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Keywords: local global coordinate transform geometry
Forum: Geometry
Re: Question Local/Global coordinate transformation to establish primary vertex? (James Odegaard)
Re: Feedback Re: Local/Global coordinate transformation to establish primary vertex? (Gabriele Cosmo)
Date: 23 Jan, 2007
From: Jason Detwiler <Jason Detwiler>

Dear Gabriele,

I have the same question as James, except I don't have a moveable phantom. I'm trying to simulate radioactive sources and I don't want to have to calculate it's global position by hand in order to set the primary vertex.

I don't follow the logic in your reply to James. To the extent that one can write a description of a geometry in C++, the coordinate transformation of every volume is defined explicitly outside of a run. I can understand that in order to allow for various configurations from the same C++ code, a geometry isn't truly "defined" until a Construct stage, in which the flags are handled and a particular geometry is compiled. However, the notion that one "must" select some global point in order to find the location of a particular volume is, I think, absurd. At least by the end of the Construct stage, G4 should be able to search the geometry tree for a physical volume name and determine whether or not several copies of the same name exist. If someone wants to find the global position / rotation / transformation of a particular volume, they should be able to do so outside of tracking (e.g. in the primary vertex generation phase) by supplying a name and, if necessary, a copy number. Can't something like this be implemented somewhere in G4, so that users don't have to do this themselves all the time? I would think that in the majority of cases in which this would be useful, the user is going to be requesting some particular volume that is placed only once, so only those with lots of copies are going to need to do some work by hand (i.e. to find the copy number).

thanks, Jason

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1 More: Re: Local/Global coordinate transformation to establish primary vertex?   (Gabriele Cosmo - 24 Jan, 2007)
3 None: Re: Local/Global coordinate transformation to establish primary vertex?   (John Allison - 24 Jan, 2007)
1 Feedback: Re: Local/Global coordinate transformation to establish primary vertex?   (Jason Detwiler - 24 Jan, 2007)
(_ More: Re: Local/Global coordinate transformation to establish primary vertex?   (Gabriele Cosmo - 25 Jan, 2007)
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