TrackFastSimSD.cxx

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/*
  Copyright (C) 2002-2025 CERN for the benefit of the ATLAS collaboration
*/
 
// Class header
#include "TrackWriteFastSim/TrackFastSimSD.h"
 
// Athena headers
#include "HitManagement/HitCollectionMap.h"
#include "MCTruth/AtlasG4EventUserInfo.h"
#include "MCTruth/TrackHelper.h"
 
// Geant4 headers
#include "G4ChargedGeantino.hh"
#include "G4DynamicParticle.hh"
#include "G4EventManager.hh"
#include "G4Geantino.hh"
#include "G4Track.hh"
#include "G4VPhysicalVolume.hh"
#include "G4VSolid.hh"
 
// STL headers
#include <cmath>
#include <memory>
 
TrackFastSimSD::TrackFastSimSD(const std::string& name, const std::string& outputCollectionName, const int SD_type)
  : G4VSensitiveDetector( name )
  , m_outputCollectionName( outputCollectionName )
  , m_SD_type( SD_type )
{
}
 
// Initialize from G4.
void TrackFastSimSD::Initialize(G4HCofThisEvent *)
{
  m_trackRecordCollection = getTrackRecordCollection();
}
 
G4bool TrackFastSimSD::ProcessHits(G4Step* aStep,G4TouchableHistory* )
{
  if (!m_SD_type) { return false; }
  const G4StepPoint *preStep=aStep->GetPreStepPoint();
  const G4VPhysicalVolume *preVol=preStep->GetPhysicalVolume();
  const G4StepPoint *postStep=aStep->GetPostStepPoint();
  const G4VPhysicalVolume *postVol=postStep->GetPhysicalVolume();
 
  if (preVol==postVol) { return false; }
 
  const G4Track *track(aStep->GetTrack());
 
  // PDG Code
  int pdgcode = (track->GetDefinition())?track->GetDefinition()->GetPDGEncoding():0;
  if (track->GetDefinition() == G4Geantino::Definition() ) pdgcode=999;
  if (track->GetDefinition() == G4ChargedGeantino::Definition() ) pdgcode=998;
 
  // Position and Momentum
  G4ThreeVector pos=postStep->GetPosition();
  G4ThreeVector mom=postStep->GetMomentum();
 
  if(m_SD_type==2)
    {
      // need to get the local position
      const G4TouchableHistory* touchHist = static_cast<const G4TouchableHistory*>(preStep->GetTouchable());
      const G4AffineTransform trans = track->GetTouchable()->GetHistory()->GetTopTransform(); // trans from global to local
      G4ThreeVector localPos=trans.TransformPoint(pos);
      G4ThreeVector localMom=mom;
      trans.ApplyAxisTransform(localMom); // rotate momentum as needed
      const G4VSolid *shape= touchHist->GetSolid();
      const G4ThreeVector normal=shape->SurfaceNormal(localPos);
      // check if particle is entering. if it is extiting don't record it.
      if(normal.dot(localPos)>=0.) return false;
    }
 
  // Energy
  const double ener=postStep->GetTotalEnergy();
 
  // Time
  const double time=postStep->GetGlobalTime();
 
  // Barcode
  TrackHelper trHelp(track);
  const int barcode = trHelp.GetBarcode(); // FIXME barcode based
  const int id = trHelp.GetUniqueID();
  const int status = trHelp.GetStatus();
 
  //create the TimedTrackRecord
  return AddHit(pdgcode,
                status,
                ener,
                mom,
                pos,
                time,
                barcode, // FIXME barcode based
                id,
                preVol->GetName());
}
 
void TrackFastSimSD::WriteTrack(const G4Track* track, const bool originPos, const bool originMom)
{
  if (!track) { G4cout << "ERROR: the track pointer was zero" << G4endl; return; }
 
  G4VPhysicalVolume *preVol=track->GetVolume();
 
  const int pdgcode = (track->GetDefinition())?track->GetDefinition()->GetPDGEncoding():0;
 
  const G4ThreeVector pos = originPos?track->GetVertexPosition():track->GetPosition();
  const double ener=originMom?(track->GetVertexKineticEnergy()+track->GetDynamicParticle()->GetMass()):track->GetTotalEnergy();
  G4ThreeVector mom = track->GetMomentum();
  if (originMom){
    double mommag = std::sqrt(std::pow(ener,2)-std::pow(track->GetDynamicParticle()->GetMass(),2));
    mom = track->GetVertexMomentumDirection()*mommag;
  }
 
  const double time=track->GetGlobalTime();
  TrackHelper trHelp(track);
  const int barcode = trHelp.GetBarcode(); // FIXME barcode based
  const int id = trHelp.GetUniqueID();
  const int status = trHelp.GetStatus();
 
  //create the TimedTrackRecord
  AddHit(pdgcode,
         status,
         ener,
         mom,
         pos,
         time,
         barcode, // FIXME barcode based
         id,
         preVol ? preVol->GetName() : "Unknown");
}
 
TrackRecordCollection* TrackFastSimSD::getTrackRecordCollection() const
{
  auto* eventManager = G4EventManager::GetEventManager();
  if (!eventManager) {
    return nullptr;
  }
 
  auto* eventInfo =
    dynamic_cast<AtlasG4EventUserInfo*>(eventManager->GetUserInformation());
  if (!eventInfo) {
    return nullptr;
  }
 
  std::shared_ptr<HitCollectionMap> hitCollections = eventInfo->GetHitCollectionMap();
  return hitCollections ? hitCollections->Find<TrackRecordCollection>(m_outputCollectionName)
                        : nullptr;
}