LAIAndPROSAILToSensorResponse.cxx

Example usage:

./LAIAndPROSAILToSensorResponse Input/LAIverySmallFSATSW.tif \
                                Input/Simu_label_LAI.png \
                                Input/Simu_mask_LAI_1.png \
                                Input/label-params-SO-2006-Level-2.txt \
                                Input/acqui-params.txt \
                                Input/Radiometry/Test/rep6S.dat \
                                Output/siTvLAIAndPROSAILToSensorResponse.tif \
                                5

Example source code (LAIAndPROSAILToSensorResponse.cxx):

// The following code is an example of Sensor spectral response image generated using image of labeled objects image, objects properties (vegetation classes are
// handled using PROSAIL model, non-vegetation classes are characterized using \href{http://speclib.jpl.nasa.gov/}{Aster database} characteristics provided by a
// text file), acquisition parameters, sensor characteristics, and LAI (Leaf Area Index) image.
//
// Sensor RSR is modeled by 6S (Second Simulation of a Satellite Signal in the Solar Spectrum) model \cite{Vermote1997}. Detailed information about 6S can be
// found \href{http://6s.ltdri.org/6S_code2_thiner_stuff/6S_Manual_Part_1.pdf}{here}.
//
// Let's look at the minimal code required to use this algorithm. First, the
// following headers must be included.

#include "otbImageFileWriter.h"
#include "otbImageFileReader.h"
#include "otbVectorDataFileReader.h"
#include "otbStandardWriterWatcher.h"
#include "itkImageRegionConstIterator.h"
#include "otbMultiChannelExtractROI.h"
#include "itkOrImageFilter.h"

#include "otbLeafParameters.h"
#include "otbReduceSpectralResponse.h"
#include "otbImageSimulationMethod.h"
#include "otbSpatialisationFilter.h"
#include "otbAttributesMapLabelObject.h"
#include "itkTernaryFunctorImageFilter.h"
#include "itkUnaryFunctorImageFilter.h"
#include "otbVectorDataToLabelMapWithAttributesFilter.h"

namespace otb
{

// \code{ImageUniqueValuesCalculator} class is defined here. Method \code{GetUniqueValues()} returns an array with all values contained in an image.
// This class is implemented and used to test if all labels in labeled image are present in label parameter file.

template <class TImage>
class ITK_EXPORT ImageUniqueValuesCalculator : public itk::Object
{
public:
  using Self         = ImageUniqueValuesCalculator<TImage>;
  using Superclass   = itk::Object;
  using Pointer      = itk::SmartPointer<Self>;
  using ConstPointer = itk::SmartPointer<const Self>;

  itkNewMacro(Self);

  itkTypeMacro(ImageUniqueValuesCalculator, itk::Object);

  itkStaticConstMacro(ImageDimension, unsigned int, TImage::ImageDimension);

  using PixelType = typename TImage::PixelType;

  using ImageType = TImage;

  using ArrayType = std::vector<PixelType>;

  using ImagePointer      = typename ImageType::Pointer;
  using ImageConstPointer = typename ImageType::ConstPointer;

  virtual void SetImage(const ImageType* image)
  {
    if (m_Image != image)
    {
      m_Image = image;
      this->Modified();
    }
  }


  ArrayType GetUniqueValues() const
  {
    ArrayType uniqueValues;
    if (!m_Image)
    {
      return uniqueValues;
    }

    itk::ImageRegionConstIterator<ImageType> it(m_Image, m_Image->GetRequestedRegion());

    uniqueValues.push_back(it.Get());
    ++it;
    while (!it.IsAtEnd())
    {
      if (std::find(uniqueValues.begin(), uniqueValues.end(), it.Get()) == uniqueValues.end())
      {
        uniqueValues.push_back(it.Get());
      }
      ++it;
    }

    return uniqueValues;
  }


protected:
  ImageUniqueValuesCalculator()
  {
    m_Image = nullptr;
  }
  ~ImageUniqueValuesCalculator() override
  {
  }
  void PrintSelf(std::ostream& os, itk::Indent indent) const override
  {
    Superclass::PrintSelf(os, indent);
    os << indent << "Image: " << m_Image.GetPointer() << std::endl;
  }

private:
  ImageUniqueValuesCalculator(const Self&) = delete;
  void operator=(const Self&) = delete;

  ImageConstPointer m_Image;

