1. Detector Geometry Description
LHCb Software Week
24-26 November 1999
P. Mato, on behalf of I. Belyaev
The following are few slides intended to trigger a discussion/brainstorming with the goal of producing an Architecture for the DCS kernel.
Definition on Architecture: “The architecture of a system is the structure of the system”. Two main ingredients: A set of building blocks, and a set of collaborations that specify how those building blocks cooperate to provide various system functions.
An DCS architecture will allow us to provide set of control applications or control systems that fulfill a range of needs within the DCS domain. An architecture encourages reuse.
Analogies in the real world: Gothic architecture, Lego Basic® architecture, Lego Technique® architecture.
“To be successful, an object-oriented project must craft an architecture that is both coherent and resilient and then must propagate and evolve the vision of this architecture to the entire development team”, G. Booch, Object Solutions.
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Geometry Description

2. Outline Detector Description Geometry Description Design
Using the geometry
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3. Detector Description Logical Structure Geometry Structure
Breakdown of detectors
Identification
Geometry Structure
Hierarchy of geometrical volumes
LogicalVolumes (unplaced)
PhysicalVolumes (placed)
Other detector data
Calibration, Alignment, Readout maps, Slow control, etc.
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4. Two Hierarchies Logical structure Geometry structure
DetElement
LHCb
DetElement
LHCb
LVolume
Experiment
DetElement
Tracking
DetElement
Calo
PVolume
PVolume
PVolume
LVolume
ECAL
LVolume
HCAL
LVolume
RICH
DetElement
HCAL
DetElement
ECAL
PVolume
PVolume
DetElement
Module1
DetElement
Module2
LVolume
HCALModule
Detector Description
Geometry
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5. Class Diagram (simplified)
DataObject
Hierarchy
Association resolved on demand *
IDetElement
IGeometryInfo
Geometry Info
ILVolume
LVolume
Material
IReadOut *
IMaterial
DetElement
ReadOut
ISolid
Solid
IPVolume
Calibration
ICalibration
PVolume
Mixture
Element
Isotope * *
Solid
MuonStation
Solid
Specific detector description questions from algorithms
SolidBox
Detector Description
Geometry
Material
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6. Detector Element Provides an identifier
e.g. “/LHCb/VELO/Station1”
Time validity range and versioning
Access point to all “detector data”
Geometry, readout, slow control, etc.
Specific code to answer specific questions can be implemented by inheriting from it
e.g. “MuonStation”, “EcalModule”
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Geometry Description

7. Geometry Structure
Constructed using “Logical Volumes” and “Physical Volumes” (Geant 4)
Logical Volume: Unplaced detector type described as a solid of a given material and a set of daughters (physical volumes).
Physical Volume: Association of a logical volume and a transformation (rotation & translation).
Solids
A number of basic solids (boxes, tubes, cones, trds, spheres,…)
Boolean solids (unions, intersections and subtractions)
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8. Geometry Info class IGeometryInfo {
// transformation matrix from the Global Reference system to the Local one
virtual const HepTransform3D& matrix() = 0; // from Global to Local
// transformation matrix from the Local Reference system to the Global one
virtual const HepTransform3D& matrixInv() = 0; // from Local to Global
// transformation from the Global Reference System to Local Reference system
virtual HepPoint3D toLocal( const HepPoint3D& globalPoint ) = 0;
// transformation from the Local Reference System to Global Reference system
virtual HepPoint3D toGlobal( const HepPoint3D& localPoint ) = 0;
// Check if a 3D point is inside volume
virtual bool isInside( const HepPoint3D& globalPoint ) = 0;
// C++ pointer to daughter to which the given (global) point belongs to
virtual IGeometryInfo* belongsTo( const HepPoint3D& globalPoint ,
// return the information about the support
virtual StatusCode location( IGeometryInfo*& start ,
ILVolume::ReplicaPath& replicaPath ) = 0 };
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9. Usage Example
SmartDataPtr<DetectorElement> setup(detDataService(),"/dd/Structure/LHCb");
if( !setup ){
log << MSG::ERROR << "Can't retrieve /dd/Structure/LHCb" << endreq;
return StatusCode::FAILURE; }
// Get the envelop solid
ISolid* sol = setup->geometry()->lvolume()->solid()->coverTop();
SolidBox* box = dynamic_cast<SolidBox*>(sol);
log << MSG::INFO << ”LHCb Z size is " << box->zHalfLength()*2 << endreq;
// Now retrieve the custom, user defined detector element "Vertex" with
SmartDataPtr<DeVertexDetector> vertex( setup, "Vertex" );
if( !vertex ){
log <<MSG::ERROR<<"Can't retrieve /dd/Structure/LHCb/Vertex" << endreq;
log <<MSG::INFO<<“Vertex has " << vertex->stations() << " stat" << endreq;
ILVolume* lv = vertex->geometry()->lvolume();
log <<MSG::INFO <<“Vertex is made of " << lv->materialName() << endreq;
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10. Detector Specific
Sub-detector can start developing their specific Detector Element
They need to answer the questions coming from Simulation, Reconstruction algorithms.
Sub-detector specific data can be stored together with common data.
DetElement
MyDetector
IDetElement
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