The geom.C file
Everything the converter does ends up in one ROOT macro, and it is the artefact worth caring about.
It exports two functions: get_builder_hook_unchecked(), which is what o2-sim calls when it loads
your geometry, and build_and_export(), which you already used to look at the model on its own.
Alongside it, the output folder holds the binary payloads the macro reads — facets_*.bin for meshed
parts, surfaces_*.bin for exact ones and flatcsg_*.bin for flat CSG solids — plus
csg_report.json, which records what each part became and why.
The macro and its binaries travel together
geom.C loads those .bin files relative to its own location. Move or copy the macro withoutthe rest of its folder and it will build an empty geometry without complaining. Always move thedirectory.
build_and_export() runs CheckOverlaps only when asked, because on large models it is slow:
root -l -b -q -e '.L geom.C' -e 'build_and_export("geom.root", true, true);'
Info in <TGeoManager::CloseGeometry>: 14 nodes/ 14 volume UID's in geom
Info in <TGeoNodeMatrix::CheckOverlaps>: Checking overlaps for Assembly and daughters within 0.1
Info in <TGeoNodeMatrix::CheckOverlaps>: Number of illegal overlaps/extrusions : 0
Finally, a structural point that shapes how you organise your work: each converted directory holds
exactly one geom.C, and each geom.C describes one thing you hook into the simulation. If your
study involves three CAD subsystems, you run the converter three times into three folders. They
coexist without trouble, because the loader compiles each macro into its own namespace at run time,
so the identical function names inside them never collide.