TGeoManager node identifier questions

Hello All,

I'm using TGeoManager to handle the T2K near detector geometries, and I'm trying to chase down a problem being reported by collaboration members with the use of TGeoNode identifiers in our code.

My questions:

1. Is it a safe assumption that a particular value of a node ID will always refer to the same TGeoNode in a geometry, even when the geometry has been written and re-read? [The geometry *shouldn't* be changing]
2. If it's not a save assumption that a node ID will uniquely specify a particular TGeoNode, what is the correct way to specify a particular volume?

In my current code, I'm using the TGeoNode id's as an identifier for the volume element corresponding to a hit so that the class is generically

class Hit {

   int fNodeId;
   float fTime;
   float fCharge;
};

The geometry for a specific set of events is then saved in the file with a tree of events. During analysis, the geometry is first read from an input file, and then re-saved in an output file. [This a temporary situation. Eventually I expect to save the geometries separately].

I've been getting reports from collaboration members, that the TGeoNode associated with a node id is changing between files and as a result hits are being assigned to the wrong geometry element. I personally haven't been able to reproduce the problem, and before I spend a lot of time debugging my code, I would like to check ROOT's intended behavior.

Thanks,
Clark

-- 
Clark McGrew, Asst. Prof., Physics and Astronomy, University at Stony Brook
<clark.mcgrew_at_stonybrook.edu>   631-632-8299