11

Usage of ROOT Usage of ROOT geometry with geometry with

GEANT4GEANT4

Andrei Gheata, Mihaela Gheata Andrei Gheata, Mihaela Gheata (CERN/ALICE)(CERN/ALICE)

ROOT 2007, March 26-28ROOT 2007, March 26-28

22

OutlineOutline

MotivationMotivation

TGeo@VMCTGeo@VMC

ImplementationImplementation

Integration in GEANT4 VMCIntegration in GEANT4 VMC

Ongoing tests & validation Ongoing tests & validation procedureprocedure

Preliminary resultsPreliminary results

ConclusionsConclusions

33

MotivationMotivationRunning GEANT4 simulation with ROOT geometry Running GEANT4 simulation with ROOT geometry modellermodeller

The only way to run full ALICE simulation with G4The only way to run full ALICE simulation with G4 ROOT TGeo is a multi-purpose geometry engine independent ROOT TGeo is a multi-purpose geometry engine independent

from any MC frameworkfrom any MC frameworkDeveloped by ALICE offline in collaboration with ROOT teamDeveloped by ALICE offline in collaboration with ROOT teamOptimized for Optimized for navigation performancenavigation performance in detector geometries in detector geometriesAdditional features:Additional features: checking tools, visualization, alignment checking tools, visualization, alignment tools, ROOT persistency, …tools, ROOT persistency, …

Having an external geometry description as alternative Having an external geometry description as alternative to MC-embedded modelsto MC-embedded models

Geometry is used a lot outside the simulation frameworkGeometry is used a lot outside the simulation framework Having 3 transport MC’s interfaced with Having 3 transport MC’s interfaced with TGeoTGeo Important component in making a simulation application Important component in making a simulation application

survive outside the specific MC framework survive outside the specific MC framework → → VVirtual irtual MMonte onte CCarloarlo

44

Can take advantage of

graphics accelerators

Automatic illegal overlap detection

Run-time volume assemblies

Misalignment of ideal geometry

55

The Virtual Monte Carlo ideaThe Virtual Monte Carlo idea

Make user application independent of Make user application independent of specific transport codespecific transport code

GEANT3, GEANT4 and FLUKAGEANT3, GEANT4 and FLUKA supported so far supported so far Keeping the Keeping the SAMESAME definition for geometry, I/O definition for geometry, I/O

formats and detector response simulationformats and detector response simulationAllows running the same application with different Allows running the same application with different MC’sMC’s

VMC decouples user code from the concrete VMC decouples user code from the concrete MC MC

Provides MC-independent API for :Provides MC-independent API for :Geometry definitionGeometry definition, setting up physics, setting up , setting up physics, setting up cuts, handling particle stack … cuts, handling particle stack … (features very (features very different from one MC to another)different from one MC to another)Querying MC machine state and kinematics during Querying MC machine state and kinematics during stepping callbacks stepping callbacks (very similar mechanisms)(very similar mechanisms)

66

VMC conceptVMC concept

UserCode

VMC

GEANT4 VMC

ParticlesHits

GEANT4

GEANT3

Output

FLUKA VMC

FLUKA

Input

GEANT3 VMC

77

VMC designVMC design

Communication only via Communication only via interfacesinterfaces

TVirtualMCApplicationTVirtualMCApplication

TVirtualMCStackTVirtualMCStack

TVirtualMCTVirtualMC

TVirtualMCDecayerTVirtualMCDecayer

UserApplicationUserApplication

UserStackUserStack TGeant3TGeant3 Pythia6Pythia6

TGeant4TGeant4

TFlukaTFluka

88

Geometry in VMCGeometry in VMCInitially the idea was to keep a unique VMC API for Initially the idea was to keep a unique VMC API for geometry constructiongeometry construction

Fill different native geometries with calls Fill different native geometries with calls à la GEANT3à la GEANT3 VMC VMC provides this API supporting some common provides this API supporting some common

featuresfeaturesGeometry models are quite different for different Geometry models are quite different for different MC’sMC’s

There is a common denominator G3/G4There is a common denominator G3/G4 FLUKA geometry completely differentFLUKA geometry completely different What do we do to provide the geometry that transport What do we do to provide the geometry that transport

