TLineFitter.cxx

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//-----------------------------------------------------------------------------
// $Id: TLineFitter.cxx,v 1.8 2010/03/31 09:58:59 liucy Exp $
//-----------------------------------------------------------------------------
// Filename : TLineFitter.cc
// Section  : Tracking
// Owner    : Yoshi Iwasaki
// Email    : yoshihito.iwasaki@kek.jp
//-----------------------------------------------------------------------------
// Description : A class to fit a TTrackBase object to a line.
//               See http://bsunsrv1.kek.jp/~yiwasaki/tracking/
//-----------------------------------------------------------------------------
 
#include "TrkReco/TLineFitter.h"
#include "TrkReco/TMLine.h"
#include "TrkReco/TMLink.h"
#include "TrkReco/TTrackBase.h"
 
TLineFitter::TLineFitter( const std::string& name )
    : TMFitter( name ), _a( 0. ), _b( 0. ), _det( 0. ) {}
 
TLineFitter::~TLineFitter() {}
 
int TLineFitter::fit( TTrackBase& t ) const {
 
  //...Already fitted ?...
  if ( t.fitted() ) return TFitAlreadyFitted;
 
  //...Check # of hits...
  if ( t.links().length() < 2 ) return TFitErrorFewHits;
 
  unsigned n = t.links().length();
  if ( _det == 0. && n == 2 )
  {
    double x0 = t.links()[0]->position().x();
    double y0 = t.links()[0]->position().y();
    double x1 = t.links()[1]->position().x();
    double y1 = t.links()[1]->position().y();
    if ( x0 == x1 ) return TFitFailed;
    _a = ( y0 - y1 ) / ( x0 - x1 );
    _b = -_a * x1 + y1;
  }
  else
  {
    double sum  = (double)n;
    double sumX = 0., sumY = 0., sumX2 = 0., sumXY = 0., sumY2 = 0.;
    for ( unsigned i = 0; i < n; i++ )
    {
      const HepPoint3D& p = t.links()[i]->position();
      double            x = p.x();
      double            y = p.y();
      sumX += x;
      sumY += y;
      sumX2 += x * x;
      sumXY += x * y;
      sumY2 += y * y;
    }
 
    _det = sum * sumX2 - sumX * sumX;
#ifdef TRKRECO_DEBUG_DETAIL
    cout << "        TLineFitter::fit ... det=" << _det << std::endl;
#endif
    if ( _det == 0. ) { return TFitFailed; }
    else
    {
      _a = ( sumXY * sum - sumX * sumY ) / _det;
      _b = ( sumX2 * sumY - sumX * sumXY ) / _det;
    }
  }
 
  if ( t.objectType() == Line ) ( (TMLine&)t ).property( _a, _b, _det );
  fitDone( t );
  return 0;
}