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Casting

vtk-examples/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

If you have a question about this example, please use the VTK Discourse Forum

Code

Casting.cxx

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

int main(int, char*[])
{
  // Create points.
  vtkNew<vtkPoints> points;

  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
  vtkNew<vtkPolyData> polydata;
  polydata->SetPoints(points);

  // Add distances to each point
  vtkNew<vtkDoubleArray> distances;
  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 3.12 FATAL_ERROR)

project(Casting)

find_package(VTK COMPONENTS 
  CommonCore
  CommonDataModel
)

if (NOT VTK_FOUND)
  message(FATAL_ERROR "Casting: 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(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}
)

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.