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A Geometrical Modeller for HEP

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					        A Geometrical Modeller for HEP



             René Brun, Andrei Gheata, Mihaela Gheata




March 2003                   CHEP03
General introduction
   Intended as a toolkit to provide geometrical description of an
   experiment, full navigation functionality and additional tools to
   ease-up building, checking and debugging a geometry.
   Its development is a common ALICE/ ROOT effort that started 1.5
   years ago.
        Driven by ALICE specific needs related to the simulation/
         reconstruction framework, it is however designed as an experiment-
         independent package.
   This component is being integrated in a general Virtual Monte
   Carlo scheme enabling running transparently several simulation
   MC’s starting from the same user code (see talk of Ivana
   Hrivnacova) and using the same geometry.
   Based on a GEANT-like architecture, it is able to map and
   confirmed to optimize the geometry performance of several HEP
   experiments. The gain in speed for navigation tasks ranges from
   20% (ATLAS) to 800% (CDF) compared to G3


 March 2003                         CHEP03
 Why a new geometrical modeller
     Handling so many geometries provide a
    The idea would be to be able toin a single
          framework description
    unique geometry can be painful ...
                   Other                         Simulation
                geometries...
                                 Monitoring       program G3 geometry
                                                Geant3-based
C++ classes                                     Geant4-basedG4 geometry
                                 Geometry       Fluka-based
                                 package
                                                                 FLUKA
                                                                 geometry
 Geometry,
 Calibration,                   Visualization   Reconstruction
 Alignment                      Event display      program
     DB
                                                Reconstruction
   March 2003                          CHEP03
                                                  geometry
Design overview
 Based on some initial                     GEANT-like flavor (CSG based
 requirements                              on container-contained
     Provide basic navigation
      features : “Where am I?”,            concept)
      “How far from next                       main elements : volumes and
      boundary ?”, …                            nodes
     Map Geant3 geometries ->             Extensible set of 16 primitives
      smooth transition
                                           + composite (boolean) +
     Scalability : we deal with big
      geometries                           parametrized shapes + support
     Performance : it rather be           for “MANY” concept
      faster than existing                 Volumetric pixelized navigation
      modelers
     Interactivity : should be at         Make use of symmetries -
      highest possible level - users       divisions
      should easily build, access
                                           Geometry checking interactive
      and debug their geometry
                                           tool

March 2003                        CHEP03
Navigation features
  These make the difference between a geometrical modeller
  and a transient store providing geometrical input for other
  applications.
  Long way from implementing to validating/optimizing/
  tuning these features => took most of the time
       Luckily we had a gold mine of G3 geometries to test upon.
  ''Where am I ?'' => up to 2000% performance gain
  compared to GEANT3
  Computing the distance to next boundary => up to 800%
  gain;
  Safety => computed when needed
  Normals to crossed surfaces => on demand (ongoing work)




March 2003                      CHEP03
Automatic conversion from G3
                                                                         Mygeom.C
Zebra memory          Root > .x mygeom.C
                                             void gexam1()
Data structure                               {TGeoMaterial *mat;
                                             TGeoMixture *mix;

  JVOLUM                                     TGeoManager *gexam1 = new TGeoManager("gexam1",
                                                                             "gexam1.C");
 JMATE,etc                                   //-----------List of Materials and Mixtures--------------

                                             mat = new TGeoMaterial("mat9","ALUMINIUM",
                                                                   26.98,13,2.7);
                                             mix = new TGeoMixture("mix10","IRON(COMPOUND)“
                                                                    ,3);
                                              mix->DefineElement(0,55.847,26,0.703964);
                                              mix->DefineElement(1,58.71,28,0.9900000E-01);
                                              mix->DefineElement(2,51.998,24,0.197);
 Geant > RZ/File 21
 mygeom.geom on




       Zebra RZ                            g2root mygeom.geom
                                                mygeom.C
     mygeom.geom
March 2003                   CHEP03
Collecting samples & validation
 Used one million points generated by Geant3 with full physics switched on




 March 2003                         CHEP03
Benchmarks & performance for
“Where am I?” vs. GEANT3
         Performance for "Where am I" - physics
                          case

             TESLA
             BTEV
   MINOS_NEAR
            CDF
         BRAHMS
              CMS
             ATLAS                                   ROOT
         Gexam 4                                     G3
         Gexam 3
         Gexam 1
                     0       10            20   30

                           microsec/point
                         (1 milion points)



March 2003                        CHEP03
User interface & other features
   Quite simple API : Material(), Volume(), Node(), Division(), …
   managed by a single class.
   Browsable geometry with functionality in the context menus :
   ray-tracing, lego plots, weight estimation, geometry checking
   tool, …
   Perspective geometry viewing allowing picking, zooming,
   animation.
   ROOT I/O – size of geometry and time to load are very
   important during geometry design/testing
       Geometry N objects G3 RZ file .root file CPU time
                (nodes)   (kBytes)   (kBytes)   PIII/800[s]
       AMS         112777      7372       4059       10.59
       ATLAS     29046966      9863       4231        6.38
       BTEV        295310      2048         839       1.30
       CDF          24422      1818       1113        1.00

