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.

Question

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Code¶

ConnectedComponents.cxx

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

int main(int, char*[])
{
  vtkNew<vtkMutableUndirectedGraph> g;

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

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

  vtkNew<vtkBoostConnectedComponents> connectedComponents;
  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 3.12 FATAL_ERROR)

project(ConnectedComponents)

find_package(VTK COMPONENTS 
  CommonCore
  CommonDataModel
  InfovisBoostGraphAlgorithms
)

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

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.