1.1);
      distances->InsertNextValue(2.2);
      distances->InsertNextValue(3.3);

      polydata->GetPointData()->AddArray ( distances );

      // Get the distances from the polydata
      vtkDoubleArray* array = vtkDoubleArray::SafeDownCast ( polydata->GetPointData()->GetArray ( "Distances" ) );

      if ( array )
      {
        for ( unsigned int i = 0; i < numberOfPoints; i++ )
        {
          double dist;
          dist = array->GetValue ( i );
          std::cout << "Distance: " << dist << std::endl;
        }
      }

      // Cast the double distances to ints
      vtkDoubleArray* doubleDistances = vtkDoubleArray::SafeDownCast(
                       polydata->GetPointData()->GetArray("Distances"));
      vtkIntArray* intDistances = vtkIntArray::SafeDownCast(doubleDistances);

      if(intDistances)
      {
        for(unsigned int i = 0; i < numberOfPoints; i++)
        {
          int dist;
          dist = intDistances->GetValue ( i );
          std::cout << "Distance: " << dist << std::endl;
        }
      }
      else
      {
        std::cout << "invalid cast." << std::endl;
      }

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

    project(Casting)

    find_package(VTK COMPONENTS
      vtkCommonCore
      vtkCommonDataModel QUIET)
    if (NOT VTK_FOUND)
      message("Skipping Casting: ${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(Casting MACOSX_BUNDLE Casting.cxx )
      target_link_libraries(Casting PRIVATE ${VTK_LIBRARIES})
    else ()
      # include all components
      add_executable(Casting MACOSX_BUNDLE Casting.cxx )
      target_link_libraries(Casting PRIVATE ${VTK_LIBRARIES})
      # vtk_module_autoinit is needed
      vtk_module_autoinit(
        TARGETS Casting
        MODULES ${VTK_LIBRARIES}
        )
    endif ()

### Download and Build Casting

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

    cd Casting/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:

    ./Casting

WINDOWS USERS

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