1. Common Geometry Primitives library WP3 – date
M. Gheata, CERN EP/SFT
for the USolids/VecGeom team

2. M.Gheata - Common Geometry Primitives library
Outline
Motivation
Status
Directions and work plan
Conclusions
16/06/16
M.Gheata - Common Geometry Primitives library

3. Motivation for the development
Originally seen as a consolidation of solids algorithms in Geant4 and ROOT, for better performance and easier maintainability
Scope extended due to new requirements added by GeantV
Vectorization
Portability to other architectures (GPU, MIC, …)
The larger scope required developing a new geometry package: VecGeom
Development of USolids an VecGeom merged into a single package
This path aiming to release a single high performance product used more or less everywhere
Activity part of AIDA-2020/WP3
~1995
~2002
~2010
~2013
Geant4
geometry
modeler
ROOT/TGeo
AIDA USolids
VecGeom
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M.Gheata - Common Geometry Primitives library

4. VecGeom: targeting vectorization
Vector signatures
Internal algorithm vectorization
internal loop over
lateral planes for
distance calculation
“parallel” collision detection 
For vectorized transport (GeantV)
Beneficial for current scalar
simulations
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M.Gheata - Common Geometry Primitives library

5. Available shapes: status
Both in USolids and VecGeom:
Box, Orb, Trapezoid (Trap), Simple Trapezoid (Trd), Sphere (+ sphere section), Tube (+ cylindrical section) , Cone (+ conical section), Generic Trapezoid (Arb8), Polycone, Polyhedron
Only in USolids:
Tetrahedron (Tet), Multi-Union, Tessellated Solid, Extruded Solid, Generic Polycone
Only in VecGeom:
Paraboloid, Parallelepiped (Para), Hyperboloid, Ellipsoid, Torus (+ torus section), Scaled Solid, Boolean (addition, subtraction, intersection)
Missing:
Elliptical Cone, Elliptical Tube, Cut Tube (composable)
Twisted shapes (box, trap, tube) – complex & infrequent use
Working on a comprehensive common set
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M.Gheata - Common Geometry Primitives library

6. Correctness: ShapeTester testing suite
Geant4 tests
- Unit tests
- SBT(solid batch test)
- SurfaceChecker
- OpticalEscape
- SurfaceVisTest
- testDistanceAccuracy.cc …
Extensive Testing Suite
USolids tests
-SBT
-OpticalEscape
-SBTperformance (Comparison
Usolids, Root, Geant4)
Root tests
CheckShape:
-ShapesDistances()
-ShapesSafety()
-ShapeNormal()
Possibility to run tests interactively through ROOT
Shape Tester
Geant4+USolids+Root tests
New 'X-Ray Scan' Test
SBTperformance
Unit tests
VecGeom Testing Suite
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M.Gheata - Common Geometry Primitives library

7. Coverage extension in Shape Tester - ongoing
One shape for each different topology
Sections, shells, …
Degenerated configurations
Pathological cases (long/thin shapes, …)
Shapes selection from a DB
DB generated from imported LHC experiments geometries
Random generation of shapes
Per type, dimension and position in space
Batch or interactive mode
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M.Gheata - Common Geometry Primitives library

8. New features: precision on boundaries
p1 = p0 + Dref*v v
ε = max|Dback-Dref|vn -v
Dback= DistanceToIn(p1, -v) p0 p1 n
Systematic check in Shape Tester for every shape
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M.Gheata - Common Geometry Primitives library

9. Performance monitoring after changes
Goal: develop algorithms as accurate but faster than Geant4/ROOT/USolids
Plot on polyhedron performance, evolution with commits
Needs systematic checks
Time[s]
Less accurate: using bbox
Less accurate: limited to current Z segment
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M.Gheata - Common Geometry Primitives library

10. Current status of shapes in Shape Tester
Conventions test
Stress tests
Box OK
Tube
Trapezoid
Generic Trapezoid (Arb8)
Simple Trapezoid (Trd)
Orb
Sphere
Cone (x)
Parallelepiped (Para)
Polycone (x)
Failures
Polyhedron (x)
Torus (x)
All other shapes either missing or showing failures -> to be addressed
(x) Being worked out now…
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M.Gheata - Common Geometry Primitives library

11. Shapes: immediate open issues to address
Fix errors reported by Shape Tester
Including any new added topologies
Provide missing auxiliary functions (GetPointOnSurface, Capacity, SurfaceArea)
Already implemented in USolids
Required by Geant4
Improve Trap and Cone performance
DistanceToIn() in UTrap is faster
Scalar performance for Cone can be improved for distance functions
Improve scalability for Polycone and Polyhedron
Poor performance with high number of Z-sections in VecGeom shapes
Internal vectorisation on Z sections not yet working – to be developed
Review application of conventions for points on the “wrong side”
Final validation: robustness and fixes for problems detected only when running on complex setups
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M.Gheata - Common Geometry Primitives library

12. Integration with Geant4 and ROOT
Objective: profit from demonstrated VecGeom scalar performance improvements in existing setups
Without requiring user code to change
Important step for validating the new package as replacement of geometry
Usolids/VecGeom integrated with Geant4 as optional alternative
Work done to integrate VecGeom solids with ROOT
Implementation: bridge classes deriving from the base class for solids (G4VSolid, TGeoShape)
Delegating navigation methods to the VecGeom library
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M.Gheata - Common Geometry Primitives library

