#include <string>
#include <vtkSmartPointer.h>
#include <vtkGenericDataObjectReader.h>
#include <vtkVersion.h>
#include <vtkXMLUnstructuredGridWriter.h>
#include <vtkUnstructuredGrid.h>
int main(int argc, char *argv[])
  if(argc < 3)
    std::cerr << "Required arguments: input.vtk output.vtu" << std::endl;
    return EXIT_FAILURE;
  std::string inputFileName = argv[1];
  std::string outputFileName = argv[2];
  vtkSmartPointer<vtkGenericDataObjectReader> reader = vtkSmartPointer<vtkGenericDataObjectReader>::New();
  reader->SetFileName(inputFileName.c_str());
  reader->Update();
  vtkSmartPointer<vtkXMLUnstructuredGridWriter> writer = vtkSmartPointer<vtkXMLUnstructuredGridWriter>::New();
  writer->SetFileName(outputFileName.c_str());
  writer->SetInputConnection(reader->GetOutputPort());
  writer->Update();
  return EXIT_SUCCESS;
}

# vtk DataFile Version 3.1
Lattice Boltzmann data
ASCII
DATASET UNSTRUCTURED_GRID
POINTS 9 INT 
0 0 0 1 0 0 2 0 0 
0 1 0 1 1 0 2 1 0 
0 2 0 1 2 0 2 2 0 
CELLS 4 20
4 0 1 3 4 
4 1 2 4 5 
4 3 4 6 7 
4 4 5 7 8 
CELL_TYPES 4
8 8 8 8 
CELL_DATA 4
SCALARS Scal_1 DOUBLE
LOOKUP_TABLE default
1 2 1 0 
SCALARS Scal_2 DOUBLE