[u/mrichter/AliRoot.git] / EMCAL / doc / geometry.tex

\section{EMCAL geometry software - Marco +++}


This page is intended for a description of the EMCAL geometry and the methods to access it.  
{\it This is a very preliminary version that needs work.}

 \subsection {Classes description}

The EMCAL geometry is implemented in several classes : {\color{red} (right now very brief description, it should be completed) }
\begin{itemize}
\item AliEMCALGeoUtils: Steering geometry class.  No dependencies on STEER or EMCAL non geometry classes. Can be called during the analysis without loading all aliroot classes.
\item AliEMCALGeometry: Derives from AliEMCALGeoUtils, contains dependencies on other EMCAL classes (AliEMCALRecPoint).
\item AliEMCALEMCGeometry: Does the geometry initialization. Does all the definitions of the geometry (towers composition, size, Super Modules number ...)
\item AliEMCALGeoParams:  Class container of some of the geometry parameters so that it can be accessed everywhere in the EMCAL code, to avoid "magic numbers". Its use has to be propagated to all the code.
\item AliEMCALShishKebabTrd1Module: Here the modules are defined and the position of the modules in the local super module reference system is calculated
\end{itemize}

\subsection{Accessing the geometry}
One can get the geometry pointer in the following ways:
\begin{itemize}
\item If galice.root is available:

\begin{DDbox}{\linewidth}
\begin{lstlisting}
AliRunLoader *rl = AliRunLoader::Open("galice.root",AliConfig::GetDefaultEventFolderName(),"read"); 
rl->LoadgAlice();//Needed to get geometry
AliEMCALLoader *emcalLoader = dynamic\_cast<AliEMCALLoader*>(rl->GetDetectorLoader("EMCAL"));
AliRun * alirun = rl->GetAliRun();
AliEMCAL * emcal = (AliEMCAL*)alirun->GetDetector("EMCAL"); AliEMCALGeometry * geom = emcal->GetGeometry();
else, if galice.root is not available:
AliEMCALGeometry * geom =  AliEMCALGeometry::GetInstance("EMCAL\_COMPLETE") ;

\end{lstlisting}
\end{DDbox}
\end{itemize}
In this case you might need the file geometry.root if you want to access to certain methods that require local to global position transformations. This file can be generated doing a simple simulation, it just contains the transformation matrix to go from global to local.

The way to load this file is:
%\begin{DDbox}{\linewidth}
\begin{lstlisting}
TGeoManager::Import("geometry.root");
\end{lstlisting}
%\end{DDbox}

The transformation matrices are also stored in the ESDs so if you do not load this file, you can have to load these matrices from the ESDs.

 If you want to see different parameters used in the geometry printed (cells centers, distance to IP, etc), one just has to execute the method PrintGeometry().
 

\subsection{Geometry configuration options}
Right now the following geometry options are implemented:
\begin{itemize}
\item EMCAL\_COMPLETE: 12 Super Modules (2 half Super Modules)
\item EMCAL\_FIRSTYEAR: 4 Super Modules (year 2010)
\item EMCAL\_FIRSTYEARV1: 4 Super Modules, corrected geometry (year 2010)
\item EMCAL\_COMPLETEV1: 10 Super Modules, corrected geometry (year 2011)
\item EMCAL\_COMPLETE12SMV1: 12 Super Modules (10+2/3), corrected geometry (year 2012)
\end{itemize}

Other options exists but need to be removed as they {\bf should not be used}:
\begin{itemize}
\item EMCAL\_PDC06: Old geometry, for reading old data (which do not exist anymore).
\item EMCAL\_WSU: Prototype geometry. 
\end{itemize}

By default, the geometry is loaded with the EMCAL\_COMPLETE12SMV1 configuration.

