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Geant4 Geometry and Transport Working Group Meeting

→ Europe/Zurich
32/1-A24 (CERN)

32/1-A24

CERN

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    • Status and Plans for 2025: Brief Reports and Discussion

      Round-table discussion of 2024 achievements and proposed 2025 deliverables / work topics

      • Proposed objectives / deliverables
        • Improved GPU navigation using surfaces (VecGeom) - Severin & Andre
          • Improvements in stability
          • Merge into VecGeom master (targetting release 2.0)
          • Optimisation
      • Progress reports and items of ongoing contribution
        • Raman S. : looking to resume contributing to VecGeom, including attending bi-weekly meetings
        • Guilherme L. : in 2024 fixed a few solids' implementations, created implementations of shapes for surface model, and investigated issues; intend to contribute in similar manner in 2025.
        • Ben M. : have & will tackle issues related to CMake configuration ; investigating use of HepNumerics (geant4/global category) use and optimisation in Geant4 in general - so any relevant to geometry will be included in this.

        • Ivana H. : reconsile the defaults of the field module with the default of the new Field ‘Builder’ classes

        • Seth J. : discussed the use of geometry debugging tools for potential contribution, 

          • a material scanner, for identifying problems with the different geometry modellers and implementations of solids (e.g. identified issue with twisted solid later reported by CMS )

          • a second tool provides a graphical representation of the isotropic safety distance on a place (or other 2-d surfaces?); useful for debugging this.

        • Evgueni: (2024 & future) implroving the robustness and performance of various G4Solids.  In 2024 these were: twisted Tubs, Generic Trap, poly-cone and polyhedra.  Also extending their testing suites.

       

      New topics for investigation (Stewart B.)

      1. Symplecticity of navigation can be destroyed in the case of a multiple volume geometry by repeated geometry transformation, in inaccuracies due to the composition of rotations.  For simpler use cases (likely including a g-2 type experiment) a simple solution is to create a single large volume with the field and geometry of the setup.  Potentially a geometry with just surfaces, that does not require transformations will help? For complex cases where multiple volumes are required, a new approach may be required.
        • To note as topic for future consideration: "Symplecticity and the impact of inaccuracies due to repeated composition of transformations (or from errors due simply to displacements from the inaccuracies going around a single revolution being amplified by repeated application)"
        • Stewart will gives us a reference or excerpt to document this issue
      2. Interest in having a geometry modeller that allows the user to define a geometry setup using intersections of planes and quadratic (quadric?) half-spaces (‘half-space representation’)  to address use cases from accelerator application - ranging from LHC to medical applications.
        • Many geometries are described for simulation by FLUKA / MCNP / PHITS, and for simulation in Geant4 currently the geometry must be recreated, which is a significant burden
          • potential for performant implementation of these geometries with a compatible geometry modeller mentioned
        • Potential approaches discussed
          • developing Orange further for use by MCNP derived, OpenMC and related (FLUKA / PHITS) geometry descriptions ; an approach that adapted this to the G4 geometry state (a la ALICE / TGeo to G4 )  - Seth
          • consulting with Fluka team on their plans for a Geant4-embedded navigation system
          • [ recalled later / John ] a way to describe solids using half-spaces created by a student from Germany ( we should still have access to his repository - to be confirmed. )
        • Agreed to organise a dedicated meeting to discuss this in more depth.

       

      • 1
        Status and Outlook
        Speaker: John Apostolakis (CERN)
        Geometry-WG-Meeting-January2025.pdf
      • 2
        Reports, Open Topics and Plans - roundtable
        2024 Deliverables
      • 3
        Key goals for 2025

        Recall topics mentioned in 2024:

        Navigation / modelling
        - Vecgeom surface-based modeller
        Performance / interfaces
        - Reduction of initialisation time and overlap checking using Multi-Threading
        Field:
        - Robustness improvement of QSS3
        - High order symplectic stepper (needs person)

        Impact / Coupling with other developments (in Geometry & Transport and beyond)

        See Deliverables (2023 & 2024) and potential deliverables (future)

        2023 Deliverables (for reference)
        Potential future development
      • 4
        Discussion
    • VecGeom bi-weekly progress meeting: Status Updates, open issues, plans
    • AOB: Other topics