/data/refman/pasoursint/CMSSW_5_3_3/src/TrackingTools/PatternTools/src/TwoTrackMinimumDistanceLineLine.cc

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#include "TrackingTools/PatternTools/interface/TwoTrackMinimumDistanceLineLine.h"
#include "TrackingTools/TrajectoryParametrization/interface/GlobalTrajectoryParameters.h"
#include "DataFormats/GeometryVector/interface/GlobalVector.h"
#include "FWCore/MessageLogger/interface/MessageLogger.h"
#include "MagneticField/Engine/interface/MagneticField.h"


bool TwoTrackMinimumDistanceLineLine::calculate(
    const GlobalTrajectoryParameters & theG,
    const GlobalTrajectoryParameters & theH)
{
  GlobalPoint gOrig = theG.position();
  GlobalPoint hOrig = theH.position();
  bool isLineG = theG.magneticField().inTesla(gOrig).z() == 0 || theG.charge() == 0;
  bool isLineH = theH.magneticField().inTesla(hOrig).z() == 0 || theH.charge() == 0;
  if ( ! (isLineG && isLineH) )
  {
    edm::LogWarning ("TwoTrackMinimumDistanceLineLine")
      << "charge of input track is not zero or field non zero"
      << "\n positions: "<<gOrig<<" , "<<hOrig
      << "\n Bz fields: "<<theG.magneticField().inTesla(gOrig).z()<<" , "<<theH.magneticField().inTesla(hOrig).z()
      << "\n charges: "<<theG.charge()<<" , "<<theH.charge();
    return true;
  };

  GlobalVector gVec = theG.momentum();
  const double gMag= theG.momentum().mag(); double gMag2 = gMag*gMag;
  GlobalVector hVec = theH.momentum();
  const double hMag= theH.momentum().mag(); double hMag2 = hMag*hMag;

  if ( gMag == 0. || hMag == 0. )
  {
    edm::LogWarning ("TwoTrackMinimumDistanceLineLine")
      << "momentum of input trajectory is zero.";
    return true;
  };

  phiG = theG.momentum().phi();
  phiH = theH.momentum().phi();

  double gVec_Dot_hVec = gVec.dot(hVec);
  double norm  = gVec_Dot_hVec*gVec_Dot_hVec - gMag2*hMag2;

  if ( norm == 0 )
  {
    edm::LogWarning ("TwoTrackMinimumDistanceLineLine")
      << "Tracks are parallel.";
    return true;
  }

  GlobalVector posDiff = gOrig - hOrig;

  double tG = (posDiff.dot(gVec) * hMag2 - gVec_Dot_hVec * posDiff.dot(hVec))/ norm;
  double tH = (gVec_Dot_hVec * posDiff.dot(gVec) - posDiff.dot(hVec) * gMag2)/ norm;

  gPos = GlobalPoint ( gOrig + tG * gVec);
  hPos = GlobalPoint ( hOrig + tH * hVec);
//   cout << "TwoTrackMinimumDistanceLineLine "<<gPos<<hPos<<endl;

  pathG = tG * gMag;
  pathH = tH * hMag;
  return false;
}

std::pair<GlobalPoint, GlobalPoint> TwoTrackMinimumDistanceLineLine::points() const
{
  return std::pair<GlobalPoint, GlobalPoint > ( gPos, hPos );
}

std::pair<double, double> TwoTrackMinimumDistanceLineLine::pathLength() const
{
  return std::pair<double, double> ( pathG, pathH);
}