G4ITTransportation.cc

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// $Id: G4ITTransportation.cc 71125 2013-06-11 15:39:09Z gcosmo $
//
/// \brief This class is a slightly modified version of G4Transportation
///        initially written by John Apostolakis and colleagues
///        But it should use the exact same algorithm
//
// Contact : Mathieu Karamitros (kara (AT) cenbg . in2p3 . fr)
//
// History :
// -----------
// =======================================================================
// Modified:
//   28 Oct  2011, P.Gumpl./J.Ap: Detect gravity field, use magnetic moment
//   20 Nov  2008, J.Apostolakis: Push safety to helper - after ComputeSafety
//    9 Nov  2007, J.Apostolakis: Flag for short steps, push safety to helper
//   19 Jan  2006, P.MoraDeFreitas: Fix for suspended tracks (StartTracking)
//   11 Aug  2004, M.Asai: Add G4VSensitiveDetector* for updating stepPoint.
//   21 June 2003, J.Apostolakis: Calling field manager with
//                     track, to enable it to configure its accuracy
//   13 May  2003, J.Apostolakis: Zero field areas now taken into
//                     account correclty in all cases (thanks to W Pokorski).
//   29 June 2001, J.Apostolakis, D.Cote-Ahern, P.Gumplinger:
//                     correction for spin tracking
//   20 Febr 2001, J.Apostolakis:  update for new FieldTrack
//   22 Sept 2000, V.Grichine:     update of Kinetic Energy
//  ---------------------------------------------------
//   10 Oct  2011, M.Karamitros:   G4ITTransportation created
// Created:  19 March 1997, J. Apostolakis
// =======================================================================
//
// -------------------------------------------------------------------

#include "G4ITTransportation.hh"
#include "G4SystemOfUnits.hh"
#include "G4TransportationManager.hh"
#include "G4ITTransportationManager.hh"
#include "G4ProductionCutsTable.hh"
#include "G4ParticleTable.hh"
#include "G4ITNavigator.hh"
#include "G4PropagatorInField.hh"
#include "G4FieldManager.hh"
#include "G4ChordFinder.hh"
#include "G4SafetyHelper.hh"
#include "G4FieldManagerStore.hh"

#include "G4UnitsTable.hh"

class G4VSensitiveDetector;

#ifndef State
#define State(theXInfo) (fTransportationState->theXInfo)
#endif

//#define G4DEBUG_TRANSPORT 1

G4ITTransportation::G4ITTransportation(const G4String& aName, int verbose) :
    G4VITProcess(aName, fTransportation),
    InitProcessState(fTransportationState, fpState),
    fThreshold_Warning_Energy( 100 * MeV ),
    fThreshold_Important_Energy( 250 * MeV ),
    fThresholdTrials( 10 ),
    fUnimportant_Energy( 1 * MeV ),  // Not used
    fSumEnergyKilled( 0.0 ), fMaxEnergyKilled( 0.0 ),
    fShortStepOptimisation(false),    // Old default: true (=fast short steps)
    fVerboseLevel( verbose )
{
    pParticleChange = &fParticleChange;
    G4TransportationManager* transportMgr ;
    transportMgr = G4TransportationManager::GetTransportationManager() ;
    G4ITTransportationManager* ITtransportMgr ;
    ITtransportMgr = G4ITTransportationManager::GetTransportationManager() ;
    fLinearNavigator = ITtransportMgr->GetNavigatorForTracking() ;
    fFieldPropagator = transportMgr->GetPropagatorInField() ;
    fpSafetyHelper =   0; // transportMgr->GetSafetyHelper();  // New

    // Cannot determine whether a field exists here, as it would
    //  depend on the relative order of creating the detector's
    //  field and this process. That order is not guaranted.
    // Instead later the method DoesGlobalFieldExist() is called

    enableAtRestDoIt    = false;
    enableAlongStepDoIt = true;
    enablePostStepDoIt  = true;
    SetProcessSubType(60);
    SetInstantiateProcessState(true);
    G4VITProcess::SetInstantiateProcessState(false);
    fInstantiateProcessState = true;
}


G4ITTransportation::G4ITTransportation(const G4ITTransportation& right) :
    G4VITProcess(right),
    InitProcessState(fTransportationState, fpState)
{
    // Copy attributes
    fVerboseLevel               = right.fVerboseLevel ;
    fThreshold_Warning_Energy   = right.fThreshold_Warning_Energy;
    fThreshold_Important_Energy = right.fThreshold_Important_Energy;
    fThresholdTrials            = right.fThresholdTrials;
    fUnimportant_Energy         = right.fUnimportant_Energy;
    fSumEnergyKilled            = right.fSumEnergyKilled;
    fMaxEnergyKilled            = right.fMaxEnergyKilled;
    fShortStepOptimisation      = right.fShortStepOptimisation;