}; // class ImageUniqueValuesCalculator


namespace Functor
{

// \code{ProsailSimulatorFunctor} functor is defined here.
//

template <class TLAI, class TLabel, class TMask, class TOutput, class TLabelSpectra, class TLabelParameter, class TAcquistionParameter, class TSatRSR>
class ProsailSimulatorFunctor
{
public:
  /** Standard class typedefs */

  // \code{ProsailSimulatorFunctor} functor is defined here.
  //

  using LAIPixelType            = TLAI;
  using LabelPixelType          = TLabel;
  using MaskPixelType           = TMask;
  using OutputPixelType         = TOutput;
  using LabelSpectraType        = TLabelSpectra;
  using LabelParameterType      = TLabelParameter;
  using AcquistionParameterType = TAcquistionParameter;
  using SatRSRType              = TSatRSR;
  using SatRSRPointerType       = typename SatRSRType::Pointer;
  using ProspectType            = typename otb::ProspectModel;
  using SailType                = typename otb::SailModel;

  using PrecisionType                 = double;
  using PairType                      = std::pair<PrecisionType, PrecisionType>;
  using VectorPairType                = typename std::vector<PairType>;
  using ResponseType                  = otb::SpectralResponse<PrecisionType, PrecisionType>;
  using ResponsePointerType           = ResponseType::Pointer;
  using ReduceResponseType            = otb::ReduceSpectralResponse<ResponseType, SatRSRType>;
  using ReduceResponseTypePointerType = typename ReduceResponseType::Pointer;

  // In this example spectra are generated form $400$ to $2400nm$. the number of simulated band is set by \code{SimNbBands} value.
  //

  static const unsigned int SimNbBands = 2000;
  /** Constructor */
  ProsailSimulatorFunctor()
  {
    m_SatRSR       = SatRSRType::New();
    m_InvertedMask = false;
  }

  /** Destructor */
  ~ProsailSimulatorFunctor(){};

  void SetInvertedMask(bool ivm)
  {
    m_InvertedMask = ivm;
  }

  /** Implementation of the () operator*/
  inline OutputPixelType operator()(const LAIPixelType& lai, const LabelPixelType& label, const MaskPixelType& mask)
  {

    // mask value is read to know if the pixel have to be calculated, it is set to 0 otherwise.

    OutputPixelType pix;
    pix.SetSize(m_SatRSR->GetNbBands());
    if ((!mask && !m_InvertedMask) || (mask && m_InvertedMask))
    {
      for (unsigned int i = 0; i < m_SatRSR->GetNbBands(); i++)
        pix[i]            = static_cast<typename OutputPixelType::ValueType>(0);
      return pix;
    }


    // Object reflectance \code{hxSpectrum} is calculated. If object label correspond to vegetation label then Prosail code is used, aster database is used
    // otherwise.

    VectorPairType hxSpectrum;

    for (unsigned int i = 0; i < SimNbBands; i++)
    {
      PairType resp;
      resp.first = static_cast<PrecisionType>((400.0 + i) / 1000);
      hxSpectrum.push_back(resp);
    }

    // either the spectrum has to be simulated by Prospect+Sail
    if (m_LabelParameters.find(label) != m_LabelParameters.end())
    {
      ProspectType::Pointer prospect = ProspectType::New();
      prospect->SetInput(m_LabelParameters[label]);

      SailType::Pointer sail = SailType::New();

      sail->SetLAI(lai);
      sail->SetAngl(m_AcquisitionParameters[std::string("Angl")]);
      sail->SetPSoil(m_AcquisitionParameters[std::string("PSoil")]);
      sail->SetSkyl(m_AcquisitionParameters[std::string("Skyl")]);
      sail->SetHSpot(m_AcquisitionParameters[std::string("HSpot")]);
      sail->SetTTS(m_AcquisitionParameters[std::string("TTS")]);
      sail->SetTTO(m_AcquisitionParameters[std::string("TTO")]);
      sail->SetPSI(m_AcquisitionParameters[std::string("PSI")]);
      sail->SetReflectance(prospect->GetReflectance());
      sail->SetTransmittance(prospect->GetTransmittance());
      sail->Update();

      for (unsigned int i = 0; i < SimNbBands; i++)
      {
        hxSpectrum[i].second = static_cast<typename OutputPixelType::ValueType>(sail->GetHemisphericalReflectance()->GetResponse()[i].second);
      }
    }
    // or the spectra has been set from outside the functor (ex. bare soil, etc.)
    else if (m_LabelSpectra.find(label) != m_LabelSpectra.end())
    {
      for (unsigned int i    = 0; i < SimNbBands; i++)
        hxSpectrum[i].second = static_cast<typename OutputPixelType::ValueType>(m_LabelSpectra[label][i]);
    }
    // or the class does not exist
    else
    {
      for (unsigned int i    = 0; i < SimNbBands; i++)
        hxSpectrum[i].second = static_cast<typename OutputPixelType::ValueType>(0);
    }
    // Spectral response \code{aResponse} is set using \code{hxSpectrum}.

