# KDTreeAccessPoints

VTKExamples/Cxx/DataStructures/KDTreeAccessPoints

### Description

This example demonstrates how to build a KDTree, get its number of points, and get a point by ID.

### Code

KDTreeAccessPoints.cxx

    #include <vtkSmartPointer.h>
    #include <vtkPoints.h>
    #include <vtkCellArray.h>
    #include <vtkPolyData.h>
    #include <vtkXMLPolyDataReader.h>
    #include <vtkIdList.h>
    #include <vtkKdTree.h>
    #include <vtkDataSetCollection.h>
    #include <vtkVertexGlyphFilter.h>

    int main(int, char *[])
    {
      //Setup point coordinates
      double x[3] = {1.0, 0.0, 0.0};
      double y[3] = {0.0, 1.0, 0.0};
      double z[3] = {0.0, 0.0, 1.0};

      vtkSmartPointer<vtkPoints> points =
        vtkSmartPointer<vtkPoints>::New();
      points->InsertNextPoint (x);
      points->InsertNextPoint (y);
      points->InsertNextPoint (z);

      vtkSmartPointer<vtkPolyData> polydata =
        vtkSmartPointer<vtkPolyData>::New();
      polydata->SetPoints(points);

      //the tree needs cells, so add vertices to each point
      vtkSmartPointer<vtkVertexGlyphFilter> vertexFilter =
        vtkSmartPointer<vtkVertexGlyphFilter>::New();
      vertexFilter->SetInputData(polydata);
      vertexFilter->Update();

      //Create the tree
      vtkSmartPointer<vtkKdTree> kDTree =
        vtkSmartPointer<vtkKdTree>::New();
      kDTree->AddDataSet(vertexFilter->GetOutput());
      kDTree->BuildLocator();

      //get the number of points in the tree like this
      kDTree->GetDataSets()->InitTraversal();
      std::cout << "Number of points in tree: " << kDTree->GetDataSets()->GetNextDataSet()->GetNumberOfPoints() << std::endl;

      //or you can get the number of points in the tree like this
      std::cout << "Number of points in tree: " << kDTree->GetDataSet(0)->GetNumberOfPoints() << std::endl;

      //get the 0th point in the tree
      double p[3];
      kDTree->GetDataSet(0)->GetPoint(0,p);
      std::cout << "p: " << p[0] << " " << p[1] << " " << p[2] << std::endl;

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

    project(KDTreeAccessPoints)

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

### Download and Build KDTreeAccessPoints

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

    cd KDTreeAccessPoints/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:

    ./KDTreeAccessPoints

WINDOWS USERS

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