    // Setup Navigators
    G4TransportationManager* transportMgr ;
    transportMgr = G4TransportationManager::GetTransportationManager() ;
    G4ITTransportationManager* ITtransportMgr ;
    ITtransportMgr = G4ITTransportationManager::GetTransportationManager() ;
    fLinearNavigator = ITtransportMgr->GetNavigatorForTracking() ;
    fFieldPropagator = transportMgr->GetPropagatorInField() ;
    fpSafetyHelper =   0; //transportMgr->GetSafetyHelper();  // New

    // Cannot determine whether a field exists here, as it would
    //  depend on the relative order of creating the detector's
    //  field and this process. That order is not guaranted.
    // Instead later the method DoesGlobalFieldExist() is called

    enableAtRestDoIt    = false;
    enableAlongStepDoIt = true;
    enablePostStepDoIt  = true;

    pParticleChange = &fParticleChange;
    SetInstantiateProcessState(true);
    G4VITProcess::SetInstantiateProcessState(false);
    fInstantiateProcessState = right.fInstantiateProcessState;
}

G4ITTransportation& G4ITTransportation::operator=(const G4ITTransportation& right)
{
    if(this == &right) return *this;
    return *this;
}

//////////////////////////////////////////////////////////////////////////////
/// Process State
//////////////////////////////////////////////////////////////////////////////
G4ITTransportation::G4ITTransportationState::G4ITTransportationState() : G4ProcessState(),
    fCurrentTouchableHandle(0)
{
    fTransportEndPosition = G4ThreeVector(0,0,0);
    fTransportEndMomentumDir = G4ThreeVector(0,0,0);
    fTransportEndKineticEnergy = -1;
    fTransportEndSpin = G4ThreeVector(0,0,0);
    fMomentumChanged = false;
    fEnergyChanged = false;
    fEndGlobalTimeComputed = false;
    fCandidateEndGlobalTime = -1;
    fParticleIsLooping = false;
    static G4ThreadLocal G4TouchableHandle *nullTouchableHandle = 0;
    if (!nullTouchableHandle) nullTouchableHandle = new  G4TouchableHandle; // Points to (G4VTouchable*) 0
    fCurrentTouchableHandle = *nullTouchableHandle;
    fGeometryLimitedStep = false;
    fPreviousSftOrigin = G4ThreeVector(0,0,0);
    fPreviousSafety = 0.0;
    fNoLooperTrials = false;
    endpointDistance= -1;
}

G4ITTransportation::G4ITTransportationState::~G4ITTransportationState()
{
    ;
}

G4ITTransportation::~G4ITTransportation()
{
#ifdef G4VERBOSE
    if( (fVerboseLevel > 0) && (fSumEnergyKilled > 0.0 ) )
    {
        G4cout << " G4ITTransportation: Statistics for looping particles " << G4endl;
        G4cout << "   Sum of energy of loopers killed: " <<  fSumEnergyKilled << G4endl;
        G4cout << "   Max energy of loopers killed: " <<  fMaxEnergyKilled << G4endl;
    }
#endif
}

G4bool G4ITTransportation::DoesGlobalFieldExist()
{
    G4TransportationManager* transportMgr;
    transportMgr= G4TransportationManager::GetTransportationManager();

    // fFieldExists= transportMgr->GetFieldManager()->DoesFieldExist();
    // return fFieldExists;
    return transportMgr->GetFieldManager()->DoesFieldExist();
}


//////////////////////////////////////////////////////////////////////////
//
// Responsibilities:
//    Find whether the geometry limits the Step, and to what length
//    Calculate the new value of the safety and return it.
//    Store the final time, position and momentum.
G4double G4ITTransportation::AlongStepGetPhysicalInteractionLength(
        const G4Track& track,
        G4double ,
        G4double currentMinimumStep,
        G4double& currentSafety,
        G4GPILSelection* selection)
{
    G4double geometryStepLength(-1.0), newSafety(-1.0) ;

    State(fParticleIsLooping) = false ;
    State(fEndGlobalTimeComputed) = false ;
    State(fGeometryLimitedStep) = false ;

    // Initial actions moved to  StartTrack()
    // --------------------------------------
    // Note: in case another process changes touchable handle
    //    it will be necessary to add here (for all steps)
    State(fCurrentTouchableHandle) = track.GetTouchableHandle();

    // GPILSelection is set to defaule value of CandidateForSelection
    // It is a return value
    //
    *selection = CandidateForSelection ;

    // Get initial Energy/Momentum of the track
    //
    const G4DynamicParticle*    pParticle  = track.GetDynamicParticle() ;
//    const G4ParticleDefinition* pParticleDef   = pParticle->GetDefinition() ;
    G4ThreeVector startMomentumDir       = pParticle->GetMomentumDirection() ;
    G4ThreeVector startPosition          = track.GetPosition() ;

