ConnectedComponents

VTKExamples/Cxx/Graphs/ConnectedComponents

Description

This example constructs a graph with 4 vertices and 2 edges. V1 and V2 are not connected to V3 or V4. We wish to obtain all of the connected components of the graph. The output of the example is a list of component IDs. All vertices with the same ID can be reached from any vertex with the same ID.

Code

ConnectedComponents.cxx

#include <vtkSmartPointer.h>

#include <vtkBoostConnectedComponents.h>
#include <vtkDataArray.h>
#include <vtkDataSetAttributes.h>
#include <vtkGraph.h>
#include <vtkIntArray.h>
#include <vtkMutableUndirectedGraph.h>

int main ( int, char *[] )
{
  vtkSmartPointer<vtkMutableUndirectedGraph> g =
    vtkSmartPointer<vtkMutableUndirectedGraph>::New();

  vtkIdType v1 = g->AddVertex();
  vtkIdType v2 = g->AddVertex();
  vtkIdType v3 = g->AddVertex();
  vtkIdType v4 = g->AddVertex();

  g->AddEdge ( v1, v2 );
  g->AddEdge ( v3, v4 );

  vtkSmartPointer<vtkBoostConnectedComponents> connectedComponents =
    vtkSmartPointer<vtkBoostConnectedComponents>::New();
  connectedComponents->SetInput(g);
  connectedComponents->Update();

  vtkGraph* outputGraph = connectedComponents->GetOutput();

  vtkIntArray* components = dynamic_cast<vtkIntArray*>(
    outputGraph->GetVertexData()->GetArray("component"));

  for(vtkIdType i = 0; i < components->GetNumberOfTuples(); i++)
  {
    int val = components->GetValue(i);
    std::cout << val << std::endl;
  }

  return EXIT_SUCCESS;
}

CMakeLists.txt

cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

project(ConnectedComponents)

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

Download and Build ConnectedComponents

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

cd ConnectedComponents/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:

./ConnectedComponents

WINDOWS USERS

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