Example: TkrDigi Analysis

Note:  The following code was taken directly from RootTreeAnalysis in the RootAnalysis package stored in Offline's CVS repository. In this context, the variable "evt" is a DigiEvent object which was filled in RootTreeAnalysis::Go( ) method.  All file handling is done within the initialization of the RootTreeAnalysis object and is not shown here.

The complete documentation of the digiRootData library which defines DigiEvent and all digitization (detector) classes can be found at:

http://confluence.slac.stanford.edu/display/WB/digiRootData

Code snippet
Description
void RootTreeAnalysis::DigiTkr() {
    // Purpose and Method: Process on TKR digi event
   
    // The full collection of TkrDigis for this event
    const TObjArray* tkrDigiCol = evt->getTkrDigiCol();
    if (!tkrDigiCol) return;

    // Total number of TkrDigis for this event
    Int_t numTkrDigi = tkrDigiCol->GetEntries();

    Int_t totalHits = 0;

 		 Retrieve the full collection of TkrDigis from the DigiEvent object.

Then determine how many TkrDigis exist in this event.
   // Loop over all TkrDigis
    TIter tkrIter(tkrDigiCol);
    TkrDigi *tkr = 0;
    while (tkr = (TkrDigi*)tkrIter.Next()) {
      // Identify the tower and layer
      Int_t tower = tkr->getTower().id();
      Int_t layer = tkr->getBilayer();

      // get to ToT
      Int_t tot0 = tkr->getToT(0);
      Int_t tot1 = tkr->getToT(1);
    
      Int_t lastController0 = tkr->getLastController0Strip();

      // Returns the orientation of the strips
      GlastAxis::axis view = tkr->getView();

      UInt_t numHits = tkr->getNumHits();
      totalHits += numHits;
      // Loop through collection of hit strips for this TkrDigi
      UInt_t ihit;
      for (ihit = 0; ihit < numHits; ihit++) {
        // Retrieve the strip number
        Int_t stripNum = tkr->getStrip(ihit);
        if (layer == 5)
           ((TH1F*)GetObjectPtr("TKRSTRIPSLYR5"))->Fill(stripNum);

      }
    }

 		 Create a ROOT iterator (TIter) for looping over the full collection of TkrDigis, the while loop uses this iterator to control the looping, where tkr then contains the current TkrDigi* object.

Next determine the tower and layer number of the TkrDigi.

Retrieve the ToT from both ends.

Find which strip is the last one associated with controller zero.

Determine the orientation (view:  X or Y) of the TkrDigi.

Find the number of hits associated with this TkrDigi.

Then loop over all the strips and find their strip numbers, if we are on bilayer 5, update the TKRSTRIPSLYR5 histogram with the current strip number.
  
    ((TH1F*)GetObjectPtr("NUMTKRDIGI"))->Fill((Float_t)numTkrDigi);

    // example of filling a simple tree
    Float_t digiArr[2] = { (Float_t)numTkrDigi, (Float_t)totalHits };
    ((TNtuple*)GetObjectPtr("tkrDigiTup"))->Fill(digiArr);

    return;
}
 		 Fill the histograms and ntuples.

 

If you desire to download this piece of code - here is a full copy:

void RootTreeAnalysis::DigiTkr() {
    // Purpose and Method: Process on TKR digi event
   
    // The full collection of TkrDigis for this event
    const TObjArray* tkrDigiCol = evt->getTkrDigiCol();
    if (!tkrDigiCol) return;

    // Total number of TkrDigis for this event
    Int_t numTkrDigi = tkrDigiCol->GetEntries();
    Int_t totalHits = 0;

    // Loop over all TkrDigis
    TIter tkrIter(tkrDigiCol);
    TkrDigi *tkr = 0;
    while (tkr = (TkrDigi*)tkrIter.Next()) {
      // Identify the tower and layer
      Int_t tower = tkr->getTower().id();
      Int_t layer = tkr->getBilayer();

      // get to ToT
      Int_t tot0 = tkr->getToT(0);
      Int_t tot1 = tkr->getToT(1);
    
      Int_t lastController0 = tkr->getLastController0Strip();

      // Returns the orientation of the strips
      GlastAxis::axis view = tkr->getView();

      UInt_t numHits = tkr->getNumHits();
      totalHits += numHits;
      // Loop through collection of hit strips for this TkrDigi
      UInt_t ihit;
      for (ihit = 0; ihit < numHits; ihit++) {
        // Retrieve the strip number
        Int_t stripNum = tkr->getStrip(ihit);
        if (layer == 5) ((TH1F*)GetObjectPtr("TKRSTRIPSLYR5"))->Fill(stripNum);
      }
    }

    ((TH1F*)GetObjectPtr("NUMTKRDIGI"))->Fill((Float_t)numTkrDigi);

    // example of filling a simple tree
    Float_t digiArr[2] = { (Float_t)numTkrDigi, (Float_t)totalHits };
    ((TNtuple*)GetObjectPtr("tkrDigiTup"))->Fill(digiArr);

    return;
}