    // G4double   theTime        = track.GetGlobalTime() ;

    // The Step Point safety can be limited by other geometries and/or the
    // assumptions of any process - it's not always the geometrical safety.
    // We calculate the starting point's isotropic safety here.
    //
    G4ThreeVector OriginShift = startPosition - State(fPreviousSftOrigin) ;
    G4double      MagSqShift  = OriginShift.mag2() ;
    if( MagSqShift >= sqr(State(fPreviousSafety)) )
    {
        currentSafety = 0.0 ;
    }
    else
    {
        currentSafety = State(fPreviousSafety) - std::sqrt(MagSqShift) ;
    }

    // Is the particle charged ?
    //
    G4double              particleCharge = pParticle->GetCharge() ;


    // There is no need to locate the current volume. It is Done elsewhere:
    //   On track construction
    //   By the tracking, after all AlongStepDoIts, in "Relocation"

    // Check whether the particle have an (EM) field force exerting upon it
    //
    G4FieldManager* fieldMgr=0;
    G4bool          fieldExertsForce = false ;
    if( (particleCharge != 0.0) )
    {
        fieldMgr= fFieldPropagator->FindAndSetFieldManager( track.GetVolume() );
        if (fieldMgr != 0)
        {
            // Message the field Manager, to configure it for this track
            fieldMgr->ConfigureForTrack( &track );
            // Moved here, in order to allow a transition
            //   from a zero-field  status (with fieldMgr->(field)0
            //   to a finite field  status

            // If the field manager has no field, there is no field !
            fieldExertsForce = (fieldMgr->GetDetectorField() != 0);
        }
    }

    // G4cout << " G4Transport:  field exerts force= " << fieldExertsForce
    //   << "  fieldMgr= " << fieldMgr << G4endl;

    // Choose the calculation of the transportation: Field or not
    //
    if( !fieldExertsForce )
    {
        G4double linearStepLength ;
        if( fShortStepOptimisation && (currentMinimumStep <= currentSafety) )
        {
            // The Step is guaranteed to be taken
            //
            geometryStepLength   = currentMinimumStep ;
            State(fGeometryLimitedStep) = false ;
        }
        else
        {
            //  Find whether the straight path intersects a volume
            //
            linearStepLength = fLinearNavigator->ComputeStep( startPosition,
                                                              startMomentumDir,
                                                              currentMinimumStep,
                                                              newSafety) ;
            // Remember last safety origin & value.
            //
            State(fPreviousSftOrigin) = startPosition ;
            State(fPreviousSafety)    = newSafety ;
            // fpSafetyHelper->SetCurrentSafety( newSafety, startPosition);

            // The safety at the initial point has been re-calculated:
            //
            currentSafety = newSafety ;

            State(fGeometryLimitedStep)= (linearStepLength <= currentMinimumStep);
            if( State(fGeometryLimitedStep) )
            {
                // The geometry limits the Step size (an intersection was found.)
                geometryStepLength   = linearStepLength ;
            }
            else
            {
                // The full Step is taken.
                geometryStepLength   = currentMinimumStep ;
            }
        }
        State(endpointDistance) = geometryStepLength ;

        // Calculate final position
        //
        State(fTransportEndPosition) = startPosition+geometryStepLength*startMomentumDir ;

        // Momentum direction, energy and polarisation are unchanged by transport
        //
        State(fTransportEndMomentumDir)   = startMomentumDir ;
        State(fTransportEndKineticEnergy) = track.GetKineticEnergy() ;
        State(fTransportEndSpin)          = track.GetPolarization();
        State(fParticleIsLooping)         = false ;
        State(fMomentumChanged)           = false ;
        State(fEndGlobalTimeComputed)     = true ;
        State(theInteractionTimeLeft)     = State(endpointDistance)/track.GetVelocity();
        State(fCandidateEndGlobalTime)    = State(theInteractionTimeLeft)+track.GetGlobalTime();

        //        G4cout << "track.GetVelocity() : " << track.GetVelocity() << G4endl;
        //        G4cout << "State(endpointDistance) : " << G4BestUnit(State(endpointDistance),"Length") << G4endl;
        //        G4cout << "State(theInteractionTimeLeft) : " << G4BestUnit(State(theInteractionTimeLeft),"Time") << G4endl;
        //        G4cout << "track.GetGlobalTime() : " << G4BestUnit(track.GetGlobalTime(),"Time") << G4endl;

    }
    else   //  A field exerts force
    {

        G4ExceptionDescription exceptionDescription;
        exceptionDescription << "ITTransportation does not support external fields.";
        exceptionDescription << " If you are dealing with a tradiational MC simulation, ";
        exceptionDescription << "please use G4Transportation.";

