# ThresholdPoints

VTKExamples/Cxx/PolyData/ThresholdPoints

### Code

ThresholdPoints.cxx

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

    int main(int, char *[])
    {
      vtkSmartPointer<vtkPoints> points =
        vtkSmartPointer<vtkPoints>::New();
      points->InsertNextPoint(0,0,0);
      points->InsertNextPoint(1,1,1);
      points->InsertNextPoint(2,2,2);
      points->InsertNextPoint(3,3,3);
      points->InsertNextPoint(4,4,4);

      std::cout << "There are " << points->GetNumberOfPoints()
                << " points before thresholding." << std::endl;

      //setup position index
      vtkSmartPointer<vtkIntArray> index =
        vtkSmartPointer<vtkIntArray>::New();
      index->SetNumberOfComponents(1);
      index->SetName("index");
      index->InsertNextValue(0);
      index->InsertNextValue(1);
      index->InsertNextValue(2);
      index->InsertNextValue(3);
      index->InsertNextValue(4);

      vtkSmartPointer<vtkPolyData> polydata =
        vtkSmartPointer<vtkPolyData>::New();
      polydata->SetPoints(points);
      polydata->GetPointData()->AddArray(index);

      vtkSmartPointer<vtkThresholdPoints> threshold =
        vtkSmartPointer<vtkThresholdPoints>::New();
      threshold->SetInputData(polydata);
      threshold->ThresholdByLower(2);
      threshold->SetInputArrayToProcess(0, 0, 0, vtkDataObject::FIELD_ASSOCIATION_POINTS, "index");
      threshold->Update();

      //vtkPolyData* thresholdedPolydata = threshold->GetOutput();
      vtkPolyData* thresholdedPolydata = threshold->GetOutput();
      std::cout << "There are " << thresholdedPolydata->GetNumberOfPoints()
                << " points after thresholding." << std::endl;
      for(vtkIdType i = 0; i < thresholdedPolydata->GetNumberOfPoints(); i++)
      {
        double p[3];
        thresholdedPolydata->GetPoint(i,p);
        std::cout << "Point " << i << " : " << p[0] << " " << p[1] << " " << p[2] << std::endl;
      }

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

    project(ThresholdPoints)

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

### Download and Build ThresholdPoints

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

    cd ThresholdPoints/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:

    ./ThresholdPoints

WINDOWS USERS

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