VTKVolume doesn't transform

#include <vtkSmartPointer.h>
#include <vtkConeSource.h>
#include <vtkTransform.h>
#include <vtkPolyData.h>
#include <vtkPolyDataMapper.h>
#include <vtkProp3D.h>
#include <vtkActor.h>
#include <vtkProperty.h>
#include <vtkRenderWindow.h>
#include <vtkRenderer.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkProjectedTetrahedraMapper.h>
#include <vtkDoubleArray.h>
#include <vtkRectilinearGrid.h>
#include <vtkUnstructuredGrid.h>
#include <vtkRectilinearGridToTetrahedra.h>
#include <vtkVolumeProperty.h>
#include <vtkPointData.h>
#include <vtkColorTransferFunction.h>

// Creates a cube volume
vtkSmartPointer<vtkVolume> cubeVolume(double r, double g, double b){

    // Create the coordinates
    vtkSmartPointer<vtkDoubleArray> xArray = vtkSmartPointer<vtkDoubleArray>::New();
    xArray->InsertNextValue(0.0);
    xArray->InsertNextValue(1.0);
    vtkSmartPointer<vtkDoubleArray> yArray = vtkSmartPointer<vtkDoubleArray>::New();
    yArray->InsertNextValue(0.0);
    yArray->InsertNextValue(1.0);
    vtkSmartPointer<vtkDoubleArray> zArray = vtkSmartPointer<vtkDoubleArray>::New();
    zArray->InsertNextValue(0.0);
    zArray->InsertNextValue(1.0);

    // Create the RectilinearGrid
    vtkSmartPointer<vtkRectilinearGrid> grid = vtkSmartPointer<vtkRectilinearGrid>::New();
    grid->SetDimensions(2,2,2);
    grid->SetXCoordinates(xArray);
    grid->SetYCoordinates(yArray);
    grid->SetZCoordinates(zArray);

    // Obtain an UnstructuredGrid made of tetrahedras
    vtkSmartPointer<vtkRectilinearGridToTetrahedra> rectilinearGridToTetrahedra = vtkSmartPointer<vtkRectilinearGridToTetrahedra>::New();
    rectilinearGridToTetrahedra->SetInputData(grid);
    rectilinearGridToTetrahedra->Update();
    vtkSmartPointer<vtkUnstructuredGrid> ugrid = rectilinearGridToTetrahedra->GetOutput();

    // Add scalars to the grid
    vtkSmartPointer<vtkDoubleArray> scalars = vtkSmartPointer<vtkDoubleArray>::New();
    for (int i = 0; i < 8; i++){
        scalars->InsertNextValue(0);
    }
    ugrid->GetPointData()->SetScalars(scalars);

    // Volume Rendering Mapper
    vtkSmartPointer<vtkProjectedTetrahedraMapper> mapper = vtkSmartPointer<vtkProjectedTetrahedraMapper>::New();
    mapper->SetInputData(ugrid);
    mapper->Update();

    // Create the volume
    vtkSmartPointer<vtkVolume> volume = vtkSmartPointer<vtkVolume>::New();
    volume->SetMapper(mapper);

    // Apply a ColorTransferFunction to the volume
    vtkSmartPointer<vtkColorTransferFunction> colorTransferFunction = vtkSmartPointer<vtkColorTransferFunction>::New();
    colorTransferFunction->AddRGBPoint(0.0, r, g, b);
    volume->GetProperty()->SetColor(colorTransferFunction);

    return volume;
}

// Creates a cone actor
vtkSmartPointer<vtkActor> coneActor(double r, double g, double b){

    // Simple cone mapper
    vtkSmartPointer<vtkPolyDataMapper> mapper = vtkSmartPointer<vtkPolyDataMapper>::New();
    mapper->SetInputConnection(vtkSmartPointer<vtkConeSource>::New()->GetOutputPort());

    // Create the actor
    vtkSmartPointer<vtkActor> actor = vtkSmartPointer<vtkActor>::New();
    actor->GetProperty()->SetColor(r,g,b);
    actor->SetMapper(mapper);

    return actor;
}


int main(int, char *[]){

    // Create the props
    vtkSmartPointer<vtkProp3D> volume1 = cubeVolume(1, 0, 0);   // The red cube volume
    vtkSmartPointer<vtkProp3D> volume2 = cubeVolume(0, 0, 1);   // The blue cube volume
    vtkSmartPointer<vtkProp3D> actor1 = coneActor(1, 0, 0); // The red cone actor
    vtkSmartPointer<vtkProp3D> actor2 = coneActor(0, 0, 1); // The blue cone actor

    // Translate the blue props by (2,2)
    vtkSmartPointer<vtkTransform> transform = vtkSmartPointer<vtkTransform>::New();
    transform->Translate(2, 2, 0);
    volume2->SetUserTransform(transform);
    actor2->SetUserTransform(transform);

    // Create a renderer, render window, 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);

    // Add the props to the scene
    renderer->AddActor(volume1);
    renderer->AddActor(volume2);
    renderer->AddActor(actor1);
    renderer->AddActor(actor2);
    renderer->SetBackground(1,1,1); // Background color white

    // Render and interact
    renderWindow->Render();
    renderWindowInteractor->Start();

    return EXIT_SUCCESS;
}