        G4Exception("G4ITTransportation::AlongStepGetPhysicalInteractionLength","NoExternalFieldSupport",
                    FatalException,exceptionDescription);
 /*
        G4double       momentumMagnitude = pParticle->GetTotalMomentum() ;
        //        G4ThreeVector  EndUnitMomentum ;
        G4double       lengthAlongCurve ;
        G4double       restMass = pParticleDef->GetPDGMass() ;

        fFieldPropagator->SetChargeMomentumMass( particleCharge,    // in e+ units
                                                 momentumMagnitude, // in Mev/c
                                                 restMass           ) ;

        G4ThreeVector spin        = track.GetPolarization() ;
        G4FieldTrack  aFieldTrack = G4FieldTrack( startPosition,
                                                  track.GetMomentumDirection(),
                                                  0.0,
                                                  track.GetKineticEnergy(),
                                                  restMass,
                                                  track.GetVelocity(),
                                                  track.GetGlobalTime(), // Lab.
                                                  track.GetProperTime(), // Part.
                                                  &spin                  ) ;
        if( currentMinimumStep > 0 )
        {
            // Do the Transport in the field (non recti-linear)
            //
            lengthAlongCurve = fFieldPropagator->ComputeStep( aFieldTrack,
                                                              currentMinimumStep,
                                                              currentSafety,
                                                              track.GetVolume() ) ;
            State(fGeometryLimitedStep)= lengthAlongCurve < currentMinimumStep;
            if( State(fGeometryLimitedStep) )
            {
                geometryStepLength   = lengthAlongCurve ;
            }
            else
            {
                geometryStepLength   = currentMinimumStep ;
            }

            // Remember last safety origin & value.
            //
            State(fPreviousSftOrigin) = startPosition ;
            State(fPreviousSafety)    = currentSafety ;
            fpSafetyHelper->SetCurrentSafety( newSafety, startPosition);
        }
        else
        {
            geometryStepLength   = lengthAlongCurve= 0.0 ;
            State(fGeometryLimitedStep) = false ;
        }

        // Get the End-Position and End-Momentum (Dir-ection)
        //
        State(fTransportEndPosition) = aFieldTrack.GetPosition() ;

        // Momentum:  Magnitude and direction can be changed too now ...
        //
        State(fMomentumChanged)         = true ;
        State(fTransportEndMomentumDir) = aFieldTrack.GetMomentumDir() ;

        State(fTransportEndKineticEnergy)  = aFieldTrack.GetKineticEnergy() ;

        if( fFieldPropagator->GetCurrentFieldManager()->DoesFieldChangeEnergy() )
        {
            // If the field can change energy, then the time must be integrated
            //    - so this should have been updated
            //
            State(fCandidateEndGlobalTime)   = aFieldTrack.GetLabTimeOfFlight();
            State(fEndGlobalTimeComputed)    = true;

            State(theInteractionTimeLeft) = State(fCandidateEndGlobalTime) - track.GetGlobalTime() ;

            // was ( State(fCandidateEndGlobalTime) != track.GetGlobalTime() );
            // a cleaner way is to have FieldTrack knowing whether time is updated.
        }
        else
        {
            // The energy should be unchanged by field transport,
            //    - so the time changed will be calculated elsewhere
            //
            State(fEndGlobalTimeComputed) = false;

            // Check that the integration preserved the energy
            //     -  and if not correct this!
            G4double  startEnergy= track.GetKineticEnergy();
            G4double  endEnergy= State(fTransportEndKineticEnergy);

            static G4int no_inexact_steps=0, no_large_ediff;
            G4double absEdiff = std::fabs(startEnergy- endEnergy);
            if( absEdiff > perMillion * endEnergy )
            {
                no_inexact_steps++;
                // Possible statistics keeping here ...
            }
#ifdef G4VERBOSE
            if( fVerboseLevel > 1 )
            {
                if( std::fabs(startEnergy- endEnergy) > perThousand * endEnergy )
                {
                    static G4int no_warnings= 0, warnModulo=1,  moduloFactor= 10;
                    no_large_ediff ++;
                    if( (no_large_ediff% warnModulo) == 0 )
                    {
                        no_warnings++;
                        G4cout << "WARNING - G4Transportation::AlongStepGetPIL() "
                               << "   Energy change in Step is above 1^-3 relative value. " << G4endl
                               << "   Relative change in 'tracking' step = "
                               << std::setw(15) << (endEnergy-startEnergy)/startEnergy << G4endl
                               << "     Starting E= " << std::setw(12) << startEnergy / MeV << " MeV " << G4endl
                               << "     Ending   E= " << std::setw(12) << endEnergy   / MeV << " MeV " << G4endl;
                        G4cout << " Energy has been corrected -- however, review"
                               << " field propagation parameters for accuracy."  << G4endl;
                        if( (fVerboseLevel > 2 ) || (no_warnings<4) || (no_large_ediff == warnModulo * moduloFactor) )
                        {
                            G4cout << " These include EpsilonStepMax(/Min) in G4FieldManager "
                                   << " which determine fractional error per step for integrated quantities. " << G4endl
                                   << " Note also the influence of the permitted number of integration steps."
                                   << G4endl;
                        }
                        G4cerr << "ERROR - G4Transportation::AlongStepGetPIL()" << G4endl
                               << "        Bad 'endpoint'. Energy change detected"
                               << " and corrected. "
                               << " Has occurred already "
                               << no_large_ediff << " times." << G4endl;
                        if( no_large_ediff == warnModulo * moduloFactor )
                        {
                            warnModulo *= moduloFactor;
                        }
                    }
                }
            }  // end of if (fVerboseLevel)
#endif
            // Correct the energy for fields that conserve it
            //  This - hides the integration error
            //       - but gives a better physical answer
            State(fTransportEndKineticEnergy)= track.GetKineticEnergy();
        }

