Helix (LCSim 3.1.7 API)

java.lang.Object
- org.lcsim.util.swim.Helix

All Implemented Interfaces:

Trajectory

Direct Known Subclasses:

HelixYField
```
public class Helix
extends Object
implements Trajectory
```
This class represents a helix with its axis aligned along Z. All quantities in this class are dimensionless. It has no dependencies except for Hep3Vector (which could easily be removed).
For more info on swimming see this paper by Paul Avery.

Version:

$Id: Helix.java,v 1.30 2010/04/29 13:41:37 cassell Exp $

Author:

tonyj

Field Summary

Fields
Modifier and Type	Field and Description
`private double`	`abs_r`
`protected double`	`cosLambda`
`protected double`	`cosPhi`
`private double`	`eps`
`(package private) Hep3Vector`	`origin`
`protected double`	`phi`
`private double`	`px`
`private double`	`py`
`private double`	`pz`
`protected double`	`radius`
`private double`	`rho`
`protected double`	`sinLambda`
`protected double`	`sinPhi`
`(package private) double`	`xCenter`
`(package private) double`	`yCenter`

Constructor Summary

Constructors
Constructor and Description

Helix(Hep3Vector org, double r, double p, double lambda)
Creates a new instance of Helix.

Constructors
Constructor and Description
`Helix(Hep3Vector org, double r, double p, double lambda)` Creates a new instance of Helix.

Method Summary

Methods
Modifier and Type	Method and Description
`Hep3Vector`	`getCenterXY()`
`double`	`getDistanceToInfiniteCylinder(double r)` Calculates the distance along the Helix until it hits a cylinder centered along z
`double`	`getDistanceToPoint(Hep3Vector point)` Obtain the point of closest approach (POCA) of the trajectory to a point.
`double`	`getDistanceToPolyhedra(double r, int nsides)`
`double`	`getDistanceToXYPosition(Hep3Vector point)` Swims the helix along its trajectory to the point of closest approach to the given SpacePoint.
`double`	`getDistanceToZPlane(double z)` Calculate the distance along the trajectory to reach a given Z plane.
`SpacePoint`	`getPointAtDistance(double alpha)` returns a point on the Helix at a distance alpha from the origin along the trajectory.
`double`	`getRadius()`
`double`	`getSecondDistanceToInfiniteCylinder(double r)`
`double`	`getSignedClosestDifferenceToPoint(Hep3Vector point)` Calculates the signed distance in mm between the Helix and an arbitrary point in Space
`Hep3Vector`	`getTangentAtDistance(double alpha)`
`SpaceVector`	`getUnitTangentAtLength(double alpha)` Returns the momentum at a given distance from the origin
`double`	`getZPeriod()`
`private Hep3Vector`	`propagateDirection(Hep3Vector u, double s)` Propagates the direction unit vector a distance s along the helix
`private Hep3Vector`	`propagatePosition(Hep3Vector pos, Hep3Vector u, double s)` Propagate a point on the helix by a specified distance
`void`	`setExtrapToPointPrecision(double prec)`
`private void`	`setSpatialParameters()` Sets the parameterization in terms of "momentum" and charge

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

- Field Detail
  - origin
```
Hep3Vector origin
```
  - xCenter
```
double xCenter
```
  - yCenter
```
double yCenter
```
  - radius
```
protected double radius
```
  - sinLambda
```
protected double sinLambda
```
  - cosLambda
```
protected double cosLambda
```
  - sinPhi
```
protected double sinPhi
```
  - cosPhi
```
protected double cosPhi
```
  - phi
```
protected double phi
```
  - px
```
private double px
```
  - py
```
private double py
```
  - pz
```
private double pz
```
  - abs_r
```
private double abs_r
```
  - rho
```
private double rho
```
  - eps
```
private double eps
```
- Constructor Detail
  - Helix
```
public Helix(Hep3Vector org,
     double r,
     double p,
     double lambda)
```
    Creates a new instance of Helix. Parameters according to the L3 conventions
    Please also have a look at
    
    Parameters:
    origin - A point on the helix
    radius - The signed radius of curvature of the helix. The conventions is such that for positive radii, the direction is clockwise.
    phi - The polar angle of the helix momentum in x-y plane w/rt positive x-axis at the origin
    lambda - The dip angle w/rt positive part of the x-y plane
- Method Detail
  - getPointAtDistance
```
public SpacePoint getPointAtDistance(double alpha)
```
    returns a point on the Helix at a distance alpha from the origin along the trajectory. alpha == 2*PI*radius/cos(lambda) is one rotation in the x-y plane
    
    Specified by:
    
    getPointAtDistance in interface Trajectory
  - getRadius
```
public double getRadius()
```
  - getCenterXY
```
public Hep3Vector getCenterXY()
```
  - getDistanceToZPlane
```
public double getDistanceToZPlane(double z)
```
    Description copied from interface: Trajectory
    
    Calculate the distance along the trajectory to reach a given Z plane. Note distance may be negative.
    
