# VelocityProfile

VTKExamples/Cxx/VisualizationAlgorithms/VelocityProfile

### Description

This example shows shows warped planes in a structured grid dataset. The planes are warped according to flow momentum. The relative back and forward flow are clearly visible in the deformation of the planes.

### Code

VelocityProfile.cxx

    // Translated from velProf.tcl.

    #include <vtkActor.h>
    #include <vtkAppendPolyData.h>
    #include <vtkCamera.h>
    #include <vtkLookupTable.h>
    #include <vtkMultiBlockDataSet.h>
    #include <vtkMultiBlockPLOT3DReader.h>
    #include <vtkNamedColors.h>
    #include <vtkPolyDataMapper.h>
    #include <vtkPolyDataNormals.h>
    #include <vtkProperty.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkRenderer.h>
    #include <vtkSmartPointer.h>
    #include <vtkStructuredGrid.h>
    #include <vtkStructuredGridGeometryFilter.h>
    #include <vtkStructuredGridOutlineFilter.h>
    #include <vtkWarpVector.h>

    #include <algorithm>
    #include <array>
    #include <string>

    int main(int argc, char* argv[])
    {
      auto Scale = [](std::vector<double>& v, double scale) {
        std::transform(std::begin(v), std::end(v), std::begin(v),
                       [=](double const& n) { return n / scale; });
        return;
      };

      if (argc < 2)
      {
        std::cout << "Usage: " << argv[0] << " filename1 filename2" << std::endl;
        std::cout << "where: filename1 is combxyz.bin and filename2 is combq.bin."
                  << std::endl;
        std::cout << "Produces figure 6-14(b) Flow momentum from the VTK Textbook."
                  << std::endl;
        return EXIT_FAILURE;
      }

      std::string fileName1 = argv[1];
      std::string fileName2 = argv[2];

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

      // Set the background color, match those in VTKTextbook.pdf.
      auto SetColor = [&colors](std::array<double, 3>& v,
                                std::string const& colorName) {
        auto const scaleFactor = 255.0;
        std::transform(std::begin(v), std::end(v), std::begin(v),
                       [=](double const& n) { return n / scaleFactor; });
        colors->SetColor(colorName, v.data());
        return;
      };
      std::array<double, 3> bkg{{65, 99, 149}};
      SetColor(bkg, "BkgColor");

      // Read a vtk file
      //
      vtkSmartPointer<vtkMultiBlockPLOT3DReader> pl3d =
        vtkSmartPointer<vtkMultiBlockPLOT3DReader>::New();
      pl3d->SetXYZFileName(fileName1.c_str());
      pl3d->SetQFileName(fileName2.c_str());
      pl3d->SetScalarFunctionNumber(100); // Density
      pl3d->SetVectorFunctionNumber(202); // Momentum
      pl3d->Update();

      vtkStructuredGrid* pl3dOutput =
        vtkStructuredGrid::SafeDownCast(pl3d->GetOutput()->GetBlock(0));

      // What do we know about the data?
      // Get the extent of the data: imin,imax, jmin,jmax, kmin,kmax
      int extent[6] = {0, 0, 0, 0, 0, 0};
      pl3dOutput->GetExtent(extent);
      double scalarRange[2] = {0.0, 0.0};
      pl3dOutput->GetScalarRange(scalarRange);

      // Planes are specified using a imin,imax, jmin,jmax, kmin,kmax coordinate
      // specification. Min and max i,j,k values are clamped to 0 and maximum value.
      // See the variable named extent for the values.
      //
      vtkSmartPointer<vtkStructuredGridGeometryFilter> plane =
        vtkSmartPointer<vtkStructuredGridGeometryFilter>::New();
      plane->SetInputData(pl3dOutput);
      plane->SetExtent(10, 10, 1, extent[3], 1, extent[5]);

      vtkSmartPointer<vtkStructuredGridGeometryFilter> plane2 =
        vtkSmartPointer<vtkStructuredGridGeometryFilter>::New();
      plane2->SetInputData(pl3dOutput);
      plane2->SetExtent(30, 30, 1, extent[3], 1, extent[5]);

      vtkSmartPointer<vtkStructuredGridGeometryFilter> plane3 =
        vtkSmartPointer<vtkStructuredGridGeometryFilter>::New();
      plane3->SetInputData(pl3dOutput);
      plane3->SetExtent(45, 45, 1, extent[3], 1, extent[5]);

      // We use an append filter because that way we can do the warping, etc. just
      // using a single pipeline and actor.
      //
      vtkSmartPointer<vtkAppendPolyData> appendF =
        vtkSmartPointer<vtkAppendPolyData>::New();
      appendF->AddInputConnection(plane->GetOutputPort());
      appendF->AddInputConnection(plane2->GetOutputPort());
      appendF->AddInputConnection(plane3->GetOutputPort());

      // Warp
      vtkSmartPointer<vtkWarpVector> warp = vtkSmartPointer<vtkWarpVector>::New();
      warp->SetInputConnection(appendF->GetOutputPort());
      warp->SetScaleFactor(0.005);
      warp->Update();

      vtkSmartPointer<vtkPolyDataNormals> normals =
        vtkSmartPointer<vtkPolyDataNormals>::New();
      normals->SetInputData(warp->GetPolyDataOutput());
      normals->SetFeatureAngle(45);

      vtkSmartPointer<vtkPolyDataMapper> planeMapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      planeMapper->SetInputConnection(normals->GetOutputPort());
      planeMapper->SetScalarRange(scalarRange);

      vtkSmartPointer<vtkActor> planeActor = vtkSmartPointer<vtkActor>::New();
      planeActor->SetMapper(planeMapper);

      // The outline provides context for the data and the planes.
      vtkSmartPointer<vtkStructuredGridOutlineFilter> outline =
        vtkSmartPointer<vtkStructuredGridOutlineFilter>::New();
      outline->SetInputData(pl3dOutput);

      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 the RenderWindow, Renderer and both Actors
      //
      vtkSmartPointer<vtkRenderer> ren = vtkSmartPointer<vtkRenderer>::New();
      vtkSmartPointer<vtkRenderWindow> renWin =
        vtkSmartPointer<vtkRenderWindow>::New();
      renWin->AddRenderer(ren);

      vtkSmartPointer<vtkRenderWindowInteractor> iren =
        vtkSmartPointer<vtkRenderWindowInteractor>::New();
      iren->SetRenderWindow(renWin);

      // Add the actors to the renderer, set the background and size
      //
      ren->AddActor(planeActor);
      ren->AddActor(outlineActor);
      ren->SetBackground(colors->GetColor3d("BkgColor").GetData());
      renWin->SetSize(512, 512);

      iren->Initialize();

      renWin->Render();

      ren->GetActiveCamera()->SetPosition(19.8562, -31.8912, 47.0755);
      ren->GetActiveCamera()->SetFocalPoint(8.255, 0.147815, 29.7631);
      ren->GetActiveCamera()->SetViewUp(-0.0333325, 0.465756, 0.884285);
      ren->GetActiveCamera()->SetClippingRange(17.3078, 64.6375);

      iren->Start();

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 2.8)

    PROJECT(VelocityProfile)

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

    add_executable(VelocityProfile MACOSX_BUNDLE VelocityProfile.cxx )

    target_link_libraries(VelocityProfile ${VTK_LIBRARIES})

### Download and Build VelocityProfile

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

    cd VelocityProfile/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:

    ./VelocityProfile

WINDOWS USERS

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