        State(fTransportEndSpin) = aFieldTrack.GetSpin();
        State(fParticleIsLooping) = fFieldPropagator->IsParticleLooping() ;
        State(endpointDistance)   = (State(fTransportEndPosition) - startPosition).mag() ;
        //        State(theInteractionTimeLeft) = track.GetVelocity()/State(endpointDistance) ;
*/
    }

    // If we are asked to go a step length of 0, and we are on a boundary
    // then a boundary will also limit the step -> we must flag this.
    //
    if( currentMinimumStep == 0.0 )
    {
        if( currentSafety == 0.0 )
        {
            State(fGeometryLimitedStep) = true ;
//            G4cout << "!!!! Safety is NULL, on the Boundary !!!!!" << G4endl;
//            G4cout << " Track position : " << track.GetPosition() /nanometer << G4endl;
        }
    }

    // Update the safety starting from the end-point,
    // if it will become negative at the end-point.
    //
    if( currentSafety < State(endpointDistance) )
    {
        // if( particleCharge == 0.0 )
        //    G4cout  << "  Avoiding call to ComputeSafety : charge = 0.0 " << G4endl;

        if( particleCharge != 0.0 )
        {

            G4double endSafety =
                    fLinearNavigator->ComputeSafety( State(fTransportEndPosition)) ;
            currentSafety      = endSafety ;
            State(fPreviousSftOrigin) = State(fTransportEndPosition) ;
            State(fPreviousSafety)    = currentSafety ;
            fpSafetyHelper->SetCurrentSafety( currentSafety, State(fTransportEndPosition));

            // Because the Stepping Manager assumes it is from the start point,
            //  add the StepLength
            //
            currentSafety     += State(endpointDistance) ;

#ifdef G4DEBUG_TRANSPORT
            G4cout.precision(12) ;
            G4cout << "***G4Transportation::AlongStepGPIL ** " << G4endl  ;
            G4cout << "  Called Navigator->ComputeSafety at " << State(fTransportEndPosition)
                   << "    and it returned safety= " << endSafety << G4endl ;
            G4cout << "  Adding endpoint distance " << State(endpointDistance)
                   << "   to obtain pseudo-safety= " << currentSafety << G4endl ;
#endif
        }
    }

    //    fParticleChange.ProposeTrueStepLength(geometryStepLength) ;

    return geometryStepLength ;
}


void G4ITTransportation::ComputeStep(const G4Track& track,
                                     const G4Step& /*step*/,
                                     const double timeStep,
                                     double& oPhysicalStep)
{
    const G4DynamicParticle*    pParticle  = track.GetDynamicParticle() ;
    G4ThreeVector startMomentumDir       = pParticle->GetMomentumDirection() ;
    G4ThreeVector startPosition          = track.GetPosition() ;

    track.CalculateVelocity();
    G4double initialVelocity   = track.GetVelocity() ;

    State(fGeometryLimitedStep) = false;

    /////////////////////////
    // !!! CASE NO FIELD !!!
    /////////////////////////
    State(fCandidateEndGlobalTime) = timeStep + track.GetGlobalTime();
    State(fEndGlobalTimeComputed) = true ;

    // Choose the calculation of the transportation: Field or not
    //
    if( !State(fMomentumChanged) )
    {
        //        G4cout << "Momentum has not changed" << G4endl;
        fParticleChange.ProposeVelocity(initialVelocity);
        oPhysicalStep =  initialVelocity*timeStep ;

        // Calculate final position
        //
        State(fTransportEndPosition) = startPosition + oPhysicalStep*startMomentumDir ;
    }
}


//////////////////////////////////////////////////////////////////////////
//
//   Initialize ParticleChange  (by setting all its members equal
//                               to corresponding members in G4Track)
#include "G4ParticleTable.hh"
G4VParticleChange* G4ITTransportation::AlongStepDoIt( const G4Track& track,
                                                      const G4Step&  stepData )
{

