Fix the length of the Imaging Barrel ECAL about epic HOT 2 CLOSED

@wdconinc, I could assign in ecal_barrel_interlayers.xml the length z to abs(z_min) + z_max from the database, but I'm not sure what to do with the offset (i.e., how much calo is shifted from (0,0,0)). I could set just (z_min + z_max)/2, but it will be then independent from the global offset set in definitions.xml

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To be honest, I have no idea what the offset means in the detector parameter table. In the geometry, and for barrel detectors, it is whether the detector's center should be shifted from the interaction point or not. That is what EcalBarrel_offset is set to, for both calorimeter options: assuming EcalBarrel_zmin and EcalBarrel_zmax, what is the corresponding shift.

I think in your case, I'd probably recommend to simply use an offset of zero (ignoring what is defined by the definitions file). You could then use the length to be 2*min(EcalBarrel_zmin,EcalBarrel_zmax) and it would always fit. Or you could just define a local offset as you write, as (EcalBarrel_zmin - EcalBarrel_zmax) / 2.

There is no requirement to use all the dimensions set in the definitions file, just that when you go outside the volume that is defined there it is going to be your fault ;-)

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