 
 \subsection{Mapping}
The tower row/column mapping online and offline follows the alice numbering convention. Figures~\ref{fig:Map1} to \ref{fig:Map2} display the position of the super modules from different points of view and the position of the tower index in them.

\begin{figure}[ht]
\begin{center}
\includegraphics[width=1.0\textwidth]{figures/EMCALMap0_0.pdf}
\end{center}
\caption{\label{fig:Map1}}
\end{figure}

\begin{figure}[ht]
\begin{center}
\includegraphics[width=1.0\textwidth]{figures/EMCALMap1.pdf}
\end{center}
\caption{\label{fig:Map0}}
\end{figure}


\begin{figure}[ht]
\begin{center}
\includegraphics[width=1.0\textwidth]{figures/EMCALMap2.pdf}
\end{center}
\caption{\label{fig:Map2}}
\end{figure}


\subsection{Tower index transformation methods}
\subsubsection{Absolute tower ID to Row/Column index}

Each EMCAL supermodule is composed of 24x48 towers (phi,eta), grouped in 4x4 modules. Each tower (even each module) has a unique number assigned, called in the code "absolute ID" number (absId). This number can be transformed into a row (phi direction) or column (eta direction) index. The procedure to go from the absId to the (row, col) formulation or viceversa is as follow:

\begin{itemize}
\item From absId to col-row: 

\begin{DDbox}{\linewidth}
\begin{lstlisting}
Int\_t nSupMod, nModule, nIphi, nIeta, iphi, ieta;
//Check if this absId exists
if(!CheckAbsCellId(absId)) return kFALSE;
// Get from the absId the super module number, the module number and the eta-phi index (0 or 1) in the module
GetCellIndex(absId, nSupMod, nModule, nIphi, nIeta);
// Get from the  the super module number, the module number and the eta-phi index (0 or 1) in the module the tower row (iphi) and column (ieta) 
GetCellPhiEtaIndexInSModule(nSupMod,nModule,nIphi,nIeta, iphi, ieta); 
\end{lstlisting}
\end{DDbox}

\item From col-row to absId, following the same notation as above: 

\begin{DDbox}{\linewidth}
\begin{lstlisting}

absid = GetAbsCellIdFromCellIndexes(nSupMode, iphi, ieta);
\end{lstlisting}
\end{DDbox}

or

\begin{DDbox}{\linewidth}
\begin{lstlisting}

absid = GetAbsCellId(nSupMod, nModule, nIphi, nIeta);
\end{lstlisting}
\end{DDbox}

\item Other interesting method is

\begin{DDbox}{\linewidth}
\begin{lstlisting}

Int\_t   GetSuperModuleNumber(Int\_t absId)  
\end{lstlisting}
\end{DDbox}
\end{itemize}

\subsection{Tower index to local / global reference system position}
\subsubsection{Local coordinates}

To correlate the tower index and its position in local coordinates, the following methods are available:

\begin{DDbox}{\linewidth}
\begin{lstlisting}
  Bool\_t  AliEMCALGeoUtils::RelPosCellInSModule(Int\_t absId, Double\_t \&xr, Double\_t \&yr, Double\_t \&zr) const;

  Bool\_t  AliEMCALGeoUtils::RelPosCellInSModule(Int\_t absId, Double\_t loc[3]) const;

  Bool\_t  AliEMCALGeoUtils::RelPosCellInSModule(Int\_t absId, TVector3 \&vloc) const;
\end{lstlisting}
\end{DDbox}

To which the input is the absId and the output are the coordinates of the center of towers in the local coordinates of the Super Module. This method gets the column and row index of the cell from the absId, independently of the Super Module (like above), and gets the center of the cell from 3 arrays (x,y,z) filled with such quantities. Such central positions are calculated during the initialization of the geometry, where the arrys are filled, in the method :

\begin{DDbox}{\linewidth}
\begin{lstlisting}

  AliEMCALGeoUtils::CreateListOfTrd1Modules()
\end{lstlisting}
\end{DDbox}

{\color{red}<<<<<Someone else should explain how it works>>>>>}

 
In case we calculate the cluster position, things are a bit different.

 
{\color{red}<<<<< This explanation should go to the clusterization section>>>>}

 
This is done in 

\begin{DDbox}{\linewidth}
\begin{lstlisting}
void AliEMCALRecPoint::EvalLocalPosition()
\end{lstlisting}
\end{DDbox}

First we calculate the cell position with the  method 

\begin{DDbox}{\linewidth}
\begin{lstlisting}
AliEMCALGeometry::RelPosCellInSModule(Int\_t absId, Int\_t maxAbsId, Double\_t tmax, Double\_t \&xr, Double\_t \&yr, Double\_t \&zr)
\end{lstlisting}
\end{DDbox}

The calculation of the cell position done here is different in the "x-z" but the same in "y". 

