OptDetDigitizer_module.cc

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// OptDetDigitizer_module.cc
// Kazuhiro Terao <kazuhiro@nevis.columbia.edu>, Jul 2013
// based on code by Ben Jones and Christie Chiu, MIT, Sept 2012
//   bjpjones@mit.edu, cschiu@mit.edu
//
// This module starts from MC truth sim::OnePhoton objects
// and produces a digitized waveform.

// LArSoft includes
#include "larsim/Simulation/SimListUtils.h"
#include "lardataobj/Simulation/SimPhotons.h"
#include "lardataobj/OpticalDetectorData/OpticalTypes.h"
#include "lardataobj/OpticalDetectorData/ChannelData.h"
#include "lardataobj/OpticalDetectorData/ChannelDataGroup.h"
#include "larana/OpticalDetector/OpDigiProperties.h"
#include "larcore/Geometry/Geometry.h"

// ART includes
#include "art/Framework/Core/EDProducer.h"
#include "art/Framework/Core/ModuleMacros.h"
#include "art/Framework/Principal/Event.h"
#include "fhiclcpp/ParameterSet.h"
#include "art/Framework/Services/Registry/ServiceHandle.h"

// nurandom
#include "nurandom/RandomUtils/NuRandomService.h"

// CLHEP includes
#include "CLHEP/Random/RandFlat.h"
#include "CLHEP/Random/RandPoisson.h"

// C++ language includes
#include <cstring>

namespace opdet {

  class OptDetDigitizer : public art::EDProducer{
  public:
    explicit OptDetDigitizer(const fhicl::ParameterSet&);

  private:
    void produce(art::Event&) override;

    // The parameters we'll read from the .fcl file.
    std::string fInputModule;              // Input tag for OpDet collection
    float fSampleFreq;                     // in MHz
    float fTimeBegin;                      // in us
    float fTimeEnd;                        // in us
    float fQE;                             // quantum efficiency of opdet
    optdata::ADC_Count_t fSaturationScale;           // adc count w/ saturation occurs
    std::vector<optdata::ADC_Count_t> fPedMeanArray; // Array of pedestal baseline (per ch)
    float fDarkRate;                       // Noise rate in Hz
    optdata::ADC_Count_t fPedFlucAmp;                     // Pedestal fluctuation amplitude
    float fPedFlucRate;                    // Pedestal fluctuation rate
  //  float fWFRandTimeOffsetLow;            // The lower bound of WF's T=0 offset from Trigger
  //  float fWFRandTimeOffsetHigh;           // The upper bound of WF's T=0 offset from Trigger
    std::vector<double> fSinglePEWaveform;

    bool fSimGainSpread;

    CLHEP::HepRandomEngine& fEngine;
    CLHEP::RandFlat    fFlatRandom;
    CLHEP::RandPoisson fPoissonRandom;
    void AddDarkNoise (std::vector<double> &RawWF,double gain);
    void AddWaveform(optdata::TimeSlice_t time,
                     std::vector<double>& OldPulse,
                     std::vector<double>& NewPulse,
                     double factor,
                     bool extend=false);
    optdata::ChannelData ApplyDigitization (std::vector<double> const RawWF,
                                            optdata::Channel_t const ch) const;
    art::ServiceHandle<OpDigiProperties> fOpDigiProperties;
    art::ServiceHandle<geo::Geometry const> fGeom;

  };
} // namespace opdet

namespace opdet{

  DEFINE_ART_MODULE(OptDetDigitizer)

} //end namespace opdet

namespace opdet {

  OptDetDigitizer::OptDetDigitizer(fhicl::ParameterSet const& pset)
    : EDProducer{pset}
    , fEngine(art::ServiceHandle<rndm::NuRandomService>()->createEngine(*this, pset, "Seed"))
    , fFlatRandom{fEngine}
    , fPoissonRandom{fEngine}
  {
    // Infrastructure piece
    produces<std::vector< optdata::ChannelDataGroup> >();

    optdata::ChannelDataGroup dg;
    // Input Module and histogram parameters come from .fcl
    fInputModule   = pset.get<std::string>("InputModule");
    fSimGainSpread = pset.get<bool       >("SimGainSpread");
    fTimeBegin  = fOpDigiProperties->TimeBegin();
    fTimeEnd    = fOpDigiProperties->TimeEnd();
    fSampleFreq = fOpDigiProperties->SampleFreq();
    fQE         = fOpDigiProperties->QE();
    fDarkRate   = fOpDigiProperties->DarkRate();
    fPedFlucAmp = fOpDigiProperties->PedFlucAmp();
    fPedFlucRate= fOpDigiProperties->PedFlucRate();
    fSaturationScale = fOpDigiProperties->SaturationScale();
    fPedMeanArray = fOpDigiProperties->PedMeanArray();

