ExtractEdges

VTKExamples/Cxx/Meshes/ExtractEdges


Description

This example shows how to extract the edges from a PolyData. In this case, we convert a sphere into a wireframe sphere. We demonstrate how to traverse the resulting edges.

Other Languages

See (CSharp)

Question

If you have a simple question about this example contact us at VTKExamplesProject If your question is more complex and may require extended discussion, please use the VTK Discourse Forum

Code

ExtractEdges.cxx

#include <vtkSmartPointer.h>
#include <vtkPolyData.h>
#include <vtkExtractEdges.h>
#include <vtkSphereSource.h>
#include <vtkCellArray.h>
#include <vtkPoints.h>
#include <vtkPolyDataMapper.h>
#include <vtkActor.h>
#include <vtkRenderWindow.h>
#include <vtkRenderer.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkLine.h>

int main(int, char *[])
{
  vtkSmartPointer<vtkSphereSource> sphereSource =
    vtkSmartPointer<vtkSphereSource>::New();
  sphereSource->Update();

  std::cout << "Sphere" << endl << "----------" << endl;
  std::cout << "There are " << sphereSource->GetOutput()->GetNumberOfCells() << " cells." << std::endl;
  std::cout << "There are " << sphereSource->GetOutput()->GetNumberOfPoints() << " points." << std::endl;

  vtkSmartPointer<vtkExtractEdges> extractEdges =
    vtkSmartPointer<vtkExtractEdges>::New();
  extractEdges->SetInputConnection(sphereSource->GetOutputPort());
  extractEdges->Update();

  vtkCellArray* lines= extractEdges->GetOutput()->GetLines();
  vtkPoints* points = extractEdges->GetOutput()->GetPoints();

  std::cout << std::endl << "Edges" << endl << "----------" << std::endl;
  std::cout << "There are " << lines->GetNumberOfCells() << " cells." << std::endl;
  std::cout << "There are " << points->GetNumberOfPoints() << " points." << std::endl;

  // Traverse all of the edges
  for(vtkIdType i = 0; i < extractEdges->GetOutput()->GetNumberOfCells(); i++)
  {
    //std::cout << "Type: " << extractEdges->GetOutput()->GetCell(i)->GetClassName() << std::endl;
    vtkSmartPointer<vtkLine> line = dynamic_cast<vtkLine*>(extractEdges->GetOutput()->GetCell(i));
    std::cout << "Line " << i << " : " << *line << std::endl;
  }

  // Visualize the edges

  // Create a mapper and actor
  vtkSmartPointer<vtkPolyDataMapper> mapper =
    vtkSmartPointer<vtkPolyDataMapper>::New();
  mapper->SetInputConnection(extractEdges->GetOutputPort());
  vtkSmartPointer<vtkActor> actor =
    vtkSmartPointer<vtkActor>::New();
  actor->SetMapper(mapper);

  // Create a renderer, render window, and interactor
  vtkSmartPointer<vtkRenderer> renderer =
    vtkSmartPointer<vtkRenderer>::New();
  vtkSmartPointer<vtkRenderWindow> renderWindow =
    vtkSmartPointer<vtkRenderWindow>::New();
  renderWindow->AddRenderer(renderer);
  vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
    vtkSmartPointer<vtkRenderWindowInteractor>::New();
  renderWindowInteractor->SetRenderWindow(renderWindow);

  // Add the actor to the scene
  renderer->AddActor(actor);
  renderer->SetBackground(1,1,1); // Background color white

  // Render and interact
  renderWindow->Render();
  renderWindowInteractor->Start();

  return EXIT_SUCCESS;
}

CMakeLists.txt

cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

project(ExtractEdges)

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

Download and Build ExtractEdges

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

cd ExtractEdges/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:

./ExtractEdges

WINDOWS USERS

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