DMagneticFieldStepper.h

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#ifndef __DMAGNETICFIELDSTEPPER_H__
#define __DMAGNETICFIELDSTEPPER_H__

#include <math.h>

#include <DVector3.h>
#include "JANA/jerror.h"

#include "HDGEOMETRY/DMagneticFieldMap.h"


/// DMagneticFieldStepper class
///
/// This class will step a particle track through a magnetic
/// field. It has methods to find the point on the track which
/// comes closest to a specified point in space.


class DMagneticFieldStepper
{
   public:

      DMagneticFieldStepper(const DMagneticFieldMap *map, double q=1.0);
      DMagneticFieldStepper(const DMagneticFieldMap *map, double q, const DVector3 *x, const DVector3 *p);
      ~DMagneticFieldStepper();
   
      jerror_t SetStartingParams(double q, const DVector3 *x, const DVector3 *p);
      jerror_t SetMagneticFieldMap(const DMagneticFieldMap *map);
      jerror_t SetStepSize(double step);
      void SetCharge(double q){this->q = q;}
      double Step(DVector3 *newpos=NULL, DVector3 *B=NULL,double stepsize=0.0);
      double FastStep(double stepsize=0.0);

      void GetDirs(DVector3 &xdir, DVector3 &ydir, DVector3 &zdir);
      void GetBField(DVector3 &B){B = this->B;}
      void GetMomentum(DVector3 &mom){mom = this->mom;}
      void GetPosition(DVector3 &pos){pos = this->pos;}
      double GetCharge(void){return q;}
      void GetPosMom(DVector3 &pos, DVector3 &mom){pos=this->pos; mom=this->mom;}
      bool SwimToPlane(DVector3 &pos, DVector3 &mom, const DVector3 &origin, const DVector3 &norm, double *pathlen=NULL);
      bool DistToPlane(DVector3 &pos, const DVector3 &origin, const DVector3 &norm);
      bool SwimToRadius(DVector3 &pos, DVector3 &mom, double R, double *pathlen=NULL);
      bool DistToRadius(DVector3 &pos, double R);

      inline double GetRo(void){return fabs(Ro);}
      inline double Getdz_dphi(void){return Ro*mom.Dot(zdir)/mom.Dot(ydir);}
      inline double GetStepSize(void) const{return stepsize;}
   
      bool SwimToPOCAtoBeamLine(double q,DVector3 &pos, DVector3 &mom); 
        
   private:
      const DMagneticFieldMap *bfield; ///< pointer to magnetic field map
      double stepsize;     ///< maximum distance(cm) to move particle when Step() is called
      double last_stepsize;///< stepsize (cm) used for last step
      double q;            ///< electric charge in units of e
      DVector3 pos;        ///< current position of particle
      DVector3 mom;        ///< current location of particle
      DVector3 start_pos;  ///< starting position of track
      DVector3 start_mom;  ///< starting momentum of track
      DVector3 B;
      double Ro, Rp;
      double cos_theta, sin_theta;
      
      DVector3 xdir, ydir, zdir;
      
      void CalcDirs(double *Bvals=NULL);
};

#endif // __DMAGNETICFIELDSTEPPER_H__