 March 2003                   CHEP03
  Geometry checker
        It has to be able to check (in reasonable time) for
        illegal extrusions/overlaps in the geometry definition.
        Extrusions
Detected            Not detected




        Overlaps
    Detected           Not detected



Geometry         Overlaps/Extrusions                      No error-free
                 > 1 mm         >100 m            >10 m   geometry found…
                                                          (up to 20K > 1mm)
ALICE            154            764               1460
    March 2003                           CHEP03
The Virtual MC integration
   Allows running several MC's starting from the same code and having
   the same geometry for simulation, reconstruction and event display
                                                    Geant3.tar.gz includes
           Geant4_mc.tar.gz includes
          the TVirtualMC <--> Geant4                  an upgraded Geant3
               interface classes                     with a C++ interface



                                                  G3                G3 transport
User
                    VMC                           G4                G4 transport
code
                                                                        FLUKA
                                                FLUKA                 transport
                      Virtual
                    Geometrical
                     Modeller                   Geometrical
                                                 Modeller

  Reconstruction               Visualisation
 March 2003                            CHEP03
Conclusions
  A new geometrical modeller able to represent a large
  number of HEP experiments is being developed by
  ALICE and ROOT teams.
  This will provide an unique representation of ALICE
  geometry and will allow running transparently several
  MC’s starting from the same user-code.
  Performance was the highest priority during the
  development and this is reflected by the benchmarks.

             The code is available in ROOT and we
               welcome everybody to use it !
March 2003                 CHEP03
Benchmarks & performance for
“Where am I?” vs. G3
 Geometry Nobjects <nodes   FN_phys. FN_phys. ROOT/G3 FN_rand. FN_rand. ROOT/G3
                   /volume> G3       ROOT              G3       ROOT
 Gexam1        425     0.17     1.18      0.73    1.62     2.41      1.18   2.04
 Gexam3         86     2.04     1.10      0.65    1.69     1.19      0.66   1.80
 Gexam4      12781     1.67     0.96      0.62    1.55     4.34      2.58   1.68
 ATLAS    29046966     7.48     3.24      2.49    1.30    13.25      6.19   2.14
 CMS       1166310     6.18    12.95      2.15    6.02    10.53      5.12   2.06
 BRAHMS       2649     6.04     6.04      0.79    7.65     7.95      0.53  15.00
 CDF         28525    11.45    25.04      1.90   13.18     5.60      1.07   5.23
 MINOS_NEAR 30988      4.32    10.87      5.08    2.14     7.64      3.00   2.55
 BTEV       295310     6.88    12.31      1.53    8.05    50.31      2.04  24.66
 TESLA       15370     1.04     2.35      0.81    2.90     4.53      1.84   2.46
     Performance for "Where am I" - physics             Performance for "Where am I" - random
                      case                                               case

       TESLA                                               TESLA
        BTEV                                                BTEV
  MINOS_NEAR                                         MINOS_NEAR
         CDF                                                 CDF
     BRAHMS                                              BRAHMS
        CMS                                                  CMS
       ATLAS                                  ROOT                                              ROOT
                                                           ATLAS
      Gexam4                                  G3          Gexam4                                G3
      Gexam3                                              Gexam3
      Gexam1                                              Gexam1
               0       10     20       30                          0       20     40       60

                     microsec/point                                      microsec/point
                   (1 milion points)                                   (1 milion points)

March 2003                                     CHEP03
Benchmarks & performance for
“distance to next” vs. G3
                  Geometry FNB_phys.FNB_phys.ROOT/G3 FNB_rand FNB_rand ROOT/G3
                           G3       ROOT              G3        ROOT
                  Gexam1       0.87      1.08    0.81      3.89      1.65  2.36
                  Gexam3       1.54      1.74    0.89      3.61      3.32  1.09
                  Gexam4       0.73      1.26    0.58      5.04      3.56  1.42
                  ATLAS        6.89      5.53    1.25     63.31    20.05   3.16
                  CMS         12.94      6.00    2.16     19.23      8.65  2.22
                  BRAHMS      17.25      2.95    5.85     16.34      4.13  3.96
                  CDF         71.10      7.33    9.70     54.24      6.18  8.78
                  MINOS_NEAR 27.01     14.43     1.87     25.52      9.89  2.58
                  BTEV        23.80    13.46     1.77    102.20    19.14   5.34
                  TESLA        2.84      2.76    1.03     23.27      9.74  2.39

      Performance for "Next boundary" -                    Performance for "Next boundary" -
               physics case                                         random case


      TESLA                                                TESLA
       BTEV                                                 BTEV
MINOS_NEAR                                           MINOS_NEAR
        CDF                                                  CDF
    BRAHMS                                               BRAHMS
        CMS                                                  CMS
      ATLAS                                 ROOT           ATLAS                                 ROOT
     Gexam4                                 G3            Gexam4                                 G3
     Gexam3                                               Gexam3
     Gexam1                                               Gexam1
              0       20    40    60   80                          0       50    100       150

                   microsec/point (1                                   microsec/point (1
                    milion points)                                       milion points)

March 2003                                       CHEP03

				
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posted:3/28/2011
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