SiSmearedDigitizationTool.cxx

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/*
  Copyright (C) 2002-2026 CERN for the benefit of the ATLAS collaboration
*/

// SiSmearedDigitizationTool.cxx
//   Implementation file for class SiSmearedDigitizationTool
 
// Pixel digitization includes
#include "FastSiDigitization/SiSmearedDigitizationTool.h"
 
// Det Descr
#include "Identifier/Identifier.h"
#include "InDetIdentifier/SCT_ID.h"
#include "InDetReadoutGeometry/SiDetectorElement.h"
 
#include "ReadoutGeometryBase/SiReadoutCellId.h"
#include "InDetReadoutGeometry/SiDetectorDesign.h"
#include "ReadoutGeometryBase/SiCellId.h"
#include "InDetIdentifier/PixelID.h"
#include "InDetSimData/InDetSimDataCollection.h"
 
// Random numbers
#include "AthenaKernel/RNGWrapper.h"
#include "CLHEP/Random/RandGaussZiggurat.h"
#include "CLHEP/Random/RandFlat.h"
#include "CLHEP/Random/RandGauss.h"
#include "CLHEP/Random/RandLandau.h"
#include "CLHEP/Vector/ThreeVector.h"
 
// Pile-up
#include "PileUpTools/PileUpMergeSvc.h"
 
#include "PixelReadoutGeometry/PixelModuleDesign.h"
#include "SCT_ReadoutGeometry/SCT_ModuleSideDesign.h"
#include "SCT_ReadoutGeometry/SCT_BarrelModuleSideDesign.h"
#include "SCT_ReadoutGeometry/SCT_ForwardModuleSideDesign.h"
 
// Fatras
#include "InDetPrepRawData/PixelCluster.h"
#include "SiClusterizationTool/ClusterMakerTool.h"
#include "TrkExUtils/LineIntersection2D.h"
#include "InDetPrepRawData/SiWidth.h"
#include "InDetSimEvent/SiHitCollection.h"
#include "SiClusterizationTool/IPixelClusteringTool.h"
#include "InDetPrepRawData/SiClusterContainer.h"
#include "InDetPrepRawData/SCT_Cluster.h"
#include "InDetPrepRawData/SiCluster.h"
#include "EventPrimitives/EventPrimitivesHelpers.h"
 
#include "TrkSurfaces/DiscSurface.h"
 
// Root
#include "TTree.h"
#include "TFile.h"
 
#include <cmath>
#include <memory>
 
using namespace InDetDD;
 
// Constructor with parameters:
SiSmearedDigitizationTool::SiSmearedDigitizationTool(const std::string &type, const std::string &name,
                                                     const IInterface* parent):
  PileUpToolBase(type, name, parent),
  m_pixel_ID(nullptr),
  m_sct_ID(nullptr),
  m_randomEngineName("SiSmearedDigitization"),
  m_pitch_X(0),
  m_pitch_Y(0),
  m_merge(false),
  m_nSigma(0.),
  m_useDiscSurface(false),
  m_pixelClusterContainer(nullptr),
  m_sctClusterContainer(nullptr),
  m_mergeSvc("PileUpMergeSvc",name),
  m_HardScatterSplittingMode(0),
  m_HardScatterSplittingSkipper(false),
  m_prdTruthNamePixel("PRD_MultiTruthPixel"),
  m_prdTruthNameSCT("PRD_MultiTruthSCT"),
  m_SmearPixel(true), //true: smear pixel --- false: smear SCT
  m_emulateAtlas(true), // error rotation for endcap SCT
  m_checkSmear(false),
  m_outputFile(nullptr),
  m_currentTree(nullptr),
  m_x_pixel(0),
  m_y_pixel(0),
  m_x_exit_pixel(0),
  m_y_exit_pixel(0),
  m_z_exit_pixel(0),
  m_x_entry_pixel(0),
  m_y_entry_pixel(0),
  m_z_entry_pixel(0),
  m_x_pixel_global(0),
  m_y_pixel_global(0),
  m_z_pixel_global(0),
  m_x_SCT(0),
  m_x_exit_SCT(0),
  m_y_exit_SCT(0),
  m_z_exit_SCT(0),
  m_x_entry_SCT(0),
  m_y_entry_SCT(0),
  m_z_entry_SCT(0),
  m_x_SCT_global(0),
  m_y_SCT_global(0),
  m_z_SCT_global(0),
  m_x_pixel_smeared(0),
  m_y_pixel_smeared(0),
  m_x_SCT_smeared(0),
  m_Err_x_pixel(0),
  m_Err_y_pixel(0),
  m_Err_x_SCT(0),
  m_Err_y_SCT(0)
{
  declareProperty("RndmEngine",                   m_randomEngineName, "Random engine name");
  declareProperty("InputObjectName",              m_inputObjectName="PixelHits", "Input Object name" );
  declareProperty("pitch_X",                      m_pitch_X);
  declareProperty("pitch_Y",                      m_pitch_Y);
  declareProperty("MergeClusters",                m_merge);
  declareProperty("Nsigma",                       m_nSigma);
  declareProperty("SmearPixel",                   m_SmearPixel, "Enable Pixel or SCT Smearing");
  declareProperty("PixelClusterContainerName",    m_pixel_SiClustersName="PixelClusters");
  declareProperty("SCT_ClusterContainerName",     m_Sct_SiClustersName="SCT_Clusters");
  declareProperty("CheckSmear",                   m_checkSmear);
 
  declareProperty("HardScatterSplittingMode"     , m_HardScatterSplittingMode, "Control pileup & signal splitting" );
 
}
 
 
// Initialize method:
StatusCode SiSmearedDigitizationTool::initialize()
{
 
  ATH_MSG_DEBUG ( "SiSmearedDigitizationTool::initialize()" );
 
  //locate the AtRndmGenSvc and initialize our local ptr
  if (!m_rndmSvc.retrieve().isSuccess())
    {
      ATH_MSG_ERROR ( "Could not find given RndmSvc" );
      return StatusCode::FAILURE;
    }
 
  if (detStore()->retrieve(m_pixel_ID, "PixelID").isFailure()) {
    ATH_MSG_ERROR ( "Could not get Pixel ID helper" );
    return StatusCode::FAILURE;
  }
 
  if (not m_SmearPixel){ // Smear SCT
    if (detStore()->retrieve(m_sct_ID, "SCT_ID").isFailure()) {
      ATH_MSG_ERROR ( "Could not get SCT ID helper" );
      return StatusCode::FAILURE;
    }
 
    m_inputObjectName="SCT_Hits"; // Set the input object name
  }
 
  // Initialize ReadCondHandleKeys
  ATH_CHECK(m_pixelDetEleCollKey.initialize(m_SmearPixel));
  ATH_CHECK(m_SCTDetEleCollKey.initialize(not m_SmearPixel));
 
  if (m_inputObjectName.empty())
    {
      ATH_MSG_FATAL ( "Property InputObjectName not set !" );
      return StatusCode::FAILURE;
    }
  else
    {
      ATH_MSG_DEBUG ( "Input objects: '" << m_inputObjectName << "'" );
    }
 