MC wants?MC wants? There are several geometry convertors, working to a There are several geometry convertors, working to a certain extentcertain extent

g2root (G3 g2root (G3 → TGeo), g3tog4 (G3 → G4)→ TGeo), g3tog4 (G3 → G4) Most advanced: Most advanced: VGMVGM (G4 ↔ XML (AGDD, GDML) ↔ TGeo) (G4 ↔ XML (AGDD, GDML) ↔ TGeo)

http://ivana.home.cern.ch/ivana/VGM.html

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Geometry definition and Geometry definition and TGeoTGeo

ROOT ROOT geometrygeometry

I/OI/OGeometry.rootGeometry.rootGeometry.CGeometry.C

Geometry.xmlGeometry.xml

User codeUser code

GEANT3 GEANT3 geometrygeometry g2rootg2root

GEANT4 GEANT4 geometrygeometry

VGMVGM

1010

External geometry – a External geometry – a coherent solutioncoherent solution

Experience shows that all conversions have Experience shows that all conversions have serious limitationsserious limitations

Not all features can be convertedNot all features can be convertedMatters a bit when results get different due to Matters a bit when results get different due to geometry differencesgeometry differencesMatters a lot when not all geometry can be convertedMatters a lot when not all geometry can be converted

One of the reasons TGeo was developedOne of the reasons TGeo was developed Navigation speed was a priorityNavigation speed was a priority

Even behind an interface TGeo gains ~8% in Even behind an interface TGeo gains ~8% in simulation speed in case of ALICE compared to simulation speed in case of ALICE compared to GEANT3 nativeGEANT3 native

Even more in case of non-optimized geometriesEven more in case of non-optimized geometries

In case of FLUKA there were no other way In case of FLUKA there were no other way out for running ALICE simulationout for running ALICE simulationWe needed to make all supported MC transport We needed to make all supported MC transport engines able to work directly with TGeoengines able to work directly with TGeo

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TGeo@VMC conceptTGeo@VMC concept

TGeo as navigator for all TGeo as navigator for all transport MC’stransport MC’s

UserCode

VMC

GEANT4 VMC

ParticlesHitsGEANT4

GEANT3

Output

FLUKA VMC FLUKA

Input

GEANT3 VMC

TGeo

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Navigation interfacesNavigation interfaces

Interface mechanisms providing geometry Interface mechanisms providing geometry answers to queries posted by transportationanswers to queries posted by transportation

Thin layer based on wrapper functions/ virtual Thin layer based on wrapper functions/ virtual methods “spying” the geometry channelsmethods “spying” the geometry channels

GEANT3 – Geant3TGeo interfaceGEANT3 – Geant3TGeo interface ValidatedValidated

FLUKA – Fluka MC Geometry interfaceFLUKA – Fluka MC Geometry interface ValidatedValidated

GEANT4 – GEANT4 – G4ROOTG4ROOT interface interface 2 modes supported:2 modes supported:

Via VMCVia VMCWith a native G4 application With a native G4 application with geometry defined with geometry defined via Root (or converted to ROOT structures)via Root (or converted to ROOT structures)

Ongoing testsOngoing tests

1313

Geometry access during MC Geometry access during MC transportationtransportation

GEANT3 GEANT3 transporttransport

GEANT4GEANT4transporttransport

FLUKAFLUKAtransporttransport

GEANT4 GEANT4 geometrygeometry

ROOT ROOT geometrygeometry

TGeant3TGeoTGeant3TGeoNavigation wrappersNavigation wrappers

G4ROOTG4ROOTNavigation interfaceNavigation interface

TFlukaMCGeometryTFlukaMCGeometryNavigation wrappersNavigation wrappers

G4NavigatorG4NavigatorNavigation interfaceNavigation interface

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How the navigation validation was How the navigation validation was done…done…

FLUKA electron transport in thin layers

•AlAuAl FLUKA native example

•1000 electrons at 1 MeV, EM cascades

• Same final random number after simulations with FLUKA native and TFluka

•The same for all 3 tested examples

1515

Implementation of G4 Implementation of G4 navigation interfacenavigation interface

GEANT4 transportation as well as GEANT4 transportation as well as several physics processes need real G4 several physics processes need real G4 geometry objectsgeometry objects Sensitive detectors, user limits, optical Sensitive detectors, user limits, optical

properties are connected to properties are connected to G4LogicalVolumeG4LogicalVolume