    //    G4cout << "G4ITTransportation::AlongStepDoIt" << G4endl;
    // set  pdefOpticalPhoton
    //Andrea Dotti: the following statement should be in a single line:
    // G4-MT transformation tools get confused if statement spans two lines
    // If needed contact: adotti@slac.stanford.edu
    static G4ThreadLocal  G4ParticleDefinition* pdefOpticalPhoton  = 0 ; if (!pdefOpticalPhoton) pdefOpticalPhoton= G4ParticleTable::GetParticleTable()->FindParticle("opticalphoton");

    static G4ThreadLocal G4int noCalls=0;
    noCalls++;

    fParticleChange.Initialize(track) ;

    //  Code for specific process
    //
    fParticleChange.ProposePosition(State(fTransportEndPosition)) ;
    fParticleChange.ProposeMomentumDirection(State(fTransportEndMomentumDir)) ;
    fParticleChange.ProposeEnergy(State(fTransportEndKineticEnergy)) ;
    fParticleChange.SetMomentumChanged(State(fMomentumChanged)) ;

    fParticleChange.ProposePolarization(State(fTransportEndSpin));

    G4double deltaTime = 0.0 ;

    // Calculate  Lab Time of Flight (ONLY if field Equations used it!)
    // G4double endTime   = State(fCandidateEndGlobalTime);
    // G4double delta_time = endTime - startTime;

    G4double startTime = track.GetGlobalTime() ;
    ///___________________________________________________________________________
    /// !!!!!!!
    /// A REVOIR !!!!
    if (State(fEndGlobalTimeComputed) == false)
    {
        // The time was not integrated .. make the best estimate possible
        //
        G4double initialVelocity = stepData.GetPreStepPoint()->GetVelocity() ;
        G4double stepLength      = track.GetStepLength() ;

        deltaTime= 0.0;  // in case initialVelocity = 0
        if (track.GetParticleDefinition() == pdefOpticalPhoton)
        {
            // For only Optical Photon, final velocity is used
            double finalVelocity = track.CalculateVelocityForOpticalPhoton();
            fParticleChange.ProposeVelocity(finalVelocity);
            deltaTime = stepLength/finalVelocity ;
        }
        else if( initialVelocity > 0.0 )
        {
            deltaTime = stepLength/initialVelocity ;
        }

        State(fCandidateEndGlobalTime)   = startTime + deltaTime ;
    }
    else
    {
        deltaTime = State(fCandidateEndGlobalTime) - startTime ;
    }

    fParticleChange.ProposeGlobalTime( State(fCandidateEndGlobalTime) ) ;
    fParticleChange.ProposeLocalTime(  track.GetLocalTime() + deltaTime) ;
    /*
    // Now Correct by Lorentz factor to get delta "proper" Time

    G4double  restMass       = track.GetDynamicParticle()->GetMass() ;
    G4double deltaProperTime = deltaTime*( restMass/track.GetTotalEnergy() ) ;

    fParticleChange.ProposeProperTime(track.GetProperTime() + deltaProperTime) ;
*/

    fParticleChange. ProposeTrueStepLength( track.GetStepLength() ) ;

    ///___________________________________________________________________________
    ///

    // If the particle is caught looping or is stuck (in very difficult
    // boundaries) in a magnetic field (doing many steps)
    //   THEN this kills it ...
    //
    if ( State(fParticleIsLooping) )
    {
        G4double endEnergy= State(fTransportEndKineticEnergy);

        if( (endEnergy < fThreshold_Important_Energy)
                || (State(fNoLooperTrials) >= fThresholdTrials ) )
        {
            // Kill the looping particle
            //
            //            G4cout << "G4ITTransportation will killed the molecule"<< G4endl;
            fParticleChange.ProposeTrackStatus( fStopAndKill )  ;

            // 'Bare' statistics
            fSumEnergyKilled += endEnergy;
            if( endEnergy > fMaxEnergyKilled)
            {
                fMaxEnergyKilled= endEnergy;
            }

#ifdef G4VERBOSE
            if( (fVerboseLevel > 1) ||
                    ( endEnergy > fThreshold_Warning_Energy )  )
            {
                G4cout << " G4ITTransportation is killing track that is looping or stuck "
                       << G4endl
                       << "   This track has " << track.GetKineticEnergy() / MeV
                       << " MeV energy." << G4endl;
                G4cout << "   Number of trials = " << State(fNoLooperTrials)
                       << "   No of calls to AlongStepDoIt = " << noCalls
                       << G4endl;
            }
#endif
            State(fNoLooperTrials)=0;
        }
        else
        {
            State(fNoLooperTrials) ++;
#ifdef G4VERBOSE
            if( (fVerboseLevel > 2) )
            {
                G4cout << "   G4ITTransportation::AlongStepDoIt(): Particle looping -  "
                       << "   Number of trials = " << State(fNoLooperTrials)
                       << "   No of calls to  = " << noCalls
                       << G4endl;
            }
#endif
        }
    }
    else
    {
        State(fNoLooperTrials)=0;
    }

    // Another (sometimes better way) is to use a user-limit maximum Step size
    // to alleviate this problem ..