  //locate the PileUpMergeSvc and initialize our local ptr
  if (!m_mergeSvc.retrieve().isSuccess()) {
    ATH_MSG_ERROR ( "Could not find PileUpMergeSvc" );
    return StatusCode::FAILURE;
  }
 
  if (m_checkSmear){
 
    // get THistSvc
    ATH_CHECK(m_thistSvc.retrieve());
 
    if (m_SmearPixel){
      m_outputFile = new TFile("CheckSmearing_Pixel.root","RECREATE");
      m_currentTree = new TTree("PixelTree","Check smearing Pixel");
      m_currentTree->Branch("pixel_X"            , &m_x_pixel         , "m_x_pixel/D");
      m_currentTree->Branch("pixel_Y"            , &m_y_pixel         , "m_y_pixel/D");
      m_currentTree->Branch("pixel_X_exit"       , &m_x_exit_pixel    , "m_x_exit_pixel/D");
      m_currentTree->Branch("pixel_Y_exit"       , &m_y_exit_pixel    , "m_y_exit_pixel/D");
      m_currentTree->Branch("pixel_Z_exit"       , &m_z_exit_pixel    , "m_z_exit_pixel/D");
      m_currentTree->Branch("pixel_X_entry"      , &m_x_entry_pixel   , "m_x_entry_pixel/D");
      m_currentTree->Branch("pixel_Y_entry"      , &m_y_entry_pixel   , "m_y_entry_pixel/D");
      m_currentTree->Branch("pixel_Z_entry"      , &m_z_entry_pixel   , "m_z_entry_pixel/D");
      m_currentTree->Branch("pixel_X_global"     , &m_x_pixel_global  , "m_x_pixel_global/D");
      m_currentTree->Branch("pixel_Y_global"     , &m_y_pixel_global  , "m_y_pixel_global/D");
      m_currentTree->Branch("pixel_Z_global"     , &m_z_pixel_global  , "m_z_pixel_global/D");
      m_currentTree->Branch("pixel_X_smear"      , &m_x_pixel_smeared , "m_x_pixel_smeared/D");
      m_currentTree->Branch("pixel_Y_smear"      , &m_y_pixel_smeared , "m_y_pixel_smeared/D");
      m_currentTree->Branch("pixel_Err_X"        , &m_Err_x_pixel     , "m_Err_x_pixel/D");
      m_currentTree->Branch("pixel_Err_Y"        , &m_Err_y_pixel     , "m_Err_y_pixel/D");
 
      if( m_thistSvc->regTree("PixelTree",m_currentTree).isFailure()) {
        ATH_MSG_ERROR("Cannot register Ttree");
        return StatusCode::FAILURE;
      }else{
        ATH_MSG_DEBUG ( "Ttree registered" );
      }
    }
    else{
      m_outputFile = new TFile("CheckSmearing_SCT.root","RECREATE");
      m_currentTree = new TTree("SCT_Tree","Check smearing SCT");
      m_currentTree->Branch("SCT_X"             , &m_x_SCT         , "m_x_SCT/D");
      m_currentTree->Branch("SCT_exit_X"        , &m_x_exit_SCT    , "m_x_exit_SCT/D");
      m_currentTree->Branch("SCT_exit_Y"        , &m_y_exit_SCT    , "m_y_exit_SCT/D");
      m_currentTree->Branch("SCT_exit_Z"        , &m_z_exit_SCT    , "m_z_exit_SCT/D");
      m_currentTree->Branch("SCT_entry_X"       , &m_x_entry_SCT   , "m_x_entry_SCT/D");
      m_currentTree->Branch("SCT_entry_Y"       , &m_y_entry_SCT   , "m_y_entry_SCT/D");
      m_currentTree->Branch("SCT_entry_Z"       , &m_z_entry_SCT   , "m_z_entry_SCT/D");
      m_currentTree->Branch("SCT_X_global"      , &m_x_SCT_global  , "m_x_SCT_global/D");
      m_currentTree->Branch("SCT_Y_global"      , &m_y_SCT_global  , "m_y_SCT_global/D");
      m_currentTree->Branch("SCT_Z_global"      , &m_z_SCT_global  , "m_z_SCT_global/D");
      m_currentTree->Branch("SCT_X_smear"       , &m_x_SCT_smeared , "m_x_SCT_smeared/D");
      m_currentTree->Branch("SCT_Err_X"         , &m_Err_x_SCT     , "m_Err_x_SCT/D");
 
      if( m_thistSvc->regTree("SCT_Tree",m_currentTree).isFailure()) {
        ATH_MSG_ERROR("Cannot register Ttree");
        return StatusCode::FAILURE;
      }else{
        ATH_MSG_DEBUG ( "Ttree registered" );
      }
    }
 
 
  }
 
  return StatusCode::SUCCESS;
}
 
// Finalize method:
StatusCode SiSmearedDigitizationTool::finalize()
{
 
  if (m_checkSmear){
    m_outputFile->cd();
    m_currentTree->Write();
    m_outputFile->Close();
    ATH_MSG_DEBUG ( "SiSmearedDigitizationTool : Writing Tree" );
 
  }
 
  ATH_MSG_DEBUG ( "SiSmearedDigitizationTool : finalize()" );
 
 
  return StatusCode::SUCCESS;
 
}
 
StatusCode SiSmearedDigitizationTool::prepareEvent(const EventContext& /*ctx*/, unsigned int)
{
 
  ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: in pixel prepareEvent() ---" );
 
  m_siHitCollList.clear();
  m_HardScatterSplittingSkipper = false;
 
  return StatusCode::SUCCESS;
}
 
 
StatusCode SiSmearedDigitizationTool::processBunchXing(int bunchXing,
                                                       SubEventIterator bSubEvents,
                                                       SubEventIterator eSubEvents)
{
  ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: in pixel processBunchXing() ---" );
  //decide if this event will be processed depending on HardScatterSplittingMode & bunchXing
  if (m_HardScatterSplittingMode == 2 && !m_HardScatterSplittingSkipper ) { m_HardScatterSplittingSkipper = true; return StatusCode::SUCCESS; }
  if (m_HardScatterSplittingMode == 1 && m_HardScatterSplittingSkipper )  { return StatusCode::SUCCESS; }
  if (m_HardScatterSplittingMode == 1 && !m_HardScatterSplittingSkipper ) { m_HardScatterSplittingSkipper = true; }
 
  using TimedHitCollList = PileUpMergeSvc::TimedList<SiHitCollection>::type;
  TimedHitCollList hitCollList;
 
  if (!(m_mergeSvc->retrieveSubSetEvtData(m_inputObjectName, hitCollList, bunchXing,
                                          bSubEvents, eSubEvents).isSuccess()) &&
      hitCollList.empty()) {
    ATH_MSG_ERROR("Could not fill TimedHitCollList");
    return StatusCode::FAILURE;
  } else {
    ATH_MSG_VERBOSE(hitCollList.size() << " SiHitCollections with key " <<
                    m_inputObjectName << " found");
  }
 
