OOC Reconstruction Model based on GEANT3

1
OO/C Reconstruction Model based on GEANT3

• Yuri Fisyak, Valery Fine,
• Pavel Nevski, Torre Wenaus

2
Outlook

• Motivations
• Advantages and limitations of GEANT3 geometry
• Compact and open geometries
• Hits/Digits structure
• User interface iterators
• Conclusions

3
Motivations

• One the main task which has to be solved by a
  reconstruction is to provide access to geometry
  and calibration information for a given
  hit/digit and vise versa.
• A lot of current HENP experiments still have
  their most detailed geometry in GEANT3. It looks
  very attractive to be able to access this
  geometry description from the modern OO/C
  reconstruction.
• As an example, in ATLAS Muon reconstruction
  access to detailed detector description,
  including dead material information, is
  mandatory because of very high performance
  requirements.

4
Advantages of the compact geometry model

• An existing experience with GEANT3 allows to
  formulate so called compact detector model.
• It provides a model for ideal detector
• which accounts symmetries of the detector, and
• it is compact because it doesn't contain any
  duplication of the geometrical nodes,
• an example of such type geometry is the ATLAS
  detector GEANT3 description which contains 30M
  copies of 7 K different types of volumes.

5
ATLAS Detector View With G3
6
Limitation of compact geometry

• However this compact model cannot facilitate
  the real reconstruction needs
• a subset of geometrical nodes (detector elements)
  might have their own unique list of parameters
• calibrations,
• alignment,
• The OO model where each physical detector
  element corresponds to the dedicated object
  instance we will call "open" geometry.
• This open geometry also is very suitable for
  detector response (hits, digits) structuring.

7
Compact and Open geometry

• Even though the "open" structure looks very
  attractive it is still non realistic to keep it
  in memory for whole detector.
• Thus geometry model for reconstruction has to
  contain a combination of compact geometry
  for whole detector and open one for its subset.
  

8
Compact open geometry in ROOT

• A geometry package is being developed within ROOT
  framework to provide such functionality.
• The package uses of ROOT Geometry classes
  (root/g3d)
• TShape (TBRIK, TCONE,), TMaterial, TMixture,
  TRotMatrix
• The package includes
• the "compact" model with multiple reuse of
  geometry objects, providing a C detector view
  "a la GEANT3" (root/table)
• TVolume and TVolumePositon classes
• the open model which is created by a request
  for a subset of the compact presentation and
  contains full description, where each detector
  element is presented by a separate object
• TVolumeView class

9
TVolume and TVolumeView hierarchical container
of containers
List of positions
List of nodes
TVolume
TVolumePosition (relative wrt parent)
TVolumeView
TShape
TVolumePosition (position wrt global)

TMaterial
TVolumePosition
TVolume
TVolumeView
TVolume
List of daughter nodes
10
TVolume and TVolumeView (cont.)

• TVolume
• does not know about its position,
• can be positioning in any part of the geometry
  tree with respect to parent TVolume,
• provides only downstream navigation I.e. you can
  find children of the given TVolume but you dont
  know its parent.
• TVolumeView
• does know about its position with respect to any
  fixed system of coordinates (global, with respect
  to parent, ),
• Provides navigation both downstream and upstream,
• can contain any information (calibrations, )
  unique for the given node.

11
Exporting G3 geometry to ROOT
Open geometry
Compact geometry
Mark Sensitive volumes
Iterator over developed G3 geometry as it
sees a particle during propagation
TVolume

• TVolumeView

12
TVolume/TVolumeView browsing
Full G3 tree 29042213 nodes
3512 marked nodes
TVolume
TVolume
ctor
TVolumeView
TVolumePosition
TVolume
TVolumePosition
TVolume structure
TVolumeView structure
13
ATLAS muon system in ROOT
14
Hits/Digits

• The package also provides a generic hit/digit
  C class together with tools supporting
  navigation from hits to geometry and vice versa.
  . TResponseTable self describing array of
  c-structs containing hits/digits information.
• TIndexTable list of indexes in TResponseTable
  array corresponding a given detector element
  (TVolumeView) in order to speed up the navigation
  from geometry to digits/hits structure.

