# RayCastIsosurface

VTKExamples/Cxx/VolumeRendering/RayCastIsosurface

### Description

This examples show how volume rendering can produce isosurface-like images. Using vtkOpenGLGPUVolumeRayCastMapper with an isosurface blend mode, two isosurfaces are created using appropriate transfer functions. The effect is similar to what is shown in MedicalDemo2. The user can specify the .mhd file and the two isosurface values. The example uses 500 and 1150 for the two isosurface values. The volume rendering "surfaces" are fuzzier than the hard surfaces created by vtkMarchingCubes in MedicalDemo3.

Usage

RayCastIsosurface FullHead.mhd 500 1150

Info

The example uses FullHead.mhd which references FullHead.raw.gz.

### Code

RayCastIsosurface.cxx

    #include "vtkSmartPointer.h"
    #include "vtkOpenGLGPUVolumeRayCastMapper.h"

    #include "vtkPiecewiseFunction.h"
    #include "vtkColorTransferFunction.h"
    #include "vtkContourValues.h"

    #include "vtkInteractorStyleTrackballCamera.h"
    #include "vtkMetaImageReader.h"
    #include "vtkRenderWindow.h"
    #include "vtkRenderWindowInteractor.h"
    #include "vtkRenderer.h"
    #include "vtkCamera.h"

    #include "vtkVolume.h"
    #include "vtkVolumeProperty.h"
    #include "vtkNamedColors.h"

    int main (int argc, char *argv[])
    {
      double iso1 = 500.0;
      double iso2 = 1150.0;

      if (argc < 2)
      {
        std::cout << "Usage: " << argv[0] << " file.mnd [iso1=500] [iso2=1150]" << std::endl;
        return EXIT_FAILURE;
      }

      vtkSmartPointer<vtkMetaImageReader> reader =
        vtkSmartPointer<vtkMetaImageReader>::New();
      reader->SetFileName(argv[1]);

      auto colors =
        vtkSmartPointer<vtkNamedColors>::New();

      auto mapper =
        vtkSmartPointer<vtkOpenGLGPUVolumeRayCastMapper>::New();
      mapper->SetInputConnection(reader->GetOutputPort());
      mapper->AutoAdjustSampleDistancesOff();
      mapper->SetSampleDistance(0.5);
      mapper->SetBlendModeToIsoSurface();

      if (argc > 3)
      {
        iso1 = atof(argv[2]);
        iso2 = atof(argv[3]);
      }
      auto colorTransferFunction =
        vtkSmartPointer<vtkColorTransferFunction>::New();
      colorTransferFunction->RemoveAllPoints();
      colorTransferFunction->AddRGBPoint(
        iso2,
        colors->GetColor3d("ivory").GetData()[0],
        colors->GetColor3d("ivory").GetData()[1],
        colors->GetColor3d("ivory").GetData()[2]);
      colorTransferFunction->AddRGBPoint(
        iso1,
        colors->GetColor3d("flesh").GetData()[0],
        colors->GetColor3d("flesh").GetData()[1],
        colors->GetColor3d("flesh").GetData()[2]);

      auto scalarOpacity =
        vtkSmartPointer<vtkPiecewiseFunction>::New();
      scalarOpacity->AddPoint(iso1, .3);
      scalarOpacity->AddPoint(iso2, 0.6);

      auto volumeProperty =
        vtkSmartPointer<vtkVolumeProperty>::New();
      volumeProperty->ShadeOn();
      volumeProperty->SetInterpolationTypeToLinear();
      volumeProperty->SetColor(colorTransferFunction);
      volumeProperty->SetScalarOpacity(scalarOpacity);

      auto volume =
        vtkSmartPointer<vtkVolume>::New();
      volume->SetMapper(mapper);
      volume->SetProperty(volumeProperty);

      auto renderer =
        vtkSmartPointer<vtkRenderer>::New();
      renderer->AddVolume(volume);
      renderer->SetBackground(colors->GetColor3d("cornflower").GetData());
      renderer->ResetCamera();

      auto renderWindow =
        vtkSmartPointer<vtkRenderWindow>::New();
      renderWindow->SetSize(800, 600);
      renderWindow->AddRenderer(renderer);

      auto style =
        vtkSmartPointer<vtkInteractorStyleTrackballCamera>::New();

      auto interactor =
        vtkSmartPointer<vtkRenderWindowInteractor>::New();
      interactor->SetRenderWindow(renderWindow);
      interactor->SetInteractorStyle(style);

      // Add some contour values to draw iso surfaces
      volumeProperty->GetIsoSurfaceValues()->SetValue(0, iso1);
      volumeProperty->GetIsoSurfaceValues()->SetValue(1, iso2);

      // Generate a good view
      vtkSmartPointer<vtkCamera> aCamera =
        vtkSmartPointer<vtkCamera>::New();
      aCamera->SetViewUp (0, 0, -1);
      aCamera->SetPosition (0, -1, 0);
      aCamera->SetFocalPoint (0, 0, 0);

      renderer->SetActiveCamera(aCamera);
      renderer->ResetCamera();

      aCamera->Azimuth(30.0);
      aCamera->Elevation(30.0);
      aCamera->Dolly(1.5);
      renderer->ResetCameraClippingRange ();

      renderWindow->Render();

      interactor->Start();

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

    project(RayCastIsosurface)

    find_package(VTK COMPONENTS
      vtkCommonColor
      vtkCommonCore
      vtkCommonDataModel
      vtkCommonMisc
      vtkIOImage
      vtkInteractionStyle
      vtkRenderingContextOpenGL2
      vtkRenderingCore
      vtkRenderingFreeType
      vtkRenderingGL2PSOpenGL2
      vtkRenderingOpenGL2
      vtkRenderingVolumeOpenGL2 QUIET)
    if (NOT VTK_FOUND)
      message("Skipping RayCastIsosurface: ${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(RayCastIsosurface MACOSX_BUNDLE RayCastIsosurface.cxx )
      target_link_libraries(RayCastIsosurface PRIVATE ${VTK_LIBRARIES})
    else ()
      # include all components
      add_executable(RayCastIsosurface MACOSX_BUNDLE RayCastIsosurface.cxx )
      target_link_libraries(RayCastIsosurface PRIVATE ${VTK_LIBRARIES})
      # vtk_module_autoinit is needed
      vtk_module_autoinit(
        TARGETS RayCastIsosurface
        MODULES ${VTK_LIBRARIES}
        )
    endif ()

### Download and Build RayCastIsosurface

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

    cd RayCastIsosurface/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:

    ./RayCastIsosurface

WINDOWS USERS

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