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ExtractEdges

vtk-examples/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 question about this example, please use the VTK Discourse Forum

Code

ExtractEdges.cxx

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

int main(int, char*[])
{
  vtkNew<vtkNamedColors> colors;

  vtkNew<vtkSphereSource> sphereSource;
  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;

  vtkNew<vtkExtractEdges> extractEdges;
  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;
    auto line = dynamic_cast<vtkLine*>(extractEdges->GetOutput()->GetCell(i));
    std::cout << "Line " << i << " : " << *line << std::endl;
  }

  // Visualize the edges

  // Create a mapper and actor
  vtkNew<vtkPolyDataMapper> mapper;
  mapper->SetInputConnection(extractEdges->GetOutputPort());
  vtkNew<vtkActor> actor;
  actor->SetMapper(mapper);
  actor->GetProperty()->SetColor(colors->GetColor3d("Gold").GetData());

  // Create a renderer, render window, and interactor
  vtkNew<vtkRenderer> renderer;
  vtkNew<vtkRenderWindow> renderWindow;
  renderWindow->AddRenderer(renderer);
  renderWindow->SetWindowName("ExtractEdges");

  vtkNew<vtkRenderWindowInteractor> renderWindowInteractor;
  renderWindowInteractor->SetRenderWindow(renderWindow);

  // Add the actor to the scene
  renderer->AddActor(actor);
  renderer->SetBackground(
      colors->GetColor3d("RoyalBlue").GetData()); // Background color white

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

  return EXIT_SUCCESS;
}

CMakeLists.txt

cmake_minimum_required(VERSION 3.12 FATAL_ERROR)

project(ExtractEdges)

find_package(VTK COMPONENTS 
  CommonColor
  CommonCore
  CommonDataModel
  FiltersCore
  FiltersSources
  InteractionStyle
  RenderingContextOpenGL2
  RenderingCore
  RenderingFreeType
  RenderingGL2PSOpenGL2
  RenderingOpenGL2
  QUIET
)

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

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.