  TimedHitCollList::iterator iColl(hitCollList.begin());
  TimedHitCollList::iterator endColl(hitCollList.end());
 
  for( ; iColl != endColl; ++iColl) {
    SiHitCollection *siHitColl = new SiHitCollection(*iColl->second);
    PileUpTimeEventIndex timeIndex(iColl->first);
    ATH_MSG_DEBUG("SiHitCollection found with " << siHitColl->size() <<
                  " hits");
    ATH_MSG_VERBOSE("time index info. time: " << timeIndex.time()
                    << " index: " << timeIndex.index()
                    << " type: " << timeIndex.type());
    m_siHitCollList.push_back(siHitColl);
  }
 
  return StatusCode::SUCCESS;
}
 
 
StatusCode SiSmearedDigitizationTool::processAllSubEvents(const EventContext& ctx) {
 
  ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: in pixel processAllSubEvents() ---" );
 
  InDet::SiClusterContainer* symSiContainer=nullptr;
 
  if(m_SmearPixel){ // Smear Pixel
    m_pixelClusterContainer = new InDet::PixelClusterContainer(m_pixel_ID->wafer_hash_max());
 
    if(!m_pixelClusterContainer) {
      ATH_MSG_FATAL( "[ --- ] Could not create PixelClusterContainer");
      return StatusCode::FAILURE;
    }
 
    // --------------------------------------
    // PixelCluster container registration
 
    m_pixelClusterContainer->cleanup();
    if ((evtStore()->record(m_pixelClusterContainer, m_pixel_SiClustersName)).isFailure())   {
      if ((evtStore()->retrieve(m_pixelClusterContainer, m_pixel_SiClustersName)).isFailure())   {
        ATH_MSG_FATAL("[ hitproc ] Error while registering PixelCluster container");
        return StatusCode::FAILURE;
      }
    }
 
    // symlink the Pixel Container
    // Pixel
 
    if ((evtStore()->symLink(m_pixelClusterContainer,symSiContainer)).isFailure()) {
      ATH_MSG_FATAL( "[ --- ] PixelClusterContainer could not be symlinked to SiClusterContainter in StoreGate !" );
      return StatusCode::FAILURE;
    } else {
      ATH_MSG_INFO( "[ hitproc ] PixelClusterContainer symlinked to SiClusterContainer in StoreGate" );
    }
 
  }else{ // Smear SCT
    m_sctClusterContainer = new InDet::SCT_ClusterContainer(m_sct_ID->wafer_hash_max());
 
    if(!m_sctClusterContainer) {
      ATH_MSG_FATAL( "[ --- ] Could not create SCT_ClusterContainer");
      return StatusCode::FAILURE;
    }
 
    // --------------------------------------
    // SCT_Cluster container registration
    m_sctClusterContainer->cleanup();
    if ((evtStore()->record(m_sctClusterContainer, m_Sct_SiClustersName)).isFailure())   {
      ATH_MSG_FATAL("[ hitproc ] Error while registering SCT_Cluster container");
      return StatusCode::FAILURE;
    }
    // symlink the SCT Container
    // SCT
 
    if ((evtStore()->symLink(m_sctClusterContainer,symSiContainer)).isFailure()) {
      ATH_MSG_FATAL( "[ --- ] SCT_ClusterContainer could not be symlinked to SiClusterContainter in StoreGate !" );
      return StatusCode::FAILURE;
    } else {
      ATH_MSG_DEBUG( "[ hitproc ] SCT_ClusterContainer symlinked to SiClusterContainer in StoreGate" );
    }
 
  }
 
  if (retrieveTruth().isFailure()) {
    ATH_MSG_FATAL ( "retrieveTruth() failed!" );
    return StatusCode::FAILURE;
  }
 
  //  get the container(s)
  using TimedHitCollList = PileUpMergeSvc::TimedList<SiHitCollection>::type;
 
  m_simHitColl = new SiHitCollection;
 
  //this is a list<pair<time_t, DataLink<SCTUncompressedHitCollection> > >
  TimedHitCollList hitCollList;
  unsigned int numberOfSimHits(0);
  if ( !(m_mergeSvc->retrieveSubEvtsData(m_inputObjectName, hitCollList, numberOfSimHits).isSuccess()) && hitCollList.empty() ) {
    ATH_MSG_ERROR ( "Could not fill TimedHitCollList" );
    return StatusCode::FAILURE;
  } else {
    ATH_MSG_DEBUG ( hitCollList.size() << " SiHitCollections with key " << m_inputObjectName << " found" );
  }
 
  // Define Hit Collection
  TimedHitCollection<SiHit> thpcsi(numberOfSimHits);
 
  //now merge all collections into one
  TimedHitCollList::iterator   iColl(hitCollList.begin());
  TimedHitCollList::iterator endColl(hitCollList.end()  );
 
  m_HardScatterSplittingSkipper = false;
  // loop on the hit collections
  while ( iColl != endColl ) {
    if (m_HardScatterSplittingMode == 2 && !m_HardScatterSplittingSkipper ) { m_HardScatterSplittingSkipper = true; ++iColl; continue; }
    if (m_HardScatterSplittingMode == 1 && m_HardScatterSplittingSkipper )  { ++iColl; continue; }
    if (m_HardScatterSplittingMode == 1 && !m_HardScatterSplittingSkipper ) { m_HardScatterSplittingSkipper = true; }
    const SiHitCollection* p_collection(iColl->second);
    thpcsi.insert(iColl->first, p_collection);
    ATH_MSG_DEBUG ( "SiHitCollection found with " << p_collection->size() << " hits" );
    ++iColl;
  }
 
  // Process the Hits straw by straw: get the iterator pairs for given straw
  if(this->digitize(ctx, thpcsi).isFailure()) {
    ATH_MSG_FATAL ( "digitize method failed!" );
    return StatusCode::FAILURE;
  }
 
  if (m_merge)
    if(this->mergeEvent(ctx).isFailure()) {
      ATH_MSG_FATAL ( "merge method failed!" );
      return StatusCode::FAILURE;
    }
 
  if (createAndStoreRIOs(ctx).isFailure()) {
    ATH_MSG_FATAL ( "createAndStoreRIOs() failed!" );
    return StatusCode::FAILURE;
  }
  else {
    ATH_MSG_DEBUG ( "createAndStoreRIOs() succeeded" );
  }
 
  return StatusCode::SUCCESS;
 
}
 
StatusCode SiSmearedDigitizationTool::retrieveTruth(){
 
 
  if(m_SmearPixel){ // Smear Pixel
 
    m_pixelPrdTruth = new PRD_MultiTruthCollection;
 
    if ((evtStore()->contains<PRD_MultiTruthCollection>(m_prdTruthNamePixel))){
      if((evtStore()->retrieve(m_pixelPrdTruth, m_prdTruthNamePixel)).isFailure()){
        ATH_MSG_FATAL("Could not retrieve collection " << m_prdTruthNamePixel);
        return StatusCode::FAILURE;
      }
    }else{
      if((evtStore()->record(m_pixelPrdTruth, m_prdTruthNamePixel)).isFailure()){
        ATH_MSG_FATAL("Could not record collection " << m_prdTruthNamePixel);
        return StatusCode::FAILURE;
      }
    }
  }else{ // Smear SCT
    m_SCTPrdTruth = new PRD_MultiTruthCollection;
 
    if ((evtStore()->contains<PRD_MultiTruthCollection>(m_prdTruthNameSCT))){
      if((evtStore()->retrieve(m_SCTPrdTruth, m_prdTruthNameSCT)).isFailure()){
        ATH_MSG_FATAL("Could not retrieve collection " << m_prdTruthNameSCT);
        return StatusCode::FAILURE;
      }
    }else{
      if((evtStore()->record(m_SCTPrdTruth, m_prdTruthNameSCT)).isFailure()){
        ATH_MSG_FATAL("Could not record collection " << m_prdTruthNameSCT);
        return StatusCode::FAILURE;
      }
    }
  }
 
 
  return StatusCode::SUCCESS;
 
