# CellLocator

VTKExamples/Cxx/PolyData/CellLocator

### Description

This example creates a sphere and then finds the closest point on the sphere to a test point.

### Code

CellLocator.cxx

    #include <vtkSmartPointer.h>
    #include <vtkSphereSource.h>
    #include <vtkCellLocator.h>

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

      // Create the tree
      vtkSmartPointer<vtkCellLocator> cellLocator =
        vtkSmartPointer<vtkCellLocator>::New();
      cellLocator->SetDataSet(sphereSource->GetOutput());
      cellLocator->BuildLocator();

      double testPoint[3] = {2.0, 0.0, 0.0};

      //Find the closest points to TestPoint
      double closestPoint[3];//the coordinates of the closest point will be returned here
      double closestPointDist2; //the squared distance to the closest point will be returned here
      vtkIdType cellId; //the cell id of the cell containing the closest point will be returned here
      int subId; //this is rarely used (in triangle strips only, I believe)
      cellLocator->FindClosestPoint(testPoint, closestPoint, cellId, subId, closestPointDist2);

      std::cout << "Coordinates of closest point: " << closestPoint[0] << " " << closestPoint[1] << " " << closestPoint[2] << std::endl;
      std::cout << "Squared distance to closest point: " << closestPointDist2 << std::endl;
      std::cout << "CellId: " << cellId << std::endl;

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

    project(CellLocator)

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

### Download and Build CellLocator

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

    cd CellLocator/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:

    ./CellLocator

WINDOWS USERS

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