DTSegmentUpdator.cc

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/* This Class Header */
#include "RecoLocalMuon/DTSegment/src/DTSegmentUpdator.h"

/* Collaborating Class Header */

//mene
#include "DataFormats/DTRecHit/interface/DTChamberRecSegment2D.h"

#include "DataFormats/DTRecHit/interface/DTRecSegment2D.h"
#include "DataFormats/DTRecHit/interface/DTSLRecSegment2D.h"
#include "DataFormats/DTRecHit/interface/DTChamberRecSegment2D.h"
#include "DataFormats/DTRecHit/interface/DTRecSegment4D.h"
#include "DataFormats/DTRecHit/interface/DTRecHit1D.h"
#include "DataFormats/GeometryCommonDetAlgo/interface/ErrorFrameTransformer.h"

#include "RecoLocalMuon/DTSegment/src/DTSegmentCand.h"
#include "RecoLocalMuon/DTRecHit/interface/DTRecHitAlgoFactory.h"
#include "RecoLocalMuon/DTSegment/src/DTLinearFit.h"

#include "Geometry/Records/interface/MuonGeometryRecord.h"
#include "Geometry/DTGeometry/interface/DTGeometry.h"
#include "Geometry/DTGeometry/interface/DTLayer.h"

#include "FWCore/Utilities/interface/Exception.h"
#include "FWCore/MessageLogger/interface/MessageLogger.h"
#include "FWCore/Framework/interface/EventSetup.h"
#include "FWCore/ParameterSet/interface/ParameterSet.h"

/* C++ Headers */
#include <string>

using namespace std;
using namespace edm;

/* ====================================================================== */

DTSegmentUpdator::DTSegmentUpdator(const ParameterSet& config) :
  theFitter(new DTLinearFit()) ,
  vdrift_4parfit(config.getParameter<bool>("performT0_vdriftSegCorrection")),
  T0_hit_resolution(config.getParameter<double>("hit_afterT0_resolution")),
  perform_delta_rejecting(config.getParameter<bool>("perform_delta_rejecting")),
  debug(config.getUntrackedParameter<bool>("debug",false)) 
{  
  string theAlgoName = config.getParameter<string>("recAlgo");
  theAlgo = DTRecHitAlgoFactory::get()->create(theAlgoName, 
                                               config.getParameter<ParameterSet>("recAlgoConfig"));

  if(debug)
    cout << "[DTSegmentUpdator] Constructor called" << endl;
}

DTSegmentUpdator::~DTSegmentUpdator() {
  delete theFitter;
}

/* Operations */ 

void DTSegmentUpdator::setES(const EventSetup& setup){
  setup.get<MuonGeometryRecord>().get(theGeom);
  theAlgo->setES(setup);
}

void DTSegmentUpdator::update(DTRecSegment4D* seg, const bool calcT0, bool allow3par) const {

  if(debug) cout << "[DTSegmentUpdator] Starting to update the DTRecSegment4D" << endl;

  const bool hasPhi = seg->hasPhi();
  const bool hasZed = seg->hasZed();

  //reject the bad hits (due to delta rays)
  if(perform_delta_rejecting && hasPhi) rejectBadHits(seg->phiSegment());

  int step = (hasPhi && hasZed) ? 3 : 2;
  if(calcT0) step = 4;

  if(debug) cout << "Step of update is " << step << endl;

  GlobalPoint  pos = theGeom->idToDet(seg->geographicalId())->toGlobal(seg->localPosition());
  GlobalVector dir = theGeom->idToDet(seg->geographicalId())->toGlobal(seg->localDirection());

  if(calcT0) calculateT0corr(seg);

  if(hasPhi) updateHits(seg->phiSegment(),pos,dir,step);
  if(hasZed) updateHits(seg->zSegment()  ,pos,dir,step);

  fit(seg,allow3par);
}

void DTSegmentUpdator::update(DTRecSegment2D* seg, bool allow3par) const {
  if(debug) cout << "[DTSegmentUpdator] Starting to update the DTRecSegment2D" << endl;
  GlobalPoint pos = (theGeom->idToDet(seg->geographicalId()))->toGlobal(seg->localPosition());
  GlobalVector dir = (theGeom->idToDet(seg->geographicalId()))->toGlobal(seg->localDirection());