}
 
template<typename CLUSTER>
StatusCode SiSmearedDigitizationTool::FillTruthMap(PRD_MultiTruthCollection * map, CLUSTER * cluster, const TimedHitPtr<SiHit>& hit){
 
  ATH_MSG_DEBUG("Truth map filling with cluster " << *cluster << " and link = " << hit->particleLink());
  if (hit->particleLink().isValid()){
    if (!HepMC::ignoreTruthLink(hit->particleLink(), m_vetoPileUpTruthLinks)) {
      map->insert(std::make_pair(cluster->identify(), hit->particleLink()));
      ATH_MSG_DEBUG("Truth map filled with cluster " << *cluster << " and link = " << hit->particleLink());
    }
  }else{
    ATH_MSG_DEBUG("Particle link NOT valid!! Truth map NOT filled with cluster" << cluster << " and link = " << hit->particleLink());
  }
 
  return StatusCode::SUCCESS;
}
 
StatusCode SiSmearedDigitizationTool::mergeEvent(const EventContext& /*ctx*/){
 
  if (m_SmearPixel)
    return mergeClusters(m_pixelClusterMap);
  else
    return mergeClusters(m_sctClusterMap);
}
 
template<typename CLUSTER>
double SiSmearedDigitizationTool::calculateDistance(CLUSTER * clusterA, CLUSTER * clusterB){
 
  // take needed information on the first clusters
  Amg::Vector2D intersection_a = clusterA->localPosition();
 
  // take needed information on the second clusters
  Amg::Vector2D intersection_b = clusterB->localPosition();
 
  ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: intersection_a = " << intersection_a);
  ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: intersection_b = " << intersection_b);
 
  double distX = intersection_a.x() - intersection_b.x();
  double distY = intersection_a.y() - intersection_b.y();
 
  return sqrt(distX*distX + distY*distY);
}
 
template<typename CLUSTER>
double SiSmearedDigitizationTool::calculateSigma(CLUSTER * clusterA, CLUSTER * clusterB){
  // take needed information on the first cluster
  const Amg::MatrixX& clusterErr_a = clusterA->localCovariance();
 
  // take needed information on the second clusters
  const Amg::MatrixX& clusterErr_b = clusterB->localCovariance();
 
  double sigmaX = sqrt(Amg::error(clusterErr_a,Trk::locX) * Amg::error(clusterErr_a,Trk::locX) +
                       Amg::error(clusterErr_b,Trk::locX) * Amg::error(clusterErr_b,Trk::locX));
 
  double sigmaY = sqrt(Amg::error(clusterErr_a,Trk::locY) * Amg::error(clusterErr_a,Trk::locY) +
                       Amg::error(clusterErr_b,Trk::locY) * Amg::error(clusterErr_b,Trk::locY));
 
  return sqrt(sigmaX*sigmaX + sigmaY*sigmaY);
}
 
template<typename CLUSTER>
ClusterInfo SiSmearedDigitizationTool::calculateNewCluster(CLUSTER * clusterA, CLUSTER * clusterB) {
  // take needed information on the first clusters
  Amg::Vector2D intersection_a = clusterA->localPosition();
  const Amg::MatrixX& clusterErr_a = clusterA->localCovariance();
 
  // take needed information on the second clusters
  Amg::Vector2D intersection_b = clusterB->localPosition();
  const Amg::MatrixX& clusterErr_b = clusterB->localCovariance();
 
  double sigmaX = sqrt(Amg::error(clusterErr_a,Trk::locX) * Amg::error(clusterErr_a,Trk::locX) +
                       Amg::error(clusterErr_b,Trk::locX) * Amg::error(clusterErr_b,Trk::locX));
 
  double sigmaY = sqrt(Amg::error(clusterErr_a,Trk::locY) * Amg::error(clusterErr_a,Trk::locY) +
                       Amg::error(clusterErr_b,Trk::locY) * Amg::error(clusterErr_b,Trk::locY));
 
  double interX = 0.5*(intersection_a.x()+intersection_b.x());
  double interY = 0.5*(intersection_a.y()+intersection_b.y());
 
  Amg::Vector2D intersection(interX, interY);
 
  ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: intersection = " << intersection);
 
  const InDet::SiWidth& siWidth_a = clusterA->width();
  const InDet::SiWidth& siWidth_b = clusterB->width();
 
  ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: siWidth_a = " << siWidth_a);
  ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: siWidth_b = " << siWidth_b);
 
  Amg::Vector2D colRow = siWidth_a.colRow() + siWidth_b.colRow();
  Amg::Vector2D  phiRz = siWidth_a.widthPhiRZ() + siWidth_b.widthPhiRZ();
 
  InDet::SiWidth siWidth(colRow, phiRz);
 
  ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: siWidth = " << siWidth);
 
  AmgSymMatrix(2) covariance;
  covariance.setIdentity();
  covariance(Trk::locX,Trk::locX) = sigmaX*sigmaX;
  covariance(Trk::locY,Trk::locY) = sigmaY*sigmaY;
  Amg::MatrixX clusterErr = covariance;
 
  return ClusterInfo( intersection, siWidth, clusterErr );
 
}
 
StatusCode SiSmearedDigitizationTool::mergeClusters(Pixel_detElement_RIO_map * cluster_map)
{
  // The idea is first to check how many cluster we have to merge and then merge them.
  // The loop is done until there aren't any clusters to merge
 
  ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: in mergeClusters() using PixelClusters --- ");
 
  Pixel_detElement_RIO_map::iterator i = cluster_map->begin();
  Pixel_detElement_RIO_map::iterator e = cluster_map->end();
 
  for (; i != e; i = cluster_map->upper_bound(i->first)){
    IdentifierHash current_id = i->first;
    // Check if clusters with current_id have been already considered
 
    bool NewMerge = true;
 
    while (NewMerge) {
      NewMerge = false;
      std::pair <Pixel_detElement_RIO_map::iterator, Pixel_detElement_RIO_map::iterator> range = cluster_map->equal_range(current_id);
 
      for ( Pixel_detElement_RIO_map::iterator iter = range.first; iter != range.second;  ++iter){
        for (Pixel_detElement_RIO_map::iterator inner_iter = std::next(iter); inner_iter != range.second; ++inner_iter){
 
          double dist = calculateDistance((*iter).second,(*inner_iter).second);
          double sigma = calculateSigma((*iter).second,(*inner_iter).second);
 
          if( dist <= m_nSigma * sigma) {
 
            std::vector<Identifier> rdoList;
 