 
{\color{red}<<<<< <<<<<Someone else should explain how it works>>>>>}

 
In this particular case the position calculation per tower depends on the position of the maximum cell, and the sum of the energy of the cells of the cluster. The maximum depth (tmax) is calculated with the method

\begin{DDbox}{\linewidth}
\begin{lstlisting}
  Double\_t AliEMCALRecPoint::TmaxInCm(const Double\_t e){

      //e: energy sum of cells

static Double\_t ca = 4.82;// shower max parameter - first guess; ca=TMath::Log(1000./8.07)

      static Double\_t x0 = 1.23; // radiation lenght (cm)

      static Double\_t tmax = 0.; // position of electromagnetic shower max in cm

      tmax = TMath::Log(e) + ca+0.5;

      tmax *= x0; // convert to cm

  }
\end{lstlisting}
\end{DDbox}

After the cells position of the cluster is accessed, the position of the cluster is calculated averaging the cell positions with a logarithmic weight:

\begin{DDbox}{\linewidth}
\begin{lstlisting}
  w(cell i) = TMath::Max( 0., logWeight + TMath::Log( energy[cell i] / summed\_cluster\_cell\_energy ));
\end{lstlisting}
\end{DDbox}

where the logWeight was chosen to be 4.5 (this value was taken from PHOS, never optimized as far as I know)

So in the end the position,  is 

\begin{DDbox}{\linewidth}
\begin{lstlisting}
f = Sum(f(i) * w(i))/Sum(w(i))
\end{lstlisting}
\end{DDbox}

where f=x,y,z.

 
 \subsubsection{Global coordinates}
 

To transform from local to global we have the methods

\begin{DDbox}{\linewidth}
\begin{lstlisting}

  void GetGlobal(const Double\_t *loc, Double\_t *glob, int ind) const;

  void GetGlobal(const TVector3 \&vloc, TVector3 \&vglob, int ind) const;

  void GetGlobal(Int\_t absId, Double\_t glob[3]) const;

  void GetGlobal(Int\_t absId, TVector3 \&vglob) const;
\end{lstlisting}
\end{DDbox}

 
 These methods take the local coordinates and transform them into global coordinates using the transformation matrix of the Super Module.

\begin{DDbox}{\linewidth}
\begin{lstlisting}
 

TGeoHMatrix* m = GetMatrixForSuperModule(nSupMod);

if(m) m->LocalToMaster(loc, glob);

\end{lstlisting}
\end{DDbox}
 

 GetGlobal is called in the following useful methods in the geometry class:

 
\begin{itemize}
\item Return the eta and phi angular position of the cell from the AbsId

\begin{DDbox}{\linewidth}
\begin{lstlisting}
void    EtaPhiFromIndex(Int\_t absId, Double\_t \&eta, Double\_t \&phi) const;
void    EtaPhiFromIndex(Int\_t absId, Float\_t \&eta, Float\_t \&phi) const;
\end{lstlisting}
\end{DDbox}
\item Print information of the cells. For "pri>0" returns more information. "tit" has not much use, this value is printed.

\begin{DDbox}{\linewidth}
\begin{lstlisting}
void PrintCellIndexes(Int\_t absId, int pri, const char *tit)
\end{lstlisting}
\end{DDbox}
\end{itemize} 

\subsection{Geometry Alignment}
AliRoot contains a frame for the correction of the misplacement of geometry objects with respect to the ideal positions which are kept in the STEER/ directory of the following classes:

\begin{DDbox}{\linewidth}
\begin{lstlisting}
AliAlignObj  
AliAlignObjMatrix  
AliAlignObjParams  
AliAlignmentTracks
\end{lstlisting}
\end{DDbox}

