BDSSDSampler.cc

/* 
Beam Delivery Simulation (BDSIM) Copyright (C) BDSIM Collaboration, 2001 - 2026.
 
This file is part of BDSIM.
 
BDSIM is free software: you can redistribute it and/or modify 
it under the terms of the GNU General Public License as published 
by the Free Software Foundation version 3 of the License.
 
BDSIM is distributed in the hope that it will be useful, but 
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.
 
You should have received a copy of the GNU General Public License
along with BDSIM.  If not, see <http://www.gnu.org/licenses/>.
*/
#include "BDSGlobalConstants.hh" 
#include "BDSDebug.hh"
#include "BDSHitSampler.hh"
#include "BDSParticleCoordsFull.hh"
#include "BDSPhysicalConstants.hh"
#include "BDSSamplerRegistry.hh"
#include "BDSSDSampler.hh"
#include "BDSUtilities.hh"
 
#include "globals.hh" // geant4 types / globals
#include "G4AffineTransform.hh"
#include "G4DynamicParticle.hh"
#include "G4ParticleDefinition.hh"
#include "G4SDManager.hh"
#include "G4Step.hh"
#include "G4StepPoint.hh"
#include "G4ThreeVector.hh"
#include "G4TouchableHistory.hh"
#include "G4Track.hh"
#include "G4VPhysicalVolume.hh"
#include "G4VTouchable.hh"
 
#include <vector>
 
BDSSDSampler::BDSSDSampler(const G4String& name):
  BDSSensitiveDetector("sampler/" + name),
  SamplerCollection(nullptr),
  itsCollectionName(name),
  itsHCID(-1),
  registry(nullptr),
  globals(nullptr)
{
  collectionName.insert(name);
}
 
BDSSDSampler::~BDSSDSampler()
{;}
 
void BDSSDSampler::Initialize(G4HCofThisEvent* HCE)
{
  // Create Sampler hits collection
  SamplerCollection = new BDSHitsCollectionSampler(GetName(),itsCollectionName);
 
  // Record id for use in EventAction to save time - slow string lookup by collection name
  if (itsHCID < 0)
    {itsHCID = G4SDManager::GetSDMpointer()->GetCollectionID(SamplerCollection);}
  HCE->AddHitsCollection(itsHCID,SamplerCollection);
 
  registry = BDSSamplerRegistry::Instance(); // cache pointer to registry
  globals  = BDSGlobalConstants::Instance(); // cache pointer to globals
}
 
G4bool BDSSDSampler::ProcessHits(G4Step* aStep, G4TouchableHistory* /*readOutTH*/)
{
  // Do not store hit if the particle pre step point is not on the boundary
  G4StepPoint* postStepPoint = aStep->GetPostStepPoint();
  if(postStepPoint->GetStepStatus() != fGeomBoundary)
    {
#ifdef BDSDEBUG
      G4cout << __METHOD_NAME__ << "not storing as not on geometry boundary" << G4endl;
#endif
      return false; // this step was not stored
    }
  
  G4Track* track    = aStep->GetTrack();
  const G4DynamicParticle* dp = track->GetDynamicParticle();
  G4int TrackID     = track->GetTrackID();           // unique ID of track
  G4int ParentID    = track->GetParentID();          // unique ID of track's mother
  G4double T        = track->GetGlobalTime();        // time since beginning of event
  G4double energy   = track->GetTotalEnergy();       // total track energy
  G4double charge   = dp->GetCharge(); // dynamic effective charge
  G4int turnstaken  = globals->TurnsTaken();         // turn Number
  const G4ThreeVector& pos = track->GetPosition();          // current particle position (global)
  const G4ThreeVector& mom = track->GetMomentumDirection(); // current particle direction (global) (unit)
  G4double weight   = track->GetWeight();            // weighting
  G4int nElectrons  = dp->GetTotalOccupancy();
  G4double mass     = dp->GetMass();
  G4double rigidity = 0;
  if (BDS::IsFinite(charge))
    {rigidity = BDS::Rigidity(track->GetMomentum().mag(), charge);}
  G4double p = dp->GetTotalMomentum();
  
  // The copy number of physical volume is the sampler ID in BDSIM scheme.
  // track->GetVolume gives the volume in the mass world. pre/postStepPoint->->GetVolume()
  // give the ones in the parallel sampler world this SD is attached to. If the post step
  // point is on a boundary, it belongs to the next volume - ie not the one of interest
  // so always use the pre step point for volume identification.
  G4StepPoint* preStepPoint = aStep->GetPreStepPoint();
  G4int samplerID   = preStepPoint->GetTouchable()->GetVolume()->GetCopyNo();
 
  //Initialize variables for the local position and direction
  G4ThreeVector localPosition;
  G4ThreeVector localDirection;
  
  // Get coordinate transform and prepare local coordinates
  G4Transform3D globalToLocal = registry->GetTransformInverse(samplerID);
  if (globalToLocal == G4Transform3D::Identity) // no transform was provided - look it up
    {
#ifdef BDSDEBUG
      G4cout << __METHOD_NAME__ << "Getting transform dynamically from geometry." << G4endl;
#endif
      // Transform not provided so look up geometry and get the transform. OK in mass world
      // but error-prone in parallel worlds for very thin volumes.
      // NOTE: we're looking up mass world here!
      G4AffineTransform tf = preStepPoint->GetTouchableHandle()->GetHistory()->GetTopTransform();
      localPosition  = tf.TransformPoint(pos);
      localDirection = tf.TransformAxis(mom);
    }
  else
    {
      // The global to local transform is defined in the registry.
      // Cast 3 vector to 'point' to transform position (required to be explicit for * operator)
      localPosition  = globalToLocal * (HepGeom::Point3D<G4double>)pos;
      // Now, if the sampler is infinitely thin, the local z should be 0, but it's finite.
      // Account for this by purposively setting local z to be 0.
      localPosition.setZ(0.0);
      // Cast 3 vector to 3 vector to transform vector (required to be explicit for * operator)
      localDirection = globalToLocal * (HepGeom::Vector3D<G4double>)mom;
    }
 
  const BDSSamplerPlacementRecord& info = registry->GetInfo(samplerID);
  G4double s           = info.SPosition();
  G4int beamlineIndex  = info.BeamlineIndex();
  G4int    PDGtype     = track->GetDefinition()->GetPDGEncoding();
  G4String pName       = track->GetDefinition()->GetParticleName();
 
  BDSParticleCoordsFull coords(localPosition.x(),
                               localPosition.y(),
                               localPosition.z(),
                               localDirection.x(),
                               localDirection.y(),
                               localDirection.z(),
                               T,
                               s,
                               energy,
                               weight);
 
  BDSHitSampler* smpHit = new BDSHitSampler(samplerID,
                                            coords,
                                            p,
                                            mass,
                                            charge,
                                            rigidity,
                                            PDGtype,
                                            ParentID,
                                            TrackID,
                                            turnstaken,
                                            beamlineIndex,
                                            nElectrons);
  
  SamplerCollection->insert(smpHit);
  return true; // the hit was stored
}
 
G4VHit* BDSSDSampler::last() const
{
  BDSHitSampler* lastHit = SamplerCollection->GetVector()->back();
  return dynamic_cast<G4VHit*>(lastHit);
}