  updateHits(seg,pos,dir);
  fit(seg,allow3par,0);
}

void DTSegmentUpdator::fit(DTRecSegment4D* seg, bool allow3par)  const {
  if(debug) cout << "[DTSegmentUpdator] Fit DTRecSegment4D:" << endl;
  // after the update must refit the segments
  
  if (debug) {
    if(seg->hasPhi()) cout << "    4D Segment contains a Phi segment. t0= " << seg->phiSegment()->t0()  << "  chi2= " << seg->phiSegment()->chi2() << endl;
    if(seg->hasZed()) cout << "    4D Segment contains a Zed segment. t0= " << seg->zSegment()->t0()  << "  chi2= " << seg->zSegment()->chi2() << endl;
  }
  
  
  // use the 2-par fit UNLESS the 4D segment only has the Phi projection or is out of time by more than 20ns
  // - in these cases use the 3-par fit
  if(seg->hasPhi()) {
    if(seg->hasZed()) {

      // fit in-time Phi segments with the 2par fit and out-of-time segments with the 3par fit
      if (fabs(seg->phiSegment()->t0())<40.) {
        fit(seg->phiSegment(),allow3par,1);
        fit(seg->zSegment(),allow3par,1);      
      } else {
        fit(seg->phiSegment(),allow3par,0);
        fit(seg->zSegment(),allow3par,0);      
      }

    } else fit(seg->phiSegment(),allow3par,0);
  } else fit(seg->zSegment(),allow3par,0);
 
  const DTChamber* theChamber = theGeom->chamber(seg->chamberId());

  if(seg->hasPhi() && seg->hasZed() ) {

    DTChamberRecSegment2D *segPhi=seg->phiSegment();
    DTSLRecSegment2D *segZed=seg->zSegment();

    // NB Phi seg is already in chamber ref
    LocalPoint posPhiInCh = segPhi->localPosition();
    LocalVector dirPhiInCh= segPhi->localDirection();

    // Zed seg is in SL one
    const DTSuperLayer* zSL = theChamber->superLayer(segZed->superLayerId());
    LocalPoint zPos(segZed->localPosition().x(), 
            (zSL->toLocal(theChamber->toGlobal(segPhi->localPosition()))).y(),
            0.);

    LocalPoint posZInCh = theChamber->toLocal(zSL->toGlobal(zPos));

    LocalVector dirZInCh = theChamber->toLocal(zSL->toGlobal(segZed->localDirection()));

    LocalPoint posZAt0 = posZInCh + dirZInCh*(-posZInCh.z())/cos(dirZInCh.theta());

    // given the actual definition of chamber refFrame, (with z poiniting to IP),
    // the zed component of direction is negative.
    LocalVector dir=LocalVector(dirPhiInCh.x()/fabs(dirPhiInCh.z()),dirZInCh.y()/fabs(dirZInCh.z()),-1.);

    seg->setPosition(LocalPoint(posPhiInCh.x(),posZAt0.y(),0.));
    seg->setDirection(dir.unit());

    AlgebraicSymMatrix mat(4);

    // set cov matrix
    mat[0][0] = segPhi->parametersError()[0][0]; //sigma (dx/dz)
    mat[0][2] = segPhi->parametersError()[0][1]; //cov(dx/dz,x)
    mat[2][2] = segPhi->parametersError()[1][1]; //sigma (x)

    seg->setCovMatrix(mat);
    seg->setCovMatrixForZed(posZInCh);
  }
  else if (seg->hasPhi()) {
    DTChamberRecSegment2D *segPhi=seg->phiSegment();

    seg->setPosition(segPhi->localPosition());
    seg->setDirection(segPhi->localDirection());