    // Introduce smooth curved trajectories to particle-change
    //
    fParticleChange.SetPointerToVectorOfAuxiliaryPoints
            (fFieldPropagator->GimmeTrajectoryVectorAndForgetIt() );

    return &fParticleChange ;
}

//////////////////////////////////////////////////////////////////////////
//
//  This ensures that the PostStep action is always called,
//  so that it can do the relocation if it is needed.
//

G4double G4ITTransportation::
PostStepGetPhysicalInteractionLength(
        const G4Track&  , // track
        G4double , // previousStepSize
        G4ForceCondition* pForceCond
        )
{
    *pForceCond = Forced ;
    return DBL_MAX ;  // was kInfinity ; but convention now is DBL_MAX
}

/////////////////////////////////////////////////////////////////////////////
//

G4VParticleChange* G4ITTransportation::PostStepDoIt( const G4Track& track,
                                                     const G4Step& )
{
    //    G4cout << "G4ITTransportation::PostStepDoIt" << G4endl;
    G4TouchableHandle retCurrentTouchable ;   // The one to return
    G4bool isLastStep= false;

    // Initialize ParticleChange  (by setting all its members equal
    //                             to corresponding members in G4Track)
    fParticleChange.Initialize(track) ;  // To initialise TouchableChange

    fParticleChange.ProposeTrackStatus(track.GetTrackStatus()) ;

    // If the Step was determined by the volume boundary,
    // logically relocate the particle

    if(State(fGeometryLimitedStep))
    {

        //        G4cout << "Step is limited by geometry " <<  "track ID : " << track.GetTrackID() << G4endl;

        // fCurrentTouchable will now become the previous touchable,
        // and what was the previous will be freed.
        // (Needed because the preStepPoint can point to the previous touchable)

        if( State(fCurrentTouchableHandle)->GetVolume() == 0 )
        {
            G4ExceptionDescription exceptionDescription ;
            exceptionDescription << "No current touchable found " ;
            G4Exception(" G4ITTransportation::PostStepDoIt","G4ITTransportation001",
                        FatalErrorInArgument,exceptionDescription);
        }

        fLinearNavigator->SetGeometricallyLimitedStep() ;
        fLinearNavigator->
                LocateGlobalPointAndUpdateTouchableHandle( track.GetPosition(),
                                                           track.GetMomentumDirection(),
                                                           State(fCurrentTouchableHandle),
                                                           true                      ) ;
        // Check whether the particle is out of the world volume
        // If so it has exited and must be killed.
        //
        if( State(fCurrentTouchableHandle)->GetVolume() == 0 )
        {
#ifdef G4VERBOSE
            if(fVerboseLevel > 0)
            {
                G4cout << "Track position : " << track.GetPosition() / nanometer << " [nm]"
                       << " Track ID : " << track.GetTrackID()<< G4endl;
                G4cout << "G4ITTransportation will killed the track because State(fCurrentTouchableHandle)->GetVolume() == 0"<< G4endl;
            }
#endif
            fParticleChange.ProposeTrackStatus( fStopAndKill ) ;
        }

        retCurrentTouchable = State(fCurrentTouchableHandle) ;

//        G4cout << "Current volume : " << track.GetVolume()->GetName()
//               << " Next volume : "
//               << (State(fCurrentTouchableHandle)->GetVolume() ? State(fCurrentTouchableHandle)->GetVolume()->GetName():"OutWorld")
//               << " Position : " << track.GetPosition() / nanometer
//               << " track ID : " << track.GetTrackID()
//               << G4endl;

        fParticleChange.SetTouchableHandle( State(fCurrentTouchableHandle) ) ;

        // Update the Step flag which identifies the Last Step in a volume
        isLastStep =  fLinearNavigator->ExitedMotherVolume()
                | fLinearNavigator->EnteredDaughterVolume() ;

#ifdef G4DEBUG_TRANSPORT
        //  Checking first implementation of flagging Last Step in Volume
        G4bool exiting =  fLinearNavigator->ExitedMotherVolume();
        G4bool entering = fLinearNavigator->EnteredDaughterVolume();

        if( ! (exiting || entering) )
        {
            G4cout << " Transport> :  Proposed isLastStep= " << isLastStep
                   << " Exiting "  << fLinearNavigator->ExitedMotherVolume()
                   << " Entering " << fLinearNavigator->EnteredDaughterVolume()
                   << " Track position : " << track.GetPosition() /nanometer << " [nm]"
                   << G4endl;
            G4cout << " Track position : " << track.GetPosition() /nanometer << G4endl;
        }
#endif
    }
    else                 // fGeometryLimitedStep  is false
    {
        // This serves only to move the Navigator's location
        //
        fLinearNavigator->LocateGlobalPointWithinVolume( track.GetPosition() ) ;

