ROOT   Reference Guide
TGeoHelix Class Reference

Class representing a helix curve.

A helix is a curve defined by the following equations:

x = (1/c) * COS(q*phi)
y = (1/c) * SIN(q*phi)
z = s * alfa
#define c(i)
Definition: RSha256.hxx:101
float * q
Definition: THbookFile.cxx:89
Double_t y[n]
Definition: legend1.C:17
Double_t x[n]
Definition: legend1.C:17
static constexpr double s

where:

c = 1/Rxy - curvature in XY plane
phi - phi angle
S = 2*PI*s - vertical separation between helix loops
q = +/- 1 - (+)=left-handed, (-)=right-handed
#define PI
Option_t Option_t TPoint TPoint angle
RooArgSet S(Args_t &&... args)
Definition: RooArgSet.h:240

In particular, a helix describes the trajectory of a charged particle in magnetic field. In such case, the helix is right-handed for negative particle charge. To define a helix, one must define:

• the curvature - positive defined
• the Z step made after one full turn of the helix
• the particle charge sign
• the initial particle position and direction (force normalization to unit)
• the magnetic field direction

A helix provides:

• propagation to a given Z position (in global frame) Double_t *point = TGeoHelix::PropagateToZ(Double_t z);
• propagation to an arbitrary plane, returning also the new point
• propagation in a geometry until the next crossed surface
• computation of the total track length along a helix

Definition at line 20 of file TGeoHelix.h.

## Public Types

enum  EGeoHelixTypes { kHelixNeedUpdate = (1ULL << ( 16 )) , kHelixStraight = (1ULL << ( 17 )) , kHelixCircle = (1ULL << ( 18 )) }

Public Types inherited from TObject
enum  {
kIsOnHeap = 0x01000000 , kNotDeleted = 0x02000000 , kZombie = 0x04000000 , kInconsistent = 0x08000000 ,
}

enum  { kSingleKey = (1ULL << ( 0 )) , kOverwrite = (1ULL << ( 1 )) , kWriteDelete = (1ULL << ( 2 )) }

enum  EDeprecatedStatusBits { kObjInCanvas = (1ULL << ( 3 )) }

enum  EStatusBits {
kCanDelete = (1ULL << ( 0 )) , kMustCleanup = (1ULL << ( 3 )) , kIsReferenced = (1ULL << ( 4 )) , kHasUUID = (1ULL << ( 5 )) ,
kCannotPick = (1ULL << ( 6 )) , kNoContextMenu = (1ULL << ( 8 )) , kInvalidObject = (1ULL << ( 13 ))
}

## Public Member Functions

TGeoHelix ()
Dummy constructor. More...

TGeoHelix (Double_t curvature, Double_t step, Int_t charge=1)
Normal constructor. More...

virtual ~TGeoHelix ()
Destructor. More...

Double_t ComputeSafeStep (Double_t epsil=1E-6) const
Compute safe linear step that can be made such that the error between linear-helix extrapolation is less than EPSIL. More...

const Double_tGetCurrentDirection () const

const Double_tGetCurrentPoint () const

Double_t GetStep () const

Double_t GetTotalCurvature () const
Compute helix total curvature. More...

Double_t GetXYcurvature () const

void InitDirection (Double_t *dir, Bool_t is_normalized=kTRUE)
Initialize particle direction (tangent on the helix in initial point) More...

void InitDirection (Double_t dirx, Double_t diry, Double_t dirz, Bool_t is_normalized=kTRUE)
Initialize particle direction (tangent on the helix in initial point) More...

void InitPoint (Double_t *point)
Set initial point on the helix. More...

void InitPoint (Double_t x0, Double_t y0, Double_t z0)
Initialize coordinates of a point on the helix. More...

virtual TClassIsA () const

Bool_t IsRightHanded () const

void ResetStep ()
Reset current point/direction to initial values. More...

void SetCharge (Int_t charge)
Positive charge means left-handed helix. More...

void SetField (Double_t bx, Double_t by, Double_t bz, Bool_t is_normalized=kTRUE)
Initialize particle direction (tangent on the helix in initial point) More...

void SetHelixStep (Double_t hstep)
Set Z step of the helix on a complete turn. Positive or null. More...

void SetXYcurvature (Double_t curvature)
Set XY curvature: c = 1/Rxy. More...

void Step (Double_t step)
Make a step from current point along the helix and compute new point, direction and angle To reach a plane/ shape boundary, one has to: More...