The class AliEMCALSurvey creates the corrections to the alignable objects.  The class AliEMCALSurvey was established to take the survey parameters from OCDB, calculate the shift in position of the center of the end faces of the supermodules from the nominal position, and convert this to a transformation matrix for each supermodule which is applied to correct the global position of the supermodules.  All calculations of global positions would then use these corrected supermodule positions to determine their locations within the ALICE global coordinate system.
Commit	Line	Data
f5c540cb	1	\section{EMCAL geometry software - Marco +++}
02582a78	2
02582a78	3
f5c540cb	4	This page is intended for a description of the EMCAL geometry and the methods to access it.
f5c540cb	5	{\it This is a very preliminary version that needs work.}
02582a78	6
f5c540cb	7	\subsection {Classes description}
	8
	9	The EMCAL geometry is implemented in several classes : {\color{red} (right now very brief description, it should be completed) }
02582a78	10	\begin{itemize}
f5c540cb	11	\item AliEMCALGeoUtils: Steering geometry class. No dependencies on STEER or EMCAL non geometry classes. Can be called during the analysis without loading all aliroot classes.
f5c540cb	12	\item AliEMCALGeometry: Derives from AliEMCALGeoUtils, contains dependencies on other EMCAL classes (AliEMCALRecPoint).
02582a78	13	\item AliEMCALEMCGeometry: Does the geometry initialization. Does all the definitions of the geometry (towers composition, size, Super Modules number ...)
	14	\item AliEMCALGeoParams: Class container of some of the geometry parameters so that it can be accessed everywhere in the EMCAL code, to avoid "magic numbers". Its use has to be propagated to all the code.
	15	\item AliEMCALShishKebabTrd1Module: Here the modules are defined and the position of the modules in the local super module reference system is calculated
	16	\end{itemize}
	17
f5c540cb	18	\subsection{Accessing the geometry}
	19	One can get the geometry pointer in the following ways:
	20	\begin{itemize}
	21	\item If galice.root is available:
	22
	23	\begin{DDbox}{\linewidth}
	24	\begin{lstlisting}
	25	AliRunLoader *rl = AliRunLoader::Open("galice.root",AliConfig::GetDefaultEventFolderName(),"read");
	26	rl->LoadgAlice();//Needed to get geometry
	27	AliEMCALLoader emcalLoader = dynamic\_cast<AliEMCALLoader>(rl->GetDetectorLoader("EMCAL"));
	28	AliRun * alirun = rl->GetAliRun();
	29	AliEMCAL * emcal = (AliEMCAL)alirun->GetDetector("EMCAL"); AliEMCALGeometry geom = emcal->GetGeometry();
	30	else, if galice.root is not available:
	31	AliEMCALGeometry * geom = AliEMCALGeometry::GetInstance("EMCAL\_COMPLETE") ;
	32
	33	\end{lstlisting}
	34	\end{DDbox}
	35	\end{itemize}
02582a78	36	In this case you might need the file geometry.root if you want to access to certain methods that require local to global position transformations. This file can be generated doing a simple simulation, it just contains the transformation matrix to go from global to local.
02582a78	37
f5c540cb	38	The way to load this file is:
	39	%\begin{DDbox}{\linewidth}
	40	\begin{lstlisting}
	41	TGeoManager::Import("geometry.root");
	42	\end{lstlisting}
	43	%\end{DDbox}
02582a78	44
	45	The transformation matrices are also stored in the ESDs so if you do not load this file, you can have to load these matrices from the ESDs.
	46
f5c540cb	47	If you want to see different parameters used in the geometry printed (cells centers, distance to IP, etc), one just has to execute the method PrintGeometry().
02582a78	48
	49
	50	\subsection{Geometry configuration options}