            Amg::Vector2D intersection;
            InDet::SiWidth siWidth;
            Amg::MatrixX clusterErr;
            std::tie( intersection, siWidth, clusterErr ) = calculateNewCluster( iter->second, inner_iter->second );
 
            const InDetDD::SiDetectorElement* hitSiDetElement = (((*inner_iter).second)->detectorElement());
            Identifier intersectionId = hitSiDetElement->identifierOfPosition(intersection);
 
            rdoList.push_back(intersectionId);
 
            InDetDD::SiCellId currentCellId = hitSiDetElement->cellIdFromIdentifier(intersectionId);
 
            if ( !currentCellId.isValid() ) {
              continue;
            }
 
            InDet::PixelCluster* pixelCluster = new InDet::PixelCluster(intersectionId,
                                                                        intersection,
                                                                        std::move(rdoList),
                                                                        siWidth,
                                                                        hitSiDetElement,
                                                                        std::move(clusterErr));
            ((*inner_iter).second) = pixelCluster;
 
            cluster_map->erase(iter);
            NewMerge = true;
            goto REPEAT_LOOP;
          }
        }
      }
    REPEAT_LOOP: ;
    }
  }
 
  return StatusCode::SUCCESS;
}
 
StatusCode
SiSmearedDigitizationTool::mergeClusters(SCT_detElement_RIO_map* cluster_map)
{
  ATH_MSG_DEBUG(
    "--- SiSmearedDigitizationTool: in mergeClusters() using SCT_Clusters ---");
 
  if (!cluster_map) {
    ATH_MSG_FATAL("Null SCT cluster map passed to mergeClusters()");
    return StatusCode::FAILURE;
  }
 
  auto i = cluster_map->begin();
 
  while (i != cluster_map->end()) {
    const IdentifierHash current_id = i->first;
    bool mergedThisPass;
 
    do {
      mergedThisPass = false;
      const auto range = cluster_map->equal_range(current_id);
 
      auto iter = range.first;
 
      while (iter != range.second && !mergedThisPass) {
        auto inner_iter = std::next(iter);
 
        while (inner_iter != range.second) {
          const double dist =
            calculateDistance(iter->second, inner_iter->second);
          const double sigma =
            calculateSigma(iter->second, inner_iter->second);
 
          if (dist > m_nSigma * sigma) {
            ++inner_iter;
            continue;
          }
 
          Amg::Vector2D intersection;
          InDet::SiWidth siWidth;
          Amg::MatrixX clusterErr;
 
          std::tie(intersection, siWidth, clusterErr) =
            calculateNewCluster(iter->second, inner_iter->second);
 
          const InDetDD::SiDetectorElement* hitSiDetElement =
            inner_iter->second->detectorElement();
 
          const Identifier intersectionId =
            hitSiDetElement->identifierOfPosition(intersection);
 
          const InDetDD::SiCellId currentCellId =
            hitSiDetElement->cellIdFromIdentifier(intersectionId);
 
          if (!currentCellId.isValid()) {
            ++inner_iter;
            continue;
          }
 
          std::vector<Identifier> rdoList{intersectionId};
 
          auto sctCluster = std::make_unique<InDet::SCT_Cluster>(
            intersectionId,
            intersection,
            std::move(rdoList),
            siWidth,
            hitSiDetElement,
            std::move(clusterErr));
 
          auto* const oldIterCluster = iter->second;
          auto* const oldInnerCluster = inner_iter->second;
 
          inner_iter->second = sctCluster.release();
 
          delete oldIterCluster;
          delete oldInnerCluster;
 
          cluster_map->erase(iter);
 
          mergedThisPass = true;
          break;
        }
 
        if (!mergedThisPass) {
          ++iter;
        }
      }
    } while (mergedThisPass);
 
    i = cluster_map->upper_bound(current_id);
  }
 
  return StatusCode::SUCCESS;
}
StatusCode SiSmearedDigitizationTool::digitize(const EventContext& ctx,
                                               TimedHitCollection<SiHit>& thpcsi)
{
  // Set the RNG to use for this event.
  ATHRNG::RNGWrapper* rngWrapper = m_rndmSvc->getEngine(this, m_randomEngineName);
  const std::string rngName = name()+m_randomEngineName;
  rngWrapper->setSeed( rngName, ctx );
  CLHEP::HepRandomEngine *rndmEngine = rngWrapper->getEngine(ctx);
 
  ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: in SiSmearedDigizationTool::digitize() ---" );
 
  // Get PixelDetectorElementCollection
  const InDetDD::SiDetectorElementCollection* elementsPixel = nullptr;
  if (m_SmearPixel) {
    SG::ReadCondHandle<InDetDD::SiDetectorElementCollection> pixelDetEle(m_pixelDetEleCollKey, ctx);
    elementsPixel = pixelDetEle.retrieve();
    if (elementsPixel==nullptr) {
      ATH_MSG_FATAL(m_pixelDetEleCollKey.fullKey() << " could not be retrieved");
      return StatusCode::FAILURE;
    }
  }
  // Get SCT_DetectorElementCollection
  const InDetDD::SiDetectorElementCollection* elementsSCT = nullptr;
  if (not m_SmearPixel) {
    SG::ReadCondHandle<InDetDD::SiDetectorElementCollection> sctDetEle(m_SCTDetEleCollKey, ctx);
    elementsSCT = sctDetEle.retrieve();
    if (elementsSCT==nullptr) {
      ATH_MSG_FATAL(m_SCTDetEleCollKey.fullKey() << " could not be retrieved");
      return StatusCode::FAILURE;
    }
  }
 
  TimedHitCollection<SiHit>::const_iterator i, e;
 
  if(m_SmearPixel) { // Smear Pixel
    m_pixelClusterMap = new Pixel_detElement_RIO_map;
  } else {// Smear SCT
    m_sctClusterMap = new SCT_detElement_RIO_map;
  }
 
  while (thpcsi.nextDetectorElement(i, e)) {
 
    while (i != e) {
      m_useDiscSurface = false;
 
      const TimedHitPtr<SiHit>& hit(*i++);
      int barrelEC  = hit->getBarrelEndcap();
      int layerDisk = hit->getLayerDisk();
      int phiModule = hit->getPhiModule();
      int etaModule = hit->getEtaModule();
      int side      = 0;
 
      const InDetDD::SiDetectorElement* hitSiDetElement = nullptr;
 
      if(m_SmearPixel) { // Smear Pixel
        Identifier wafer_id = m_pixel_ID->wafer_id(barrelEC,layerDisk,phiModule,etaModule);
        IdentifierHash wafer_hash = m_pixel_ID->wafer_hash(wafer_id);
        const InDetDD::SiDetectorElement* hitSiDetElement_temp = elementsPixel->getDetectorElement(wafer_hash);
        ATH_MSG_DEBUG("Pixel SiDetectorElement --> barrel_ec " << barrelEC << ", layer_disk " << layerDisk << ", phi_module " << phiModule << ", eta_module " << etaModule );
        hitSiDetElement = hitSiDetElement_temp;
      } else { // Smear SCT
        side = hit->getSide();
        Identifier idwafer = m_sct_ID->wafer_id(barrelEC,layerDisk,phiModule,etaModule,side);
        IdentifierHash idhash = m_sct_ID->wafer_hash(m_sct_ID->wafer_id(idwafer));
        const InDetDD::SiDetectorElement* hitSiDetElement_temp = elementsSCT->getDetectorElement(idhash);
        ATH_MSG_DEBUG("SCT SiDetectorElement --> barrel_ec " << barrelEC << ", layer_disk " << layerDisk << ", phi_module " << phiModule << ", eta_module " << etaModule << ", side " << side);
        hitSiDetElement = hitSiDetElement_temp;
      }
 