    Specified by:
    
    getDistanceToZPlane in interface Trajectory
  - getDistanceToInfiniteCylinder
```
public double getDistanceToInfiniteCylinder(double r)
```
    Calculates the distance along the Helix until it hits a cylinder centered along z
    
    Specified by:
    
    getDistanceToInfiniteCylinder in interface Trajectory
    
    Parameters:
    r - the radius of the cylinder
    
    Returns:
    the distance along the trajectory or Double.NAN if the cylinder can never be hit
  - getDistanceToPolyhedra
```
public double getDistanceToPolyhedra(double r,
                            int nsides)
```
  - getDistanceToPoint
```
public double getDistanceToPoint(Hep3Vector point)
```
    Description copied from interface: Trajectory
    
    Obtain the point of closest approach (POCA) of the trajectory to a point. The return value is the distance parameter s, such that getPointAtDistance(s) is the POCA.
    
    Specified by:
    
    getDistanceToPoint in interface Trajectory
    
    Parameters:
    point - Point in space to swim to
    
    Returns:
    The length parameter s
  - getDistanceToXYPosition
```
public double getDistanceToXYPosition(Hep3Vector point)
```
    Swims the helix along its trajectory to the point of closest approach to the given SpacePoint. For more info on swimming see Paul Avery's excellent text
    
    Parameters:
    point - Point in Space to swim to.
    
    Returns:
    the length Parameter alpha
  - getSignedClosestDifferenceToPoint
```
public double getSignedClosestDifferenceToPoint(Hep3Vector point)
```
    Calculates the signed distance in mm between the Helix and an arbitrary point in Space
    
    Parameters:
    point - the point in space to calculate the distance to
    
    Returns:
    the distance in mm between the point and the helix at the point of closest approach
  - getTangentAtDistance
```
public Hep3Vector getTangentAtDistance(double alpha)
```
  - getSecondDistanceToInfiniteCylinder
```
public double getSecondDistanceToInfiniteCylinder(double r)
```
  - getZPeriod
```
public double getZPeriod()
```
  - setSpatialParameters
```
private void setSpatialParameters()
```
    Sets the parameterization in terms of "momentum" and charge
  - propagateDirection
```
private Hep3Vector propagateDirection(Hep3Vector u,
                            double s)
```
    Propagates the direction unit vector a distance s along the helix
    
    Parameters:
    u - initial direction unit vector
    s - distance to propagate
    
    Returns:
    propagated direction unit vector
  - propagatePosition
```
private Hep3Vector propagatePosition(Hep3Vector pos,
                           Hep3Vector u,
                           double s)
```
    Propagate a point on the helix by a specified distance
    
    Parameters:
    pos - starting position
    u - starting direction unit vector
    s - distance to propagate
    
    Returns:
    propagated point on helix
  - getUnitTangentAtLength
```
public SpaceVector getUnitTangentAtLength(double alpha)
```
    Description copied from interface: Trajectory
    
    Returns the momentum at a given distance from the origin
    
    Specified by:
    
    getUnitTangentAtLength in interface Trajectory
    
    Parameters:
    alpha - The distance along the trajectory in the x-y plane
    
    Returns:
    The unit vector of the momentum
  - setExtrapToPointPrecision
```
public void setExtrapToPointPrecision(double prec)
```

Class Helix

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

origin

xCenter

yCenter

radius

sinLambda

cosLambda

sinPhi

cosPhi

phi

px

py

pz

abs_r

rho

eps

Constructor Detail

Helix

Method Detail

getPointAtDistance

getRadius

getCenterXY

getDistanceToZPlane

getDistanceToInfiniteCylinder

getDistanceToPolyhedra

getDistanceToPoint

getDistanceToXYPosition

getSignedClosestDifferenceToPoint

getTangentAtDistance

getSecondDistanceToInfiniteCylinder

getZPeriod

setSpatialParameters

propagateDirection

propagatePosition

getUnitTangentAtLength

setExtrapToPointPrecision