        // The value of the track's current Touchable is retained.
        // (and it must be correct because we must use it below to
        // overwrite the (unset) one in particle change)
        //  It must be fCurrentTouchable too ??
        //
        fParticleChange.SetTouchableHandle( track.GetTouchableHandle() ) ;
        retCurrentTouchable = track.GetTouchableHandle() ;

        isLastStep= false;
#ifdef G4DEBUG_TRANSPORT
        //  Checking first implementation of flagging Last Step in Volume
        G4cout << " Transport> Proposed isLastStep= " << isLastStep
               << " Geometry did not limit step. Position : "
               << track.GetPosition()/ nanometer << G4endl;
#endif
    }         // endif ( fGeometryLimitedStep )

    fParticleChange.ProposeLastStepInVolume(isLastStep);

    const G4VPhysicalVolume* pNewVol = retCurrentTouchable->GetVolume() ;
    const G4Material* pNewMaterial   = 0 ;
    const G4VSensitiveDetector* pNewSensitiveDetector   = 0 ;

    if( pNewVol != 0 )
    {
        pNewMaterial= pNewVol->GetLogicalVolume()->GetMaterial();
        pNewSensitiveDetector= pNewVol->GetLogicalVolume()->GetSensitiveDetector();
    }

    // ( <const_cast> pNewMaterial ) ;
    // ( <const_cast> pNewSensitiveDetector) ;

    fParticleChange.SetMaterialInTouchable( (G4Material *) pNewMaterial ) ;
    fParticleChange.SetSensitiveDetectorInTouchable( (G4VSensitiveDetector *) pNewSensitiveDetector ) ;

    const G4MaterialCutsCouple* pNewMaterialCutsCouple = 0;
    if( pNewVol != 0 )
    {
        pNewMaterialCutsCouple=pNewVol->GetLogicalVolume()->GetMaterialCutsCouple();
    }

    if( pNewVol!=0 && pNewMaterialCutsCouple!=0 && pNewMaterialCutsCouple->GetMaterial()!=pNewMaterial )
    {
        // for parametrized volume
        //
        pNewMaterialCutsCouple =
                G4ProductionCutsTable::GetProductionCutsTable()
                ->GetMaterialCutsCouple(pNewMaterial,
                                        pNewMaterialCutsCouple->GetProductionCuts());
    }
    fParticleChange.SetMaterialCutsCoupleInTouchable( pNewMaterialCutsCouple );

    // temporarily until Get/Set Material of ParticleChange,
    // and StepPoint can be made const.
    // Set the touchable in ParticleChange
    // this must always be done because the particle change always
    // uses this value to overwrite the current touchable pointer.
    //
    fParticleChange.SetTouchableHandle(retCurrentTouchable) ;

    return &fParticleChange ;
}

// New method takes over the responsibility to reset the state of G4Transportation
//   object at the start of a new track or the resumption of a suspended track.

void
G4ITTransportation::StartTracking(G4Track* track)
{
    G4VProcess::StartTracking(track);
    if(fInstantiateProcessState)
        G4VITProcess::fpState = new G4ITTransportationState();
    // Will set in the same time fTransportationState

    // The actions here are those that were taken in AlongStepGPIL
    //   when track.GetCurrentStepNumber()==1

    // reset safety value and center
    //
    //    State(fPreviousSafety)    = 0.0 ;
    //    State(fPreviousSftOrigin) = G4ThreeVector(0.,0.,0.) ;

    // reset looping counter -- for motion in field
    //    State(fNoLooperTrials)= 0;
    // Must clear this state .. else it depends on last track's value
    //  --> a better solution would set this from state of suspended track TODO ?
    // Was if( aTrack->GetCurrentStepNumber()==1 ) { .. }

    // ChordFinder reset internal state
    //
    if( DoesGlobalFieldExist() )
    {
        fFieldPropagator->ClearPropagatorState();
        // Resets all state of field propagator class (ONLY)
        //  including safety values (in case of overlaps and to wipe for first track).

        // G4ChordFinder* chordF= fFieldPropagator->GetChordFinder();
        // if( chordF ) chordF->ResetStepEstimate();
    }

    // Make sure to clear the chord finders of all fields (ie managers)
    static G4ThreadLocal G4FieldManagerStore* fieldMgrStore = 0 ; if (!fieldMgrStore) fieldMgrStore= G4FieldManagerStore::GetInstance();
    fieldMgrStore->ClearAllChordFindersState();

    // Update the current touchable handle  (from the track's)
    //
    State(fCurrentTouchableHandle) = track->GetTouchableHandle();

    G4VITProcess::StartTracking(track);
}

#undef State