# ExtractLargestIsosurface

VTKExamples/Cxx/Modelling/ExtractLargestIsosurface

### Description

- Contributed by: Jinyoung Hwang

This example reads a structured points dataset stored in a .vtk file and constructs a 3D model using vtkMarchingCubes. vtkPolyDataConnectivityFilter is used to extract the largest isosurface.

Data is available at:

1. test.vtk: http://web.kaist.ac.kr/~hjy/test.vtk

2. brainweb.img: http://web.kaist.ac.kr/~hjy/brainweb.img

3. brainweb.hdr: http://web.kaist.ac.kr/~hjy/brainweb.hdr

Second and third datasets can be downloaded from BrainWeb, which is free of charge in use for a research. "test.vtk" was converted from "brainweb.img" using a program by Erik Vidholm (http://www.cb.uu.se/~erik/vtk/rawToVTK.cpp).

The examples expects 2 or 3 argments:

     ExtractLargestIsosurface InputFilename Threshold (ExtractLargest)

if ExtractLargest is omitted or 1, the largest isosurface is extracted

if ExtractLargest is 0, all of the isosurfaces are extracted

Try

ExtractLargestIsosurface test.vtk 50 1

and compare the results to

ExtractLargestIsosurface test.vtk 50 0

### Code

ExtractLargestIsosurface.cxx

    #include "vtkSmartPointer.h"
    #include "vtkStructuredPointsReader.h"
    #include "vtkMarchingCubes.h"
    #include "vtkPolyDataConnectivityFilter.h"
    #include "vtkPolyDataMapper.h"
    #include "vtkActor.h"
    #include "vtkProperty.h"
    #include "vtkRenderer.h"
    #include "vtkRenderWindow.h"
    #include "vtkRenderWindowInteractor.h"

    int main(int argc, char* argv[])
    {
      if (argc < 3)
      {
        std::cerr << "Usage: " << argv[0]
                  << " InputFile(.vtk) Threshold" << std::endl;
        return EXIT_FAILURE;
      }
      const char* fileName = argv[1];
      float threshold = atof(argv[2]);
      int extractLargest = 1;
      if (argc == 4)
      {
        extractLargest = atoi(argv[3]);
      }

      // Load data
      vtkSmartPointer<vtkStructuredPointsReader> reader =
        vtkSmartPointer<vtkStructuredPointsReader>::New();
      reader->SetFileName(fileName);

      // Create a 3D model using marching cubes
      vtkSmartPointer<vtkMarchingCubes> mc =
        vtkSmartPointer<vtkMarchingCubes>::New();
      mc->SetInputConnection(reader->GetOutputPort());
      mc->ComputeNormalsOn();
      mc->ComputeGradientsOn();
      mc->SetValue(0, threshold);  // second value acts as threshold

      // To remain largest region
      vtkSmartPointer<vtkPolyDataConnectivityFilter> confilter =
        vtkSmartPointer<vtkPolyDataConnectivityFilter>::New();
      confilter->SetInputConnection(mc->GetOutputPort());
      confilter->SetExtractionModeToLargestRegion();

      // Create a mapper
      vtkSmartPointer<vtkPolyDataMapper> mapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      if (extractLargest)
      {
        mapper->SetInputConnection(confilter->GetOutputPort());
      }
      else
      {
        mapper->SetInputConnection(mc->GetOutputPort());
      }

      mapper->ScalarVisibilityOff();    // utilize actor's property I set

      // Visualize
      vtkSmartPointer<vtkActor> actor =
        vtkSmartPointer<vtkActor>::New();
      actor->GetProperty()->SetColor(1,1,1);
      actor->SetMapper(mapper);

      vtkSmartPointer<vtkRenderer> renderer =
        vtkSmartPointer<vtkRenderer>::New();
      renderer->AddActor(actor);

      vtkSmartPointer<vtkRenderWindow> renwin =
        vtkSmartPointer<vtkRenderWindow>::New();
      renwin->AddRenderer(renderer);

      vtkSmartPointer<vtkRenderWindowInteractor> iren =
        vtkSmartPointer<vtkRenderWindowInteractor>::New();
      iren->SetRenderWindow(renwin);
      iren->Initialize();
      iren->Start();

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 2.8)

    PROJECT(ExtractLargestIsosurface)

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

    add_executable(ExtractLargestIsosurface MACOSX_BUNDLE ExtractLargestIsosurface.cxx )

    target_link_libraries(ExtractLargestIsosurface ${VTK_LIBRARIES})

### Download and Build ExtractLargestIsosurface

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

    cd ExtractLargestIsosurface/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:

    ./ExtractLargestIsosurface

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.