The converter package basically consists of two parts: a data definition of the TTable class for storing the data in Root, and a converter class for translating between DataObject and TTable. In this case, the DataObject is LArCellContainer , (basically an ObjectVector), and the TTable class LArCellContainerRoot is defined as follows:

#ifndef _LArCellContainerRoot_H_
#define _LArCellContainerRoot_H_
#include "TTable.h"
#include "Ttypes.h"
typedef struct
{
float energy; // Energy deposited by hit [GeV]
float eta; // eta cell
float phi; // phi cell
float t; // time
float q; // quality dummy for now.
short channel[8]; // channel
} LArCellContainerRoot_t;

class LArCellContainerRoot : public TTable
{
public:
ClassDefTable(LArCellContainerRoot,LArCellContainerRoot_t)
ClassDef(LArCellContainerRoot,1) //C++ container for hits
};
#endif

This defines a TTable class that consists of rows of C-struct of LArCellContainerRoot_t.

In order for Root to understand this object, it is necessary to generate a Dictionary class for this data object. This is done by the command, rootcint, which is in a script MakeDict . After executing this script, LArGaudiRootDict.cxx and LArGaudiRootDict.h files are created.

The converter (LArCellGaudiRootCnv) is a derived class of GaudiRootConverter

The basic functionality of a converter is taken care of in the base class GaudiRootConverter. The derived class for a particular data type is only supposed to convert between a DataObject and a TDataSet. For objects that does not contain reference to other objects, basically there are two methods to be implemented,

virtual StatusCode DataObjectToTDataSet(DataObject* d, TDataSet*& t, string tname);
// create a TDataSet object from DataObject
virtual StatusCode TDataSetToDataObject(TDataSet* t, DataObject*& d);
// create a DataObject from TDataSet object.

See LArCellGaudiRootCnv.cxx for detail.