PixelFitterByHelixProjections.cc

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#include "RecoPixelVertexing/PixelTrackFitting/interface/PixelFitterByHelixProjections.h"
#include "FWCore/ParameterSet/interface/ParameterSet.h"

#include "FWCore/Framework/interface/EventSetup.h"
#include "FWCore/Framework/interface/ESHandle.h"
#include "Geometry/Records/interface/TrackerDigiGeometryRecord.h"
#include "Geometry/TrackerGeometryBuilder/interface/TrackerGeometry.h"

#include "DataFormats/GeometryVector/interface/LocalPoint.h"
#include "DataFormats/GeometryVector/interface/GlobalPoint.h"
#include "DataFormats/GeometryCommonDetAlgo/interface/GlobalError.h"

#include "TrackingTools/DetLayers/interface/DetLayer.h"
#include "Geometry/CommonDetUnit/interface/GeomDet.h"
#include "DataFormats/TrackingRecHit/interface/TrackingRecHit.h"
//#include "DataFormats/SiPixelDetId/interface/PixelSubdetector.h"
#include "RecoTracker/TkMSParametrization/interface/PixelRecoUtilities.h"

#include "MagneticField/Engine/interface/MagneticField.h"
#include "MagneticField/Records/interface/IdealMagneticFieldRecord.h"
#include "TrackingTools/TransientTrackingRecHit/interface/TransientTrackingRecHitBuilder.h"
#include "TrackingTools/Records/interface/TransientRecHitRecord.h"

#include "CommonTools/Statistics/interface/LinearFit.h"
#include "DataFormats/GeometryCommonDetAlgo/interface/Measurement1D.h"

#include "Geometry/CommonDetUnit/interface/GeomDetUnit.h"
#include "Geometry/CommonDetUnit/interface/GeomDetType.h"
#include "FWCore/Framework/interface/ESWatcher.h"


#include "FWCore/MessageLogger/interface/MessageLogger.h"

#include "RZLine.h"
#include "CircleFromThreePoints.h"
#include "PixelTrackBuilder.h"
#include "DataFormats/GeometryVector/interface/Pi.h"

using namespace std;

namespace {

  int charge(const std::vector<GlobalPoint> & points) {
    // the cross product will tell me...
    float dir = (points[1].x()-points[0].x())*(points[2].y()-points[1].y())
      - (points[1].y()-points[0].y())*(points[2].x()-points[1].x());
    
    /*
      GlobalVector v21 = points[1]-points[0];
      GlobalVector v32 = points[2]-points[1];
      float dphi = v32.phi() - v21.phi();
      while (dphi >  Geom::fpi()) dphi -=  Geom::ftwoPi();
      while (dphi < -Geom::fpi()) dphi +=  Geom::ftwoPi();
      return (dphi > 0) ? -1 : 1;
    */
    return (dir>0) ? -1 : 1;
  }

  float cotTheta(const GlobalPoint& inner, const GlobalPoint& outer) {
    float dr = outer.perp()-inner.perp();
    float dz = outer.z()-inner.z();
    return (std::abs(dr) > 1.e-3f) ? dz/dr : 0;
  }

  inline float phi(float xC, float yC, int charge) {
    return  (charge>0) ? std::atan2(xC,-yC) :  std::atan2(-xC,yC);
  }

  float zip(float d0, float phi_p, float curv, 
        const GlobalPoint& pinner, const GlobalPoint& pouter) {
    //
    //phi = asin(r*rho/2) with asin(x) ~= x+x**3/(2*3) = x(1+x*x/6);
    //
    
    float phi0 = phi_p - Geom::fhalfPi();
    GlobalPoint pca(d0*std::cos(phi0), d0*std::sin(phi0),0.);
    
    float rho2 = curv*curv;
    float r1s = (pinner-pca).perp2();
    double phi1 = std::sqrt(r1s)*(curv*0.5f)*(1.f+r1s*(rho2/24.f));
    float r2s = (pouter-pca).perp2();
    double phi2 = std::sqrt(r2s)*(curv*0.5f)*(1.f+r2s*(rho2/24.f));
    double z1 = pinner.z();
    double z2 = pouter.z();

    if (fabs(curv)>1.e-5) 
      return z1 - phi1/(phi1-phi2)*(z1-z2);
    else {
      double dr = std::max(std::sqrt(r2s)-std::sqrt(r1s),1.e-5f);
      return z1-std::sqrt(r1s)*(z2-z1)/dr;
    }
  }
  
  double errZip( float apt, float eta) {
    double ziperr=0;
    double pt = (apt <= 10.) ? apt: 10.;
    double p1=0, p2=0,p3=0,p4=0;
    float feta = std::abs(eta);
    if (feta<=0.8){
      p1 = 0.12676e-1;
      p2 = -0.22411e-2;
      p3 = 0.2987e-3;
      p4 = -0.12779e-4;
    } else if (feta <=1.6){
      p1 = 0.24047e-1;
      p2 = -0.66935e-2;
      p3 = 0.88111e-3;
      p4 = -0.38482e-4;
    } else {
      p1 = 0.56084e-1;
      p2 = -0.13960e-1;
      p3 = 0.15744e-2;
      p4 = -0.60757e-4;
    }
    ziperr = p1 + p2*pt + p3*pt*pt +p4*pt*pt*pt;
    return ziperr;
  }
  
