Skip to content

CellPointNeighbors

vtk-examples/Cxx/PolyData/CellPointNeighbors


Description

Determine which cells share at least a single point with a specified cell.

Question

If you have a question about this example, please use the VTK Discourse Forum

Code

CellPointNeighbors.cxx

#include <vtkActor.h>
#include <vtkDataSetMapper.h>
#include <vtkExtractSelection.h>
#include <vtkIdList.h>
#include <vtkIdTypeArray.h>
#include <vtkNamedColors.h>
#include <vtkNew.h>
#include <vtkProperty.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkRenderer.h>
#include <vtkSelection.h>
#include <vtkSelectionNode.h>
#include <vtkSphereSource.h>
#include <vtkTriangleFilter.h>

#include <list>

int main(int, char*[])
{
  // Create a sphere.
  vtkNew<vtkSphereSource> sphereSource;
  sphereSource->Update();

  vtkNew<vtkTriangleFilter> triangleFilter;
  triangleFilter->SetInputConnection(sphereSource->GetOutputPort());
  triangleFilter->Update();

  // Find all cells connected to point 0.
  vtkIdType cellId = 0;

  vtkNew<vtkIdList> cellPointIds;
  triangleFilter->GetOutput()->GetCellPoints(cellId, cellPointIds);

  // Neighbor cells may be listed multiple times.
  // Use std::set instead of std::list if you want a unique list of neighbors.
  std::list<vtkIdType> neighbors;

  /* For each vertex of the cell, we calculate which cells use that point.
   So if we do this for each vertex, we have all the neighbors.
   In the case of using "cellPointIds" as a parameter of "GetCellNeighbors",
   we will obtain an empty set. This is because the only cell that is using that
   set of points is the current one. That is why we have to make each vertice at
   time.*/

  for (vtkIdType i = 0; i < cellPointIds->GetNumberOfIds(); i++)
  {
    vtkNew<vtkIdList> idList;
    idList->InsertNextId(cellPointIds->GetId(i));

    // Get the neighbors of the cell.
    vtkNew<vtkIdList> neighborCellIds;

    triangleFilter->GetOutput()->GetCellNeighbors(cellId, idList,
                                                  neighborCellIds);

    for (vtkIdType j = 0; j < neighborCellIds->GetNumberOfIds(); j++)
    {
      neighbors.push_back(neighborCellIds->GetId(j));
    }
  }

  std::cout << "Point neighbor ids are: " << std::endl;

  for (auto it1 = neighbors.begin(); it1 != neighbors.end(); ++it1)
  {
    std::cout << " " << *it1;
  }
  std::cout << std::endl;

  vtkNew<vtkNamedColors> colors;

  vtkNew<vtkDataSetMapper> sphereMapper;
  sphereMapper->SetInputConnection(sphereSource->GetOutputPort());
  sphereMapper->SetResolveCoincidentTopologyToPolygonOffset();

  vtkNew<vtkActor> sphereActor;
  sphereActor->SetMapper(sphereMapper);
  sphereActor->GetProperty()->SetEdgeColor(
      colors->GetColor3d("Lamp_Black").GetData());
  sphereActor->GetProperty()->EdgeVisibilityOn();
  sphereActor->GetProperty()->SetLineWidth(3);

  vtkNew<vtkDataSetMapper> mainCellMapper;

  vtkNew<vtkDataSetMapper> neighborCellsMapper;

  // Create a dataset with the cell of interest.
  {
    vtkNew<vtkIdTypeArray> ids;
    ids->SetNumberOfComponents(1);
    ids->InsertNextValue(cellId);

    vtkNew<vtkSelectionNode> selectionNode;
    selectionNode->SetFieldType(vtkSelectionNode::CELL);
    selectionNode->SetContentType(vtkSelectionNode::INDICES);
    selectionNode->SetSelectionList(ids);

    vtkNew<vtkSelection> selection;
    selection->AddNode(selectionNode);

    vtkNew<vtkExtractSelection> extractSelection;
    extractSelection->SetInputConnection(0, sphereSource->GetOutputPort());
    extractSelection->SetInputData(1, selection);
    extractSelection->Update();

    mainCellMapper->SetInputConnection(extractSelection->GetOutputPort());
  }

  vtkNew<vtkActor> mainCellActor;
  mainCellActor->SetMapper(mainCellMapper);
  mainCellActor->GetProperty()->SetColor(
      colors->GetColor3d("Tomato").GetData());

  // Create a dataset with the neighbor cells.
  {
    vtkNew<vtkIdTypeArray> ids;
    ids->SetNumberOfComponents(1);
    for (auto it1 = neighbors.begin(); it1 != neighbors.end(); ++it1)
    {
      ids->InsertNextValue(*it1);
    }

    vtkNew<vtkSelectionNode> selectionNode;
    selectionNode->SetFieldType(vtkSelectionNode::CELL);
    selectionNode->SetContentType(vtkSelectionNode::INDICES);
    selectionNode->SetSelectionList(ids);

    vtkNew<vtkSelection> selection;
    selection->AddNode(selectionNode);

    vtkNew<vtkExtractSelection> extractSelection;
    extractSelection->SetInputConnection(0, sphereSource->GetOutputPort());
    extractSelection->SetInputData(1, selection);
    extractSelection->Update();

    neighborCellsMapper->SetInputConnection(extractSelection->GetOutputPort());
  }

  vtkNew<vtkActor> neighborCellsActor;
  neighborCellsActor->SetMapper(neighborCellsMapper);
  neighborCellsActor->GetProperty()->SetColor(
      colors->GetColor3d("Mint").GetData());

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

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

  // Add the actors to the scene.
  renderer->AddActor(sphereActor);
  renderer->AddActor(mainCellActor);
  renderer->AddActor(neighborCellsActor);
  renderer->SetBackground(colors->GetColor3d("SlateGray").GetData());

  // Render and interact.
  renderWindow->SetSize(640, 480);
  renderWindow->Render();
  renderWindowInteractor->Start();

  return EXIT_SUCCESS;
}

CMakeLists.txt

cmake_minimum_required(VERSION 3.12 FATAL_ERROR)

project(CellPointNeighbors)

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

if (NOT VTK_FOUND)
  message(FATAL_ERROR "CellPointNeighbors: 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(CellPointNeighbors MACOSX_BUNDLE CellPointNeighbors.cxx )
  target_link_libraries(CellPointNeighbors PRIVATE ${VTK_LIBRARIES}
)
# vtk_module_autoinit is needed
vtk_module_autoinit(
  TARGETS CellPointNeighbors
  MODULES ${VTK_LIBRARIES}
)

Download and Build CellPointNeighbors

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

cd CellPointNeighbors/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:

./CellPointNeighbors

WINDOWS USERS

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