    ResponseType::Pointer aResponse = ResponseType::New();
    aResponse->SetResponse(hxSpectrum);

    // Satellite RSR is initialized and set with \code{aResponse}. Reflectance
    // mode is used in this case to take into account solar irradiance into
    // spectral response reduction.

    ReduceResponseTypePointerType reduceResponse = ReduceResponseType::New();
    reduceResponse->SetInputSatRSR(m_SatRSR);
    reduceResponse->SetInputSpectralResponse(aResponse);

    reduceResponse->SetReflectanceMode(true);

    reduceResponse->CalculateResponse();
    VectorPairType reducedResponse = reduceResponse->GetReduceResponse()->GetResponse();


    // \code{pix} value is returned for desired Satellite bands

    for (unsigned int i = 0; i < m_SatRSR->GetNbBands(); i++)
      pix[i]            = static_cast<typename OutputPixelType::ValueType>(reducedResponse[i].second);
    return pix;
  }

  bool operator!=(const ProsailSimulatorFunctor& other) const
  {
    return (m_AcquisitionParameters != other.m_AcquisitionParameters || m_LabelParameters != other.m_LabelParameters);
  }

  bool operator==(const ProsailSimulatorFunctor& other) const
  {
    return (m_AcquisitionParameters == other.m_AcquisitionParameters && m_LabelParameters == other.m_LabelParameters);
  }

  /** The spectra associated with labels are supposed to have the same
   * sampling as a Prosail simulation, that is, 2000 bands starting at
   * 400nm up to 2400 nm*/
  inline void SetLabelSpectra(const TLabelSpectra& lSpectra)
  {
    m_LabelSpectra = lSpectra;
  }

  inline void SetLabelParameters(const TLabelParameter& lParameters)
  {
    m_LabelParameters = lParameters;
  }

  inline void SetAcquisitionParameters(const TAcquistionParameter& aParameters)
  {
    m_AcquisitionParameters = aParameters;
  }

  inline void SetRSR(const SatRSRPointerType rsr)
  {
    m_SatRSR = rsr;
  }

  inline SatRSRPointerType GetRSR() const
  {
    return m_SatRSR;
  }

protected:
  /** Spectra associated to labels*/
  LabelSpectraType m_LabelSpectra;
  /** Prospect+sail parameters to labels*/
  LabelParameterType m_LabelParameters;
  /** Prospect+sail acquisition parameters*/
  AcquistionParameterType m_AcquisitionParameters;
  /** Satellite Relative spectral response*/
  SatRSRPointerType m_SatRSR;

  /** Simulate pixels with mask != 0 ==> m_InvertedMask = false; */
  bool m_InvertedMask;
};

} // namespace Functor

// \code{TernaryFunctorImageFilterWithNBands} class is defined here.
// This class inherits form \doxygen{itk}{TernaryFunctorImageFilter} with additional nuber of band parameters.
// It's implementation is done to process Label, LAI, and mask image with Simulation functor.

template <class TInputImage1, class TInputImage2, class TInputImage3, class TOutputImage, class TFunctor>
class ITK_EXPORT TernaryFunctorImageFilterWithNBands : public itk::TernaryFunctorImageFilter<TInputImage1, TInputImage2, TInputImage3, TOutputImage, TFunctor>
{
public:
  using Self         = TernaryFunctorImageFilterWithNBands<TInputImage1, TInputImage2, TInputImage3, TOutputImage, TFunctor>;
  using Superclass   = itk::TernaryFunctorImageFilter<TInputImage1, TInputImage2, TInputImage3, TOutputImage, TFunctor>;
  using Pointer      = itk::SmartPointer<Self>;
  using ConstPointer = itk::SmartPointer<const Self>;

  /** Method for creation through the object factory. */
  itkNewMacro(Self);