Double_t StepToPlane (Double_t *point, Double_t *norm)
Propagate initial point up to a given Z position in MARS. More...

virtual void Streamer (TBuffer &)
Stream an object of class TObject. More...

void StreamerNVirtual (TBuffer &ClassDef_StreamerNVirtual_b)

void UpdateHelix ()
Update the local helix matrix. More...

Public Member Functions inherited from TObject
TObject ()
TObject constructor. More...

TObject (const TObject &object)
TObject copy ctor. More...

virtual ~TObject ()
TObject destructor. More...

void AbstractMethod (const char *method) const
Use this method to implement an "abstract" method that you don't want to leave purely abstract. More...

virtual void AppendPad (Option_t *option="")
Append graphics object to current pad. More...

virtual void Browse (TBrowser *b)
Browse object. May be overridden for another default action. More...

ULong_t CheckedHash ()
Check and record whether this class has a consistent Hash/RecursiveRemove setup (*) and then return the regular Hash value for this object. More...

virtual const char * ClassName () const
Returns name of class to which the object belongs. More...

virtual void Clear (Option_t *="")

virtual TObjectClone (const char *newname="") const
Make a clone of an object using the Streamer facility. More...

virtual Int_t Compare (const TObject *obj) const
Compare abstract method. More...

virtual void Copy (TObject &object) const
Copy this to obj. More...

virtual void Delete (Option_t *option="")
Delete this object. More...

virtual Int_t DistancetoPrimitive (Int_t px, Int_t py)
Computes distance from point (px,py) to the object. More...

virtual void Draw (Option_t *option="")
Default Draw method for all objects. More...

virtual void DrawClass () const
Draw class inheritance tree of the class to which this object belongs. More...

virtual TObjectDrawClone (Option_t *option="") const
Draw a clone of this object in the current selected pad with: gROOT->SetSelectedPad(c1). More...

virtual void Dump () const
Dump contents of object on stdout. More...

virtual void Error (const char *method, const char *msgfmt,...) const
Issue error message. More...

virtual void Execute (const char *method, const char *params, Int_t *error=nullptr)
Execute method on this object with the given parameter string, e.g. More...

virtual void Execute (TMethod *method, TObjArray *params, Int_t *error=nullptr)
Execute method on this object with parameters stored in the TObjArray. More...

virtual void ExecuteEvent (Int_t event, Int_t px, Int_t py)
Execute action corresponding to an event at (px,py). More...

virtual void Fatal (const char *method, const char *msgfmt,...) const
Issue fatal error message. More...

virtual TObjectFindObject (const char *name) const
Must be redefined in derived classes. More...

virtual TObjectFindObject (const TObject *obj) const
Must be redefined in derived classes. More...

virtual Option_tGetDrawOption () const
Get option used by the graphics system to draw this object. More...

virtual const char * GetIconName () const
Returns mime type name of object. More...

virtual const char * GetName () const
Returns name of object. More...

virtual char * GetObjectInfo (Int_t px, Int_t py) const
Returns string containing info about the object at position (px,py). More...

virtual Option_tGetOption () const

virtual const char * GetTitle () const
Returns title of object. More...

virtual UInt_t GetUniqueID () const
Return the unique object id. More...

virtual Bool_t HandleTimer (TTimer *timer)
Execute action in response of a timer timing out. More...

virtual ULong_t Hash () const
Return hash value for this object. More...

Bool_t HasInconsistentHash () const
Return true is the type of this object is known to have an inconsistent setup for Hash and RecursiveRemove (i.e. More...

virtual void Info (const char *method, const char *msgfmt,...) const
Issue info message. More...

virtual Bool_t InheritsFrom (const char *classname) const
Returns kTRUE if object inherits from class "classname". More...

virtual Bool_t InheritsFrom (const TClass *cl) const
Returns kTRUE if object inherits from TClass cl. More...

virtual void Inspect () const
Dump contents of this object in a graphics canvas. More...

void InvertBit (UInt_t f)

virtual TClassIsA () const

Bool_t IsDestructed () const
IsDestructed. More...

virtual Bool_t IsEqual (const TObject *obj) const
Default equal comparison (objects are equal if they have the same address in memory). More...

virtual Bool_t IsFolder () const
Returns kTRUE in case object contains browsable objects (like containers or lists of other objects). More...

