Casting

VTKEx/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.

Question

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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 = dynamic_cast<vtkDoubleArray*> ( 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 = dynamic_cast<vtkDoubleArray*>(
                   polydata->GetPointData()->GetArray("Distances"));
  vtkIntArray* intDistances = dynamic_cast<vtkIntArray*>(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 
  vtkvtkCommonCore
  vtkvtkCommonDataModel 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.