    fSinglePEWaveform = fOpDigiProperties->SinglePEWaveform();
  }

  //-------------------------------------------------

  void OptDetDigitizer::AddWaveform (optdata::TimeSlice_t const time,
                                     std::vector<double> &OldPulse,
                                     std::vector<double> &NewPulse,
                                     double const factor,
                                     bool const extend)
  {
    if( (time+NewPulse.size()) > OldPulse.size() && extend )
      OldPulse.resize(time + NewPulse.size());
    for(size_t i = 0; i<NewPulse.size() && (time+i)<OldPulse.size(); ++i)
      OldPulse[time+i] += NewPulse[i] * factor;
  }

  //-------------------------------------------------

  void OptDetDigitizer::AddDarkNoise(std::vector<double> &RawWF, double gain){
    // Add dark noise
    double MeanDarkPulses = fDarkRate * (fTimeEnd-fTimeBegin) / 1000000;

    unsigned int NumberOfPulses = fPoissonRandom.fire(MeanDarkPulses);
    for(size_t i=0; i!=NumberOfPulses; ++i)
      {
        double PulseTime_ns = fTimeBegin*1000 + (fTimeEnd-fTimeBegin)*1000*(fFlatRandom.fire(1.0)); // Should be in ns
        optdata::TimeSlice_t PulseTime_ts = fOpDigiProperties->GetTimeSlice(PulseTime_ns);
        AddWaveform( PulseTime_ts,
                     RawWF,
                     fSinglePEWaveform,
                     gain);
      }

  }

  optdata::ChannelData OptDetDigitizer::ApplyDigitization(std::vector<double> const rawWF,
                                                          optdata::Channel_t const ch ) const
  {
    //
    // Digitization includes...
    //     (a) amplitude digitization
    //     (b) saturation
    //     (c) pedestal fluctuation
    //

    // prepare return data container
    optdata::ChannelData chData(ch);
    chData.reserve(rawWF.size());
    optdata::ADC_Count_t baseMean(fPedMeanArray.at(ch));
    for(optdata::TimeSlice_t time=0; time<rawWF.size(); ++time)
      {
        double thisSample = rawWF[time];

        optdata::ADC_Count_t thisCount = (optdata::ADC_Count_t)(thisSample)+baseMean;

        // (a) amplitude digitization
        if(CLHEP::RandFlat::shoot(1.0) < (thisSample - int(thisSample)))
          thisCount+=1;

        // (b) saturation
        if(thisCount > fSaturationScale) thisCount = fSaturationScale;

        chData.push_back(thisCount);
      }

    // (c) pedestal fluctuation
    double timeSpan = chData.size() * 1.e-6/(fOpDigiProperties->SampleFreq());
    unsigned int nFluc = CLHEP::RandPoisson::shoot(fPedFlucRate * timeSpan);
    for(size_t i=0; i<nFluc; ++i)
      {
        optdata::TimeSlice_t pulseTime(CLHEP::RandFlat::shoot(0.0,(double)(chData.size())));
        optdata::ADC_Count_t amp = chData[pulseTime];
        if( CLHEP::RandFlat::shoot(0.,1.) > 0.5)
          {
            amp += fPedFlucAmp;
            if(amp > fSaturationScale) amp=fSaturationScale;
          }
        else
          amp -= fPedFlucAmp;
        chData[pulseTime] = amp;
      }

    return chData;
  }

  //-------------------------------------------------

  void OptDetDigitizer::produce(art::Event& evt)
  {

    //
    // Event-wise initialization
    //

    // Infrastructure piece
    std::unique_ptr< std::vector<optdata::ChannelDataGroup > > StoragePtr (new std::vector<optdata::ChannelDataGroup>);

    // Read in the Sim Photons
    sim::SimPhotonsCollection ThePhotCollection = sim::SimListUtils::GetSimPhotonsCollection(evt,fInputModule);

    // Convert units into ns from us/MHz
    double timeBegin_ns  = fTimeBegin  *  1000;
    double timeEnd_ns    = fTimeEnd    *  1000;
    double sampleFreq_ns = fSampleFreq /  1000;

    // Compute # of timeslices to be stored in the output. This is defined by a user input (fcl file)
    optdata::TimeSlice_t timeSliceWindow(fOpDigiProperties->GetTimeSlice(timeEnd_ns));