    AlgebraicSymMatrix mat(4);
    // set cov matrix
    mat[0][0] = segPhi->parametersError()[0][0]; //sigma (dx/dz)
    mat[0][2] = segPhi->parametersError()[0][1]; //cov(dx/dz,x)
    mat[2][2] = segPhi->parametersError()[1][1]; //sigma (x)

    seg->setCovMatrix(mat);
  }
  else if (seg->hasZed()) {
    DTSLRecSegment2D *segZed = seg->zSegment();

    // Zed seg is in SL one
    GlobalPoint glbPosZ = ( theGeom->superLayer(segZed->superLayerId()) )->toGlobal(segZed->localPosition());
    LocalPoint posZInCh = ( theGeom->chamber(segZed->superLayerId().chamberId()) )->toLocal(glbPosZ);

    GlobalVector glbDirZ = (theGeom->superLayer(segZed->superLayerId()) )->toGlobal(segZed->localDirection());
    LocalVector dirZInCh = (theGeom->chamber(segZed->superLayerId().chamberId()) )->toLocal(glbDirZ);

    LocalPoint posZAt0 = posZInCh+
      dirZInCh*(-posZInCh.z())/cos(dirZInCh.theta());

    seg->setPosition(posZAt0);
    seg->setDirection(dirZInCh);

    AlgebraicSymMatrix mat(4);
    // set cov matrix
    seg->setCovMatrix(mat);
    seg->setCovMatrixForZed(posZInCh);
  }
}



bool DTSegmentUpdator::fit(DTSegmentCand* seg, bool allow3par, const bool fitdebug) const {

//  if (debug && fitdebug) cout << "[DTSegmentUpdator] Fit DTRecSegment2D" << endl;
  if (!seg->good()) return false;

//  DTSuperLayerId DTid = (DTSuperLayerId)seg->superLayer()->id();
//  if (DTid.superlayer()==2)  
//    allow3par = 0;

  vector<float> x;
  vector<float> y;
  vector<float> sigy;
  vector <int> lfit;
  vector <double> dist;
  int i=0;
  
  x.reserve(8);
  y.reserve(8);
  sigy.reserve(8);
  lfit.reserve(8);
  dist.reserve(8);

  DTSegmentCand::AssPointCont hits=seg->hits();
  for (DTSegmentCand::AssPointCont::const_iterator iter=hits.begin(); iter!=hits.end(); ++iter) {
    LocalPoint pos = (*iter).first->localPosition((*iter).second);
    float xwire = (((*iter).first)->localPosition(DTEnums::Left).x() + ((*iter).first)->localPosition(DTEnums::Right).x()) /2.;
    float distance = pos.x() - xwire;

    if ((*iter).second==DTEnums::Left) lfit.push_back(1);
      else lfit.push_back(-1);

    dist.push_back(distance);
    sigy.push_back(sqrt((*iter).first->localPositionError().xx()));
    x.push_back(pos.z()); 
    y.push_back(pos.x());
    i++;
  }

  LocalPoint pos;
  LocalVector dir;
  AlgebraicSymMatrix covMat(2);
  float cminf =0.;
  float vminf =0.;
  double chi2 = 0.;
  double t0_corr = 0.;
  
  fit(x,y,lfit,dist,sigy,pos,dir,cminf,vminf,covMat,chi2,allow3par);
  if (cminf!=0) t0_corr=-cminf/0.00543; // convert drift distance to time

  if (debug && fitdebug) cout << "  DTcand chi2: " << chi2 << endl;
  if (debug && fitdebug) cout << "  DTcand   t0: " << t0_corr << endl;

  seg->setPosition(pos);
  seg->setDirection(dir);
  seg->sett0(t0_corr);
  seg->setCovMatrix(covMat);
  seg->setChi2(chi2);

  // cout << "pos " << pos << endl;
  // cout << "dir " << dir << endl;
  // cout << "Mat " << covMat << endl;

  return true;
}

void DTSegmentUpdator::fit(DTRecSegment2D* seg, bool allow3par, bool block3par) const {

  if(debug) cout << "[DTSegmentUpdator] Fit DTRecSegment2D - 3par: " << allow3par << endl;

  vector<float> x;
  vector<float> y;
  vector<float> sigy;
  vector <int> lfit;
  vector <double> dist;
  x.reserve(8);
  y.reserve(8);
  sigy.reserve(8);
  lfit.reserve(8);
  dist.reserve(8);

