HelicalTrackFitter (LCSim 3.1.7 API)

java.lang.Object
- org.lcsim.fit.helicaltrack.HelicalTrackFitter

```
public class HelicalTrackFitter
extends Object
```
Fit a helix to a set of space points. First, a circle is fit to the x-y coordinates. A straight-line fit is then performed on the s-z coordinates. If there are too few 3D hits to perform the s-z fit, the ZSegmentFitter is used to find the s-z parameters. For disk hits, the measured coordinate is r, not z. In this case, we use an estimate of the track slope to transform the uncertainty in r to an equivalent uncertainty in z using dz = dr * slope. The r-phi and z coordinate measurements are assumed to be uncorrelated. A block diagonal covariance matrix is formed from the results of the circle and s-z fits, ignoring any correlations between these fits. The resulting track parameters follow the "L3 Convention" (L3 Note 1666) adopted by org.lcsim.

Version:

2.0 (R. Partridge)

Author:

Norman Graf

Nested Class Summary

Nested Classes
Modifier and Type Class and Description

static class HelicalTrackFitter.FitStatus
Status of the HelicalTrackFit.

Nested Classes
Modifier and Type	Class and Description
`static class`	`HelicalTrackFitter.FitStatus` Status of the HelicalTrackFit.

Field Summary

Fields
Modifier and Type	Field and Description
`private CircleFit`	`_cfit`
`private CircleFitter`	`_cfitter`
`private HelicalTrackFit`	`_fit`
`private SlopeInterceptLineFit`	`_lfit`
`private SlopeInterceptLineFitter`	`_lfitter`
`private double`	`_tolerance`
`private ZSegmentFit`	`_zfit`
`private ZSegmentFitter`	`_zfitter`

Constructor Summary

Constructors
Constructor and Description

HelicalTrackFitter()
Creates a new instance of HelicalTrackFitter.

Constructors
Constructor and Description
`HelicalTrackFitter()` Creates a new instance of HelicalTrackFitter.

Method Summary

Methods
Modifier and Type	Method and Description
`private CircleFit`	`CircleFix(CircleFit oldfit)` Check if the circle finder picks a "backwards" solution with the charged particle travelling in the wrong direction (e.g.
`HelicalTrackFitter.FitStatus`	`fit(double[] x, double[] y, double[] z, double[] drphi, double[] dz, int np)` Perform a helix fit using the specified coordinates and uncertainties.
`HelicalTrackFitter.FitStatus`	`fit(List<HelicalTrackHit> hitcol)` Perform a helix fit of the specified HelicalTrackHits.
`HelicalTrackFitter.FitStatus`	`fit(List<HelicalTrackHit> hitcol, Map<HelicalTrackHit,MultipleScatter> msmap, HelicalTrackFit oldhelix)` Perform a helix fit of the specified HelicalTrackHits, taking into account multiple scattering errors.
`CircleFit`	`getCircleFit()` Return the circle fit for the most recent helix fit.
`HelicalTrackFit`	`getFit()` Return the results of the most recent helix fit.
`SlopeInterceptLineFit`	`getLineFit()` Return the s-z line fit for the most recent helix fit.
`private Map<HelicalTrackHit,Double>`	`getPathLengths(List<HelicalTrackHit> hits)` Find the x-y path lengths for a list of hits.
`double`	`getTolerance()` Return the tolerance being used to extend axial strips for ZSegmentFits.
`ZSegmentFit`	`getZSegmentFit()` Return the ZSegmentFit for the most recent helix fit.
`private SymmetricMatrix`	`MakeCov(Hep3Vector pos, double drphi, double dr, double dz)` Create a Cartesian covariance matrix given uncertainties in polar coordinates.
`private double`	`MissedStripPenalty(List<HelicalTrackHit> hitcol, double[] par, SymmetricMatrix cov, Map<HelicalTrackHit,Double> smap, Map<HelicalTrackHit,MultipleScatter> msmap)` Calculate a chisq penalty if any axial strip hits lie outside the strip boundaries in z.
`void`	`setReferencePoint(double x, double y)`
`void`	`setTolerance(double tolerance)` Specify tolerance used in extending axial strips for ZSegmentFits to account for multiple scattering.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - _cfitter
```
private CircleFitter _cfitter
```
  - _lfitter
```
private SlopeInterceptLineFitter _lfitter
```
  - _zfitter
```
private ZSegmentFitter _zfitter
```
  - _cfit
```
private CircleFit _cfit
```
  - _lfit
```
private SlopeInterceptLineFit _lfit
```
  - _zfit
```
private ZSegmentFit _zfit
```
  - _fit
```
private HelicalTrackFit _fit
```
  - _tolerance
```
private double _tolerance
```
- Constructor Detail
  - HelicalTrackFitter
```
public HelicalTrackFitter()
```
    Creates a new instance of HelicalTrackFitter.
- Method Detail
  - fit
```
public HelicalTrackFitter.FitStatus fit(double[] x,
                               double[] y,
                               double[] z,
                               double[] drphi,
                               double[] dz,
                               int np)
```
    Perform a helix fit using the specified coordinates and uncertainties. This is the original fit method for HelicalTrackFitter and is being kept for backwards compatibility. Not recommened for new code, may be deprecated in the future.
    
