# CellPointNeighbors

VTKExamples/Cxx/PolyData/CellPointNeighbors

### Description

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

### Code

CellPointNeighbors.cxx

    #include <vtkVersion.h>
    #include <vtkSmartPointer.h>
    #include <vtkSphereSource.h>
    #include <vtkPolyData.h>
    #include <vtkIdList.h>
    #include <vtkCell.h>
    #include <vtkTriangleFilter.h>
    #include <vtkDataSetMapper.h>
    #include <vtkActor.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderer.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkIdTypeArray.h>
    #include <vtkSelectionNode.h>
    #include <vtkSelection.h>
    #include <vtkExtractSelection.h>
    #include <vtkProperty.h>

    #include <list>

    int main(int, char *[])
    {
      //Create a sphere
      vtkSmartPointer<vtkSphereSource> sphereSource =
          vtkSmartPointer<vtkSphereSource>::New();
      sphereSource->Update();

      vtkSmartPointer<vtkTriangleFilter> triangleFilter =
        vtkSmartPointer<vtkTriangleFilter>::New();
      triangleFilter->SetInputConnection(sphereSource->GetOutputPort());
      triangleFilter->Update();

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

      vtkSmartPointer<vtkIdList> cellPointIds =
        vtkSmartPointer<vtkIdList>::New();
      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 vertice of the cell, we calculate which cells uses that point.
       So if we make this, for each vertice, we have all the neighbors.
       In the case we use ''cellPointIds'' as a parameter of ''GeteCellNeighbors'',
       we will obtain an empty set. 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++)
      {
        vtkSmartPointer<vtkIdList> idList =
          vtkSmartPointer<vtkIdList>::New();
        idList->InsertNextId(cellPointIds->GetId(i));

        //get the neighbors of the cell
        vtkSmartPointer<vtkIdList> neighborCellIds =
          vtkSmartPointer<vtkIdList>::New();

        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(std::list<vtkIdType>::iterator it1 = neighbors.begin(); it1 != neighbors.end(); it1++)
      {
        std::cout << " " << *it1;
      }
      std::cout << std::endl;

      vtkSmartPointer<vtkDataSetMapper> sphereMapper =
        vtkSmartPointer<vtkDataSetMapper>::New();
      sphereMapper->SetInputConnection(sphereSource->GetOutputPort());
      vtkSmartPointer<vtkActor> sphereActor =
        vtkSmartPointer<vtkActor>::New();
      sphereActor->SetMapper(sphereMapper);
      sphereActor->GetProperty()->SetEdgeColor(0, 0, 0);
      sphereActor->GetProperty()->EdgeVisibilityOn();

      vtkSmartPointer<vtkDataSetMapper> mainCellMapper =
        vtkSmartPointer<vtkDataSetMapper>::New();

      vtkSmartPointer<vtkDataSetMapper> neighborCellsMapper =
        vtkSmartPointer<vtkDataSetMapper>::New();

      // Create a dataset with the cell of interest
      {
        vtkSmartPointer<vtkIdTypeArray> ids =
            vtkSmartPointer<vtkIdTypeArray>::New();
        ids->SetNumberOfComponents(1);
        ids->InsertNextValue(cellId);

        vtkSmartPointer<vtkSelectionNode> selectionNode =
          vtkSmartPointer<vtkSelectionNode>::New();
        selectionNode->SetFieldType(vtkSelectionNode::CELL);
        selectionNode->SetContentType(vtkSelectionNode::INDICES);
        selectionNode->SetSelectionList(ids);

        vtkSmartPointer<vtkSelection> selection =
            vtkSmartPointer<vtkSelection>::New();
        selection->AddNode(selectionNode);

        vtkSmartPointer<vtkExtractSelection> extractSelection =
            vtkSmartPointer<vtkExtractSelection>::New();
        extractSelection->SetInputConnection(0, sphereSource->GetOutputPort());
    #if VTK_MAJOR_VERSION <= 5
        extractSelection->SetInput(1, selection);
    #else
        extractSelection->SetInputData(1, selection);
    #endif
        extractSelection->Update();

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

      }

      vtkSmartPointer<vtkActor> mainCellActor =
        vtkSmartPointer<vtkActor>::New();
      mainCellActor->SetMapper(mainCellMapper);
      mainCellActor->GetProperty()->SetColor(1,0,0);

      // Create a dataset with the neighbor cells
      {
        vtkSmartPointer<vtkIdTypeArray> ids =
            vtkSmartPointer<vtkIdTypeArray>::New();
        ids->SetNumberOfComponents(1);
        for(std::list<vtkIdType>::iterator it1 = neighbors.begin(); it1 != neighbors.end(); it1++)
        {
          ids->InsertNextValue(*it1);
        }

        vtkSmartPointer<vtkSelectionNode> selectionNode =
          vtkSmartPointer<vtkSelectionNode>::New();
        selectionNode->SetFieldType(vtkSelectionNode::CELL);
        selectionNode->SetContentType(vtkSelectionNode::INDICES);
        selectionNode->SetSelectionList(ids);

        vtkSmartPointer<vtkSelection> selection =
            vtkSmartPointer<vtkSelection>::New();
        selection->AddNode(selectionNode);

        vtkSmartPointer<vtkExtractSelection> extractSelection =
            vtkSmartPointer<vtkExtractSelection>::New();
        extractSelection->SetInputConnection(0, sphereSource->GetOutputPort());
    #if VTK_MAJOR_VERSION <= 5
        extractSelection->SetInput(1, selection);
    #else
        extractSelection->SetInputData(1, selection);
    #endif
        extractSelection->Update();

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

      }

      vtkSmartPointer<vtkActor> neighborCellsActor =
        vtkSmartPointer<vtkActor>::New();
      neighborCellsActor->SetMapper(neighborCellsMapper);
      neighborCellsActor->GetProperty()->SetColor(0,1,0);

      //Create a renderer, render window, and interactor
      vtkSmartPointer<vtkRenderer> renderer =
        vtkSmartPointer<vtkRenderer>::New();
      vtkSmartPointer<vtkRenderWindow> renderWindow =
        vtkSmartPointer<vtkRenderWindow>::New();
      renderWindow->AddRenderer(renderer);
      vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
        vtkSmartPointer<vtkRenderWindowInteractor>::New();
      renderWindowInteractor->SetRenderWindow(renderWindow);

      //Add the actors to the scene
      renderer->AddActor(sphereActor);
      renderer->AddActor(mainCellActor);
      renderer->AddActor(neighborCellsActor);
      renderer->SetBackground(.3, .2, .1); // Background color dark red

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

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 2.8)

    PROJECT(CellPointNeighbors)

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

    add_executable(CellPointNeighbors MACOSX_BUNDLE CellPointNeighbors.cxx)

    target_link_libraries(CellPointNeighbors ${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 PLEASE NOTE: Be sure to add the VTK bin directory to your path. This will resolve the VTK dll's at run time.