      // untangling the logic: if not using custom geometry, hitSiDetElement
      // gets dereferenced (and should be checked)
      //
      // if using custom geometry, hitPlanarDetElement gets dereferenced
      // (and should be checked)
      if (not hitSiDetElement) {
        ATH_MSG_FATAL("hitSiDetElement is null in SiSmearedDigitizationTool:"<<__LINE__);
        throw std::runtime_error(std::string("hitSiDetElement is null in SiSmearedDigitizationTool::digitize() "));
      }
 
      if (m_SmearPixel && !(hitSiDetElement->isPixel())) continue;
      if (!m_SmearPixel && !(hitSiDetElement->isSCT())) continue;
 
      IdentifierHash waferID;
 
      if(m_SmearPixel) { // Smear Pixel
         waferID = m_pixel_ID->wafer_hash(hitSiDetElement->identify());
      } else { // Smear SCT
         waferID = m_sct_ID->wafer_hash(hitSiDetElement->identify());
      }
 
      HepGeom::Point3D<double> pix_localStartPosition = hit->localStartPosition();
      HepGeom::Point3D<double> pix_localEndPosition   = hit->localEndPosition();
 
      pix_localStartPosition = hitSiDetElement->hitLocalToLocal3D(pix_localStartPosition);
      pix_localEndPosition = hitSiDetElement->hitLocalToLocal3D(pix_localEndPosition);
 
      double localEntryX = pix_localStartPosition.x();
      double localEntryY = pix_localStartPosition.y();
      double localEntryZ = pix_localStartPosition.z();
      double localExitX = pix_localEndPosition.x();
      double localExitY = pix_localEndPosition.y();
      double localExitZ = pix_localEndPosition.z();
 
      double thickness = 0.0;
      thickness = hitSiDetElement->thickness();
 
      // Transform to reconstruction local coordinates (different x,y,z ordering and sign conventions compared to simulation coords)
      if (!m_SmearPixel) { // Smear SCT
        HepGeom::Point3D<double> sct_localStartPosition = hit->localStartPosition();
        HepGeom::Point3D<double> sct_localEndPosition = hit->localEndPosition();
 
        sct_localStartPosition = hitSiDetElement->hitLocalToLocal3D(sct_localStartPosition);
        sct_localEndPosition = hitSiDetElement->hitLocalToLocal3D(sct_localEndPosition);
 
        localEntryX = sct_localStartPosition.x();
        localEntryY = sct_localStartPosition.y();
        localEntryZ = sct_localStartPosition.z();
        localExitX  = sct_localEndPosition.x();
        localExitY  = sct_localEndPosition.y();
        localExitZ  = sct_localEndPosition.z();
      }
 
      double distX = std::abs(std::abs(localExitX)-std::abs(localEntryX));
      double distY = std::abs(std::abs(localExitY)-std::abs(localEntryY));
 
      if(m_SmearPixel) { // Smear Pixel
        ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: pixel start position --- " << localEntryX << ",  " << localEntryY << ",  " << localEntryZ );
        ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: pixel exit position --- " << localExitX << ",  " << localExitY << ",  " << localExitZ );
        m_x_entry_pixel = localEntryX;
        m_y_entry_pixel = localEntryY;
        m_z_entry_pixel = localEntryZ;
        m_x_exit_pixel = localExitX;
        m_y_exit_pixel = localExitY;
        m_z_exit_pixel = localExitZ;
      } else { // Smear SCT
        ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: SCT start position --- " << localEntryX << ",  " << localEntryY << ",  " << localEntryZ );
        ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: SCT exit position --- " << localExitX << ",  " << localExitY << ",  " << localExitZ );
        m_x_entry_SCT = localEntryX;
        m_y_entry_SCT = localEntryY;
        m_z_entry_SCT = localEntryZ;
        m_x_exit_SCT = localExitX;
        m_y_exit_SCT = localExitY;
        m_z_exit_SCT = localExitZ;
      }
 
      Amg::Vector2D localEntry(localEntryX,localEntryY);
      Amg::Vector2D localExit(localExitX,localExitY);
 
      // the pixel positions and other needed stuff for the geometrical clustering
      std::vector<Identifier>           rdoList;
 
      Amg::Vector3D localDirection(localExitX-localEntryX, localExitY-localEntryY, localExitZ-localEntryZ);
 
      InDetDD::SiCellId entryCellId;
      InDetDD::SiCellId exitCellId;
 
      // get the identifier of the entry and the exit
      Identifier entryId = hitSiDetElement->identifierOfPosition(localEntry);
      Identifier exitId  = hitSiDetElement->identifierOfPosition(localExit);
 
      // now get the cellIds and check whether they're valid
      entryCellId = hitSiDetElement->cellIdFromIdentifier(entryId);
      exitCellId  = hitSiDetElement->cellIdFromIdentifier(exitId);
 
      ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: entryId " << entryId << " --- exitId " << exitId );
      ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: entryCellId " << entryCellId << " --- exitCellId " << exitCellId );
 
      ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: surface " << hitSiDetElement->surface());
 
      // entry / exit validity
      bool entryValid = entryCellId.isValid();
      bool exitValid  = exitCellId.isValid();
 
      ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: entryValid? " << entryValid << " --- exitValid? " << exitValid );
 
      if (!entryValid && !exitValid) continue;
 
      // the intersecetion id and cellId of it
      double interX = 0.5*(localEntryX+localExitX);
      double interY = 0.5*(localEntryY+localExitY);
 
      ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: " << (m_SmearPixel ? "pixel" : "SCT") << " inter X --- " << interX );
      ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: " << (m_SmearPixel ? "pixel" : "SCT") << " inter Y --- " << interY );
      ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: " << (m_SmearPixel ? "pixel" : "SCT") << " dist X --- "  << distX );
      ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: " << (m_SmearPixel ? "pixel" : "SCT") << " dist Y --- "  << distY );
 
      //the particle crosses at least n pixels (in x direction you have timesX, in y direction you have timesY)
      double timesX = (m_pitch_X) ? floor(distX/m_pitch_X) : 0;
      double timesY = (m_pitch_Y) ? floor(distY/m_pitch_Y) : 0;
 
      double newdistX = distX - (timesX*m_pitch_X);
      double newdistY = distY - (timesY*m_pitch_Y);
 
      ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: times X --- " << timesX );
      ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: times Y --- " << timesY );
      ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: new dist X --- " << newdistX );
      ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: new dist Y --- " << newdistY );
      ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: thickness --- " << thickness );
 