    /*
      Create output data product, optdata::ChannelDataGroup for each gain channel.
      Note : Although the frame + sample number in DATA should have a reference of T=0 @ DAQ start time, this is
             not handled in MC. Hence we do not set them here (use constructor default)
    */
    optdata::ChannelDataGroup rawWFGroup_HighGain(optdata::kHighGain);
    optdata::ChannelDataGroup rawWFGroup_LowGain(optdata::kLowGain);
    // Reserve entries equal to # of channels
    rawWFGroup_HighGain.reserve(fGeom->NOpChannels());
    rawWFGroup_LowGain.reserve(fGeom->NOpChannels());

    /*
      Define "raw" waveform container which will be filled based on G4 photon timing + SPE waveform information.
      Note this is not completely an analog waveform because it is digitized in terms of time (as it is using std::vector).
    */
    std::vector<std::vector<double> > rawWF_HighGain(fGeom->NOpChannels(),std::vector<double>(timeSliceWindow,0.0));
    std::vector<std::vector<double> > rawWF_LowGain(fGeom->NOpChannels(),std::vector<double>(timeSliceWindow,0.0));

    /*
      Start data processing ... see following steps
      (1) Loop over input array of optical photons & fill "raw" waveform container w/ corresponding SPE waveform
      (2) Loop over filled "raw" waveform and process (digitization, adding noise, baseline spread, etc)
    */

    //
    // Step (1) ... loop over G4 optical photons
    //

    // For every OpDet, convert PE into waveform and combine all together
    for(sim::SimPhotonsCollection::const_iterator itOpDet=ThePhotCollection.begin(); itOpDet!=ThePhotCollection.end(); itOpDet++)
      {
        const sim::SimPhotons& ThePhot=itOpDet->second;

        int ch = ThePhot.OpChannel();
        // For every photon in the hit:
        for(const sim::OnePhoton& Phot: ThePhot)
          {
            // Sample a random subset according to QE
            if(fFlatRandom.fire(1.0)<=fQE)
              {
                optdata::TimeSlice_t PhotonTime(fOpDigiProperties->GetTimeSlice(Phot.Time));
                if( Phot.Time > timeBegin_ns  &&  Phot.Time < timeEnd_ns )
                  {
                    if(fSimGainSpread)
                      {
                        AddWaveform( PhotonTime, rawWF_HighGain[ch], fSinglePEWaveform, fOpDigiProperties->HighGain(ch));
                        AddWaveform( PhotonTime, rawWF_LowGain[ch], fSinglePEWaveform, fOpDigiProperties->LowGain(ch));
                      }
                    else
                      {
                        AddWaveform( PhotonTime, rawWF_HighGain[ch], fSinglePEWaveform, fOpDigiProperties->HighGainMean(ch));
                        AddWaveform( PhotonTime, rawWF_LowGain[ch], fSinglePEWaveform, fOpDigiProperties->LowGainMean(ch));
                      }
                  }
              } // random QE cut
          } // for each Photon in SimPhotons
      }

    //
    // Loop over "raw" waveform (channel-wise)
    //
    for(unsigned short iCh = 0; iCh < rawWF_LowGain.size(); ++iCh){
      rawWF_LowGain[iCh].resize((timeEnd_ns - timeBegin_ns) * sampleFreq_ns);
      rawWF_HighGain[iCh].resize((timeEnd_ns - timeBegin_ns) * sampleFreq_ns);

      // Add dark noise
      if(fSimGainSpread){
        AddDarkNoise(rawWF_LowGain[iCh],fOpDigiProperties->LowGain(iCh));
        AddDarkNoise(rawWF_HighGain[iCh],fOpDigiProperties->HighGain(iCh));
      }else{
        AddDarkNoise(rawWF_LowGain[iCh],fOpDigiProperties->LowGainMean(iCh));
        AddDarkNoise(rawWF_HighGain[iCh],fOpDigiProperties->HighGainMean(iCh));
      }

      // Apply digitization and make channel data
      optdata::ChannelData chData_HighGain(ApplyDigitization(rawWF_HighGain[iCh],iCh));
      optdata::ChannelData chData_LowGain(ApplyDigitization(rawWF_LowGain[iCh],iCh));

      rawWFGroup_HighGain.push_back(chData_HighGain);
      rawWFGroup_LowGain.push_back(chData_LowGain);
    } // for each OpDet in SimPhotonsCollection

    StoragePtr->push_back(rawWFGroup_HighGain);
    StoragePtr->push_back(rawWFGroup_LowGain);

    evt.put(std::move(StoragePtr));
  }
}