f5c540cb	51	Right now the following geometry options are implemented:
02582a78	52	\begin{itemize}
	53	\item EMCAL\_COMPLETE: 12 Super Modules (2 half Super Modules)
	54	\item EMCAL\_FIRSTYEAR: 4 Super Modules (year 2010)
	55	\item EMCAL\_FIRSTYEARV1: 4 Super Modules, corrected geometry (year 2010)
	56	\item EMCAL\_COMPLETEV1: 10 Super Modules, corrected geometry (year 2011)
	57	\item EMCAL\_COMPLETE12SMV1: 12 Super Modules (10+2/3), corrected geometry (year 2012)
	58	\end{itemize}
	59
f5c540cb	60	Other options exists but need to be removed as they {\bf should not be used}:
02582a78	61	\begin{itemize}
f5c540cb	62	\item EMCAL\_PDC06: Old geometry, for reading old data (which do not exist anymore).
02582a78	63	\item EMCAL\_WSU: Prototype geometry.
	64	\end{itemize}
	65
f5c540cb	66	By default, the geometry is loaded with the EMCAL\_COMPLETE12SMV1 configuration.
02582a78	67
	68
	69	\subsection{Mapping}
f5c540cb	70	The tower row/column mapping online and offline follows the alice numbering convention. Figures~\ref{fig:Map1} to \ref{fig:Map2} display the position of the super modules from different points of view and the position of the tower index in them.
02582a78	71
	72	\begin{figure}[ht]
	73	\begin{center}
3ae81835	74	\includegraphics[width=1.0\textwidth]{figures/EMCALMap0_0.pdf}
02582a78	75	\end{center}
	76	\caption{\label{fig:Map1}}
	77	\end{figure}
	78
	79	\begin{figure}[ht]
	80	\begin{center}
3ae81835	81	\includegraphics[width=1.0\textwidth]{figures/EMCALMap1.pdf}
02582a78	82	\end{center}
	83	\caption{\label{fig:Map0}}
	84	\end{figure}
	85
	86
	87	\begin{figure}[ht]
	88	\begin{center}
3ae81835	89	\includegraphics[width=1.0\textwidth]{figures/EMCALMap2.pdf}
02582a78	90	\end{center}
	91	\caption{\label{fig:Map2}}
	92	\end{figure}
	93
	94
	95	\subsection{Tower index transformation methods}
	96	\subsubsection{Absolute tower ID to Row/Column index}
02582a78	97
f5c540cb	98	Each EMCAL supermodule is composed of 24x48 towers (phi,eta), grouped in 4x4 modules. Each tower (even each module) has a unique number assigned, called in the code "absolute ID" number (absId). This number can be transformed into a row (phi direction) or column (eta direction) index. The procedure to go from the absId to the (row, col) formulation or viceversa is as follow:
02582a78	99
f5c540cb	100	\begin{itemize}
f5c540cb	101	\item From absId to col-row:
02582a78	102
f5c540cb	103	\begin{DDbox}{\linewidth}
	104	\begin{lstlisting}
	105	Int\_t nSupMod, nModule, nIphi, nIeta, iphi, ieta;
	106	//Check if this absId exists
02582a78	107	if(!CheckAbsCellId(absId)) return kFALSE;
02582a78	108	// Get from the absId the super module number, the module number and the eta-phi index (0 or 1) in the module
02582a78	109	GetCellIndex(absId, nSupMod, nModule, nIphi, nIeta);
02582a78	110	// Get from the the super module number, the module number and the eta-phi index (0 or 1) in the module the tower row (iphi) and column (ieta)
02582a78	111	GetCellPhiEtaIndexInSModule(nSupMod,nModule,nIphi,nIeta, iphi, ieta);
f5c540cb	112	\end{lstlisting}
f5c540cb	113	\end{DDbox}
02582a78	114
f5c540cb	115	\item From col-row to absId, following the same notation as above:
	116
	117	\begin{DDbox}{\linewidth}
	118	\begin{lstlisting}
02582a78	119
02582a78	120	absid = GetAbsCellIdFromCellIndexes(nSupMode, iphi, ieta);
f5c540cb	121	\end{lstlisting}
f5c540cb	122	\end{DDbox}
02582a78	123
	124	or
	125
f5c540cb	126	\begin{DDbox}{\linewidth}
	127	\begin{lstlisting}
	128
02582a78	129	absid = GetAbsCellId(nSupMod, nModule, nIphi, nIeta);
f5c540cb	130	\end{lstlisting}
f5c540cb	131	\end{DDbox}
02582a78	132
