DeleteCells

VTKEx/Cxx/PolyData/DeleteCells

Description¶

This example demonstrates how to delete a cell from a vtkPolyData. This is a three-step process: first, build upward-links from points to cells; second, mark cells for deletion; third, delete the marked cells. The first step is necessary to create a data structure suitable for efficient delete operations. Creating this data structure is computationally expensive, so it is only carried out before operations that need it, e.g. those that require changes to the topology.

Code¶

DeleteCells.cxx

#include <vtkSmartPointer.h>

#include <vtkActor.h>
#include <vtkCellArray.h>
#include <vtkLine.h>
#include <vtkPoints.h>
#include <vtkPolyData.h>
#include <vtkPolyDataMapper.h>
#include <vtkProperty.h>
#include <vtkRenderer.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>

#include <vtkNamedColors.h>

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

  vtkSmartPointer<vtkLine> line0 = 
    vtkSmartPointer<vtkLine>::New();
  line0->GetPointIds()->SetId(0, 0);
  line0->GetPointIds()->SetId(1, 1);

  vtkSmartPointer<vtkLine> line1 = 
    vtkSmartPointer<vtkLine>::New();
  line1->GetPointIds()->SetId(0, 1);
  line1->GetPointIds()->SetId(1, 2);

  vtkSmartPointer<vtkLine> line2 = 
    vtkSmartPointer<vtkLine>::New();
  line2->GetPointIds()->SetId(0, 2);
  line2->GetPointIds()->SetId(1, 3);

  vtkSmartPointer<vtkCellArray> lines =
    vtkSmartPointer<vtkCellArray>::New();
  lines->InsertNextCell(line0);
  lines->InsertNextCell(line1);
  lines->InsertNextCell(line2);

  vtkSmartPointer<vtkPolyData> polydata =
    vtkSmartPointer<vtkPolyData>::New();
  polydata->SetPoints(points);
  polydata->SetLines(lines);

  // Tell the polydata to build 'upward' links from points to cells.
  polydata->BuildLinks();
  // Mark a cell as deleted.
  polydata->DeleteCell(1);
  // Remove the marked cell.
  polydata->RemoveDeletedCells();

  // Visualize
  vtkSmartPointer<vtkNamedColors> colors =
    vtkSmartPointer<vtkNamedColors>::New();

  vtkSmartPointer<vtkPolyDataMapper> mapper =
    vtkSmartPointer<vtkPolyDataMapper>::New();
  mapper->SetInputDataObject(polydata);

  vtkSmartPointer<vtkActor> actor =
    vtkSmartPointer<vtkActor>::New();
  actor->SetMapper(mapper);
  actor->GetProperty()->SetColor(colors->GetColor3d("Peacock").GetData());
  actor->GetProperty()->SetLineWidth(4);

  vtkSmartPointer<vtkRenderer> renderer =
    vtkSmartPointer<vtkRenderer>::New();
  vtkSmartPointer<vtkRenderWindow> renderWindow =
    vtkSmartPointer<vtkRenderWindow>::New();
  renderWindow->AddRenderer(renderer);
  vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor = 
      vtkSmartPointer<vtkRenderWindowInteractor>::New();
  renderWindowInteractor->SetRenderWindow(renderWindow);
  renderer->AddActor(actor);

  renderer->SetBackground(colors->GetColor3d("Silver").GetData());
  renderWindow->Render();
  renderWindowInteractor->Start();

  return EXIT_SUCCESS;
}

CMakeLists.txt¶

cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

project(DeleteCells)

find_package(VTK COMPONENTS 
  vtkCommonColor
  vtkCommonCore
  vtkCommonDataModel
  vtkInteractionStyle
  vtkRenderingContextOpenGL2
  vtkRenderingCore
  vtkRenderingFreeType
  vtkRenderingGL2PSOpenGL2
  vtkRenderingOpenGL2 QUIET)
if (NOT VTK_FOUND)
  message("Skipping DeleteCells: ${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(DeleteCells MACOSX_BUNDLE DeleteCells.cxx )
  target_link_libraries(DeleteCells PRIVATE ${VTK_LIBRARIES})
else ()
  # include all components
  add_executable(DeleteCells MACOSX_BUNDLE DeleteCells.cxx )
  target_link_libraries(DeleteCells PRIVATE ${VTK_LIBRARIES})
  # vtk_module_autoinit is needed
  vtk_module_autoinit(
    TARGETS DeleteCells
    MODULES ${VTK_LIBRARIES}
    )
endif ()

Download and Build DeleteCells¶

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

cd DeleteCells/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:

./DeleteCells