HelixHelper Class Reference

Helper class representing a helical track. More...

#include <HelixHelper.h>

Collaboration diagram for HelixHelper:

Public Member Functions
	HelixHelper (float z0, float d0, float omega, float cotTheta, float phi)
	construct a helix with given helix parameters, as defined for Track objects
	HelixHelper (const ROOT::Math::XYZVector &poca, const ROOT::Math::XYZVector &momentum_in_poca, int charge)
	construct a helix at an arbitrary position 'poca' (helices built at different points are not comparable)
double	pathLengthToPoint (const ROOT::Math::XYZVector &p) const
	returns the path length (along the helix) to the helix point closest to p. More...
double	pathLengthToLine (const ROOT::Math::XYZVector &a, const ROOT::Math::XYZVector &b) const
	returns the path length (along the helix) to the helix point closest to the line going through points a and b.
ROOT::Math::XYZVector	momentum (double s=0) const
	momentum of the particle, at the helix point corresponding to a flown path length s (from poca).
ROOT::Math::XYZVector	position (double s) const
	point on helix corresponding to a flown path length s (from poca)

Static Private Member Functions
static double	distanceToPoint (double s)
	minimization function, calculates distance to minimize_distance_to_point
static double	distanceToLine (double s)
	same as distanceToPoint, but ignoring z coordinate

Private Attributes
float	m_z0
	minimal z distance of point of closest approach to origin
float	m_d0
	minimal r distance of point of closest approach to origin
float	m_omega
	signed curvature
float	m_cotTheta
	cotangens of polar angle
float	m_phi
	Phi at the perigee [-pi, pi].
ROOT::Math::XYZVector	m_poca
	point of closest approach to origin

Static Private Attributes
constexpr static double	c_cTimesB = (1.5 * 0.00299792458)
	magnetic filed times speed of light
constexpr static double	c_maxFlightLength = 150.0
	maximal path length (from origin) considered for extrapolation
static ROOT::Math::XYZVector	minimize_distance_to_point
	user supplied point we're trying to find the nearest helix point to
static ROOT::Math::XYZVector	minimize_distance_to_line_a
	first user supplied line we're trying to find the nearest helix point to
static ROOT::Math::XYZVector	minimize_distance_to_line_b
	second user supplied line we're trying to find the nearest helix point to
static HelixHelper const *	helix_object
	keep a 'this' pointer around for minimization

Detailed Description

Helper class representing a helical track.

It is used as an alternative to Genfit's track representation and provides much faster replacements for its extrapolateToLine/ extrapolateToPoint() methods.

Definition at line 28 of file HelixHelper.h.

Member Function Documentation

pathLengthToPoint()

double pathLengthToPoint ( const ROOT::Math::XYZVector &  p ) const

inline

returns the path length (along the helix) to the helix point closest to p.

a path length of 0 corresponds to p = poca

Definition at line 68 of file HelixHelper.h.

    {
      minimize_distance_to_point = p;
      helix_object = this; //ok, this is ugly
      //TODO create a functor object to wrap everything up
 
      ROOT::Math::Functor1D functor(&distanceToPoint);
      ROOT::Math::BrentMinimizer1D bm;
      bm.SetFunction(functor, 0.0, c_maxFlightLength);
      bm.Minimize(100); //#iterations, abs. error, rel. error
 
      //bm.FValMinimum() is shortest distance
      //bm.XMinimum() is corresponding path length
      return bm.XMinimum();
    }

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The documentation for this class was generated from the following file:

• reconstruction/modules/VXDDedxPID/include/HelixHelper.h