      //Probability
 
      double ProbY = 2*newdistY/(m_pitch_Y+newdistY);
      double ProbX = 2*newdistX/(m_pitch_X+newdistX);
 
      ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: ProbX --- " << ProbX );
      ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: ProbY --- " << ProbY );
 
      // create the errors
      ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: pitch X --- " << m_pitch_X );
      ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: pitch Y --- " << m_pitch_Y );
 
      double sigmaX = m_pitch_X/sqrt(12.);
      double sigmaY = m_pitch_Y/sqrt(12.);
 
      int elementX = timesX+1;
      int elementY = timesY+1;
 
      if(m_SmearPixel) {
        if (CLHEP::RandFlat::shoot(rndmEngine, 0.0, 1.0) < ProbY) { // number of crossed pixel is (timesY+1)+1
          sigmaY = (double)(timesY+2)*m_pitch_Y/sqrt(12.);
          elementY++;
        } else // number of crossed pixel is (timesY+1)
          sigmaY = (double)(timesY+1)*m_pitch_Y/sqrt(12.);
 
        if (CLHEP::RandFlat::shoot(rndmEngine, 0.0, 1.0) < ProbX) { // number of crossed pixel is (timesY+1)+1
          sigmaX = (double)(timesX+2)*m_pitch_X/sqrt(12.);
          elementX++;
        } else // number of crossed pixel is (timesY+1)
          sigmaX = (double)(timesX+1)*m_pitch_X/sqrt(12.);
      }
 
      ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool " << (m_SmearPixel ? "pixel" : "SCT") << " sigma X --- " << sigmaX);
      ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool " << (m_SmearPixel ? "pixel" : "SCT") << " sigma Y --- " << sigmaY);
 
 
      double temp_X = interX;
      double temp_Y = interY;
 
      Amg::Vector2D intersection(interX, interY);
 
      ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: Intersection after smearing: " << intersection);
 
      Identifier intersectionId;
      intersectionId = hitSiDetElement->identifierOfPosition(intersection);
 
      rdoList.push_back(intersectionId);
      InDetDD::SiCellId currentCellId = hitSiDetElement->cellIdFromIdentifier(intersectionId);
 
      if (!currentCellId.isValid()) continue;
 
      ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: Intersection Id = " << intersectionId << " --- currentCellId = " << currentCellId );
 
      if(m_SmearPixel) { // Smear Pixel --> Create Pixel Cluster
 
        double lengthX = (m_pitch_X) ? elementX*m_pitch_X : 1.;
        double lengthY = (m_pitch_Y) ? elementY*m_pitch_Y : 1.;
 
        if (m_pitch_X == 0. || m_pitch_Y == 0.)
          ATH_MSG_WARNING( "--- SiSmearedDigitizationTool: pitchX and/or pitchY are 0. Cluster length is forced to be 1. mm");
 
        InDet::SiWidth siWidth(Amg::Vector2D(elementX,elementY), Amg::Vector2D(lengthX, lengthY));
 
        InDet::PixelCluster* pixelCluster = nullptr;
 
        AmgSymMatrix(2) covariance;
        covariance.setIdentity();
        covariance(Trk::locX,Trk::locX) = sigmaX*sigmaX;
        covariance(Trk::locY,Trk::locY) = sigmaY*sigmaY;
 
        // create the cluster
        pixelCluster = new InDet::PixelCluster(intersectionId,
                                               intersection,
                                               std::move(rdoList),
                                               siWidth,
                                               hitSiDetElement,
                                               Amg::MatrixX(covariance));
        m_pixelClusterMap->insert(std::pair<IdentifierHash, InDet::PixelCluster* >(waferID, pixelCluster));
 
        if (FillTruthMap(m_pixelPrdTruth, pixelCluster, hit).isFailure()) {
          ATH_MSG_FATAL ( "FillTruthMap() for pixel failed!" );
          return StatusCode::FAILURE;
        }
 
        if (m_checkSmear) {
 
            ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: pixelCluster --> " << *pixelCluster);
            //Take info to store in the tree
            m_x_pixel = temp_X;
            m_y_pixel = temp_Y;
 
            m_x_pixel_smeared = (pixelCluster->localPosition()).x();
            m_y_pixel_smeared = (pixelCluster->localPosition()).y();
 
            ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: BEFORE SMEARING LocalPosition --> X = " << m_x_pixel << "  Y = " << m_y_pixel);
            ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: LocalPosition --> X = " << m_x_pixel_smeared << "  Y = " << m_y_pixel_smeared);
 
            ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: GlobalPosition --> X = " << (pixelCluster->globalPosition()).x() << "  Y = " << (pixelCluster->globalPosition()).y());
            m_x_pixel_global = (pixelCluster->globalPosition()).x();
            m_y_pixel_global = (pixelCluster->globalPosition()).y();
            m_z_pixel_global = (pixelCluster->globalPosition()).z();
 
            m_Err_x_pixel = Amg::error(pixelCluster->localCovariance(), Trk::locX);
            m_Err_y_pixel = Amg::error(pixelCluster->localCovariance(), Trk::locY);
 
            ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: Error --> X = " << m_Err_x_pixel << "  Y = " << m_Err_y_pixel);
 
            m_currentTree -> Fill();
          }  // End of Pix smear check
 
      } else { // Smear SCT --> Create SCT Cluster
 
        // prepare the clusters
        InDet::SCT_Cluster * sctCluster = nullptr;
 
        // Pixel Design needed -------------------------------------------------------------
        const InDetDD::SCT_ModuleSideDesign* design_sct;
 
        design_sct = dynamic_cast<const InDetDD::SCT_ModuleSideDesign*>(&hitSiDetElement->design());
 
        if (!design_sct) {
           ATH_MSG_INFO ( "Could not get design"<< design_sct) ;
           continue;
        }
 
        // Find length of strip at centre
        double clusterWidth = rdoList.size()*hitSiDetElement->phiPitch(intersection);
        const std::pair<InDetDD::SiLocalPosition, InDetDD::SiLocalPosition> ends(design_sct->endsOfStrip(intersection));
        double stripLength = std::abs(ends.first.xEta()-ends.second.xEta());
 
        InDet::SiWidth siWidth(Amg::Vector2D(int(rdoList.size()),1),
                               Amg::Vector2D(clusterWidth,stripLength) );
 
        const Amg::Vector2D& colRow = siWidth.colRow();
 
        AmgSymMatrix(2) mat;
        mat.setIdentity();
        mat(Trk::locX,Trk::locX) = sigmaX*sigmaX;
        mat(Trk::locY,Trk::locY) = hitSiDetElement->length()*hitSiDetElement->length()/12.;
 
        // single strip - resolution close to pitch/sqrt(12)
        // two-strip hits: better resolution, approx. 40% lower
 
