# TensorEllipsoids

VTKExamples/Cxx/VisualizationAlgorithms/TensorEllipsoids

### Description

This example visualizes the analytical results of Boussinesq's problem from Saada. The figure shows the results by displaying the scaled and oriented principal axes as tensor ellipsoids representing the stress tensor. (These are called tensor axes.)

Info

See Figure 6-22b in Chapter 6 the VTK Textbook.

Other Languages

See (Python)

### Code

TensorEllipsoids.cxx

    // Translated from tenEllip.tcl

    #include <vtkActor.h>
    #include <vtkCamera.h>
    #include <vtkColorSeries.h>
    #include <vtkConeSource.h>
    #include <vtkImageDataGeometryFilter.h>
    #include <vtkLookupTable.h>
    #include <vtkNamedColors.h>
    #include <vtkOutlineFilter.h>
    #include <vtkPointLoad.h>
    #include <vtkPolyDataMapper.h>
    #include <vtkPolyDataNormals.h>
    #include <vtkProp3D.h>
    #include <vtkProperty.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkRenderer.h>
    #include <vtkSmartPointer.h>
    #include <vtkSphereSource.h>
    #include <vtkTensorGlyph.h>

    namespace
    {
    void MakeLogLUT(vtkLookupTable* lut);
    }

    int main(int, char*[])
    {
      vtkSmartPointer<vtkNamedColors> colors =
        vtkSmartPointer<vtkNamedColors>::New();

      // Create the RenderWindow, Renderer and interactive renderer.
      //
      vtkSmartPointer<vtkRenderer> ren = vtkSmartPointer<vtkRenderer>::New();
      vtkSmartPointer<vtkRenderWindow> renWin =
        vtkSmartPointer<vtkRenderWindow>::New();
      renWin->AddRenderer(ren);
      vtkSmartPointer<vtkRenderWindowInteractor> iren =
        vtkSmartPointer<vtkRenderWindowInteractor>::New();
      iren->SetRenderWindow(renWin);

      // Generate the tensors.
      vtkSmartPointer<vtkPointLoad> ptLoad = vtkSmartPointer<vtkPointLoad>::New();
      ptLoad->SetLoadValue(100.0);
      ptLoad->SetSampleDimensions(6, 6, 6);
      ptLoad->ComputeEffectiveStressOn();
      ptLoad->SetModelBounds(-10, 10, -10, 10, -10, 10);

      // Extract a plane of data.
      vtkSmartPointer<vtkImageDataGeometryFilter> plane =
        vtkSmartPointer<vtkImageDataGeometryFilter>::New();
      plane->SetInputConnection(ptLoad->GetOutputPort());
      plane->SetExtent(2, 2, 0, 99, 0, 99);

      // Generate the ellipsoids.
      vtkSmartPointer<vtkSphereSource> sphere =
        vtkSmartPointer<vtkSphereSource>::New();
      sphere->SetThetaResolution(8);
      sphere->SetPhiResolution(8);
      vtkSmartPointer<vtkTensorGlyph> tensorEllipsoids =
        vtkSmartPointer<vtkTensorGlyph>::New();
      tensorEllipsoids->SetInputConnection(ptLoad->GetOutputPort());
      tensorEllipsoids->SetSourceConnection(sphere->GetOutputPort());
      tensorEllipsoids->SetScaleFactor(10);
      tensorEllipsoids->ClampScalingOn();

      vtkSmartPointer<vtkPolyDataNormals> ellipNormals =
        vtkSmartPointer<vtkPolyDataNormals>::New();
      ellipNormals->SetInputConnection(tensorEllipsoids->GetOutputPort());

      // Map contour.
      vtkSmartPointer<vtkLookupTable> lut = vtkSmartPointer<vtkLookupTable>::New();
      MakeLogLUT(lut);
      vtkSmartPointer<vtkPolyDataMapper> tensorEllipsoidsMapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      tensorEllipsoidsMapper->SetInputConnection(ellipNormals->GetOutputPort());
      tensorEllipsoidsMapper->SetLookupTable(lut);
      plane->Update(); // force update for scalar range
      tensorEllipsoidsMapper->SetScalarRange(plane->GetOutput()->GetScalarRange());

      vtkSmartPointer<vtkActor> tensorActor = vtkSmartPointer<vtkActor>::New();
      tensorActor->SetMapper(tensorEllipsoidsMapper);

      // Create an outline around the data.
      //
      vtkSmartPointer<vtkOutlineFilter> outline =
        vtkSmartPointer<vtkOutlineFilter>::New();
      outline->SetInputConnection(ptLoad->GetOutputPort());

      vtkSmartPointer<vtkPolyDataMapper> outlineMapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      outlineMapper->SetInputConnection(outline->GetOutputPort());

      vtkSmartPointer<vtkActor> outlineActor = vtkSmartPointer<vtkActor>::New();
      outlineActor->SetMapper(outlineMapper);
      outlineActor->GetProperty()->SetColor(colors->GetColor3d("Black").GetData());

      // Create a cone whose apex indicates the application of load.
      //
      vtkSmartPointer<vtkConeSource> coneSrc =
        vtkSmartPointer<vtkConeSource>::New();
      coneSrc->SetRadius(0.5);
      coneSrc->SetHeight(2);
      vtkSmartPointer<vtkPolyDataMapper> coneMap =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      coneMap->SetInputConnection(coneSrc->GetOutputPort());
      vtkSmartPointer<vtkActor> coneActor = vtkSmartPointer<vtkActor>::New();
      coneActor->SetMapper(coneMap);
      coneActor->SetPosition(0, 0, 11);
      coneActor->RotateY(90);
      coneActor->GetProperty()->SetColor(colors->GetColor3d("Red").GetData());

      vtkSmartPointer<vtkCamera> camera = vtkSmartPointer<vtkCamera>::New();
      camera->SetFocalPoint(0.113766, -1.13665, -1.01919);
      camera->SetPosition(-29.4886, -63.1488, 26.5807);
      camera->SetViewAngle(24.4617);
      camera->SetViewUp(0.17138, 0.331163, 0.927879);
      camera->SetClippingRange(1, 100);

      ren->AddActor(tensorActor);
      ren->AddActor(outlineActor);
      ren->AddActor(coneActor);
      ren->SetBackground(colors->GetColor3d("WhiteSmoke").GetData());
      ren->SetActiveCamera(camera);

      renWin->SetSize(512, 512);

      iren->Initialize();
      renWin->Render();
      iren->Start();

      return EXIT_SUCCESS;
    }

    namespace
    {
    void MakeLogLUT(vtkLookupTable* lut)
    {
      // Make the lookup using a Brewer palette.
      vtkSmartPointer<vtkColorSeries> colorSeries =
        vtkSmartPointer<vtkColorSeries>::New();
      colorSeries->SetNumberOfColors(8);
      int colorSeriesEnum = colorSeries->BREWER_DIVERGING_SPECTRAL_8;
      colorSeries->SetColorScheme(colorSeriesEnum);
      lut->SetScaleToLog10();
      colorSeries->BuildLookupTable(lut, colorSeries->ORDINAL);
      lut->SetNanColor(1, 0, 0, 1);
      // Original
      // lut->SetScaleToLog10();
      // lut->SetHueRange(.6667, 0.0);
      // lut->Build();
    }
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

    project(TensorEllipsoids)

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

### Download and Build TensorEllipsoids

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

    cd TensorEllipsoids/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:

    ./TensorEllipsoids

WINDOWS USERS

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