Geometry
I have a generic point and I would like to know in which physical
volume I'm located in my detector geometry.
The best way of doing this is by invoking the G4Navigator. First
get a pointer of the navigator through the G4TransportationManager,
and then locate the point. i.e.
#include "G4TransportationManager.hh"
#include "G4Navigator.hh"
G4ThreeVector myPoint = ....;
G4Navigator* theNavigator = G4TransportationManager::GetTransportationManager()
->GetNavigatorForTracking();
G4VPhysicalVolume* myVolume = theNavigator->LocateGlobalPointAndSetup(myPoint);
Note
by using the navigator for tracking as shown above, the actual
particle gets also -relocated- in the specified position. Therefore,
if this information is needed during tracking time, in order to
avoid affecting tracking, you should either use an alternative
G4Navigator object (which you then assign to your world-volume),
or you access the information through the track or touchable as
specified in the FAQ for tracking and steps.
How can I access the daughter volumes of a specific physical volume?
Through the associated logical volume.
G4VPhysicalVolume* myPVolume = ....;
G4LogicalVolume* myLVolume = myPVolume->GetLogicalVolume();
for (G4int i=0; iGetNoDaughters(); i++)
myPVolume = myLVolume->GetDaughter(i);
How can I identify the exact copy-number of a specific physical volume
in my mass geometry? I tried with GetCopyNo() from my physical volume
pointer, but it doesn't seem to work!
The correct way to identify -uniquely- a physical volume in your mass
geometry is by using the touchables (see also section 4.1.5 of the
User's Guide for Application Developers), as follows:
G4Step* aStep = ..;
G4StepPoint* preStepPoint = aStep->GetPreStepPoint();
G4TouchableHandle theTouchable = preStepPoint->GetTouchableHandle();
G4int copyNo = theTouchable->GetCopyNumber();
G4int motherCopyNo = theTouchable->GetCopyNumber(1);
where Copy here stays for any duplicated instance of
a physical volume, either if it is a G4PVPlacement
(multiple placements of the same logical volume) or a
G4PVReplica/G4PVParameterised.
The method GetCopyNo() is meant to return only the
serial number of placements not duplicated in the geometry tree.
How can I determine the exact position in global coordinates in my mass
geometry during tracking and how can I convert it to coordinates local
to the current volume ?
You need again to do it through the touchables (see also section 4.1.5
of the User's Guide for Application Developers), as follows:
G4Step* aStep = ..;
G4StepPoint* preStepPoint = aStep->GetPreStepPoint();
G4TouchableHandle theTouchable = preStepPoint->GetTouchableHandle();
G4ThreeVector worldPosition = preStepPoint->GetPosition();
G4ThreeVector localPosition = theTouchable->GetHistory()->
GetTopTransform().TransformPoint(worldPosition);
where worldPosition here stays for the position related
to the world volume, while localPosition refers to the
coordinates local to the volume where the particle is currently placed.