SHiP Field Service

Framework-agnostic C++20 library exposing the SHiP magnetic field maps to simulation (aegir) and reconstruction.

The library wraps covfie for storage and interpolation of regular-grid field maps. A small optional Geant4 adapter (G4MagFieldAdapter) is built when BUILD_G4_ADAPTER is enabled; the core library has no Geant4 dependency, so reconstruction can consume it without pulling Geant4 in.

Layout

• include/FieldService/IFieldSource.h — interface (point-query evaluator, list of named regions tagged by host-geometry volume name).
• include/FieldService/CovfieFieldSource.h + src/CovfieFieldSource.cpp — concrete source that loads one .cvf file per magnet via covfie.
• include/FieldService/G4MagFieldAdapter.h — Geant4 adapter, built when BUILD_G4_ADAPTER=ON.
• tools/fairship_to_cvf — convert FairShip's legacy ROOT field-map format to covfie .cvf. Built when ROOT is available.
• tools/cvf_to_text — dump a .cvf to whitespace-separated text for inspection and closure tests.
• tools/generate_constant_cvf — synthetic uniform field-map generator for closure tests.

Install with pixi

The supported way to set up a build environment is pixi. pixi.toml pins the toolchain and all required packages (mp-units, geant4, root, cmake, ninja, cxx-compiler).

git clone https://github.com/ShipSoft/field_service
cd field_service
pixi install
pixi run test

Available tasks: configure, build, install, test, clean. pixi run install deploys the library, headers and CMake package files under the pixi environment prefix so downstream consumers can find_package SHiPFieldService.

Map files are resolved relative to $SHIPFIELD_ROOT/share/field/ when a bare filename is passed; the pixi activation script sets SHIPFIELD_ROOT to the pixi environment prefix by default.

Build directly with CMake

If you prefer to bring your own dependencies:

cmake -S . -B build
cmake --build build
ctest --test-dir build

Develop

Install the pre-commit hooks (covers clang-format, cpplint, gersemi, reuse, codespell, conventional-commit validation, and CITATION.cff checks):

pixi run -e dev pre-commit install --hook-type pre-commit --hook-type commit-msg

See CONTRIBUTING.md for the full workflow.

Use from aegir

Aegir consumes this via find_package(SHiPFieldService REQUIRED COMPONENTS Core G4Adapter). The aegir provider plugin field_covfie_provider constructs a ship::CovfieFieldSource from jsonnet config and publishes it as a phlex Job product; the aegir Geant4 module installs a per-magnet G4FieldManager on each matching logical volume via the adapter.