TrackFitter.cc

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#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 "RecoTracker/PixelLowPtUtilities/interface/TrackFitter.h"
#include "RecoTracker/PixelTrackFitting/interface/CircleFromThreePoints.h"
#include "RecoTracker/PixelTrackFitting/interface/PixelTrackBuilder.h"
#include "RecoTracker/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;
  }

}  // namespace

/*****************************************************************************/
std::unique_ptr<reco::Track> TrackFitter::run(const std::vector<const TrackingRecHit*>& hits,
                                              const TrackingRegion& region) 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, *theField);
  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);
  }
}