R__ALWAYS_INLINE Bool_t IsOnHeap () const

virtual Bool_t IsSortable () const

R__ALWAYS_INLINE Bool_t IsZombie () const

virtual void ls (Option_t *option="") const
The ls function lists the contents of a class on stdout. More...

void MayNotUse (const char *method) const
Use this method to signal that a method (defined in a base class) may not be called in a derived class (in principle against good design since a child class should not provide less functionality than its parent, however, sometimes it is necessary). More...

virtual Bool_t Notify ()
This method must be overridden to handle object notification. More...

void Obsolete (const char *method, const char *asOfVers, const char *removedFromVers) const
Use this method to declare a method obsolete. More...

void operator delete (void *ptr)
Operator delete. More...

void operator delete[] (void *ptr)
Operator delete []. More...

void * operator new (size_t sz)

void * operator new (size_t sz, void *vp)

void * operator new[] (size_t sz)

void * operator new[] (size_t sz, void *vp)

TObjectoperator= (const TObject &rhs)
TObject assignment operator. More...

virtual void Paint (Option_t *option="")
This method must be overridden if a class wants to paint itself. More...

virtual void Pop ()
Pop on object drawn in a pad to the top of the display list. More...

virtual void Print (Option_t *option="") const
This method must be overridden when a class wants to print itself. More...

virtual Int_t Read (const char *name)
Read contents of object with specified name from the current directory. More...

virtual void RecursiveRemove (TObject *obj)
Recursively remove this object from a list. More...

void ResetBit (UInt_t f)

virtual void SaveAs (const char *filename="", Option_t *option="") const
Save this object in the file specified by filename. More...

virtual void SavePrimitive (std::ostream &out, Option_t *option="")
Save a primitive as a C++ statement(s) on output stream "out". More...

void SetBit (UInt_t f)

void SetBit (UInt_t f, Bool_t set)
Set or unset the user status bits as specified in f. More...

virtual void SetDrawOption (Option_t *option="")
Set drawing option for object. More...

virtual void SetUniqueID (UInt_t uid)
Set the unique object id. More...

virtual void Streamer (TBuffer &)
Stream an object of class TObject. More...

void StreamerNVirtual (TBuffer &ClassDef_StreamerNVirtual_b)

virtual void SysError (const char *method, const char *msgfmt,...) const
Issue system error message. More...

R__ALWAYS_INLINE Bool_t TestBit (UInt_t f) const

Int_t TestBits (UInt_t f) const

virtual void UseCurrentStyle ()
Set current style settings in this object This function is called when either TCanvas::UseCurrentStyle or TROOT::ForceStyle have been invoked. More...

virtual void Warning (const char *method, const char *msgfmt,...) const
Issue warning message. More...

virtual Int_t Write (const char *name=nullptr, Int_t option=0, Int_t bufsize=0)
Write this object to the current directory. More...

virtual Int_t Write (const char *name=nullptr, Int_t option=0, Int_t bufsize=0) const
Write this object to the current directory. More...

## Static Public Member Functions

static TClassClass ()

static const char * Class_Name ()

static constexpr Version_t Class_Version ()

static const char * DeclFileName ()

Static Public Member Functions inherited from TObject
static TClassClass ()

static const char * Class_Name ()

static constexpr Version_t Class_Version ()

static const char * DeclFileName ()

static Longptr_t GetDtorOnly ()
Return destructor only flag. More...

static Bool_t GetObjectStat ()
Get status of object stat flag. More...

static void SetDtorOnly (void *obj)
Set destructor only flag. More...

static void SetObjectStat (Bool_t stat)
Turn on/off tracking of objects in the TObjectTable. More...

