PRD_TruthTrajectorySelectorID.cxx

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/*
  Copyright (C) 2002-2022 CERN for the benefit of the ATLAS collaboration
*/

// PRD_TruthTrajectorySelectorID.cxx, (c) ATLAS Detector software
 
#include "InDetTruthTools/PRD_TruthTrajectorySelectorID.h"
#include "InDetPrepRawData/SCT_Cluster.h"
#include "InDetPrepRawData/TRT_DriftCircle.h"
#include "InDetPrepRawData/PixelCluster.h"
// DetectorDescription
#include "AtlasDetDescr/AtlasDetectorID.h"
// HepMC
#include "AtlasHepMC/GenParticle.h"
#include "TruthUtils/MagicNumbers.h"
 
 
InDet::PRD_TruthTrajectorySelectorID::PRD_TruthTrajectorySelectorID(const std::string& t, const std::string& n, const IInterface* p) :
AthAlgTool(t,n,p)
{
    declareInterface<Trk::IPRD_TruthTrajectorySelector>(this);
}
 
StatusCode InDet::PRD_TruthTrajectorySelectorID::initialize() {
  ATH_MSG_VERBOSE("Initializing ...");
  StatusCode sc = detStore()->retrieve(m_atlasId, "AtlasID");
  if (sc.isFailure()) {
    msg(MSG::ERROR) << "Could not get AtlasID helper !" << endmsg;
    return StatusCode::FAILURE;
  }
  return StatusCode::SUCCESS;
 
}
 
StatusCode InDet::PRD_TruthTrajectorySelectorID::finalize() {
  ATH_MSG_VERBOSE("Finalizing ...");
  return StatusCode::SUCCESS;
}
 
ThreePointCircle::ThreePointCircle(const std::vector<Amg::Vector3D>& posVec) :
    m_translation(nullptr), m_d0(0.), m_z0(0.), m_phi0(0.), m_eta(0.), m_pt(0.)
{
    if (posVec.size() <3)
        std::cout << "[WARNING] not enough points" << std::endl;
    else
        constructCircle(posVec[0],posVec[1],posVec[2]);  
}
 
ThreePointCircle::~ThreePointCircle()
{
    delete m_translation;
}
 
void ThreePointCircle::constructCircle(    const Amg::Vector3D& p1, 
                    const Amg::Vector3D& p2,
                    const Amg::Vector3D& p3) {
    
    // get the (x/y) coordinates of all points
  double translationX = m_translation ? -(m_translation->translation()).x() : 0.;
  double translationY = m_translation ? -(m_translation->translation()).y() : 0.;
    
  double bx = p1.x()+translationX; 
    double by = p1.y()+translationY;
  double cx = p2.x()+translationX;
    double cy = p2.y()+translationY;
  double dx = p3.x()+translationX;
    double dy = p3.y()+translationY;
    
  double temp = cx*cx+cy*cy;
 
    // prepare the matrix for the linear equation
  double bc = (bx*bx + by*by - temp)/2.0;
  double cd = (temp - dx*dx - dy*dy)/2.0;
  double det = (bx-cx)*(cy-dy)-(cx-dx)*(by-cy);
  //if (std::abs(det) < 1.0e-6) {
  //std::cout << "[WARNING] Determinant is close to 0 " << std::endl;
  //}
 
    // invert the determinant
  det = 1./det;
 
    // x / y coordinate of the center
  double cRx= (bc*(cy-dy)-cd*(by-cy))*det;
  double cRy = ((bx-cx)*cd-(cx-dx)*bc)*det;
 
    // get the center, radius and momentum
  m_center = Amg::Vector2D(cRx,cRy); 
  m_radius = sqrt((cRx-bx)*(cRx-bx)+(cRy-by)*(cRy-by));
    m_pt = m_radius*(0.3*2.);
 
    // transverse parameters
    m_d0 = std::sqrt(cRx*cRx+cRy*cRy)-m_radius;
 
    // longitudinal parameters
    double theta = 1./3*(p1.theta() + p2.theta() + p3.theta());
    double r1 = p1.perp();
    double z1 = p1.z();
    double deltaz = r1/tan(theta);
    m_z0 = z1 - deltaz;
    // eta
    m_eta = 1./3*(p1.eta() + p2.eta() + p3.eta());
    
  // get the point of closest approach
    Amg::Vector2D poca = -m_d0*m_center.unit();
 
  // find the closest measurement
    Amg::Vector2D closestMeasurement = p1.perp() < p2.perp() ? 
      Amg::Vector2D(p1.x(),p1.y()) : Amg::Vector2D(p2.x(),p2.y());
    if (p3.perp() < p1.perp()) closestMeasurement = Amg::Vector2D(p3.x(),p3.y());
 
  // phi0 is the most difficult one, two solution possible
    Amg::Vector2D directionOne(-cRy,cRx);
    Amg::Vector2D directionTwo(cRy,-cRx);
 
    // build difference vector closest measurement, poca
    Amg::Vector2D toFirstMeas(closestMeasurement-poca);
 
    // check with scalar product
    m_phi0 = directionOne.dot(toFirstMeas) > 0. ? directionOne.phi() : directionTwo.phi();
 
    // now sign d0
    Amg::Vector3D pocaDir(poca.x(),poca.y(),0.);
    Amg::Vector3D momDir(std::cos(m_phi0),std::sin(m_phi0),0.);
  double signD0 = pocaDir.cross(momDir).z() > 0. ? 1. : -1.;    
    m_d0 = signD0 * std::abs(m_d0);
        
    // update the center for the translation
    m_center += Amg::Vector2D(translationX,translationY);
    
}
 
bool InDet::PRD_TruthTrajectorySelectorID::pass( const Trk::PRD_TruthTrajectory & prdvec) const {
 
  std::vector<Amg::Vector3D> pos;
  std::vector<const Trk::PrepRawData* >::const_iterator prdIter  = prdvec.prds.begin();
  std::vector<const Trk::PrepRawData* >::const_iterator prdIterE = prdvec.prds.end();
 
  // look for 3 globalPositions for ThreePointCircle approximation
  for ( int i = 0; i  < 3 &&  prdIter != prdIterE; ++ prdIter ){
    if( m_atlasId->is_pixel((*prdIter)->identify()) ){
      const InDet::PixelCluster* pixclus=dynamic_cast<const InDet::PixelCluster*>(*prdIter);
      if (pixclus) {
        if(!pos.empty() && (pos.back()-pixclus->globalPosition()).squaredNorm() < 9)
          continue;
        pos.push_back (pixclus->globalPosition());
      }
    }
    else if( m_atlasId->is_sct((*prdIter)->identify()) ){
      const InDet::SCT_Cluster* sctclus=dynamic_cast<const InDet::SCT_Cluster*>(*prdIter);
      if (sctclus) { 
        if(!pos.empty() && (pos.back()-sctclus->globalPosition()).squaredNorm() < 9)
          continue;
        pos.push_back (sctclus->globalPosition());
      }
    }
    else if( m_atlasId->is_trt((*prdIter)->identify()) ){
      continue;
    }
    i++;
  }
 
  // only take trajectory if enough hits
  if( pos.size() != 3 ) return false;
  
  ThreePointCircle circle(pos);
  // trajectory only selected when within cuts
  if( ( std::abs(circle.d0()) <= 15 && !HepMC::is_simulation_particle(prdvec.genParticle)  ))  return true;
  
  return false;
}