  double errZip2( float apt, float eta) {
    double err = errZip(apt,eta);
    return err*err;
  }


  double errTip(float apt, float eta) {
    double pt = (apt <= 10.) ? apt : 10.;
    double p1=0, p2=0;
    float feta = std::abs(eta);
    if (feta<=0.8)
      {
    p1=5.9e-3;
    p2=4.7e-3;
      }
    else if (feta <=1.6){
      p1 = 4.9e-3;
      p2 = 7.1e-3;
    }
    else {
      p1 = 6.4e-3;
      p2 = 1.0e-2;
    }
    double err=0;
    if (pt != 0) err = (p1 + p2/pt);
    return err;
  }
  
  double errTip2(float apt, float eta) {
    double err = errTip(apt,eta);
    return err*err;
  }


}


PixelFitterByHelixProjections::PixelFitterByHelixProjections(
   const edm::ParameterSet& cfg) 
 : theConfig(cfg), theTracker(0), theField(0), theTTRecHitBuilder(0) { }

reco::Track* PixelFitterByHelixProjections::run(
    const edm::EventSetup& es,
    const std::vector<const TrackingRecHit * > & hits,
    const TrackingRegion & region) const
{
  int nhits = hits.size();
  if (nhits <2) return 0;

  vector<GlobalPoint> points(nhits);
  vector<GlobalError> errors(nhits);
  vector<bool> isBarrel(nhits);
  
  static edm::ESWatcher<TrackerDigiGeometryRecord> watcherTrackerDigiGeometryRecord;
  if (!theTracker || watcherTrackerDigiGeometryRecord.check(es)) {
    edm::ESHandle<TrackerGeometry> trackerESH;
    es.get<TrackerDigiGeometryRecord>().get(trackerESH);
    theTracker = trackerESH.product();
  }

  static edm::ESWatcher<IdealMagneticFieldRecord>  watcherIdealMagneticFieldRecord;
  if (!theField || watcherIdealMagneticFieldRecord.check(es)) {
    edm::ESHandle<MagneticField> fieldESH;
    es.get<IdealMagneticFieldRecord>().get(fieldESH);
    theField = fieldESH.product();
  }

  static edm::ESWatcher<TransientRecHitRecord> watcherTransientRecHitRecord;
  if (!theTTRecHitBuilder || watcherTransientRecHitRecord.check(es)) {
    edm::ESHandle<TransientTrackingRecHitBuilder> ttrhbESH;
    std::string builderName = theConfig.getParameter<std::string>("TTRHBuilder");
    es.get<TransientRecHitRecord>().get(builderName,ttrhbESH);
    theTTRecHitBuilder = ttrhbESH.product();
  }


  for ( int i=0; i!=nhits; ++i) {
    TransientTrackingRecHit::RecHitPointer recHit = theTTRecHitBuilder->build(hits[i]);
    points[i]  = GlobalPoint( recHit->globalPosition().x()-region.origin().x(), 
                  recHit->globalPosition().y()-region.origin().y(),
                  recHit->globalPosition().z()-region.origin().z() 
                  );
    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]); 

  float valPhi, valTip, valPt;

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

  if (curvature > 1.e-4) {
    float invPt = PixelRecoUtilities::inversePt( circle.curvature(), es);
    valPt = (invPt > 1.e-4f) ? 1.f/invPt : 1.e4f;
    CircleFromThreePoints::Vector2D center = circle.center();
    valTip = iCharge * (center.mag()-1.f/curvature);
    valPhi = phi(center.x(), center.y(), iCharge);
  } 
  else {
    valPt = 1.e4f; 
    GlobalVector direction(points[1]-points[0]);
    valPhi =  direction.phi(); 
    valTip = -points[0].x()*sin(valPhi) + points[0].y()*cos(valPhi); 
  }

  float errPt = 0.055f*valPt + 0.017f*valPt*valPt;
  float errValTip = errTip(valPt, points.back().eta());
  float errPhi = 0.002f;

  float valZip = zip(valTip, valPhi, curvature, points[0],points[1]);
  float errValZip = errZip(valPt, points.back().eta());

  float valCotTheta = cotTheta(points[0],points[1]);
  float errCotTheta = 0.002f;

  float chi2 = 0;
  if (nhits > 2) {
    RZLine rzLine(points,errors,isBarrel);
    float cottheta, intercept, covss, covii, covsi; 
    rzLine.fit(cottheta, intercept, covss, covii, covsi);
    chi2 = rzLine.chi2(cottheta, intercept);         //FIXME: check which intercept to use!
  }

  PixelTrackBuilder builder;
  Measurement1D pt(valPt, errPt);
  Measurement1D phi(valPhi, errPhi);
  Measurement1D cotTheta(valCotTheta, errCotTheta);
  Measurement1D tip(valTip, errValTip);
  Measurement1D zip(valZip, errValZip);

  return builder.build(pt, phi, cotTheta, tip, zip, chi2, iCharge, hits, theField, region.origin() );
}