# DiscreteMarchingCubes

VTKExamples/Cxx/Modelling/DiscreteMarchingCubes

### Description

Creates surfaces from labelled data. Volume data does not always contain samples of continuous data. A volume may contain discrete integer values, often the result of segmentation. vtkDiscreteMarchingCubes creates surfaces from these segmented volumes using a modified marching cubes algorithm. The algorithm generates one or more models representing the boundaries between the specified label and the adjacent structures. One or more label values must be specified to generate the models. The boundary positions are always defined to be half-way between adjacent voxels.

Seealso

SmoothDiscreteMarchingCubes produces smooth models.

### Code

DiscreteMarchingCubes.cxx

    #include <vtkSmartPointer.h>
    #include <vtkDiscreteMarchingCubes.h>

    #include <vtkMath.h>
    #include <vtkImageData.h>
    #include <vtkSphere.h>
    #include <vtkSampleFunction.h>
    #include <vtkImageThreshold.h>
    #include <vtkImageMathematics.h>
    #include <vtkPolyDataMapper.h>

    #include <vtkRenderer.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkActor.h>
    #include <vtkLookupTable.h>

    #include <vtkNamedColors.h>

    static vtkSmartPointer<vtkLookupTable> MakeColors (unsigned int n);
    static vtkSmartPointer<vtkImageData> MakeBlob(int n, double radius);

    int main (int /*argc*/, char * /* argv */ [])
    {
      int n = 20;
      double radius = 8;

      vtkSmartPointer<vtkImageData> blob = MakeBlob(n, radius);

      vtkSmartPointer<vtkDiscreteMarchingCubes> discrete =
        vtkSmartPointer<vtkDiscreteMarchingCubes>::New();
      discrete->SetInputData(blob);
      discrete->GenerateValues(n, 1, n);

      vtkSmartPointer<vtkLookupTable> lut = MakeColors(n);

      vtkSmartPointer<vtkPolyDataMapper> mapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      mapper->SetInputConnection(discrete->GetOutputPort());
      mapper->SetLookupTable(lut);
      mapper->SetScalarRange(0, lut->GetNumberOfColors());

    // Create the RenderWindow, Renderer and both Actors
    //
      vtkSmartPointer<vtkRenderer> ren1 =
        vtkSmartPointer<vtkRenderer>::New();
      vtkSmartPointer<vtkRenderWindow> renWin =
        vtkSmartPointer<vtkRenderWindow>::New();
      renWin->AddRenderer(ren1);
      vtkSmartPointer<vtkRenderWindowInteractor> iren =
        vtkSmartPointer<vtkRenderWindowInteractor>::New();
      iren->SetRenderWindow(renWin);

      vtkSmartPointer<vtkActor> actor =
        vtkSmartPointer<vtkActor>::New();
      actor->SetMapper(mapper);

      ren1->AddActor(actor);

      vtkSmartPointer<vtkNamedColors> colors =
        vtkSmartPointer<vtkNamedColors>::New();
      ren1->SetBackground(colors->GetColor3d("Burlywood").GetData());

      renWin->Render();

      iren->Start();

      return EXIT_SUCCESS;
    }

    vtkSmartPointer<vtkImageData> MakeBlob(int n, double radius)
    {
      vtkSmartPointer<vtkMath> math =
        vtkSmartPointer<vtkMath>::New();

      vtkSmartPointer<vtkImageData> blobImage =
        vtkSmartPointer<vtkImageData>::New();

      for (int i = 0; i < n; ++i)
      {
        vtkSmartPointer<vtkSphere> sphere =
          vtkSmartPointer<vtkSphere>::New();
        sphere->SetRadius(radius);
        double maxR = 50 - 2.0 * radius;
        sphere->SetCenter(int(math->Random(-maxR, maxR)),
                          int(math->Random(-maxR, maxR)), int(math->Random(-maxR, maxR)));

        vtkSmartPointer<vtkSampleFunction> sampler =
          vtkSmartPointer<vtkSampleFunction>::New();
        sampler->SetImplicitFunction(sphere);
        sampler->SetOutputScalarTypeToFloat();
        sampler->SetSampleDimensions(100, 100, 100);
        sampler->SetModelBounds(-50, 50, -50, 50, -50, 50);

        vtkSmartPointer<vtkImageThreshold> thres =
          vtkSmartPointer<vtkImageThreshold>::New();
        thres->SetInputConnection(sampler->GetOutputPort());
        thres->ThresholdByLower(radius * radius);
        thres->ReplaceInOn();
        thres->ReplaceOutOn();
        thres->SetInValue(i + 1);
        thres->SetOutValue(0);
        thres->Update();
        if (i == 0)
        {
          blobImage->DeepCopy(thres->GetOutput());
        }

        vtkSmartPointer<vtkImageMathematics>     maxValue =
          vtkSmartPointer<vtkImageMathematics>::New();
        maxValue->SetInputData(0, blobImage);
        maxValue->SetInputData(1, thres->GetOutput());
        maxValue->SetOperationToMax();
        maxValue->Modified();
        maxValue->Update();

        blobImage->DeepCopy(maxValue->GetOutput());
      }
      return blobImage;
    }

    // Generate some random colors
    vtkSmartPointer<vtkLookupTable> MakeColors (unsigned int n)
    {
      vtkSmartPointer<vtkLookupTable> lut =
        vtkSmartPointer<vtkLookupTable>::New();
      lut->SetNumberOfColors(n);
      lut->SetTableRange(0, n - 1);
      lut->SetScaleToLinear();
      lut->Build();
      lut->SetTableValue(0, 0, 0, 0, 1);

      vtkSmartPointer<vtkMath> math =
        vtkSmartPointer<vtkMath>::New();
      math->RandomSeed(5071);
      for ( int i = 1; i < static_cast<int>(n); ++i)
      {
        lut->SetTableValue(i, math->Random(.4, 1),
                           math->Random(.4, 1), math->Random(.4, 1), 1.0);
      }
      return lut;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

    project(DiscreteMarchingCubes)

    find_package(VTK COMPONENTS
      vtkCommonColor
      vtkCommonCore
      vtkCommonDataModel
      vtkFiltersGeneral
      vtkImagingCore
      vtkImagingHybrid
      vtkImagingMath
      vtkInteractionStyle
      vtkRenderingCore
      vtkRenderingFreeType
      vtkRenderingOpenGL2 QUIET)
    if (NOT VTK_FOUND)
      message("Skipping DiscreteMarchingCubes: ${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(DiscreteMarchingCubes MACOSX_BUNDLE DiscreteMarchingCubes.cxx )
      target_link_libraries(DiscreteMarchingCubes PRIVATE ${VTK_LIBRARIES})
    else ()
      # include all components
      add_executable(DiscreteMarchingCubes MACOSX_BUNDLE DiscreteMarchingCubes.cxx )
      target_link_libraries(DiscreteMarchingCubes PRIVATE ${VTK_LIBRARIES})
      # vtk_module_autoinit is needed
      vtk_module_autoinit(
        TARGETS DiscreteMarchingCubes
        MODULES ${VTK_LIBRARIES}
        )
    endif ()

### Download and Build DiscreteMarchingCubes

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

    cd DiscreteMarchingCubes/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:

    ./DiscreteMarchingCubes

WINDOWS USERS

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