Digitization
Digi
A hit is created by a sensitive detector when a step goes through
it. Thus, the sensitive detector is associated to the corresponding
G4LogicalVolume object(s). On the other hand, a digit is
created using information of hits and/or other digits by a
digitizer module. The digitizer module is not associated with any
volume, and you have to implicitly invoke the Digitize()
method of your concrete G4VDigitizerModule class.
Typical usages of digitizer module include:
simulate ADC and/or TDC
simulate readout scheme
generate raw data
simulate trigger logics
simulate pile up
G4VDigi
G4VDigi is an abstract base class which represents a
digit. You have to inherit this base class and derive your own
concrete digit class(es). The member data of your concrete digit
class should be defined by yourself. G4VDigi has two virtual
methods, Draw() and Print().
G4TDigiCollection
G4TDigiCollection is a template class for digits
collections, which is derived from the abstract base class
G4VDigiCollection. G4Event has a
G4DCofThisEvent object, which is a container class of
collections of digits. The usages of G4VDigi and
G4TDigiCollection are almost the same as G4VHit and
G4THitsCollection, respectively, explained in the previous
section.
Digitizer module
G4VDigitizerModule
G4VDigitizerModule is an abstract base class which
represents a digitizer module. It has a pure virtual method,
Digitize(). A concrete digitizer module must have an
implementation of this virtual method. The Geant4 kernel classes do
not have a ``built-in'' invocation to the Digitize()
method. You have to implement your code to invoke this method of
your digitizer module.
In the Digitize() method, you construct your
G4VDigi concrete class objects and store them to your
G4TDigiCollection concrete class object(s). Your
collection(s) should be associated with the G4DCofThisEvent
object.
G4DigiManager
G4DigiManager is the singleton manager class of the
digitizer modules. All of your concrete digitizer modules should be
registered to G4DigiManager with their unique names.
G4DigiManager * fDM = G4DigiManager::GetDMpointer();
MyDigitizer * myDM = new MyDigitizer( "/myDet/myCal/myEMdigiMod" );
fDM->AddNewModule(myDM);
Your concrete digitizer module can be accessed from your code using
the unique module name.
G4DigiManager * fDM = G4DigiManager::GetDMpointer();
MyDigitizer * myDM = fDM->FindDigitizerModule( "/myDet/myCal/myEMdigiMod" );
myDM->Digitize();
Also, G4DigiManager has a Digitize()
method which takes the unique module name.
G4DigiManager * fDM = G4DigiManager::GetDMpointer();
MyDigitizer * myDM = fDM->Digitize( "/myDet/myCal/myEMdigiMod" );
How to get hitsCollection and/or digiCollection
G4DigiManager has the following methods to access to the
hits or digi collections of the currently processing event or of
previous events.
First, you have to get the collection ID number of the hits or
digits collection.
G4DigiManager * fDM = G4DigiManager::GetDMpointer();
G4int myHitsCollID = fDM->GetHitsCollectionID( "hits_collection_name" );
G4int myDigiCollID = fDM->GetDigiCollectionID( "digi_collection_name" );
Then, you can get the pointer to your concrete
G4THitsCollection object or
G4TDigiCollection object of the currently processing event.
MyHitsCollection * HC = fDM->GetHitsCollection( myHitsCollID );
MyDigiCollection * DC = fDM->GetDigiCollection( myDigiCollID );
In case you want to access to the hits or digits collection of
previous events, add the second argument.
MyHitsCollection * HC = fDM->GetHitsCollection( myHitsCollID, n );
MyDigiCollection * DC = fDM->GetDigiCollection( myDigiCollID, n );
where, n indicates the hits or digits collection of the
nth previous event.