// 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 =
    dynamic_cast<vtkStructuredGrid*>(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);