# TubesFromSplines

VTKExamples/Cxx/VisualizationAlgorithms/TubesFromSplines

### Description

This example shows how to interpolate a set of points and generate tubes around the resulting polyline. Scalars associated with the points are also interpolated and used to vary the radius of the tube.

Note

This example was inspired by a question asked by ''Adam Sankowski''.

### Code

TubesFromSplines.cxx

    #include <vtkSmartPointer.h>

    #include <vtkParametricFunctionSource.h>
    #include <vtkTupleInterpolator.h>
    #include <vtkTubeFilter.h>
    #include <vtkParametricSpline.h>

    #include <vtkDoubleArray.h>
    #include <vtkPoints.h>
    #include <vtkPolyData.h>
    #include <vtkPointData.h>

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

    int main(int, char *[])
    {
      vtkSmartPointer<vtkPoints> points =
        vtkSmartPointer<vtkPoints>::New();
      points->InsertPoint(0,1,0,0);
      points->InsertPoint(1,2,0,0);
      points->InsertPoint(2,3,1,0);
      points->InsertPoint(3,4,1,0);
      points->InsertPoint(4,5,0,0);
      points->InsertPoint(5,6,0,0);

      // Fit a spline to the points
      vtkSmartPointer<vtkParametricSpline> spline =
        vtkSmartPointer<vtkParametricSpline>::New();
      spline->SetPoints(points);
      vtkSmartPointer<vtkParametricFunctionSource> functionSource =
        vtkSmartPointer<vtkParametricFunctionSource>::New();
      functionSource->SetParametricFunction(spline);
      functionSource->SetUResolution(10 * points->GetNumberOfPoints());
      functionSource->Update();

      // Interpolate the scalars
      double rad;
      vtkSmartPointer<vtkTupleInterpolator> interpolatedRadius =
        vtkSmartPointer<vtkTupleInterpolator> ::New();
      interpolatedRadius->SetInterpolationTypeToLinear();
      interpolatedRadius->SetNumberOfComponents(1);
      rad = .2; interpolatedRadius->AddTuple(0,&rad);
      rad = .2; interpolatedRadius->AddTuple(1,&rad);
      rad = .2; interpolatedRadius->AddTuple(2,&rad);
      rad = .1; interpolatedRadius->AddTuple(3,&rad);
      rad = .1; interpolatedRadius->AddTuple(4,&rad);
      rad = .1; interpolatedRadius->AddTuple(5,&rad);

      // Generate the radius scalars
      vtkSmartPointer<vtkDoubleArray> tubeRadius =
        vtkSmartPointer<vtkDoubleArray>::New();
      unsigned int n = functionSource->GetOutput()->GetNumberOfPoints();
      tubeRadius->SetNumberOfTuples(n);
      tubeRadius->SetName("TubeRadius");
      double tMin = interpolatedRadius->GetMinimumT();
      double tMax = interpolatedRadius->GetMaximumT();
      double r;
      for (unsigned int i = 0; i < n; ++i)
      {
        double t = (tMax - tMin) / (n - 1) * i + tMin;
        interpolatedRadius->InterpolateTuple(t, &r);
        tubeRadius->SetTuple1(i, r);
      }

      // Add the scalars to the polydata
      vtkSmartPointer<vtkPolyData> tubePolyData =
        vtkSmartPointer<vtkPolyData>::New();
      tubePolyData = functionSource->GetOutput();
      tubePolyData->GetPointData()->AddArray(tubeRadius);
      tubePolyData->GetPointData()->SetActiveScalars("TubeRadius");

      // Create the tubes
      vtkSmartPointer<vtkTubeFilter> tuber =
        vtkSmartPointer<vtkTubeFilter>::New();
      tuber->SetInputData(tubePolyData);
      tuber->SetNumberOfSides(20);
      tuber->SetVaryRadiusToVaryRadiusByAbsoluteScalar();

      //--------------
      // Setup actors and mappers
      vtkSmartPointer<vtkPolyDataMapper> lineMapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      lineMapper->SetInputData(tubePolyData);
      lineMapper->SetScalarRange(tubePolyData->GetScalarRange());

      vtkSmartPointer<vtkPolyDataMapper> tubeMapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      tubeMapper->SetInputConnection(tuber->GetOutputPort());
      tubeMapper->SetScalarRange(tubePolyData->GetScalarRange());

      vtkSmartPointer<vtkActor> lineActor = vtkSmartPointer<vtkActor>::New();
      lineActor->SetMapper(lineMapper);
      vtkSmartPointer<vtkActor> tubeActor = vtkSmartPointer<vtkActor>::New();
      tubeActor->SetMapper(tubeMapper);

      // Setup render window, renderer, and interactor
      vtkSmartPointer<vtkRenderer> renderer =
        vtkSmartPointer<vtkRenderer>::New();
      vtkSmartPointer<vtkRenderWindow> renderWindow =
        vtkSmartPointer<vtkRenderWindow>::New();
      renderWindow->AddRenderer(renderer);
      vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
        vtkSmartPointer<vtkRenderWindowInteractor>::New();
      renderWindowInteractor->SetRenderWindow(renderWindow);
      renderer->AddActor(lineActor);
      renderer->AddActor(tubeActor);
      renderer->SetBackground(.4, .5, .6);
      renderWindow->Render();
      renderWindowInteractor->Start();

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

    project(TubesFromSplines)

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

### Download and Build TubesFromSplines

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

    cd TubesFromSplines/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:

    ./TubesFromSplines

WINDOWS USERS

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