Retriving object in Root Core

Retriving ALFADataContainer

In the xAOD file ALFADataContainer object is stored. It has to be read first with the help of xAOD::TEvent object. When EventLoop is used the code will be the following

xAOD::TEvent* event = wk()->xaodEvent();
const xAOD::ALFADataContainer* alfaContainer = NULL;
if( ! event->retrieve( alfaContainer, "ALFADataContainer").isSuccess() ){
  Error("execute", "Failed to retrieve ALFADataContainer. Exiting." );
  return EL::StatusCode::FAILURE;
}

In the code above it is checked if reading of the ALFADataContainer was successful. Without it RootCore will issue a warning.

Note: Objects read from xAOD::TEvent are const pointers.

The retrived xAOD::ALFADataContainer has interface similar to std::vector and contains two ALFAData objects. The first object is fille with TrackingData tree and the second with EventHeader tree. The trees are described in the twiki page https://twiki.cern.ch/twiki/bin/viewauth/Atlas/ALFAntupleAlg

Warning: Both ALFAData object contain all the variables, but the variables that are not present in the corresponding tree contain default values.

Retriving an ALFAData object from ALFADataContainer

ALFAData objects can be read from the ALFADataContainer with the same interface as is used in the std::vector. It means that e.g. at() mehtod chan be used.

In order to read the get the first ALFAData object which contains TrackingData information the following code can be used:

const xAOD::ALFAData* trackingData = alfaContainer->at(0);

In order to read the get the first ALFAData object which contains TrackingData information the following code can be used:

const xAOD::ALFAData* eventData = alfaContainer->at(1);

Detailed descriptions of the functions providing access to the specific variables contain information in which tree the variable is stored.

Retriving data in Athena

In the xAOD file ALFADataContainer object is stored and it has to be retrived first. It is stored in eventStore. In the xAOD file there is only one such object, which means it can be retrived without specifing object name. Below an example code is presented.

const xAOD::ALFADataContainer* alfaContainer = 0;

CHECK( evtStore()->retrieve( alfaContainer) );

Retriving ALFAData objects from the container object is common for Athena and RootCore, so please consult subsection Retriving an ALFAData object from ALFADataContainer

Decrypting vector index from serialised 2D array for tracks

All arrays stored in xAOD are one dimensional. It means that data saved in 2D arrays has to be transformed into 1D array.

In case of the 2D arrays storing information about tracks the index of a 1D array is constructed in the following way:

   potIndex*maxTrackCnt() + trackIndex

where:

potIndex is the index of the pot ranging from 0 to 7,
maxTrackCnt() is the number of maximal number of tracks in one station,
trackIndex is the index of the track in a station.

Warning: Number of entries in the vector does not correspond to number of tracks. To say if there is a track or not it has to be checked that the value of the variable is different from default one (usually -9999).

In order to extract pot number from the array element index the following formula can be used

int potIndex = index/maxTrackCnt();

In order to extract track index from the array element index the following formula can be used

int trackIndex = index%maxTrackCnt();

Decrypting vector index from serialised 2D array for plates

All arrays stored in xAOD are one dimensional. It means that data saved in 2D arrays has to be transformed into 1D array.

In case of the 2D arrays storing information about plates the index of a 1D array is constructed in the following way:

   potIndex*numberOfPlates + plateIndex

where:

potIndex is the index of the pot ranging from 0 to 7,
numberOfPlates is the number of plates in a detector (20 for main detector and 3 for overlap detector),
plateIndex is the index of considered plate

In order to extract pot number from the array element index the following formula can be used

int potIndex = index/numberOfPlates;

In order to extract plate index from the array element index the following formula can be used

int trackIndex = index%numberOfPlates;

Decrypting vector index with track information from serialised 3D array

All arrays stored in xAOD are one dimensional. It means that data saved in 3D arrays has to be transformed into 1D array.

In case of the 3D arrays storing information about tracks and plates, an index of a 1D array is constructed in the following way:

   potIndex*maxTrackCnt()*numberOfPlates + trackIndex*numberOfPlates + plateIndex

where:

potIndex is the index of the pot ranging from 0 to 7,
maxTrackCnt() is the number of maximal number of tracks in one station,
numberOfPlates is the maximal number of plates that can be used in track reconstruction - for main detector tracks it is 20, for overlap detectors it is 3,
trackIndex is the index of the track in a station,
plateIndex index of considered plate (from 0 to 19 for main detectors or from 0 to 2 for overlap detectors)\

Warning: Number of entries in the vector does not correspond to number of tracks. To say if there is a track or not it has to be checked that the track for this pot and this index was reconstructed in one of the detectors using getDetectorPartID().

In order to extract pot number from the array element index the following formula can be used

int potIndex = index/(maxTrackCnt()*numberOfPlates);

In order to extract track index from the array element index the following formula can be used

int trackIndex = (index/numberOfPlates)%maxTrackCnt();

In order to extract plate index from the array element index the following formula can be used

int plateIndex = index%numberOfPlates;

Decrypting vector index with fibers information from serialised 3D array

All arrays stored in xAOD are one dimensional. It means that data saved in 3D arrays has to be transformed into 1D array.

In case of the 3D arrays storing information about fibers, an index of a 1D array is constructed in the following way:

   potIndex*numberOfPlates*numberOfLayers + plateIndex*numberOfLayers + layerIndex

where:

potIndex is the index of the pot ranging from 0 to 7,
numberOfPlates is the maximal number of plates that can be used in track reconstruction - for main detector tracks it is 20, for overlap detectors it is 3,
numberLayers is the number of fiber layers in a plate, which is equal to 64 for main detectors and 30 for overlap detectors,
plateIndex is the index of the considered plate of fibers (runs from 0 to 20 for main detectors and from 0 to 2 for overlap detectors)
layerIndex is the index of considered layer (runs from 0 to 63 for main detectors and from 0 to 29 for overlap detectors)

In order to extract pot number from the array element index the following formula can be used

int potIndex = index/(numberOfPlates*numberOfLayers);

In order to plate index from the array element index the following formula can be used

int plateIndex = (index/numberOfLayers)%numberOfPlates;

In order to extract layer index from the array element index the following formula can be used

int layerIndex = index%numberOfLayers;