TrackFitter.cc

Go to the documentation of this file.

#include "CommonTools/Statistics/interface/LinearFit.h"
#include "CommonTools/Utils/interface/DynArray.h"
#include "DataFormats/GeometryCommonDetAlgo/interface/GlobalError.h"
#include "DataFormats/GeometryCommonDetAlgo/interface/Measurement1D.h"
#include "DataFormats/GeometryVector/interface/GlobalPoint.h"
#include "DataFormats/GeometryVector/interface/LocalPoint.h"
#include "DataFormats/TrackingRecHit/interface/TrackingRecHit.h"
#include "FWCore/MessageLogger/interface/MessageLogger.h"
#include "FWCore/ParameterSet/interface/ParameterSet.h"
#include "Geometry/CommonDetUnit/interface/GeomDet.h"
#include "Geometry/CommonDetUnit/interface/GeomDet.h"
#include "Geometry/CommonDetUnit/interface/GeomDetType.h"
#include "Geometry/TrackerGeometryBuilder/interface/TrackerGeometry.h"
#include "MagneticField/Engine/interface/MagneticField.h"
#include "RecoPixelVertexing/PixelLowPtUtilities/interface/TrackFitter.h"
#include "RecoPixelVertexing/PixelTrackFitting/interface/CircleFromThreePoints.h"
#include "RecoPixelVertexing/PixelTrackFitting/interface/PixelTrackBuilder.h"
#include "RecoPixelVertexing/PixelTrackFitting/interface/RZLine.h"
#include "RecoTracker/TkMSParametrization/interface/PixelRecoUtilities.h"
#include "TrackingTools/DetLayers/interface/DetLayer.h"
#include "TrackingTools/TransientTrackingRecHit/interface/TransientTrackingRecHitBuilder.h"

using namespace std;

namespace {

int getCharge
  (const DynArray<GlobalPoint> & points)
{
   GlobalVector v21 = points[1]-points[0];
   GlobalVector v32 = points[2]-points[1];
   float dphi = v32.phi() - v21.phi();
   while (dphi >  M_PI) dphi -= 2*M_PI;
   while (dphi < -M_PI) dphi += 2*M_PI;
   return (dphi > 0) ? -1 : 1;
}

}


/*****************************************************************************/
std::unique_ptr<reco::Track> TrackFitter::run
  (const std::vector<const TrackingRecHit *> & hits,
   const TrackingRegion & region,
   const edm::EventSetup& setup) const
{
  std::unique_ptr<reco::Track> ret;

  int nhits = hits.size();
  if(nhits <2) return ret;

  declareDynArray(GlobalPoint,nhits, points);
  declareDynArray(GlobalError,nhits, errors);
  declareDynArray(bool,nhits, isBarrel);
  
  unsigned int i=0;
  for (auto const & ih  : hits)
  {
    auto recHit = theTTRecHitBuilder->build(ih);

    points[i] = recHit->globalPosition();
    errors[i] = recHit->globalPositionError();
    isBarrel[++i] = recHit->detUnit()->type().isBarrel();
  }

  CircleFromThreePoints circle = (nhits==2) ?
        CircleFromThreePoints(GlobalPoint(0.,0.,0.), points[0], points[1]) :
        CircleFromThreePoints(points[0],points[1],points[2]); 

  int charge = getCharge(points);
  float curvature = circle.curvature();

  // pt
  float invPt = PixelRecoUtilities::inversePt(curvature, setup);
  float valPt = (invPt > 1.e-4) ? 1./invPt : 1.e4;
  float errPt = 0.055*valPt + 0.017*valPt*valPt;

  CircleFromThreePoints::Vector2D center = circle.center();

  // tip
  float valTip = charge * (center.mag()-1/curvature);
  // zip
  float valZip = getZip(valTip, curvature, points[0],points[1]);
  // phi
  float valPhi = getPhi(center.x(), center.y(), charge);
  // cot(theta), update zip
  float valCotTheta =
     getCotThetaAndUpdateZip(points[0],points[1], 1/curvature,
                             valPhi,valTip,valZip);

  // errors
  float errTip, errZip;
  getErrTipAndErrZip(valPt, points.back().eta(), errTip,errZip);
  float errPhi      = 0.002;
  float errCotTheta = 0.002;

  float chi2 = 0;
  if(nhits > 2)
  {
    RZLine rzLine(points,errors,isBarrel);
    chi2 = rzLine.chi2();
  }

  // build pixel track
  PixelTrackBuilder builder;

  Measurement1D pt      (valPt,       errPt);
  Measurement1D phi     (valPhi,      errPhi);
  Measurement1D cotTheta(valCotTheta, errCotTheta);
  Measurement1D tip     (valTip,      errTip);
  Measurement1D zip     (valZip,      errZip);

  ret.reset(builder.build(pt, phi, cotTheta, tip, zip, chi2,
                          charge, hits, theField));
  return ret;
}


/*****************************************************************************/
float TrackFitter::getCotThetaAndUpdateZip
  (const GlobalPoint& inner, const GlobalPoint& outer,
   float radius, float phi, float d0, float& zip) const
{
   float chi = phi - M_PI_2;
   GlobalPoint IP(d0*cos(chi), d0*sin(chi),zip);

   float phi1 = 2*asin(0.5*(inner - IP).perp()/radius);
   float phi2 = 2*asin(0.5*(outer - IP).perp()/radius);

   float dr = radius*(phi2 - phi1);
   float dz = outer.z()-inner.z();

   // Recalculate ZIP
   zip = (inner.z()*phi2 - outer.z()*phi1)/(phi2 - phi1);

   return (fabs(dr) > 1.e-3) ? dz/dr : 0;
}

/*****************************************************************************/
float TrackFitter::getPhi
  (float xC, float yC, int charge) const
{
  float phiC;

  if (charge>0) phiC = atan2(xC,-yC);
           else phiC = atan2(-xC,yC);

  return phiC;
}

/*****************************************************************************/
float TrackFitter::getZip
  (float d0, float curv,
   const GlobalPoint& inner, const GlobalPoint& outer) const
{
  // phi = asin(r*rho/2) with asin(x) ~= x+x**3/(2*3)
  float rho3 = curv*curv*curv;

  float r1 = inner.perp();
  double phi1 = r1*curv/2 + inner.perp2()*r1*rho3/48.;

  float r2 = outer.perp();
  double phi2 = r2*curv/2 + outer.perp2()*r2*rho3/48.;

  double z1 = inner.z();
  double z2 = outer.z();

  return z1 - phi1/(phi1-phi2)*(z1-z2);
}

/*****************************************************************************/
void TrackFitter::getErrTipAndErrZip
  (float pt, float eta, float & errTip, float & errZip) const 
{
  float coshEta = cosh(eta);

  { // transverse
    float c_ms = 0.0115; //0.0115;
    float s_le = 0.0095; //0.0123;
    float s_ms2 = c_ms*c_ms / (pt*pt) * coshEta;

    errTip = sqrt(s_le*s_le + s_ms2                  );
  }

  { // z
    float c_ms = 0.0070;
    float s_le = 0.0135;

    errZip = sqrt( (s_le*s_le + c_ms*c_ms/(pt*pt)) * coshEta*coshEta*coshEta);
  }
}