- Remove double declaration in Digitizer

[u/mrichter/AliRoot.git] / RICH / api.txt

How to open session:
	use static method  AliRunLoader::Open("galice.root","AlicE","update")
How to get total number of events in galice.root:
	use AliRun::GetEventsPerRun()        
How to avoid using gAlice:
	detector->GetLoader()->GetRunLoader()->GetAliRun() returns gAlice global pointer.
How to retrieve pointer to alice run loader:
        use pRICH->GetLoader()->GetRunLoader() (all detector classes inherit from AliDetector which has GetLoader())
	use method AliRun::GetRunLoader for gAlice (deprecated)
How to get pointers to different root trees:
	TreeE belongs to AliRunLoader, available after AliRunLoader::LoadHeader()
	TreeK belongs to AliRunLoader, available after AliRunLoader::LoadKinematics()
	TreeH belongs to AliLoader   , available after AliLoader::LoadHits()
	TreeS belongs to AliLoader   , available after AliLoader::LoadSDigits()
	TreeD belongs to AliLoader   , available after AliLoader::LoadDigits()
	TreeR belongs to AliLoader   , available after AliLoader::LoadRecPoints()
        all methods return 0 on success. 
How to get event of interest:
	AliRunLoader::GetEvent(event_number) returns 0 on success
How to deal with the stack of particles?
        - first of all, the stack includes primary as well as secondary particles
	- pointer to the stack is taken:
         	AliRun::Stack() (global gAlice of type AliRun - deprecated way to do)
          	AliRunLoader::Stack() but before one needs to load event header by AliRunLoader::LoadHeader() otherwise both methods return 0.
          	Moreover loading header gives the information about number of particles only. 
          	To retrieve the list of particle one also needs to load kinematics by AliRunLoader::LoadKinematics()        
	- total amount of particles in stack for a given event:        
         	AliStack::GetNtrack() 
                AliRun::GetEvent() (after LoadHeader())
	- total amount of primary particles in stack for a given event (after LoadHeader()): 
        	AliStack::GetNprimary() 
How to retrieve hits:
	Hits are stored on primary by primary basis. Hits for the given primary is TClonesArray.
   	To retrieve all hits one needs to do:
     	-initialize the root tree and containers:   pRich->GetLoader()->LoadHits();  (AliLoader::LoadHits() returns 0 on success)
     	-read number of entries in TreeH:           pRich->GetLoader()->TreeH()->GetEntries()
     	-then for each entry:                       pRich->GetLoader()->TreeH()->GetEntry(i)
How to retrieve sdigits? 
	Sdigits stored in tree S with the branch of TClonesArray, all sdigits in a single TClonesArray
	So the tree has only one entry.
	One needs to say:
	-pRich->GetLoader()->LoadSDigits(); this one open file, get the tree and invoke AliRICH::SetTreeAddress()    
How to retrieve digits? 
	Digits stored in tree D with the 7 branches of TClonesArray, one per chamber, all digits of a given chamber in a single TClonesArray
	So the tree has only one entry.
	-One needs to say:
	  pRich->GetLoader()->LoadDigits(); this one opens file, gets the tree and invoke AliRICH::SetTreeAddress() which in turn corresponds 
          branches of the tree to the digits containers in memory. There are 7 containers, one per chamber, all of them belong to AliRICH.
	-Then one needs to take the tree entry (only one) to the memory:
          pRich->GetLoader()->TreeD()->GetEntry(0) 
	-Finally pRich->Digits(chamber_number) returns the pointer to TClonesArray of AliRICHdigit          
What are the debug methods avail:
        AliLog::SetGlobalDebugLevel(AliLog::kDebug)
How to get info for a given particle number:
	Header and Kinematics trees must be loaded, then possible to retrieve pointer to Stack of particles
	Int_t AliRunLoader::LoadHeader(); Int_t AliRunLoader::LoadKinematics()
	AliStack *AliRunLoader::Stack()
	TParticle *AliStack::Particle(tid)
	TParticle::Print()
How to deal with AliRunDigitizer:
	AliRunDigitizer::Exec() just call AliRunDigitizer::Digitize()	
What are the meanings of different VMC flags:         
	gMC->IsTrackAlive()
	gMC->IsTrackStop()
	gMC->IsTrackDisappeared()
How is sdigit produced from hit:
	Responsible method is AliRICH::Hits2SDigits
	One hit may affect one or more pads.
        Hit position is taken on the anode wires plane as the most of avalanche is developed there.
        This position is not directly available, track intersections with entrance and exit of amplification gap are only stored.
        So the position in the middle of the gap is calculated as average out of pHit->In() and pHit->Out() positions.
        Then, total charge collected for this hit is calculated by AliRICHParam::Hit2Qdc.    
        Area of disintegration is a list of pads affected by current hit. This is a parameter of Mathienson    
How to get pad number for a local position:
	use static TVector AliRICHParam::Loc2Pad(TVector2 position);
Why list of chambers belongs to AliRICHParam:

How to check if a given stack particle is primary:
	Stack is TClonesArray of TParticle. TParticle::GetMother(0) returns -1 if it's primary (no mother)         
How to loop over all possible object:         
  for(Int_t iEventN=0;iEventN < GetLoader()->GetRunLoader()->GetAliRun()->GetEventsPerRun();iEventN++){//events loop
    for(Int_t iEntryN=0;iEntryN < GetLoader()->TreeH()->GetEntries();iEntryN++){//TreeH loop
      GetLoader()->TreeH()->GetEntry(iEntryN);//get current entry (prim)  
      for(Int_t iHitN=0;iHitN<Hits()->GetEntries();iHitN++){//hits loop
        AliVHMPIDHit *pHit=(AliVHMPIDHit*)Hits()->At(iHitN);//get current hit 
        
      }//hits loop
    }//TreeH loop
  }//events loop