Need to provide geometry states that are Need to provide geometry states that are understandable by G4understandable by G4

TG4RootDetectorConstructionTG4RootDetectorConstruction : : public public G4VUserDetectorConstructionG4VUserDetectorConstruction

Having a Having a TGeoTGeo geometry in memory geometry in memory ((TGeoManagerTGeoManager) is a prerequisite) is a prerequisite

Construct()Construct() method building up a method building up a G4G4 hierarchy corresponding to hierarchy corresponding to TGeoTGeo one one

1616

Implementation – building the Implementation – building the structurestructure

Special user detector construction Special user detector construction registered to registered to G4RunManagerG4RunManager

Construct()Construct() method called during initialization method called during initialization G4 logical hierarchy created, but no optimization G4 logical hierarchy created, but no optimization

structures (voxels) neededstructures (voxels) needed

TGeoNode TGeoVolume

TGeoNode TGeoNodeTGeoNodeTGeoNodeTGeoVolume TGeoVolume

TGeoNode TGeoVolume TGeoNodeTGeoNodeTGeoNodeTGeoNodeTGeoNodeTGeoVolume

G4PhysicalVolume

G4LogicalVolume

G4PhysicalVolume

G4PhysicalVolumeG4Physical

VolumeG4Physical

Volume

G4LogicalVolume

G4LogicalVolume

G4PhysicalVolume

G4LogicalVolume

G4PhysicalVolumeG4Physical

VolumeG4Physical

VolumeG4Physical

VolumeG4Physical

VolumeG4LogicalVolume

Construct()

Adding only ~9MB in memory, including libs

For ALICE TGeo structures sum up to ~17MB

(optimizations included)Persistent size < 2MB

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Implementation – navigation Implementation – navigation interfaceinterface

G4NavigatorG4Navigator – base class for GEANT4 – base class for GEANT4 navigationnavigation Very useful help from GEANT4 team in Very useful help from GEANT4 team in

changing some methods/data members changing some methods/data members qualifications – made the implementation qualifications – made the implementation easiereasier

TG4RootNavigatorTG4RootNavigator : public : public G4NavigatorG4Navigator Implementing methods for locating a point, Implementing methods for locating a point,

finding the distance to next boundary, finding the distance to next boundary, computing the safety distance and the computing the safety distance and the normal to a crossed surface normal to a crossed surface

1818

Implementation – connecting Implementation – connecting to G4 geometryto G4 geometry

Several user-defined objects need to be Several user-defined objects need to be connected to the newly-created G4 connected to the newly-created G4 volumesvolumes Sensitive detectors manager, user limits, …Sensitive detectors manager, user limits, … G4 geometry objects are mapped to TGeo G4 geometry objects are mapped to TGeo

ones and accessible from ones and accessible from TG4RootDetectorConstructionTG4RootDetectorConstruction

TVirtualUserPostDetConstructionTVirtualUserPostDetConstruction Pure virtual plugin classPure virtual plugin class Initialize()Initialize() user method to implement for user method to implement for

connecting additional objects to geometry connecting additional objects to geometry

1919

Interface managementInterface management

Root-ified manager class allowing Root-ified manager class allowing connection to G4connection to G4 TG4RootNavMgrTG4RootNavMgr : public : public TObjectTObjectAdditional class interfacing TGeo Additional class interfacing TGeo shapes as G4 solids: shapes as G4 solids: TG4RootSolidTG4RootSolid : public G4VSolid : public G4VSolid Navigation methods of solids not used in Navigation methods of solids not used in

the interfacethe interfaceNavigation entirely redirected to TGeoNavigation entirely redirected to TGeo

Possibility to use directly TGeoShape Possibility to use directly TGeoShape objects in a native G4 geometryobjects in a native G4 geometry

Few methods not yet implemented at this levelFew methods not yet implemented at this levelThe feature will be supported by the interfaceThe feature will be supported by the interface

2020

How it worksHow it works

TGeoManager

pGeom

Import()

TG4RootNavigator

G4Navigator

TVirtualUserPostDetConstruction

MyPostDetConstruction

pPostDC

pMgr->Initialize(pPostDC)