## Private Member Functions

TGeoHelix (const TGeoHelix &)=delete

TGeoHelixoperator= (const TGeoHelix &)=delete

## Private Attributes

Double_t fB [3]

Double_t fC

Double_t fDir [3]

Double_t fDirInit [3]

TGeoHMatrixfMatrix {nullptr}

Double_t fPhi

Double_t fPoint [3]

Double_t fPointInit [3]

Int_t fQ

Double_t fS

Double_t fStep

## Additional Inherited Members

Protected Types inherited from TObject
enum  { kOnlyPrepStep = (1ULL << ( 3 )) }

Protected Member Functions inherited from TObject
virtual void DoError (int level, const char *location, const char *fmt, va_list va) const
Interface to ErrorHandler (protected). More...

void MakeZombie ()

#include <TGeoHelix.h>

Inheritance diagram for TGeoHelix:
[legend]

## ◆ EGeoHelixTypes

Enumerator
kHelixNeedUpdate
kHelixStraight
kHelixCircle

Definition at line 38 of file TGeoHelix.h.

## ◆ TGeoHelix() [1/3]

 TGeoHelix::TGeoHelix ( const TGeoHelix & )
privatedelete

## ◆ TGeoHelix() [2/3]

 TGeoHelix::TGeoHelix ( )

Dummy constructor.

Definition at line 62 of file TGeoHelix.cxx.

## ◆ TGeoHelix() [3/3]

 TGeoHelix::TGeoHelix ( Double_t curvature, Double_t step, Int_t charge = 1 )

Normal constructor.

Definition at line 83 of file TGeoHelix.cxx.

## ◆ ~TGeoHelix()

 TGeoHelix::~TGeoHelix ( )
virtual

Destructor.

Definition at line 105 of file TGeoHelix.cxx.

## ◆ Class()

 static TClass * TGeoHelix::Class ( )
static
Returns
TClass describing this class

## ◆ Class_Name()

 static const char * TGeoHelix::Class_Name ( )
static
Returns
Name of this class

## ◆ Class_Version()

 static constexpr Version_t TGeoHelix::Class_Version ( )
inlinestaticconstexpr
Returns
Version of this class

Definition at line 75 of file TGeoHelix.h.

## ◆ ComputeSafeStep()

 Double_t TGeoHelix::ComputeSafeStep ( Double_t epsil = 1E-6 ) const

Compute safe linear step that can be made such that the error between linear-helix extrapolation is less than EPSIL.

Definition at line 114 of file TGeoHelix.cxx.

## ◆ DeclFileName()

 static const char * TGeoHelix::DeclFileName ( )
inlinestatic
Returns
Name of the file containing the class declaration

Definition at line 75 of file TGeoHelix.h.

## ◆ GetCurrentDirection()

 const Double_t * TGeoHelix::GetCurrentDirection ( ) const
inline

Definition at line 56 of file TGeoHelix.h.

## ◆ GetCurrentPoint()

 const Double_t * TGeoHelix::GetCurrentPoint ( ) const
inline

Definition at line 55 of file TGeoHelix.h.

## ◆ GetStep()

 Double_t TGeoHelix::GetStep ( ) const
inline

Definition at line 58 of file TGeoHelix.h.

## ◆ GetTotalCurvature()

 Double_t TGeoHelix::GetTotalCurvature ( ) const

Compute helix total curvature.

Definition at line 166 of file TGeoHelix.cxx.

## ◆ GetXYcurvature()

 Double_t TGeoHelix::GetXYcurvature ( ) const
inline

Definition at line 57 of file TGeoHelix.h.

## ◆ InitDirection() [1/2]

 void TGeoHelix::InitDirection ( Double_t * dir, Bool_t is_normalized = kTRUE )

Initialize particle direction (tangent on the helix in initial point)

Definition at line 158 of file TGeoHelix.cxx.

## ◆ InitDirection() [2/2]

 void TGeoHelix::InitDirection ( Double_t dirx, Double_t diry, Double_t dirz, Bool_t is_normalized = kTRUE )

Initialize particle direction (tangent on the helix in initial point)

Definition at line 144 of file TGeoHelix.cxx.

## ◆ InitPoint() [1/2]

 void TGeoHelix::InitPoint ( Double_t * point )

Set initial point on the helix.

Definition at line 136 of file TGeoHelix.cxx.

## ◆ InitPoint() [2/2]

 void TGeoHelix::InitPoint ( Double_t x0, Double_t y0, Double_t z0 )

Initialize coordinates of a point on the helix.

Definition at line 125 of file TGeoHelix.cxx.

## ◆ IsA()

 virtual TClass * TGeoHelix::IsA ( ) const
inlinevirtual
Returns
TClass describing current object

Reimplemented from TObject.

Definition at line 75 of file TGeoHelix.h.

