Introduction

The g4system module is the geometry factory layer that translates detector descriptions stored in databases (ASCII / SQLite / GDML / CAD) into runtime Geant4 volumes (solid/logical/physical).

The module is designed so that you can add new detector systems by implementing a factory and registering it, without changing the core world-building logic.

Module overview

g4system Factory / Plugin Loader : Runtime creation of system builders and object factories
g4system Geometry Builders : Conversion from GEMC DB records into Geant4 geometry/material objects

Available Options and their usage

This module reads the following option keys from the runtime option provider:

useBackupMaterial
- Type: string
- Meaning: fallback Geant4 material name used when a requested material is not found
- Behavior:
  - when unset (equal to NO_USE_DEFAULT_MATERIAL), GEMC treats missing materials as fatal
  - when set to a valid Geant4 material (e.g. G4_AIR), missing materials are replaced by this fallback
check_overlaps
- Type: integer
- Meaning: request for Geant4 overlap checks during geometry construction
- Behavior:
  - 0 disables overlap checks
  - 1 checks overlaps at physical volume construction time
  - 2 triggers the Geant4 overlap validator with the default surface sampling
  - values > 100 trigger the Geant4 overlap validator with that many surface points
showPredefinedMaterials
- Type: boolean (switch)
- Meaning: print the inventory of GEMC predefined materials
printSystemsMaterials
- Type: boolean (switch)
- Meaning: print the materials used by the loaded systems in this simulation

Overlap checking is controlled solely by the integer check_overlaps option above.

This module’s option schema is composed by g4system::defineOptions(), which aggregates:

gsystem::defineOptions()

Additional keys contributed by gsystem::defineOptions() (e.g. sql, gsystem, experiment, runno) control what geometry is loaded and therefore indirectly affect this module.

Verbosity and debug output

Most classes in this module use the common logging infrastructure (classes derived from the logger-enabled base). The following behavior is typical:

Verbosity level 0 prints essential progress and high-level configuration (major steps, critical warnings).
Verbosity level 1 prints additional context useful during standard validation (counts, selected materials, basic dependency messages).
Verbosity level 2 prints detailed traces useful while developing geometry/factories (per-volume build results, dependency resolution steps, material/component listings).

Debug messages provide fine-grained diagnostics intended for development and troubleshooting, such as pointer assignments, dependency checks, and factory dispatch details.

Quick-start

Example of building a world from options:

auto gopts  = std::make_shared<GOptions>(argc, argv, g4system::defineOptions());
auto gworld = std::make_shared<GWorld>(gopts);
auto g4w    = std::make_shared<G4World>(gworld.get(), gopts);

Examples

g4system_example.cc : Minimal instantiation of the module, world creation, and basic diagnostic queries (volume count, sensitive detector list).