        InDetDD::DetectorShape elShape = hitSiDetElement->design().shape();
        if(m_emulateAtlas && elShape == InDetDD::Trapezoid)
        { // rotation for endcap SCT
 
          if(colRow.x() == 1) {
             mat(Trk::locX,Trk::locX) = pow(siWidth.phiR(),2)/12;
          }
          else if(colRow.x() == 2) {
             mat(Trk::locX,Trk::locX) = pow(0.27*siWidth.phiR(),2)/12;
          }
          else {
             mat(Trk::locX,Trk::locX) = pow(siWidth.phiR(),2)/12;
          }
 
          mat(Trk::locY,Trk::locY) = pow(siWidth.z()/colRow.y(),2)/12;
          double sn      = hitSiDetElement->sinStereoLocal(intersection);
          double sn2     = sn*sn;
          double cs2     = 1.-sn2;
          double w       = hitSiDetElement->phiPitch(intersection)/hitSiDetElement->phiPitch();
          double v0      = mat(Trk::locX, Trk::locX)*w*w;
          double v1      = mat(Trk::locY, Trk::locY);
          mat(Trk::locX, Trk::locX) = (cs2*v0+sn2*v1);
          mat(Trk::locY, Trk::locX) = (sn*sqrt(cs2)*(v0-v1));
          mat(Trk::locY, Trk::locY) = (sn2*v0+cs2*v1);
        }  // End of rotation endcap SCT
 
 
        sctCluster = new InDet::SCT_Cluster(intersectionId,
                                             intersection,
                                             std::move(rdoList),
                                             siWidth,
                                             hitSiDetElement,
                                             Amg::MatrixX(mat));
 
        m_sctClusterMap->insert(std::pair<IdentifierHash, InDet::SCT_Cluster* >(waferID, sctCluster));
 
        if (FillTruthMap(m_SCTPrdTruth, sctCluster, hit).isFailure()) {
          ATH_MSG_FATAL ( "FillTruthMap() for SCT failed!" );
          return StatusCode::FAILURE;
        }
 
        if (m_checkSmear) {
 
            ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: SCT_Cluster --> " << *sctCluster);
 
            //Take info to store in the tree
            m_x_SCT = m_useDiscSurface ? temp_Y : temp_X;
            m_x_SCT_smeared = (sctCluster->localPosition()).x();
 
            ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: BEFORE SMEARING LocalPosition --> X = " << m_x_SCT );
            ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: LocalPosition --> X = " << m_x_SCT_smeared );
 
            ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: GlobalPosition --> X = " << (sctCluster->globalPosition()).x() << "  Y = " << (sctCluster->globalPosition()).y());
            m_x_SCT_global = (sctCluster->globalPosition()).x();
            m_y_SCT_global = (sctCluster->globalPosition()).y();
            m_z_SCT_global = (sctCluster->globalPosition()).z();
 
            m_currentTree -> Fill();
        }  // End smear checking
      }  // End SCT
    } // while
  } //while
  return StatusCode::SUCCESS;
}
 
 
StatusCode SiSmearedDigitizationTool::createAndStoreRIOs(const EventContext& ctx)
{
  // Get PixelDetectorElementCollection
  const InDetDD::SiDetectorElementCollection* elementsPixel = nullptr;
  if (m_SmearPixel) {
    SG::ReadCondHandle<InDetDD::SiDetectorElementCollection> pixelDetEle(m_pixelDetEleCollKey, ctx);
    elementsPixel = pixelDetEle.retrieve();
    if (elementsPixel==nullptr) {
      ATH_MSG_FATAL(m_pixelDetEleCollKey.fullKey() << " could not be retrieved");
      return StatusCode::FAILURE;
    }
  }
  // Get SCT_DetectorElementCollection
  const InDetDD::SiDetectorElementCollection* elementsSCT = nullptr;
  if (not m_SmearPixel) {
    SG::ReadCondHandle<InDetDD::SiDetectorElementCollection> sctDetEle(m_SCTDetEleCollKey, ctx);
    elementsSCT = sctDetEle.retrieve();
    if (elementsSCT==nullptr) {
      ATH_MSG_FATAL(m_SCTDetEleCollKey.fullKey() << " could not be retrieved");
      return StatusCode::FAILURE;
    }
  }
 
  if ( m_SmearPixel ) { // Store Pixel RIOs
 
    ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: in pixel createAndStoreRIOs() ---" );
 
    Pixel_detElement_RIO_map::iterator i = m_pixelClusterMap->begin();
    Pixel_detElement_RIO_map::iterator e = m_pixelClusterMap->end();
 
    for ( ; i != e; i = m_pixelClusterMap->upper_bound(i->first) ) {
 
      std::pair <Pixel_detElement_RIO_map::iterator, Pixel_detElement_RIO_map::iterator> range;
      range = m_pixelClusterMap->equal_range(i->first);
 
      Pixel_detElement_RIO_map::iterator firstDetElem;
      firstDetElem = range.first;
 
      IdentifierHash waferID;
      waferID = firstDetElem->first;
 
      const InDetDD::SiDetectorElement* detElement = elementsPixel->getDetectorElement(waferID);
 
      InDet::PixelClusterCollection *clusterCollection = new InDet::PixelClusterCollection(waferID);
      clusterCollection->setIdentifier(detElement->identify());
 
      for ( Pixel_detElement_RIO_map::iterator iter = range.first; iter != range.second; ++iter ) {
 
        InDet::PixelCluster* pixelCluster = (*iter).second;
        pixelCluster->setHashAndIndex(clusterCollection->identifyHash(),clusterCollection->size());
        clusterCollection->push_back(pixelCluster);
      }
 
      if ( m_pixelClusterContainer->addCollection( clusterCollection, waferID ).isFailure() ) {
        ATH_MSG_WARNING( "Could not add collection to Identifyable container !" );
      }
    } // end for
 
    m_pixelClusterMap->clear();
 
  }
  else { // Store SCT RIOs
 
    ATH_MSG_DEBUG( "--- SiSmearedDigitizationTool: in SCT createAndStoreRIOs() ---" );
 
    SCT_detElement_RIO_map::iterator i = m_sctClusterMap->begin();
    SCT_detElement_RIO_map::iterator e = m_sctClusterMap->end();
 
    for ( ; i != e; i = m_sctClusterMap->upper_bound(i->first) ) {
      std::pair <SCT_detElement_RIO_map::iterator, SCT_detElement_RIO_map::iterator> range;
      range = m_sctClusterMap->equal_range(i->first);
 
      SCT_detElement_RIO_map::iterator firstDetElem;
      firstDetElem = range.first;
 
      IdentifierHash waferID;
      waferID = firstDetElem->first;
      const InDetDD::SiDetectorElement* detElement = elementsSCT->getDetectorElement(waferID);
 
      InDet::SCT_ClusterCollection *clusterCollection = new InDet::SCT_ClusterCollection(waferID);
      clusterCollection->setIdentifier(detElement->identify());
 
 
      for ( SCT_detElement_RIO_map::iterator iter = range.first; iter != range.second; ++iter ) {
        InDet::SCT_Cluster* sctCluster = (*iter).second;
        sctCluster->setHashAndIndex(clusterCollection->identifyHash(),clusterCollection->size());
        clusterCollection->push_back(sctCluster);
      }
 
      if ( m_sctClusterContainer->addCollection( clusterCollection, clusterCollection->identifyHash() ).isFailure() ) {
        ATH_MSG_WARNING( "Could not add collection to Identifyable container !" );
      }
 
    } // end for
 
    m_sctClusterMap->clear();
  }
 
  return StatusCode::SUCCESS;
}