//  DTSuperLayerId DTid = (DTSuperLayerId)seg->geographicalId();
//  if (DTid.superlayer()==2)  
//    allow3par = 0;

  vector<DTRecHit1D> hits=seg->specificRecHits();
  for (vector<DTRecHit1D>::const_iterator hit=hits.begin();
       hit!=hits.end(); ++hit) {

    // I have to get the hits position (the hit is in the layer rf) in SL frame...
    GlobalPoint glbPos = ( theGeom->layer( hit->wireId().layerId() ) )->toGlobal(hit->localPosition());
    LocalPoint pos = ( theGeom->idToDet(seg->geographicalId()) )->toLocal(glbPos);
    x.push_back(pos.z()); 
    y.push_back(pos.x());

    const DTLayer* layer = theGeom->layer( hit->wireId().layerId() );
    float xwire = layer->specificTopology().wirePosition(hit->wireId().wire());
    float distance = fabs(hit->localPosition().x() - xwire);
    dist.push_back(distance);

    int ilc = ( hit->lrSide() == DTEnums::Left ) ? 1 : -1;
    lfit.push_back(ilc);

    // Get local error in SL frame
    //RB: is it right in this way? 
    ErrorFrameTransformer tran;
    GlobalError glbErr = tran.transform( hit->localPositionError(),(theGeom->layer( hit->wireId().layerId() ))->surface());
    LocalError slErr = tran.transform( glbErr, (theGeom->idToDet(seg->geographicalId()))->surface());
    sigy.push_back(sqrt(slErr.xx()));
  }

  LocalPoint pos;
  LocalVector dir;
  AlgebraicSymMatrix covMat(2);
  double chi2 = 0.;
  float cminf=0.;
  float vminf=0.;
  double t0_corr = 0.;

  fit(x,y,lfit,dist,sigy,pos,dir,cminf,vminf,covMat,chi2,allow3par,block3par);
  if (cminf!=0) t0_corr=-cminf/0.00543; // convert drift distance to time

  if (debug) cout << "   DTSeg2d chi2: " << chi2 << endl;
  if (debug) cout << "   DTSeg2d Fit t0: " << t0_corr << endl;
  // cout << "pos " << segPosition << endl;
  // cout << "dir " << segDirection << endl;
  // cout << "Mat " << mat << endl;

  seg->setPosition(pos);
  seg->setDirection(dir);
  seg->setCovMatrix(covMat);
  seg->setChi2(chi2);
  seg->setT0(t0_corr);
}

void DTSegmentUpdator::fit(const vector<float>& x,
                           const vector<float>& y, 
                           const vector<int>& lfit,
                           const vector<double>& dist,
                           const vector<float>& sigy,
                           LocalPoint& pos,
                           LocalVector& dir,
                           float& cminf,
                           float& vminf,
                           AlgebraicSymMatrix& covMatrix,
                           double& chi2,
                           const bool allow3par,
                           const bool block3par)  const {

  float slope     = 0.;
  float intercept = 0.;
  float covss     = 0.;
  float covii     = 0.;
  float covsi     = 0.;

  cminf=0;
  vminf=0;

  int leftHits=0, rightHits=0;
  for (unsigned int i=0; i<lfit.size(); i++)
    if (lfit[i]==1) leftHits++; else rightHits++;

  theFitter->fit(x,y,x.size(),sigy,slope,intercept,chi2,covss,covii,covsi);

  // If we have at least one left and one right hit we can try the 3 parameter fit (if it is switched on)
  // FIXME: currently the covariance matrix from the 2-par fit is kept
  if (leftHits && rightHits && (leftHits+rightHits>3) && allow3par) {
    theFitter->fitNpar(3,x,y,lfit,dist,sigy,slope,intercept,cminf,vminf,chi2,debug);    
    double t0_corr=-cminf/0.00543;
    if (fabs(t0_corr)<20. && block3par) {
      theFitter->fit(x,y,x.size(),sigy,slope,intercept,chi2,covss,covii,covsi);
      cminf=0;
    }
  }
  
