Reconstruction/MdcPatRec/TrkBase/include/TrkBase/TrkDifPoca.h

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//--------------------------------------------------------------------------
// File and Version Information:
//      $Id: TrkDifPoca.h,v 1.2 2006/03/28 01:02:36 zhangy Exp $
//
// Description:
//     Calculate the point of closest approach between two trajectories.
//     Calculates (in ctor) the distance and the flight lengths alongs
//     the two trajectories; calculated values are obtained through accessors.
//     "Precision" is maximum allowed error on distance (in cm).
//     The input flightlengths are used as a starting point; the
//     code will find the point-of-closest-approach that is closest to that
//     point.  (A good starting point also reduces CPU time.)
//     Note that distance is a signed quantity for two trajectories.
//
// Environment:
//      Software developed for the BaBar Detector at the SLAC B-Factory.
//
// Author(s): Steve Schaffner; core algorithm stolen from Art Snyder
//
//------------------------------------------------------------------------
#ifndef TRKDIFPOCA_H
#define TRKDIFPOCA_H
#include "CLHEP/Matrix/Vector.h"
#include "MdcRecoUtil/DifNumber.h"
#include "TrkBase/TrkPocaBase.h"
using CLHEP::HepVector;
 
class TrkDifTraj;
 
// Class interface //
class TrkDifPoca : public TrkPocaBase {
 
public:
  TrkDifPoca( const TrkDifTraj& traj1, double flt1, const Trajectory& traj2, double flt2,
              double precision = 1.e-5 );
  TrkDifPoca( const TrkDifTraj& traj, double flt, const HepPoint3D& pt,
              double precision = 1.e-5 );
  ~TrkDifPoca(){};
 
  inline const DifNumber& difDoca() const;                 // distance of closest approach
  inline double           doca() const;                    //      ditto
  inline const HepVector  derivs() const;                  // deriv of doca w/r/t track params
  inline void             fetchDerivs( HepVector& ) const; // faster version
 
  // The following inherited functions are also available:
  // const TrkErrCode& status() const;      // did the calculation succeed?
  // double flt1() const;                   // path length on traj 1 @ poca
  // double flt2() const;
  // double precision();                    // In case anyone wants to know:
 
private:
  DifNumber _doca;
 
  void calcDist( const TrkDifTraj& traj1, const Trajectory& traj2 );
  void calcDist( const TrkDifTraj&, const HepPoint3D& );
 
  // Preempt
  // TrkDifPoca&   operator= (const TrkDifPoca&);
  //  TrkDifPoca(const TrkDifPoca &);
};
 
// Inlined functions
double           TrkDifPoca::doca() const { return _doca.number(); }
const DifNumber& TrkDifPoca::difDoca() const { return _doca; }
const HepVector  TrkDifPoca::derivs() const { return _doca.derivatives(); }
void TrkDifPoca::fetchDerivs( HepVector& dv ) const { _doca.fetchDerivatives( dv ); }
#endif