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Forum: Event and Track Management
Re: None PrsStepPoint vs. PostStepPoint (Andreas)
Date: 09 Dec, 2003
From: Marc Verderi <Marc Verderi>

Hi,

> If I understand the Geant4 manual correctly, then tracking consists of
> steps. A step is defined by a start point (PreStepPoint) and a stop
> point (PostStepPoint). When I have a discrete processes, like Compton
> scattering, the PostStepPoint is defined by the smallest physical
> interaction length of these processes. This means if Compton scattering
> defines this smallest physical interaction length a Compton scattering
> happens at the PostStepPoint, correct?

Yes.

> Now in the most examples, which are included in G4, e.g. the GammaRayTel
> example, in the class GammaRayTelCalorimeterSD, ProcessHits(...), the
> position of a hit is set via:
> 
> l 129: CalorimeterHit->SetPos(aStep->GetPreStepPoint()->GetPosition());
> 
> Shouldn't it be set via GetPostStepPoint?? Do I misunderstand something?

This is a different issue. Assume you have a calorimeter made of cells, if
the step is limited by the physics, using PreStepPoint or PostStepPoint to
get the geometrical information about the current cell will not make
difference. On the other hand, if the step is limited by the _geometry_
the PostStepPoint geometrical information will be updated with geometrical
information of the cell in which the track is _entering_. You must thus
always use the PreStepPoint to be garanteed that you assign the energy
deposition to the volume in which the step started and occured.

Cheers,
Marc


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1 None: Re: PreStepPoint vs. PostStepPoint   (Andreas - 10 Dec, 2003)
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