  // cout << "slope " << slope << endl;
  // cout << "intercept " << intercept << endl;

  // intercept is the x() in chamber frame when the segment cross the chamber
  // plane (at z()=0), the y() is not measured, so let's put the center of the
  // chamber.
  pos = LocalPoint(intercept,0.,0.);

  //  slope is dx()/dz(), while dy()/dz() is by definition 0, finally I want the
  //  segment to point outward, so opposite to local z
  dir = LocalVector(-slope,0.,-1.).unit();

  covMatrix = AlgebraicSymMatrix(2);
  covMatrix[0][0] = covss; // this is var(dy/dz)
  covMatrix[1][1] = covii; // this is var(y)
  covMatrix[1][0] = covsi; // this is cov(dy/dz,y)
}

// The GlobalPoint and the GlobalVector can be either the glb position and the direction
// of the 2D-segment itself or the glb position and direction of the 4D segment
void DTSegmentUpdator::updateHits(DTRecSegment2D* seg, GlobalPoint &gpos,
                                  GlobalVector &gdir, const int step) const{

  // it is not necessary to have DTRecHit1D* to modify the obj in the container
  // but I have to be carefully, since I cannot make a copy before the iteration!

  vector<DTRecHit1D> toBeUpdatedRecHits = seg->specificRecHits();
  vector<DTRecHit1D> updatedRecHits;

  for (vector<DTRecHit1D>::iterator hit= toBeUpdatedRecHits.begin(); 
       hit!=toBeUpdatedRecHits.end(); ++hit) {

    const DTLayer* layer = theGeom->layer( hit->wireId().layerId() );

    LocalPoint segPos=layer->toLocal(gpos);
    LocalVector segDir=layer->toLocal(gdir);

    // define impact angle needed by the step 2
    const float angle = atan(segDir.x()/-segDir.z());

    // define the local position (extr.) of the segment. Needed by the third step 
    LocalPoint segPosAtLayer=segPos+segDir*(-segPos.z())/cos(segDir.theta());

    DTRecHit1D newHit1D = (*hit);
    bool ok = true;

    if (step == 2) {
      ok = theAlgo->compute(layer,*hit,angle,newHit1D);

    } else if (step == 3) {

      LocalPoint hitPos(hit->localPosition().x(),+segPosAtLayer.y(),0.);
      GlobalPoint glbpos= theGeom->layer( hit->wireId().layerId() )->toGlobal(hitPos);
      newHit1D.setPosition(hitPos);
      ok = theAlgo->compute(layer,*hit,angle,glbpos,newHit1D);

    } else if (step == 4) {

      //const double vminf = seg->vDrift();   //  vdrift correction are recorded in the segment    
      double vminf =0.;
      if(vdrift_4parfit) vminf = seg->vDrift();   // use vdrift recorded in the segment only if vdrift_4parfit=True

      double cminf = 0.;
      if(seg->ist0Valid()) cminf = - seg->t0()*0.00543;

      //cout << "In updateHits: t0 = " << seg->t0() << endl;
      //cout << "In updateHits: vminf = " << vminf << endl;
      //cout << "In updateHits: cminf = " << cminf << endl;

      const float xwire = layer->specificTopology().wirePosition(hit->wireId().wire());
      const float distance = fabs(hit->localPosition().x() - xwire);
      const int ilc = ( hit->lrSide() == DTEnums::Left ) ? 1 : -1;
      const double dy_corr = (vminf*ilc*distance-cminf*ilc ); 

      LocalPoint point(hit->localPosition().x() + dy_corr, +segPosAtLayer.y(), 0.);

      //double final_hit_resol = T0_hit_resolution;
      //if(newHit1D.wireId().layerId().superlayerId().superLayer() != 2) final_hit_resol = final_hit_resol * 0.8;
      //LocalError error(final_hit_resol * final_hit_resol,0.,0.);
      LocalError error(T0_hit_resolution*T0_hit_resolution,0.,0.);
      newHit1D.setPositionAndError(point, error);

