# TensorAxes

VTKExamples/Cxx/VisualizationAlgorithms/TensorAxes

### 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 of the stress tensor. (These are called tensor axes.)

Info

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

Other Languages

See (Python)

### Code

TensorAxes.cxx

    // Translated from tenAxes.tcl

    #include <vtkAxes.h>
    #include <vtkCamera.h>
    #include <vtkConeSource.h>
    #include <vtkImageDataGeometryFilter.h>
    #include <vtkLookupTable.h>
    #include <vtkNamedColors.h>
    #include <vtkOutlineFilter.h>
    #include <vtkPointLoad.h>
    #include <vtkPolyDataMapper.h>
    #include <vtkProp3D.h>
    #include <vtkProperty.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkRenderer.h>
    #include <vtkSmartPointer.h>
    #include <vtkTensorGlyph.h>
    #include <vtkTubeFilter.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 tensor axes.
      vtkSmartPointer<vtkAxes> axes = vtkSmartPointer<vtkAxes>::New();
      axes->SetScaleFactor(0.5);

      vtkSmartPointer<vtkTubeFilter> tubeAxes =
        vtkSmartPointer<vtkTubeFilter>::New();
      tubeAxes->SetInputConnection(axes->GetOutputPort());
      tubeAxes->SetRadius(0.1);
      tubeAxes->SetNumberOfSides(6);

      vtkSmartPointer<vtkTensorGlyph> tensorAxes =
        vtkSmartPointer<vtkTensorGlyph>::New();
      tensorAxes->SetInputConnection(ptLoad->GetOutputPort());
      tensorAxes->SetSourceConnection(axes->GetOutputPort());
      tensorAxes->SetScaleFactor(10);
      tensorAxes->ClampScalingOn();

      // Map contour
      vtkSmartPointer<vtkLookupTable> lut = vtkSmartPointer<vtkLookupTable>::New();
      MakeLogLUT(lut);

      vtkSmartPointer<vtkPolyDataMapper> tensorAxesMapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      tensorAxesMapper->SetInputConnection(tensorAxes->GetOutputPort());
      tensorAxesMapper->SetLookupTable(lut);
      plane->Update(); // force update for scalar range

      tensorAxesMapper->SetScalarRange(plane->GetOutput()->GetScalarRange());

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

      // 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("BurlyWood").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)
    {
      // Original
      lut->SetScaleToLog10();
      lut->SetHueRange(.6667, 0.0);
      lut->Build();
    }
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

    project(TensorAxes)

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

### Download and Build TensorAxes

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

    cd TensorAxes/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:

    ./TensorAxes

WINDOWS USERS

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