Differentiating Events in Physical Volumes

[Brian_Yanoff]

I found this exchange from a month ago that describes my problem and a suggested solution:

Identification of unique physical volumes with IDs

Dear All, We have an application where there are several photon detectors, consisting of some plastic scintillators opticazlly coupled with SiPMs. Because of this we have only 6 physical volumes representing the SiPMs coupled to each scintillator, which in turn is placed 8 times, hence we have 48 total actual placements of the SiPMs. What we would like to do is to assign a unique ID to each SiPM PV at the start of the run (after the geometry has been closed), and at tracking time, we would like…

I was hoping that the instanceID was a unique way to identify a PV. My approach was check the chain of copy numbers the first time each PV is encountered in my UserSteppingAction() and to store the instanceID as the key in a map for easy checking of future events.

Unfortunately, it seems each PV does not get a unique ID. In fact it seems the PV instances are not stored individually by GEANT4. So it is necessary to follow the stack of nested volumes by using (for example) touchable_handle->GetVolume(stack_level) and checking the copy number of all the parent volumes

I will shift any further discussion over to the previous thread.