As of Geant4 release 8.2, this functionality for defining parallel geometries is still in beta release. We appreciate your feedback.
Occasionally, it is not straightforward to define geometries for
sensitive detectors, importance geometries or envelopes for shower
parameterization to be coherently assigned to volumes in the
tracking (mass) geometry. The new parallel navigation functionality
allows the user to define more than one worlds simultaneously. The
new G4Transportation
process will see all worlds
simultaneously; steps will be limited by both boundaries of the
mass geometry and parallel geometries.
In a parallel world, the user can define volumes in arbitrary manner with sensitivity, regions, shower parameterization setups, and/or importance weight for biasing. Volumes in different worlds can overlap.
Here are restrictions to be considered for the parallel geometry:
Materials, production thresholds and EM field are used only from the mass geometry. Even if such physical quantities are defined in a parallel world, they do not affect to the simulation.
Although all worlds will be comprehensively taken care by the
G4Transportation
process for the navigation,
each parallel world must have its own process assigned to achieve
its purpose.
For example: in case the user defines a sensitive detector to a
parallel world, a process dedicated to the parallel world is
responsible to invoke this detector.
The G4SteppingManager
treats only the detectors in the mass geometry. For this case of
detector sensitivity defined in a parallel world, a
G4ParallelWorldScoringProcess
process must be defined
in the physics list (see
Section 4.7.3).
A parallel world should be defined in the Construct()
virtual method of the user's class derived from the abstract base
class G4VUserParallelWorld.
Example 4.17. An example header file of a concrete user parallel world class.
#ifndef MyParallelWorld_h #define MyParallelWorld_h 1 #include "globals.hh" #include "G4VUserParallelWorld.hh" class MyParallelWorld : public G4VUserParallelWorld { public: MyParallelWorld(G4String worldName); virtual ~MyParallelWorld(); public: virtual void Construct(); }; #endif
A parallel world must have its unique name, which should be set
to the G4VUserParallelWorld
base class as an argument of
the base class constructor.
The world physical volume of the parallel world is provided by
the G4RunManager
as a clone of the mass geometry. In the
Construct()
virtual method of the user's class, the
pointer to this cloned world physical volume is available through
the GetWorld()
method defined in the base class. The user
should fill the volumes in the parallel world by using this
provided world volume. For a logical volume in a parallel world,
the material pointer can be NULL
. Even if specified a
valid material pointer, it will not be taken into account by any
physics process.
Example 4.18. An example source code of a concrete user parallel world class.
#include "MyParallelWorld.hh" #include "G4LogicalVolume.hh" #include "G4VPhysicalVolume.hh" #include "G4Box.hh" #include "G4PVPlacement.hh" MyParallelWorld::MyParallelWorld(G4String worldName) :G4VUserParallelWorld(worldName) {;} MyParallelWorld::~MyParallelWorld() {;} void MyParallelWorld::Construct() { G4VPhysicalVolume* ghostWorld = GetWorld(); G4LogicalVolume* worldLogical = ghostWorld->GetLogicalVolume(); // place volumes in the parallel world here. For example ... // G4Box * ghostSolid = new G4Box("GhostdBox", 60.*cm, 60.*cm, 60.*cm); G4LogicalVolume * ghostLogical = new G4LogicalVolume(ghostSolid, 0, "GhostLogical", 0, 0, 0); new G4PVPlacement(0, G4ThreeVector(), ghostLogical, "GhostPhysical", worldLogical, 0, 0); }
In case the user needs to define more than one parallel worlds,
each of them must be implemented through its dedicated class. Each
parallel world should be registered to the mass geometry class
using the method RegisterParallelWorld()
available through
the class G4VUserDetectorConstruction
. The registration
must be done -before- the mass world is registed to the
G4RunManager
.
Example 4.19.
Typical implementation in the main()
to define a parallel
world.
// RunManager construction
//
G4RunManager* runManager = new G4RunManager;
// mass world
//
MyDetectorConstruction* massWorld = new MyDetectorConstruction;
// parallel world
//
massWorld->RegisterParallelWorld(new MyParallelWorld("ParallelScoringWorld"));
// set mass world to run manager
//
runManager->SetUserInitialization(massWorld);
Any kind of G4VSensitiveDetector
object can be defined
in volumes in a parallel world, exactly at the same manner for the
mass geometry. Once the user defines the sensitive detector in a
parallel world, he/she must define a process which takes care of
these detectors.
The G4ParallelWorldScoringProcess
is the class provided
for this purpose. This process must be defined to all kinds of
particles which need to be "detected". This process must be ordered
just after G4Transporation
and prior
to any other physics processes. The name of the parallel
world where the G4ParallelWorldScoringProcess
is
responsible for, must be defined through the method
SetParallelWorld()
available from the class
G4ParallelWorldScoringProcess
. If the user has more than
one parallel worlds with detectors, for each of the parallel
worlds, dedicated G4ParallelWorldScoringProcess
objects
must be instantiated with the name of each parallel world
respectively and registered to the particles.
Example 4.20.
Define G4ParallelWorldScoringProcess
.
// Add parallel world scoring process // G4ParallelWorldScoringProcess* theParallelWorldScoringProcess = new G4ParallelWorldScoringProcess("ParaWorldScoringProc"); theParallelWorldScoringProcess->SetParallelWorld("ParallelScoringWorld"); theParticleIterator->reset(); while( (*theParticleIterator)() ) { G4ParticleDefinition* particle = theParticleIterator->value(); if (!particle->IsShortLived()) { G4ProcessManager* pmanager = particle->GetProcessManager(); pmanager->AddProcess(theParallelWorldScoringProcess); pmanager->SetProcessOrderingToLast(theParallelWorldScoringProcess, idxAtRest); pmanager->SetProcessOrdering(theParallelWorldScoringProcess, idxAlongStep, 1); pmanager->SetProcessOrderingToLast(theParallelWorldScoringProcess, idxPostStep); } }
At the end of processing an event, all hits collections made for
the parallel world are stored in G4HCofThisEvent
as well
as those for the mass geometry.