HelixParameterFit.h

/**************************************************************************
 * basf2 (Belle II Analysis Software Framework)                           *
 * Author: The Belle II Collaboration                                     *
 *                                                                        *
 * See git log for contributors and copyright holders.                    *
 * This file is licensed under LGPL-3.0, see LICENSE.md.                  *
 **************************************************************************/
 
#pragma once
 
#include <tracking/trackFindingVXD/filterMap/filterFramework/SelectionVariable.h>
#include <tracking/trackFindingVXD/filterMap/threeHitVariables/CircleCenterXY.h>
#include <tracking/trackFindingVXD/filterMap/twoHitVariables/CosDirectionXY.h>
#include <framework/geometry/B2Vector3.h>
#include <cmath>
 
#define HELIXPARAMETERFIT_NAME HelixParameterFit
 
namespace Belle2 {

  template <typename PointType >
  class HELIXPARAMETERFIT_NAME : public SelectionVariable< PointType, 3, double > {
  public:
    PUT_NAME_FUNCTION(HELIXPARAMETERFIT_NAME);
 

    static double value(const PointType& outerHit, const PointType& centerHit, const PointType& innerHit)
    {
 
      B2Vector3D cCenter = CircleCenterXY<PointType>::value(outerHit, centerHit, innerHit);
 
      B2Vector3D vecOuter2cC(outerHit.X() - cCenter.X(), outerHit.Y() - cCenter.Y(), outerHit.Z() - cCenter.Z());
      B2Vector3D vecCenter2cC(centerHit.X() - cCenter.X(), centerHit.Y() - cCenter.Y(), centerHit.Z() - cCenter.Z());
      B2Vector3D vecInner2cC(innerHit.X() - cCenter.X(), innerHit.Y() - cCenter.Y(), innerHit.Z() - cCenter.Z());
 
      double alfaAB = CosDirectionXY<B2Vector3D>::value(vecOuter2cC, vecCenter2cC);
      double alfaBC = CosDirectionXY<B2Vector3D>::value(vecCenter2cC, vecInner2cC);
 
      // real calculation: ratio is (m_vecij[2] = deltaZ): alfaAB/deltaZab : alfaBC/deltaZbc, the following equation saves two times '/'
      double result = (alfaAB * double(centerHit.Z() - innerHit.Z())) / (alfaBC * double(outerHit.Z() - centerHit.Z()));
 
      return (std::isnan(result) || std::isinf(result)) ? double(0) : result;
    } // return unit: none
  };

}