  /** Macro defining the type*/
  itkTypeMacro(TernaryFunctorImageFilterWithNBands, SuperClass);

  /** Accessors for the number of bands*/
  itkSetMacro(NumberOfOutputBands, unsigned int);
  itkGetConstMacro(NumberOfOutputBands, unsigned int);

protected:
  TernaryFunctorImageFilterWithNBands()
  {
  }
  ~TernaryFunctorImageFilterWithNBands() override
  {
  }

  void GenerateOutputInformation() override
  {
    Superclass::GenerateOutputInformation();
    this->GetOutput()->SetNumberOfComponentsPerPixel(m_NumberOfOutputBands);
  }

private:
  TernaryFunctorImageFilterWithNBands(const Self&) = delete;
  void operator=(const Self&) = delete;

  unsigned int m_NumberOfOutputBands;
};
} // namespace otb

int main(int argc, char* argv[])
{
  char* cmifname = nullptr;
  if (argc != 10)
  {
    if (argc == 11) // cloud mask filename optional parameter
    {
      cmifname = argv[10];
    }
    else
    {
      std::cerr << "Wrong Parameters " << std::endl;
      return EXIT_FAILURE;
    }
  }
  char*        laiifname = argv[1];
  char*        outfname  = argv[2];
  char*        lifname   = argv[3];
  char*        mifname   = argv[4];
  char*        lpfname   = argv[5];
  char*        apfname   = argv[6];
  char*        rsfname   = argv[7];
  unsigned int nbBands   = static_cast<unsigned int>(atoi(argv[8]));
  char*        rootPath  = argv[9];

  // Read the label parameter file. It is assumed to have the form
  // label 1 Cab Car CBrown Cw Cm N   --> for vegetation classes
  // label 0 /path/to/spectra/file    --> for other classes


  // input images typedef are presented below. This example uses \code{double} LAI image, \code{binary} mask and
  //  cloud mask, and \code{integer} label image
  //

  using LAIPixelType    = double;
  using LabelType       = unsigned short;
  using MaskPixelType   = unsigned short;
  using OutputPixelType = float;
  // Image typedef
  using LAIImageType       = otb::Image<LAIPixelType, 2>;
  using LabelImageType     = otb::Image<LabelType, 2>;
  using MaskImageType      = otb::Image<MaskPixelType, 2>;
  using SimulatedImageType = otb::VectorImage<OutputPixelType, 2>;

  // reader typedef
  using LAIReaderType   = otb::ImageFileReader<LAIImageType>;
  using LabelReaderType = otb::ImageFileReader<LabelImageType>;
  using MaskReaderType  = otb::ImageFileReader<MaskImageType>;

  // Leaf parameters typedef is defined.

  using LeafParametersType        = otb::LeafParameters;
  using LeafParametersPointerType = LeafParametersType::Pointer;
  using LabelParameterMapType     = std::map<LabelType, LeafParametersPointerType>;

  // Sensor spectral response typedef is defined

  using PrecisionType        = double;
  using SpectraType          = std::vector<PrecisionType>;
  using SpectraParameterType = std::map<LabelType, SpectraType>;

  // Acquisition response typedef is defined

  using AcquistionParsType = std::map<std::string, double>;

  // Satellite typedef is defined

  using SatRSRType = otb::SatelliteRSR<PrecisionType, PrecisionType>;


  // Filter type is the specific \code{TernaryFunctorImageFilterWithNBands} defined below with specific functor.

  using SimuFunctorType = otb::Functor::ProsailSimulatorFunctor<LAIPixelType, LabelType, MaskPixelType, SimulatedImageType::PixelType, SpectraParameterType,
                                                                LabelParameterMapType, AcquistionParsType, SatRSRType>;
  using SimulatorType = otb::TernaryFunctorImageFilterWithNBands<LAIImageType, LabelImageType, MaskImageType, SimulatedImageType, SimuFunctorType>;

  // Read the acquisition parameter file which is like
  // Angl val
  // PSoil val
  // Skyl val
  // HSpot val
  // TTS val
  // TTO val
  // PSI val

  // Acquisition parameters are loaded using text file. A detailed definition of acquisition parameters can
  // be found in class \doxygen{otb}{SailModel}.

