VTK/Examples/Cxx/PolyData/ThresholdCells

ThresholdCells.cxx

#include <vtkVersion.h>
#include <vtkIntArray.h>
#include <vtkCellData.h>
#include <vtkTriangle.h>
#include <vtkCellArray.h>
#include <vtkPoints.h>
#include <vtkPolyData.h>
#include <vtkUnstructuredGrid.h>
#include <vtkPointData.h>
#include <vtkSmartPointer.h>
#include <vtkThreshold.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);

  // Create three triangles
  vtkSmartPointer<vtkTriangle> triangle0 = 
    vtkSmartPointer<vtkTriangle>::New();
  triangle0->GetPointIds()->SetId ( 0, 0 );
  triangle0->GetPointIds()->SetId ( 1, 1 );
  triangle0->GetPointIds()->SetId ( 2, 2 );
  
  vtkSmartPointer<vtkTriangle> triangle1 = 
    vtkSmartPointer<vtkTriangle>::New();
  triangle1->GetPointIds()->SetId ( 0, 1 );
  triangle1->GetPointIds()->SetId ( 1, 2 );
  triangle1->GetPointIds()->SetId ( 2, 3 );
  
  vtkSmartPointer<vtkTriangle> triangle2 = 
    vtkSmartPointer<vtkTriangle>::New();
  triangle2->GetPointIds()->SetId ( 0, 2 );
  triangle2->GetPointIds()->SetId ( 1, 3 );
  triangle2->GetPointIds()->SetId ( 2, 4 );

  // Add the triangles to a cell array
  vtkSmartPointer<vtkCellArray> triangles = 
    vtkSmartPointer<vtkCellArray>::New();
  triangles->InsertNextCell ( triangle0 );
  triangles->InsertNextCell ( triangle1 );
  triangles->InsertNextCell ( triangle2 );
  
  // Setup index array
  vtkSmartPointer<vtkIntArray> index = 
    vtkSmartPointer<vtkIntArray>::New();
  index->SetNumberOfComponents(1);
  index->SetName("index");
  index->InsertNextValue(0);
  index->InsertNextValue(1);
  index->InsertNextValue(2);
  
  // Add points, cells and index array to a polydata
  vtkSmartPointer<vtkPolyData> polydata = 
    vtkSmartPointer<vtkPolyData>::New();
  polydata->SetPoints(points);
  polydata->SetPolys(triangles);
  polydata->GetCellData()->AddArray(index);
  
  std::cout << "There are " << polydata->GetNumberOfCells() 
            << " cells before thresholding." << std::endl;
  
  vtkSmartPointer<vtkThreshold> threshold = 
    vtkSmartPointer<vtkThreshold>::New();
#if VTK_MAJOR_VERSION <= 5
  threshold->SetInput(polydata);
#else
  threshold->SetInputData(polydata);
#endif
  threshold->ThresholdByLower(1);
  // doesn't work because the array is not added as SCALARS, i.e. via SetScalars
  // threshold->SetInputArrayToProcess(0, 0, 0, vtkDataObject::FIELD_ASSOCIATION_CELLS, vtkDataSetAttributes::SCALARS);
  // use like this:
  threshold->SetInputArrayToProcess(0, 0, 0, vtkDataObject::FIELD_ASSOCIATION_CELLS, "index");
  threshold->Update();
  
  vtkUnstructuredGrid* thresholdedPolydata = threshold->GetOutput();
  std::cout << "There are " << thresholdedPolydata->GetNumberOfCells() 
            << " cells after thresholding." << std::endl;
  
  return EXIT_SUCCESS;
}

Please try the new VTKExamples website.

CMakeLists.txt

cmake_minimum_required(VERSION 2.8)

PROJECT(ThresholdCells)

find_package(VTK REQUIRED)
include(${VTK_USE_FILE})

add_executable(ThresholdCells MACOSX_BUNDLE ThresholdCells.cxx)

if(VTK_LIBRARIES)
  target_link_libraries(ThresholdCells ${VTK_LIBRARIES})
else()
  target_link_libraries(ThresholdCells vtkHybrid vtkWidgets)
endif()

Download and Build ThresholdCells

Click here to download ThresholdCells. and its CMakeLists.txt file.

Once the tarball ThresholdCells.tar has been downloaded and extracted,

cd ThresholdCells/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:

./ThresholdCells

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