f5c540cb	133	\item Other interesting method is
02582a78	134
f5c540cb	135	\begin{DDbox}{\linewidth}
f5c540cb	136	\begin{lstlisting}
02582a78	137
f5c540cb	138	Int\_t GetSuperModuleNumber(Int\_t absId)
	139	\end{lstlisting}
	140	\end{DDbox}
	141	\end{itemize}
02582a78	142
	143	\subsection{Tower index to local / global reference system position}
	144	\subsubsection{Local coordinates}
02582a78	145
f5c540cb	146	To correlate the tower index and its position in local coordinates, the following methods are available:
	147
	148	\begin{DDbox}{\linewidth}
	149	\begin{lstlisting}
02582a78	150	Bool\_t AliEMCALGeoUtils::RelPosCellInSModule(Int\_t absId, Double\_t \&xr, Double\_t \&yr, Double\_t \&zr) const;
	151
	152	Bool\_t AliEMCALGeoUtils::RelPosCellInSModule(Int\_t absId, Double\_t loc[3]) const;
	153
	154	Bool\_t AliEMCALGeoUtils::RelPosCellInSModule(Int\_t absId, TVector3 \&vloc) const;
f5c540cb	155	\end{lstlisting}
	156	\end{DDbox}
	157
	158	To which the input is the absId and the output are the coordinates of the center of towers in the local coordinates of the Super Module. This method gets the column and row index of the cell from the absId, independently of the Super Module (like above), and gets the center of the cell from 3 arrays (x,y,z) filled with such quantities. Such central positions are calculated during the initialization of the geometry, where the arrys are filled, in the method :
02582a78	159
f5c540cb	160	\begin{DDbox}{\linewidth}
f5c540cb	161	\begin{lstlisting}
02582a78	162
02582a78	163	AliEMCALGeoUtils::CreateListOfTrd1Modules()
f5c540cb	164	\end{lstlisting}
f5c540cb	165	\end{DDbox}
02582a78	166
f5c540cb	167	{\color{red}<<<<<Someone else should explain how it works>>>>>}
02582a78	168
	169
	170
	171	In case we calculate the cluster position, things are a bit different.
	172
	173
	174
f5c540cb	175	{\color{red}<<<<< This explanation should go to the clusterization section>>>>}
02582a78	176
	177
	178
	179	This is done in
	180
f5c540cb	181	\begin{DDbox}{\linewidth}
f5c540cb	182	\begin{lstlisting}
02582a78	183	void AliEMCALRecPoint::EvalLocalPosition()
f5c540cb	184	\end{lstlisting}
f5c540cb	185	\end{DDbox}
02582a78	186
	187	First we calculate the cell position with the method
	188
f5c540cb	189	\begin{DDbox}{\linewidth}
f5c540cb	190	\begin{lstlisting}
02582a78	191	AliEMCALGeometry::RelPosCellInSModule(Int\_t absId, Int\_t maxAbsId, Double\_t tmax, Double\_t \&xr, Double\_t \&yr, Double\_t \&zr)
f5c540cb	192	\end{lstlisting}
f5c540cb	193	\end{DDbox}
02582a78	194
	195	The calculation of the cell position done here is different in the "x-z" but the same in "y".
	196
	197
	198
f5c540cb	199	{\color{red}<<<<< <<<<<Someone else should explain how it works>>>>>}
02582a78	200
	201
	202
	203
	204	In this particular case the position calculation per tower depends on the position of the maximum cell, and the sum of the energy of the cells of the cluster. The maximum depth (tmax) is calculated with the method
	205
f5c540cb	206	\begin{DDbox}{\linewidth}
f5c540cb	207	\begin{lstlisting}
02582a78	208	Double\_t AliEMCALRecPoint::TmaxInCm(const Double\_t e){
	209
	210	//e: energy sum of cells
	211
	212	static Double\_t ca = 4.82;// shower max parameter - first guess; ca=TMath::Log(1000./8.07)
	213
	214	static Double\_t x0 = 1.23; // radiation lenght (cm)
	215
	216	static Double\_t tmax = 0.; // position of electromagnetic shower max in cm
	217
	218	tmax = TMath::Log(e) + ca+0.5;
	219
	220	tmax *= x0; // convert to cm
	221
	222	}
f5c540cb	223	\end{lstlisting}
f5c540cb	224	\end{DDbox}
02582a78	225