13. Using VecGeom from Geant4 - status
USolids can be used in Geant4 since release 10.0
Passing the whole Geant4 testing suite
Some run-time warnings with CMS bench
VecGeom solids can be used seamlessly since Geant as external library
Now part of nightly builds in Geant4
VecGeom shapes from Git master
Tested on CentOS/gcc-5.3
Several tests failing or showing run-time errors/warnings
In release 10.3-beta, VecGeom will work in batch and interactive mode
Also in multi-threading (MT)
Still failing parameterisations in MT mode
Missing some auxiliary methods in VecGeom
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M.Gheata - Common Geometry Primitives library

14. Building Geant4 to use USolids/VecGeom
Install USolids/VecGeom libraries
Configure to either use USolids implementation:
cmake -DBACKEND=Scalar -DGEANT4=OFF -DUSOLIDS=ON -DUSOLIDS_VECGEOM=OFF \
[...other optional VecGeom switches as needed...] \
-DCMAKE_INSTALL_PREFIX=${VecGeomINSTALLDIR} ${VecGeomSOURCE}
make install
or VecGeom implementation:
cmake -DBACKEND=Scalar -DGEANT4=OFF -DUSOLIDS=ON -DUSOLIDS_VECGEOM=ON \
Install Geant4
export USolids_DIR=${VecGeomINSTALLDIR}/lib/Cmake/USolids
Add -DGEANT4_USE_USOLIDS=ON when configuring Geant4 with CMake
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M.Gheata - Common Geometry Primitives library

15. Expected geometry features in Geant4 10.3
Release 10.3 of Geant4 planned for December 2016
Beta preview (10.3-beta) at end of June
Ability to exercise a limited set of shapes from VecGeom
Box, Tube, Cone, Orb, Sphere, Trap, Trd, Torus, Polycone, Polyhedron
Approaching “production quality” in terms of correctness and robustness
Extension of Geant4 CMake build system to enable use of shapes individually
Ability to scale shapes along Cartesian axes
Extended GDML schema (new version 3.1.4)
Future plan: Provide specialised navigation interface class to VecGeom navigation
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M.Gheata - Common Geometry Primitives library

16. VecGeom solids used in ROOT TGeo
TPluginManager
Using ROOT plugin mechanism to avoid direct library dependencies
Load library, create the converter
TGeoVGConverter
TVirtualGeoConverter::instance()::ConvertGeometry()
A single call to convert the shapes in any TGeo geometry to VecGeom ones
libVGConverter.so
libvecgeom.a
libGeom.so
TVirtualGeoConverter
The base interface is defined in the TGeo library
::ConvertGeometry() = 0
derives
TGeoVGShape
Make VecGeom solid look like a regular ROOT shape
TGeoBBox
TGeoTube
TGeoCone …
fShape
VPlacedVolume
Keep the original ROOT shape and the corresponding converted solid
Navigation using the VecGeom converted solid
General functionality not available in VecGeom
Graphics, alignment, …
Contains()
DistanceToIn()
Safety() …
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M.Gheata - Common Geometry Primitives library

17. Status and availability
Supports any ROOT geometry (shapes not yet available are not converted)
Alignment, graphics, navigation, geometry checking, …
Used as debugging tool (ray-tracing, root shape tester)
Expecting important gains for some methods
Still to measure overheads/gains systematically (per shape) and in full transport
Committed to ROOT master (commit 0bdd34b)
New module created in geom/vecgeom creating libConverterVG.so(dyld)
Requirement – compilation of ROOT after VecGeom (and Vc) are installed
Assuming $VCROOT and $VECGEOMROOT are the install prefixes for Vc and VecGeom
-DCMAKE_PREFIX_PATH=$VCROOT/lib/cmake/Vc;$VECGEOMROOT/lib/CMake/VecGeom
-Dvc=ON –Dvecgeom=ON
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M.Gheata - Common Geometry Primitives library

18. M.Gheata - Common Geometry Primitives library
Summary
Most of the common shapes now implemented in VecGeom
Missing still some auxiliary methods to allow for full usage in Geant4
Shapes passing Shape Tester: box, tube, cone, orb, para, sphere, trd, trap, generic trap, polyhedron
Performance issues: cone, trap, polycone, polyhedron
In process to extend Shape Tester
Added new checks like boundary precision checks/tuning
Ongoing extension of coverage for shapes topologies
VecGeom through Geant4 and ROOT in place (shapes level)
Expecting near to “production quality” performance in VecGeom release in time for Geant4 10.3
16/06/16
M.Gheata - Common Geometry Primitives library

19. M.Gheata - Common Geometry Primitives library
Contributors
EP/SFT+ AIDA 2020: J.Apostolakis, G.Cosmo, A.Gheata, M. Gheata, F.Carminati, T.Nikitina, W.Pokorski
G.Amadio(UNESP), G.Lima(FNAL), R.Sehgal(BARC), E.Tcherniaev(RAS), S.Wenzel(CERN)
16/06/16
M.Gheata - Common Geometry Primitives library