  AcquistionParsType acquistionPars;
  acquistionPars[std::string("Angl")]  = 0.0;
  acquistionPars[std::string("PSoil")] = 0.0;
  acquistionPars[std::string("Skyl")]  = 0.0;
  acquistionPars[std::string("HSpot")] = 0.0;
  acquistionPars[std::string("TTS")]   = 0.0;
  acquistionPars[std::string("TTO")]   = 0.0;
  acquistionPars[std::string("PSI")]   = 0.0;

  std::ifstream acquistionParsFile;

  try
  {
    acquistionParsFile.open(apfname);
  }
  catch (...)
  {
    std::cerr << "Could not open file " << apfname << std::endl;
    return EXIT_FAILURE;
  }

  // unsigned int acPar = 0;
  while (acquistionParsFile.good())
  {
    std::string line;
    std::getline(acquistionParsFile, line);
    std::stringstream ss(line);
    std::string       parName;
    ss >> parName;
    double parValue;
    ss >> parValue;
    acquistionPars[parName] = parValue;
  }

  acquistionParsFile.close();


  // Label parameters are loaded using text file.
  // Two type of object characteristic can be found. If label corresponds to vegetation class,
  // then leaf parameters are loaded.
  // A detailed definition of leaf parameters can be found in class \doxygen{otb}{LeafParameters} class.
  // Otherwise object reflectance is generated from $400$ to $2400nm$ using \href{http://speclib.jpl.nasa.gov/}{Aster database}.

  LabelParameterMapType labelParameters;
  std::ifstream         labelParsFile;

  SpectraParameterType spectraParameters;
  try
  {
    labelParsFile.open(lpfname, std::ifstream::in);
  }
  catch (...)
  {
    std::cerr << "Could not open file " << lpfname << std::endl;
    return EXIT_FAILURE;
  }

  while (labelParsFile.good())
  {
    char fileLine[256];
    labelParsFile.getline(fileLine, 256);

    if (fileLine[0] != '#')
    {
      std::stringstream ss(fileLine);
      unsigned short    label;
      ss >> label;
      unsigned short paramsOrSpectra;
      ss >> paramsOrSpectra;
      if (paramsOrSpectra == 1)
      {
        double Cab;
        ss >> Cab;
        double Car;
        ss >> Car;
        double CBrown;
        ss >> CBrown;
        double Cw;
        ss >> Cw;
        double Cm;
        ss >> Cm;
        double N;
        ss >> N;

        LeafParametersType::Pointer leafParams = LeafParametersType::New();

        leafParams->SetCab(Cab);
        leafParams->SetCar(Car);
        leafParams->SetCBrown(CBrown);
        leafParams->SetCw(Cw);
        leafParams->SetCm(Cm);
        leafParams->SetN(N);

        labelParameters[label] = leafParams;
      }
      else
      {
        std::string spectraFilename = rootPath;
        ss >> spectraFilename;
        spectraFilename            = rootPath + spectraFilename;
        using ResponseType         = otb::SpectralResponse<PrecisionType, PrecisionType>;
        ResponseType::Pointer resp = ResponseType::New();

        // Coefficient 100 since Aster database is given in % reflectance
        resp->Load(spectraFilename, 100.0);

        SpectraType spec;
        for (unsigned int i = 0; i < SimuFunctorType::SimNbBands; i++)
          // Prosail starts at 400 and lambda in Aster DB is in micrometers
          spec.push_back(static_cast<PrecisionType>((*resp)((i + 400.0) / 1000.0)));

        spectraParameters[label] = spec;
      }
    }
  }

  labelParsFile.close();


  // LAI image is read.

  LAIReaderType::Pointer laiReader = LAIReaderType::New();
  laiReader->SetFileName(laiifname);
  laiReader->Update();
  LAIImageType::Pointer laiImage = laiReader->GetOutput();

  // Label image is then read. Label image is processed using \code{ImageUniqueValuesCalculator} in order to check if all the labels are present in the
  // labelParameters file.


  LabelReaderType::Pointer labelReader = LabelReaderType::New();
  labelReader->SetFileName(lifname);
  labelReader->Update();

  LabelImageType::Pointer labelImage = labelReader->GetOutput();

  using UniqueCalculatorType = otb::ImageUniqueValuesCalculator<LabelImageType>;

  UniqueCalculatorType::Pointer uniqueCalculator = UniqueCalculatorType::New();

  uniqueCalculator->SetImage(labelImage);