TG4RootDetectorConstruction

G4VUserDetectorConstruction

pDC

::Initialize(pDC)

::Initialize(pPostDC)

TGeoNode

G4VPhysicalVolume

pMgr->ConnectToG4()

::SetNavigatorForTracking()

::ActivateNavigator()

G4TransportationManager

TG4RootNavMgr

TG4RootNavMgr::GetInstance(pGeom)

pMgr

G4RunManager

new G4RunManager()

Construct()

MyGeometry.root

Inputs

2121

AvailabilityAvailability

Interface introduced in ROOT as Interface introduced in ROOT as G4ROOTG4ROOT module module README file describing how to compile README file describing how to compile

the modulethe module$ROOTSYS/configure --enable-g4root $ROOTSYS/configure --enable-g4root

Available starting from:Available starting from:ROOT version 5.14ROOT version 5.14GEANT4 version 8.2GEANT4 version 8.2

Direct comparison tests between Direct comparison tests between normal/g4root navigation performed normal/g4root navigation performed on modified versions of GEANT4 on modified versions of GEANT4 novice examplesnovice examples One (N06) included in G4root/testOne (N06) included in G4root/test

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Example: optical photon Example: optical photon transporttransport

Modified version of Novice example Modified version of Novice example N06N06Adds few files to N06 onesAdds few files to N06 ones Demonstrating the usage of the interfaceDemonstrating the usage of the interfaceComparing results when running with Comparing results when running with G4 or G4ROOT navigationG4 or G4ROOT navigation Geometries used in the 2 cases equivalentGeometries used in the 2 cases equivalent Same initial random seedSame initial random seed Comparison plots of XY coordinates at Comparison plots of XY coordinates at

boundary crossingsboundary crossingsShowing a graphical output of tracks Showing a graphical output of tracks over the geometryover the geometry

2323

Test outputTest output Bubble in tank

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Support for TGeo navigation in Support for TGeo navigation in GEANT4 VMCGEANT4 VMC

Support for TGeo geometrySupport for TGeo geometry Since v1.0 (Jul 2003) - via roottog4 converterSince v1.0 (Jul 2003) - via roottog4 converter From v1.6 (Mar 2005) – via VGM (Virtual Geometry From v1.6 (Mar 2005) – via VGM (Virtual Geometry

Model, the generalized version of roottog4 Model, the generalized version of roottog4 converter)converter)

Version 2.0 (December 2006) – direct use of TGeo Version 2.0 (December 2006) – direct use of TGeo geometry in Geant4 via G4Rootgeometry in Geant4 via G4Root

Several tests for consistency already done or Several tests for consistency already done or ongoingongoing

Tested on the VGM geometry tests & VMC examplesTested on the VGM geometry tests & VMC examplesIdentical results for tracking with geantinos for basic Identical results for tracking with geantinos for basic shapesshapesSmall differences for complex geometries to be Small differences for complex geometries to be investigated with VGM testbedinvestigated with VGM testbed

By Ivana Hrivnacova, By Ivana Hrivnacova, IPN OrsayIPN Orsay

2525

GEANT4-VMC run GEANT4-VMC run configurationconfiguration

User has a choice to define geometry via:User has a choice to define geometry via: VMC – GEANT3 style VMC – GEANT3 style TGeo geometry modeller in ROOTTGeo geometry modeller in ROOT Geant4 - standard Geant4 detector construction class Geant4 - standard Geant4 detector construction class

User can choose to use G4 native or G4ROOT User can choose to use G4 native or G4ROOT navigation. navigation. Selection in the run configuration object instantiated Selection in the run configuration object instantiated in the configuration macroin the configuration macro

VMCtoGeant4 VMCtoGeant4 VMCtoRoot VMCtoRoot RootToGeant4RootToGeant4 Root Root Geant4Geant4

The first word means geometry input, the second The first word means geometry input, the second one navigator to be usedone navigator to be used

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GEANT4 VMC run GEANT4 VMC run configurationconfiguration

Geant4

Geant4geometry

TGeo geometry

User codevia

VMC

G3toG4TGeoMC

Geometry

G4Root

User codevia

TGeo

VGM

With both With both geometry geometry definition via definition via VMC and TGeo VMC and TGeo user has a user has a possibility to possibility to run with both run with both G4 native and G4 native and G4Root G4Root navigationnavigation