## ◆ IsRightHanded()

 Bool_t TGeoHelix::IsRightHanded ( ) const
inline

Definition at line 60 of file TGeoHelix.h.

## ◆ operator=()

 TGeoHelix & TGeoHelix::operator= ( const TGeoHelix & )
privatedelete

## ◆ ResetStep()

 void TGeoHelix::ResetStep ( )

Reset current point/direction to initial values.

Definition at line 235 of file TGeoHelix.cxx.

## ◆ SetCharge()

 void TGeoHelix::SetCharge ( Int_t charge )

Positive charge means left-handed helix.

Definition at line 192 of file TGeoHelix.cxx.

## ◆ SetField()

 void TGeoHelix::SetField ( Double_t bx, Double_t by, Double_t bz, Bool_t is_normalized = kTRUE )

Initialize particle direction (tangent on the helix in initial point)

Definition at line 207 of file TGeoHelix.cxx.

## ◆ SetHelixStep()

 void TGeoHelix::SetHelixStep ( Double_t hstep )

Set Z step of the helix on a complete turn. Positive or null.

Definition at line 221 of file TGeoHelix.cxx.

## ◆ SetXYcurvature()

 void TGeoHelix::SetXYcurvature ( Double_t curvature )

Set XY curvature: c = 1/Rxy.

Definition at line 175 of file TGeoHelix.cxx.

## ◆ Step()

 void TGeoHelix::Step ( Double_t step )

Make a step from current point along the helix and compute new point, direction and angle To reach a plane/ shape boundary, one has to:

1. Compute the safety to the plane/boundary
2. Define / update a helix according local field and particle state (position, direction, charge)
3. Compute the magnetic safety (maximum distance for which the field can be considered constant)
4. Call TGeoHelix::Step() having as argument the minimum between 1. and 3.
5. Repeat from 1. until the step to be made is small enough.
6. Add to the total step the distance along a straight line from the last point to the plane/shape boundary

Definition at line 253 of file TGeoHelix.cxx.

## ◆ StepToPlane()

 Double_t TGeoHelix::StepToPlane ( Double_t * point, Double_t * norm )

Propagate initial point up to a given Z position in MARS.

Definition at line 285 of file TGeoHelix.cxx.

## ◆ Streamer()

 virtual void TGeoHelix::Streamer ( TBuffer & R__b )
virtual

Stream an object of class TObject.

Reimplemented from TObject.

## ◆ StreamerNVirtual()

 void TGeoHelix::StreamerNVirtual ( TBuffer & ClassDef_StreamerNVirtual_b )
inline

Definition at line 75 of file TGeoHelix.h.

## ◆ UpdateHelix()

 void TGeoHelix::UpdateHelix ( )

Update the local helix matrix.

Definition at line 339 of file TGeoHelix.cxx.

## ◆ fB

 Double_t TGeoHelix::fB[3]
private

Definition at line 31 of file TGeoHelix.h.

## ◆ fC

 Double_t TGeoHelix::fC
private

Definition at line 23 of file TGeoHelix.h.

## ◆ fDir

 Double_t TGeoHelix::fDir[3]
private

Definition at line 30 of file TGeoHelix.h.

## ◆ fDirInit

 Double_t TGeoHelix::fDirInit[3]
private

Definition at line 28 of file TGeoHelix.h.

## ◆ fMatrix

 TGeoHMatrix* TGeoHelix::fMatrix {nullptr}
private

Definition at line 33 of file TGeoHelix.h.

## ◆ fPhi

 Double_t TGeoHelix::fPhi
private

Definition at line 26 of file TGeoHelix.h.

## ◆ fPoint

 Double_t TGeoHelix::fPoint[3]
private

Definition at line 29 of file TGeoHelix.h.

## ◆ fPointInit

 Double_t TGeoHelix::fPointInit[3]
private

Definition at line 27 of file TGeoHelix.h.

## ◆ fQ

 Int_t TGeoHelix::fQ
private

Definition at line 32 of file TGeoHelix.h.

## ◆ fS

 Double_t TGeoHelix::fS
private

Definition at line 24 of file TGeoHelix.h.

## ◆ fStep

 Double_t TGeoHelix::fStep
private

Definition at line 25 of file TGeoHelix.h.

Libraries for TGeoHelix:
[legend]

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