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Forum: Event and Track Management
Re: Sad GetPreStepPoint / GetPostStepPoint confusion (Lukas Schulte)
Date: 12 Nov, 2010
From: Marc Verderi <Marc Verderi>

Hello Lukas,

That is the typical trap with PreStepPoint and PostStepPoint : at your 
sensitive detector code level, ie when this code is called, the volume 
in which the step occured is the volume of the PreStepPoint (always). 
What happens with the PostStepPoint is that, when a particle has made a 
step in your PMT and is finishing this step on a point on the surface of 
the PMT -which is the PostStepPoint- then, the Geant4 convention is that 
the particle is not considered anymore to be inside your PMT, but is 
already considered to be in the next volume, the world volume in your 
case (if I understand well).

Regards,
Marc

Le 12/11/2010 15:45, Lukas Schulte a écrit :
> *** Discussion title: Event and Track Management
>
> Hi all!
>
> What happened to me is the following: My setup is basically a big block
> of ice with some identical PMTs placed by parameterized placement which
> are my sensitive detectors for Cherenkov photons. In my hits I want to
> store the copy no of the PMT that was hit. But when I tried to access
> and set the copy no via
>
> newHit->SetDOMNo(aStep->GetPostStepPoint()->GetPhysicalVolume()->GetCopyNo());
>
> I always got 0 because the physical volume that was returned was the
> world volume (I checked this by printing the name of the returned
> volume).
>
> After a lot of frustrating work, I changed GetPostStepPoint() into
> GetPreStepPoint() just to see what would happen, and suddenly everything
> worked perfectly.
>
> So my question is: is this a known bug or is there any purpose behind
> this? Or am I just too stupid?
>
> Cheers, Lukas
>
> -------------------------------------------------------------
> Visit this GEANT4 at hypernews.slac.stanford.edu message (to reply or unsubscribe) at:
> http://hypernews.slac.stanford.edu/HyperNews/geant4/get/eventtrackmanage/973.html

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1 Ok: Re: GetPreStepPoint / GetPostStepPoint confusion   (Lukas Schulte - 12 Nov, 2010)
1 More: Re: GetPreStepPoint / GetPostStepPoint confusion   (Gumplinger Peter - 16 Nov, 2010)
2 None: Re: GetPreStepPoint / GetPostStepPoint confusion   (michel maire - 17 Nov, 2010)
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