G4Navigator

Geant4 VMC connects automatically necessary packages and activates selected navigator

2727

Using G4ROOT from a native Using G4ROOT from a native G4 application G4 application

Can this be done ?Can this be done ? Yes, an example of use G4Root with G4 native application Yes, an example of use G4Root with G4 native application

with geometry defined via Root is provided with G4Root with geometry defined via Root is provided with G4Root packagepackage

The sensitive detectors and other user are connected to The sensitive detectors and other user are connected to geometry in a bit different way as it is demonstrated on geometry in a bit different way as it is demonstrated on the example the example objects to the generated G4LogicalVolume objects to the generated G4LogicalVolume objectsobjects

Possibility to convert G4 geometry to TGeoPossibility to convert G4 geometry to TGeoMost G4 geometry features existing also in TGeoMost G4 geometry features existing also in TGeoProcedure not yet automatedProcedure not yet automatedCould be avoided in future by keeping the original G4 Could be avoided in future by keeping the original G4 geometrygeometry

Does it worth trying ?Does it worth trying ? Yes, a minimal working setup for checking performance Yes, a minimal working setup for checking performance

issues can be put together quite easilyissues can be put together quite easilyCan give fast an idea if the interface usage can save some Can give fast an idea if the interface usage can save some CPUCPU

2828

Validation procedureValidation procedure

Testing with G4 native examplesTesting with G4 native examples Comparing results given by G4/G4ROOT navigationComparing results given by G4/G4ROOT navigation Equivalent TGeo geometries with G4 onesEquivalent TGeo geometries with G4 ones Done for some Novice examplesDone for some Novice examples

Most give identical results (N01, N03, N05, N06)Most give identical results (N01, N03, N05, N06)Some differences (random seed change) observed for Some differences (random seed change) observed for N02N02

Understood – due to different isotropic safety valuesUnderstood – due to different isotropic safety values

Tests within VGM test setups Tests within VGM test setups Checking various geometry configurations and Checking various geometry configurations and

different geometry featuresdifferent geometry featuresBoolean operations, divisions, replicas, …Boolean operations, divisions, replicas, …

Revealed few bugs in the navigation interface that Revealed few bugs in the navigation interface that were fixedwere fixed

More complex geometries to be compared – More complex geometries to be compared – extremely performant debugging tool !extremely performant debugging tool !

2929

Validation procedure (cont)Validation procedure (cont)

Tests with GEANT4 VMCTests with GEANT4 VMC Novice examples with either G4 or G4ROOT Novice examples with either G4 or G4ROOT

navigation available in G4_VMC navigation available in G4_VMC Comparisons with physics switched on/off to be done Comparisons with physics switched on/off to be done

for real experiments for real experiments ALICE was the first candidateALICE was the first candidateFurther testing/feedback expected from other VMC Further testing/feedback expected from other VMC users: users:

MINOS, CBM/PANDA@GSI/FAIRMINOS, CBM/PANDA@GSI/FAIR Performance comparisons for complex geometriesPerformance comparisons for complex geometries

TGeo navigation performance demonstrated against TGeo navigation performance demonstrated against GEANT3 (faster by 8%)GEANT3 (faster by 8%)Realistic timing comparisons can only be done for Realistic timing comparisons can only be done for realistic cases (example geometries much too simple)realistic cases (example geometries much too simple)Tests with ALICE TPC and MUON detectors already Tests with ALICE TPC and MUON detectors already done !done !Performance-wise optimizations not yet done for the Performance-wise optimizations not yet done for the interfaceinterface

3030

Tests and benchmarksTests and benchmarks

AliRoot – ALICE offline frameworkAliRoot – ALICE offline framework Using VMC for simulationUsing VMC for simulation

GEANT4_VMC – the interface to GEANT4GEANT4_VMC – the interface to GEANT4 VMC API used to define VMC API used to define physicsphysics and in a similar and in a similar

way for all MC’sway for all MC’sNo special ALICE physics list yetNo special ALICE physics list yetCuts equivalent to G3 onesCuts equivalent to G3 ones

VMC+TGeo used to define VMC+TGeo used to define detector geometrydetector geometryTGeo used directly via TGeo used directly via g4rootg4rootGeometry converted with VGM to a Geometry converted with VGM to a G4 geometryG4 geometry