15
Response Table
TResponseTable mtuiHit (TResponseTable )
g3-gtDataSet("Data/Hits/MUCH/MTUI") mtuiHit-gtPrint
(0,5) TResponseTable mtuiDigit
(TResponseTable ) g3-gtDataSet("Data/Digits/MUCD/M
TUI") mtuiDigit-gtPrint(0,5)
Muon/.make/AtlSim/.data/Data/Digits/MUCD/MTUI
Allocated rows 32 Table MTUI
0 1 2
3 4 int TRACK
1 1 1
1 1 int ATLS/OUTE/MUCH 2
2 2 2 2
int BARI 10
10 10 10 10 int
BXXI 12
12 12 12 12 int
BSLI 1
1 1 2 2 int
BWAI 55 109
164 5 6 float TIME
194.6 239.31 284.96
466.39 467.12 float Z
22.309 22.398 22.487 23.008
23.056 float TDR 0.4915
0.6205 0.7495 1.2695 1.2615
Muon/.make/AtlSim/.data/Data/Hits/MUCH/MTUI
Allocated rows 36 Table MTUI
0 1 2
3 4 int TRACK
1 1 1
1 1 int ATLS/OUTE/MUCH
2 2 2 2
2 int BARI
10 10 10 10
10 int BXXI
12 12 12 12
12 int BSLI
1 1 1 2
2 int BWAI
55 109 164 5
6 float X -0.4155
-0.5245 -0.6325 -1.0715 1.0635 float
Y -0.2635 -0.3325
-0.4015 -0.6805 0.6785 float Z
22.309 22.398 22.487
23.008 23.056 float TDR
0.4915 0.6205 0.7495 1.2695
1.2615 float TOF 0.29778
0.29875 0.29973 0.30544 0.30595 float CZ
0.02975 0.02975
0.02965 0.02945 0.02945 float CX
-0.53645 -0.53655 -0.53655
-0.53685-0.53685 float CY
0.84345 0.84335 0.84335 0.84315
0.84315 float STEP 2.7505
2.6445 2.5075 1.4435 1.4715
float LGAM 2.485 2.485
2.485 2.485 2.485 -
Detector Id, path to detector element
Hit/Digit parameters
16
TIndexTable
To speed up navigation over hits/digits
information from detector elements it has been
created hits and digits trees. The trees
structure reflects one for the open geometry
and contains only nodes with hitted detector
elements. These nodes contain indexes
(TIndexTable) of hits in Hits/Digits TResponse
tables.
TObjectSet
TVolumeView
TIndexTable
TResponseTable
17
Navigation

• The main goal of the above compact and open
  geometries and Hits/Digits trees is to provide
  straight forward navigation from hits/digits to
  geometry and from geometry to hits/digits.
• Because the geometries and hits/digits are
  containers the way to navigate over them are
  iterators.
• The navigation is provided by two iterators
• TVOLUMEiterator over TVolume and TVolumeView
  structures and
• ADigitIterator / AHitIterator

18
Navigation TVOLUMEiterator

• void VIter()
• TVolume oute (TVolume )
  g3-gtFind(".const/Constants/Geometry/ATLS/OUTE")
• // or
• // TVolumeView oute (TVolumeView )
  g3-gtFind(".const/Constants/GeometryTree/ATLS/OUTE"
  )
• TVOLUMEiterator Iter(oute)
• TString BXXI("BXXI")
• for ((long) Iter ! 0 Iter)
• TVolumePosition pos Iter
• TString Name(pos.GetName())
• if (Name ! BXXI) continue
• pos.Print()
• Node BXXI
• Position x404.401 y-976.31 z0
• OBJ TRotMatrix 508523 NodeView
• 1 2
  3
• 1. -0.923879 -0.382684 -4.37114e-08

Muon system
Muon chamber
19
ADigitIterator

• TObjectSet BXXI (TObjectSet )
• g3-gtGetData("DigitsTree/ATLS/OUTE/MUCH2/BARI10
  /BXXI12")
• for (ADigitIterator iter(BXXI) (int)iter ! 0
  iter)
• ADigit digi iter
• digi.Print()
• Digit TRACK 1 ATLS/OUTE/MUCH2/BARI10
  /BXXI12/BSLI2/BWAI115
• TIME 377.098 Z 23.2315 TDR
  1.0015 E 0
• Node BWAI
• Position x1.95198e-06 y15.344 z-60
• OBJ TRotMatrix 520471 NodeView
• 1 2
  3
• 1. -4.37114e-08 4.37114e-08
  -1
• 2. -8.74228e-08 1
  -8.74228e-08
• 3. 1 -4.37114e-08
  -8.74228e-08

20
Conclusions

• It has been developed a set of classes which have
  supported structures and provide parameters
  description of both compact and open
  geometries. This approach naturally accounts for
  alignment and detector calibration information.
• It has been developed structure supporting hits
  and digits.
• It has been developed iterators which provide
  navigation from hits/digits to geometry and vise
  versa.
• This model is used in development of ATLAS muon
  reconstruction.
• But this model itself does not use any ATLAS
  specific features and can be applied for any
  reconstruction.