Problem 123

Summary:	Changing position in G4PrimaryVertex
Product:	Geant4	Reporter:	V.Hejny
Component:	event	Assignee:	Makoto.Asai
Status:	RESOLVED FIXED
Severity:	enhancement
Priority:	P2
Version:	2.0
Hardware:	All
OS:	All

Description V.Hejny 2000-07-07 01:45:18 CEST

In the current implementation there is no SetPosition() member function.
In our detector setup various target positions and beam angles (with respect
to the detector) are used. Therefore this position offset and the rotation
of the primary events have to be added in the generator itself.
To allow a modular design of code and to have the ability to use standard
primary generators without changes, it would be very helpful to have this
additional function. The changes in position and direction then could be
done later on.

Comment 1 Makoto.Asai 2000-07-07 09:04:59 CEST

It already exists with the name SetParticlePosition() in
G4ParticleGun.

 I guess you want to have more than one primary particles
starting at a point different to each other. Please note
that G4PrimaryParticle does not have position information
but G4PrimaryVertex which has primary particles has it.
In other words, a primary vertex has primary particles
which share the same vertex position. Thus it completely
violates the concept of G4PrimaryVertex to have SetPosition()
method. Please note that G4Event object can have one or
MORE G4PrimaryVertex objects.

 I advise you to make your own primary generator class which
generates many vertices and sets them to the given G4Event
object. But in case you want to utilize G4ParticleGun, do the
following.

void MyGeneratorAction::GeneratePrimaries(G4Event* anEvent)
{
  for(int i=0;i<numberOfPrimaries;i++)
  {
    particleGun->SetPrimaryParticlePosition(randomizedPosition);
    ..... any other set method invokation here .....
    particleGun->GeneratePrimaryVertex(anEvent);
  }
}

 Anyway, this report does not contain any problem in Geant4 code.

Comment 2 Makoto.Asai 2000-07-28 21:32:59 CEST

Fixes are in the most recent reference tag of geant4-02-00-ref-01.