VTK/Examples/Cxx/Graphs/ConnectedComponents

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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.

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 = vtkIntArray::SafeDownCast(
    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;
}

Please try the new VTKExamples website.

CMakeLists.txt

cmake_minimum_required(VERSION 2.8)

PROJECT(ConnectedComponents)

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

add_executable(ConnectedComponents MACOSX_BUNDLE ConnectedComponents.cxx)

if(VTK_LIBRARIES)
  target_link_libraries(ConnectedComponents ${VTK_LIBRARIES})
else()
  target_link_libraries(ConnectedComponents vtkHybrid vtkWidgets)
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 PLEASE NOTE: Be sure to add the VTK bin directory to your path. This will resolve the VTK dll's at run time.