      //FIXME: check that the hit is still inside the cell
      ok = true;

    } else throw cms::Exception("DTSegmentUpdator")<<" updateHits called with wrong step " << endl;

    if (ok) updatedRecHits.push_back(newHit1D);
    else {
      LogError("DTSegmentUpdator")<<"DTSegmentUpdator::updateHits failed update" << endl;
      throw cms::Exception("DTSegmentUpdator")<<"updateHits failed update"<<endl;
    }

  }
  seg->update(updatedRecHits);
}

void DTSegmentUpdator::rejectBadHits(DTChamberRecSegment2D* phiSeg) const {

  vector<float> x;
  vector<float> y;
  
  if(debug) cout << " Inside the segment updator, now loop on hits:   ( x == z_loc , y == x_loc) " << endl;
 
  vector<DTRecHit1D> hits = phiSeg->specificRecHits();
  for (vector<DTRecHit1D>::const_iterator hit=hits.begin();
       hit!=hits.end(); ++hit) {

    // I have to get the hits position (the hit is in the layer rf) in SL frame...
    GlobalPoint glbPos = ( theGeom->layer( hit->wireId().layerId() ) )->toGlobal(hit->localPosition());
    LocalPoint pos = ( theGeom->idToDet(phiSeg->geographicalId()) )->toLocal(glbPos);

    x.push_back(pos.z()); 
    y.push_back(pos.x());
  }

  if(debug){
    cout << " end of segment! " << endl;
    cout << " size = Number of Hits: " << x.size() << "  " << y.size() << endl;
  }
  
  // Perform the 2 par fit:
  float par[2]={0.,0.}; // q , m

  //variables to perform the fit:
  float Sx = 0.;
  float Sy = 0.;
  float Sx2 = 0.;
  float Sy2 = 0.;
  float Sxy = 0.;

  size_t N =  x.size();

  if (N == 0)
    return;
    
  for(size_t i = 0; i < N;++i){
    Sx += x.at(i);
    Sy += y.at(i);
    Sx2 += x.at(i)*x.at(i);
    Sy2 += y.at(i)*y.at(i);
    Sxy += x.at(i)*y.at(i);
        
  }
    
  const float delta = N*Sx2 - Sx*Sx;
  par[0] = ( Sx2*Sy - Sx*Sxy )/delta;
  par[1] = ( N*Sxy - Sx*Sy )/delta;

  if(debug) cout << "fit 2 parameters done ----> par0: "<< par[0] << "  par1: "<< par[1] << endl;

  // Calc residuals:
  float residuals[N];
    
  for(size_t i = 0; i < N;++i)
    residuals[i] = 0;
    
  for(size_t i = 0; i < N;++i){
    residuals[i] = y.at(i) - par[1]*x.at(i) - par[0];
    if(debug){ 
      cout<<" i: "<<i<<" y_i "<<y.at(i)<<" x_i "<<x.at(i)<<" res_i "<<residuals[i]; 
      if (i==N-1) cout<<endl;
    }
  }
    
  if(debug) cout << " Residuals computed! "<<  endl;
            
  // Perform bad hit rejecting -- update hits
  vector<DTRecHit1D> updatedRecHits;
    
  float mean_residual = 0.; //mean of the absolute values of residuals
    
  for (size_t i = 0; i < N; ++i)
    mean_residual += fabs(residuals[i]);
    
  mean_residual = mean_residual/(N - 2);    
    
  if(debug) cout << " mean_residual: "<< mean_residual << endl;
    
  int i = 0;
    
  for (vector<DTRecHit1D>::const_iterator hit=hits.begin();
       hit!=hits.end(); ++hit) {
        
    DTRecHit1D newHit1D = (*hit);

    float normResidual = mean_residual > 0 ? fabs(residuals[i])/mean_residual : 0;
    if(normResidual < 1.5){
                    
      updatedRecHits.push_back(newHit1D);
      if(debug) cout << " accepted "<< i+1 << "th hit" <<"  Irej: " << normResidual << endl;
      ++i;
    }
    else {
      if(debug) cout << " rejected "<< i+1 << "th hit" <<"  Irej: " << normResidual << endl;
      ++i;
      continue;
    }
  }
    
  phiSeg->update(updatedRecHits);