f5c540cb	226	After the cells position of the cluster is accessed, the position of the cluster is calculated averaging the cell positions with a logarithmic weight:
02582a78	227
f5c540cb	228	\begin{DDbox}{\linewidth}
f5c540cb	229	\begin{lstlisting}
02582a78	230	w(cell i) = TMath::Max( 0., logWeight + TMath::Log( energy[cell i] / summed\_cluster\_cell\_energy ));
f5c540cb	231	\end{lstlisting}
f5c540cb	232	\end{DDbox}
02582a78	233
	234	where the logWeight was chosen to be 4.5 (this value was taken from PHOS, never optimized as far as I know)
	235
	236	So in the end the position, is
	237
f5c540cb	238	\begin{DDbox}{\linewidth}
f5c540cb	239	\begin{lstlisting}
02582a78	240	f = Sum(f(i) * w(i))/Sum(w(i))
f5c540cb	241	\end{lstlisting}
f5c540cb	242	\end{DDbox}
02582a78	243
	244	where f=x,y,z.
	245
	246
	247
	248	\subsubsection{Global coordinates}
	249
	250
	251	To transform from local to global we have the methods
	252
f5c540cb	253	\begin{DDbox}{\linewidth}
	254	\begin{lstlisting}
	255
02582a78	256	void GetGlobal(const Double\_t loc, Double\_t glob, int ind) const;
	257
	258	void GetGlobal(const TVector3 \&vloc, TVector3 \&vglob, int ind) const;
	259
	260	void GetGlobal(Int\_t absId, Double\_t glob[3]) const;
	261
	262	void GetGlobal(Int\_t absId, TVector3 \&vglob) const;
f5c540cb	263	\end{lstlisting}
f5c540cb	264	\end{DDbox}
02582a78	265
	266
	267
	268	These methods take the local coordinates and transform them into global coordinates using the transformation matrix of the Super Module.
	269
f5c540cb	270	\begin{DDbox}{\linewidth}
f5c540cb	271	\begin{lstlisting}
02582a78	272
	273
	274	TGeoHMatrix* m = GetMatrixForSuperModule(nSupMod);
	275
	276	if(m) m->LocalToMaster(loc, glob);
	277
f5c540cb	278	\end{lstlisting}
f5c540cb	279	\end{DDbox}
02582a78	280
	281
	282	GetGlobal is called in the following useful methods in the geometry class:
	283
	284
f5c540cb	285	\begin{itemize}
f5c540cb	286	\item Return the eta and phi angular position of the cell from the AbsId
02582a78	287
f5c540cb	288	\begin{DDbox}{\linewidth}
f5c540cb	289	\begin{lstlisting}
02582a78	290	void EtaPhiFromIndex(Int\_t absId, Double\_t \&eta, Double\_t \&phi) const;
02582a78	291	void EtaPhiFromIndex(Int\_t absId, Float\_t \&eta, Float\_t \&phi) const;
f5c540cb	292	\end{lstlisting}
	293	\end{DDbox}
	294	\item Print information of the cells. For "pri>0" returns more information. "tit" has not much use, this value is printed.
	295
	296	\begin{DDbox}{\linewidth}
	297	\begin{lstlisting}
02582a78	298	void PrintCellIndexes(Int\_t absId, int pri, const char *tit)
f5c540cb	299	\end{lstlisting}
	300	\end{DDbox}
	301	\end{itemize}
02582a78	302
02582a78	303	\subsection{Geometry Alignment}
f5c540cb	304	AliRoot contains a frame for the correction of the misplacement of geometry objects with respect to the ideal positions which are kept in the STEER/ directory of the following classes:
	305
	306	\begin{DDbox}{\linewidth}
	307	\begin{lstlisting}
	308	AliAlignObj
	309	AliAlignObjMatrix
	310	AliAlignObjParams
	311	AliAlignmentTracks
	312	\end{lstlisting}
	313	\end{DDbox}
	314
	315	The class AliEMCALSurvey creates the corrections to the alignable objects. The class AliEMCALSurvey was established to take the survey parameters from OCDB, calculate the shift in position of the center of the end faces of the supermodules from the nominal position, and convert this to a transformation matrix for each supermodule which is applied to correct the global position of the supermodules. All calculations of global positions would then use these corrected supermodule positions to determine their locations within the ALICE global coordinate system.