Works for part of ALICEWorks for part of ALICE Comparisons made with Comparisons made with geantinos and full physicsgeantinos and full physics

Step distribution comparisons, profiling for different Step distribution comparisons, profiling for different geometry configurations (done)geometry configurations (done)Comparisons at the level of signal (digitization) and Comparisons at the level of signal (digitization) and tracking/reconstruction outputs (ongoing)tracking/reconstruction outputs (ongoing)

Comparisons between different MC’s – to be doneComparisons between different MC’s – to be done

3131

ALICE TPC testsALICE TPC tests

Main tracking Main tracking detector of ALICEdetector of ALICEComparisons with Comparisons with 100K geantinos in 100K geantinos in 44ππComparisons with Comparisons with physics ONphysics ON

5K parameterized 5K parameterized HIJING (0.5-999 GeV)HIJING (0.5-999 GeV)

L3 field ONL3 field ON

Profiling done for Profiling done for 500 tracks on both 500 tracks on both navigation setupsnavigation setups

3232

100K geantinos TPC100K geantinos TPC

220 sec.220 sec. 225 sec.225 sec.

3333

TPC – 5K particles, physics + TPC – 5K particles, physics + fieldfield

1013 sec.1013 sec. 2144 sec.2144 sec.

??????

3434

Isotropic safetyIsotropic safety

safety

3535

ProfilingProfiling1165042 steps

1152653 stepsG4ROOTG4ROOT G4G4

G4RootNavigator::ComputeStep 1143536 calls (25.9%)

G4Navigator::ComputeStep 2261101(62.8%)

G4PropagatorInField::IntersectChord

Multiple scattering processMultiple scattering process

CONCLUSION: Accurate isotropic safety computation can highly improve simulation time in an environment where low energy charged particles (curling tracks) need to be transported in magnetic field over considerable distances.

3636

ALICE MUON ARMALICE MUON ARM

10K geantinos 10K geantinos within within acceptanceacceptance500 HIJING 500 HIJING parameterized parameterized (0.5-999 GeV)(0.5-999 GeV)Step length Step length distributionsdistributionsMost particles Most particles stopped within stopped within the absorberthe absorber

3737

10 K geantinos MUON10 K geantinos MUON

27 sec.27 sec. 26.4 sec.26.4 sec.

3838

SummarySummary

A prototype of the navigation interface A prototype of the navigation interface of GEANT4 using TGeo geometry of GEANT4 using TGeo geometry availableavailable Starting with ROOT v5.14, GEANT4 v8.2Starting with ROOT v5.14, GEANT4 v8.2 Interface used by GEANT4_VMC v2.0Interface used by GEANT4_VMC v2.0The interface can be used ‘as is’ by G4-The interface can be used ‘as is’ by G4-based applications with a TGeo based applications with a TGeo geometry representation and minor geometry representation and minor additions (example available)additions (example available)Most benefits by usage via VMCMost benefits by usage via VMC User application kept unchanged for 3 MC’sUser application kept unchanged for 3 MC’s Navigation based on the same geometry Navigation based on the same geometry

allow reliable comparisons for the MC allow reliable comparisons for the MC predictionspredictions

3939

SummarySummary

Comparative tests in realistic ALICE Comparative tests in realistic ALICE setups show consistency between setups show consistency between GEANT4 and ROOT geometriesGEANT4 and ROOT geometries Still some differences at the level of 10 Still some differences at the level of 10

per million to be investigatedper million to be investigated Computation of the distance to next Computation of the distance to next

boundary at boundary at same level of performancesame level of performance for the tested geometriesfor the tested geometries

More realistic isotropic safety values in More realistic isotropic safety values in TGeo highly improve total simulation time TGeo highly improve total simulation time for ALICE TPCfor ALICE TPC

4040

AcknowledgementsAcknowledgements

GEANT4 teamGEANT4 team Support for changes in G4Navigator Support for changes in G4Navigator

to accommodate this interfaceto accommodate this interface

ALICE Offline & ROOT teamsALICE Offline & ROOT teams Supporting the development and Supporting the development and

facilitating the integration in ROOT facilitating the integration in ROOT frameworkframework

All current (and future) All current (and future) contributors…contributors…