  //final check!
  if(debug){

    vector<float> x_upd;
    vector<float> y_upd;

    cout << " Check the update action: " << endl;

    vector<DTRecHit1D> hits_upd = phiSeg->specificRecHits();
    for (vector<DTRecHit1D>::const_iterator hit=hits_upd.begin();
     hit!=hits_upd.end(); ++hit) {

      // I have to get the hits position (the hit is in the layer rf) in SL frame...
      GlobalPoint glbPos = ( theGeom->layer( hit->wireId().layerId() ) )->toGlobal(hit->localPosition());
      LocalPoint pos = ( theGeom->idToDet(phiSeg->geographicalId()) )->toLocal(glbPos);

      x_upd.push_back(pos.z()); 
      y_upd.push_back(pos.x());

      cout << " x_upd: "<< pos.z() << "  y_upd: "<< pos.x() << endl;
    }
  
    cout << " end of segment! " << endl;
    cout << " size = Number of Hits: " << x_upd.size() << "  " << y_upd.size() << endl;
    
  }// end debug
  
  return;
} //end DTSegmentUpdator::rejectBadHits

void DTSegmentUpdator::calculateT0corr(DTRecSegment4D* seg) const {
  if(seg->hasPhi()) calculateT0corr(seg->phiSegment());
  if(seg->hasZed()) calculateT0corr(seg->zSegment());
}

void DTSegmentUpdator::calculateT0corr(DTRecSegment2D* seg) const {
  // WARNING: since this method is called both with a 2D and a 2DPhi as argument
  // seg->geographicalId() can be a superLayerId or a chamberId 
  if(debug) cout << "[DTSegmentUpdator] CalculateT0corr DTRecSegment4D" << endl;

  vector<double> d_drift;
  vector<float> x;
  vector<float> y;
  vector<int> lc;

  vector<DTRecHit1D> hits=seg->specificRecHits();

  DTWireId wireId;
  int nptfit = 0;

  for (vector<DTRecHit1D>::const_iterator hit=hits.begin();
       hit!=hits.end(); ++hit) {

    // I have to get the hits position (the hit is in the layer rf) in SL frame...
    GlobalPoint glbPos = ( theGeom->layer( hit->wireId().layerId() ) )->toGlobal(hit->localPosition());
    LocalPoint pos = ( theGeom->idToDet(seg->geographicalId()) )->toLocal(glbPos);

    const DTLayer* layer = theGeom->layer( hit->wireId().layerId() );
    float xwire = layer->specificTopology().wirePosition(hit->wireId().wire());
    float distance = fabs(hit->localPosition().x() - xwire);

    int ilc = ( hit->lrSide() == DTEnums::Left ) ? 1 : -1;

    nptfit++;
    x.push_back(pos.z()); 
    y.push_back(pos.x());
    lc.push_back(ilc);
    d_drift.push_back(distance);

    // cout << " d_drift "<<distance  <<" npt= " <<npt<<endl;
  }

  double chi2fit = 0.;
  float cminf    = 0.;
  float vminf   = 0.;
  float a,b;

  if ( nptfit > 2 ) {
    //NB chi2fit is normalized
    theFitter->fit4Var(x,y,lc,d_drift,nptfit,a,b,cminf,vminf,chi2fit,vdrift_4parfit,debug);

    double t0cor = -999.;
    if(cminf > -998.) t0cor = - cminf/0.00543 ; // in ns

    //cout << "In calculateT0corr: t0 = " << t0cor << endl;
    //cout << "In calculateT0corr: vminf = " << vminf << endl;
    //cout << "In calculateT0corr: cminf = " << cminf << endl;
    //cout << "In calculateT0corr: chi2 = " << chi2fit << endl;

    seg->setT0(t0cor);          // time  and
    seg->setVdrift(vminf);   //  vdrift correction are recorded in the segment    
  }
}