  UniqueCalculatorType::ArrayType uniqueVals = uniqueCalculator->GetUniqueValues();
  if (uniqueVals.empty())
  {
    std::cerr << "No label value found!" << std::endl;
    return EXIT_FAILURE;
  }
  std::cout << "Labels are " << std::endl;
  UniqueCalculatorType::ArrayType::const_iterator uvIt = uniqueVals.begin();

  while (uvIt != uniqueVals.end())
  {
    std::cout << (*uvIt) << ", ";
    ++uvIt;
  }

  std::cout << std::endl;

  uvIt = uniqueVals.begin();

  while (uvIt != uniqueVals.end())
  {
    if (labelParameters.find(static_cast<LabelType>(*uvIt)) == labelParameters.end() &&
        spectraParameters.find(static_cast<LabelType>(*uvIt)) == spectraParameters.end() && static_cast<LabelType>(*uvIt) != 0)
    {
      std::cout << "label " << (*uvIt) << " not found in " << lpfname << std::endl;
      return EXIT_FAILURE;
    }
    ++uvIt;
  }


  // Mask image is read. If cloud mask is filename is given, a new mask image is generated with masks concatenation.


  MaskReaderType::Pointer miReader = MaskReaderType::New();
  miReader->SetFileName(mifname);
  miReader->UpdateOutputInformation();
  MaskImageType::Pointer maskImage = miReader->GetOutput();

  if (cmifname != nullptr)
  {

    MaskReaderType::Pointer cmiReader = MaskReaderType::New();
    cmiReader->SetFileName(cmifname);
    cmiReader->UpdateOutputInformation();

    using OrType             = itk::OrImageFilter<MaskImageType, MaskImageType, MaskImageType>;
    OrType::Pointer orfilter = OrType::New();

    orfilter->SetInput1(miReader->GetOutput());
    orfilter->SetInput2(cmiReader->GetOutput());

    orfilter->Update();
    maskImage = orfilter->GetOutput();
  }


  // A test is done. All images must have the same size.

  if (laiImage->GetLargestPossibleRegion().GetSize()[0] != labelImage->GetLargestPossibleRegion().GetSize()[0] ||
      laiImage->GetLargestPossibleRegion().GetSize()[1] != labelImage->GetLargestPossibleRegion().GetSize()[1] ||
      laiImage->GetLargestPossibleRegion().GetSize()[0] != maskImage->GetLargestPossibleRegion().GetSize()[0] ||
      laiImage->GetLargestPossibleRegion().GetSize()[1] != maskImage->GetLargestPossibleRegion().GetSize()[1])
  {
    std::cerr << "Image of labels, mask and LAI image must have the same size" << std::endl;
    return EXIT_FAILURE;
  }


  // Satellite RSR (Reduced Spectral Response) is defined using filename and band number given by command line arguments.

  SatRSRType::Pointer satRSR = SatRSRType::New();
  satRSR->SetNbBands(nbBands);
  satRSR->SetSortBands(false);
  satRSR->Load(rsfname);

  for (unsigned int i = 0; i < nbBands; ++i)
    std::cout << i << " " << (satRSR->GetRSR())[i]->GetInterval().first << " " << (satRSR->GetRSR())[i]->GetInterval().second << std::endl;

  // At this step all initialization have been done. The next step is to implement and initialize simulation functor \code{ProsailSimulatorFunctor}.

  SimuFunctorType simuFunctor;
  simuFunctor.SetLabelParameters(labelParameters);
  simuFunctor.SetLabelSpectra(spectraParameters);
  simuFunctor.SetAcquisitionParameters(acquistionPars);
  simuFunctor.SetRSR(satRSR);
  simuFunctor.SetInvertedMask(true);


  // Inputs and Functor are plugged to simulator filter.
  SimulatorType::Pointer simulator = SimulatorType::New();
  simulator->SetInput1(laiImage);
  simulator->SetInput2(labelImage);
  simulator->SetInput3(maskImage);
  simulator->SetFunctor(simuFunctor);
  simulator->SetNumberOfOutputBands(nbBands);

  //  The invocation of the \code{Update()} method triggers the
  //  execution of the pipeline.

  simulator->Update();


  // Write output image to disk

  using WriterType           = otb::ImageFileWriter<SimulatedImageType>;
  WriterType::Pointer writer = WriterType::New();

  writer->SetFileName(outfname);
  writer->SetInput(simulator->GetOutput());
  // writer->SetBufferNumberOfLinesDivisions(nbStreams);

  otb::StandardWriterWatcher watcher(writer, simulator, "Simulation");

  writer->Update();

  return EXIT_SUCCESS;
}