    Parameters:
    x - array of x coordinates
    y - array of y coordinates
    z - array of z coordinates
    drphi - error in r-phi hit position
    dz - error in z coordinate (negative for an axial strip of length |dz|*sqrt(12))
    np - number of points
    
    Returns:
    fit status
  - fit
```
public HelicalTrackFitter.FitStatus fit(List<HelicalTrackHit> hitcol)
```
    Perform a helix fit of the specified HelicalTrackHits. Multiple scattering errors are neglected when this method is used. The track is assumed to travel on a straight line from the origin to estimate the track slope (needed to estimate an effective uncertainty in z for disk hits).
    
    Parameters:
    hitcol - HelicalTrackHits to be fit
    
    Returns:
    fit status
  - fit
```
public HelicalTrackFitter.FitStatus fit(List<HelicalTrackHit> hitcol,
                               Map<HelicalTrackHit,MultipleScatter> msmap,
                               HelicalTrackFit oldhelix)
```
    Perform a helix fit of the specified HelicalTrackHits, taking into account multiple scattering errors. If an approximate HelicalTrackFit is provided, it will be used to obtain the track slope (needed to estimate an effective uncertainty in z for disk hits).
    
    Parameters:
    hitcol - HelicalTrackHits to be fit
    msmap - map giving multiple scattering errors for the hits
    oldhelix - approximate HelicalTrackFit (used to estimate track slope)
    
    Returns:
    fit status
  - getFit
```
public HelicalTrackFit getFit()
```
    Return the results of the most recent helix fit. Returns null if the fit was not successful.
    
    Returns:
    HelicalTrackFit from the most recent helix fit
  - getCircleFit
```
public CircleFit getCircleFit()
```
    Return the circle fit for the most recent helix fit. Returns null if the circle fit was not successful.
    
    Returns:
    circle fit from most recent helix fit
  - getLineFit
```
public SlopeInterceptLineFit getLineFit()
```
    Return the s-z line fit for the most recent helix fit. If the line fit failed or was not performed due to not having enough 3D hits, null is returned.
    
    Returns:
    line fit for most recent helix fit
  - getZSegmentFit
```
public ZSegmentFit getZSegmentFit()
```
    Return the ZSegmentFit for the most recent helix fit. If the ZSegmentFit failed or was not performed, null is returned.
    
    Returns:
    z segment fit for most recent helix fit
  - setTolerance
```
public void setTolerance(double tolerance)
```
    Specify tolerance used in extending axial strips for ZSegmentFits to account for multiple scattering. Each end of the strip will be extended by the product of the tolerance and the multiple scattering error.
    
    Parameters:
    tolerance - tolerance
  - getTolerance
```
public double getTolerance()
```
    Return the tolerance being used to extend axial strips for ZSegmentFits.
    
    Returns:
    tolerance
  - setReferencePoint
```
public void setReferencePoint(double x,
                     double y)
```
  - MakeCov
```
private SymmetricMatrix MakeCov(Hep3Vector pos,
                      double drphi,
                      double dr,
                      double dz)
```
    Create a Cartesian covariance matrix given uncertainties in polar coordinates. It is assumed that the polar coordinate uncertainties are uncorrelated.
    
    Parameters:
    pos - hit position
    drphi - uncertainty in the r*phi coordinate
    dr - uncertainty in the r coordinate
    dz - uncertainty in the z coordinate
    
    Returns:
    covariance matrix
  - CircleFix
```
private CircleFit CircleFix(CircleFit oldfit)
```
    Check if the circle finder picks a "backwards" solution with the charged particle travelling in the wrong direction (e.g. clockwise when the actual track is going counter-clockwise). If this happens, return a new circle fit that reverses the initial direction and changes the sign of the curvature and DCA. If the circle fit has the particle travelling in the right direction, return the original fit.
    
    Parameters:
    oldfit - circle fit to be checked
    hitlist - list of hits used for the circle fit
    
    Returns:
    fixed circle fit
  - getPathLengths
```
private Map<HelicalTrackHit,Double> getPathLengths(List<HelicalTrackHit> hits)
```
    Find the x-y path lengths for a list of hits.
    
    Parameters:
    hits - list of hits
    
    Returns:
    map containing the path lengths of the hits
  - MissedStripPenalty
```
private double MissedStripPenalty(List<HelicalTrackHit> hitcol,
                        double[] par,
                        SymmetricMatrix cov,
                        Map<HelicalTrackHit,Double> smap,
                        Map<HelicalTrackHit,MultipleScatter> msmap)
```
    Calculate a chisq penalty if any axial strip hits lie outside the strip boundaries in z.
    
    Parameters:
    hitcol - list of hits to check
    smap - map of x-y path lengths
    msmap - map of multiple scatter uncertainties
    
    Returns:
    chisq penalty

Class HelicalTrackFitter

Nested Class Summary

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

_cfitter

_lfitter

_zfitter

_cfit

_lfit

_zfit

_fit

_tolerance

Constructor Detail

HelicalTrackFitter

Method Detail

fit

fit

fit

getFit

getCircleFit

getLineFit

getZSegmentFit

setTolerance

getTolerance

setReferencePoint

MakeCov

CircleFix

getPathLengths

MissedStripPenalty