Skip to content

geometry.md

Latest commit

 

History

History
132 lines (86 loc) · 4.38 KB

geometry.md

File metadata and controls

132 lines (86 loc) · 4.38 KB

Detector Geometry

Use this file when the task involves detector geometry assets, simulation geometry loading, or geometry-related navigation.

Start Here

  • AtDetectors/AtTpc/AtTpc.cxx
  • AtDetectors/AtTpc/AtTpc.h
  • geometry/
  • macro/examples/run_sim.C
  • macro/tests/AT-TPC/run_sim_attpc.C
  • macro/tests/generateGeometry.sh

If the task is about pad centers, pad IDs, or pad-plane layout, also inspect:

  • AtMap/AtTpcMap.cxx
  • AtMap/AtSpecMATMap.cxx

Runtime Path

Simulation macros pass a geometry file to AtTpc with SetGeometryFileName():

AtTpc *tpc = new AtTpc("ATTPC", kTRUE);
tpc->SetGeometryFileName("ATTPC_v1.2.root");
run->AddModule(tpc);

AtTpc::ConstructGeometry() dispatches by extension:

  • .root -> ConstructRootGeometry()
  • .geo -> ASCII branch exists but is not the practical path here

For this tree, AtTpc geometry is normally loaded from generated ROOT files.

Where Geometry Lives

geometry/ contains:

  • generator macros such as ATTPC_v1_2.C, ATTPC_He1bar.C, GADGET_II.C
  • generated outputs such as ATTPC_v1.2.root and ATTPC_v1.2_geomanager.root
  • media.geo for material definitions
  • detector-specific helper assets

Do not assume geometry outputs are missing. This checkout already contains several generated .root geometry files.

Generation

Generate a geometry only if the required output is missing or stale.

Example:

cd geometry
root -l -q ATTPC_v1_2.C

This writes:

  • ATTPC_v1.2.root
  • ATTPC_v1.2_geomanager.root

Test helper:

macro/tests/generateGeometry.sh

That script generates only a fixed subset of geometries used by tests. It is not a full geometry build step.

Detector Variants

Script Detector Notes
ATTPC_v1_2.C Full AT-TPC Used by most unpacking/display macros
ATTPC_v1_1.C Full AT-TPC Older version; some example sim macros still reference this
ATTPC_Proto_v1_0.C Prototype AT-TPC Shorter drift length (500 mm)
ATTPC_He1bar.C AT-TPC, He 1 atm Used by the AT-TPC integration test
ATTPC_He*.C, ATTPC_D*.C, ATTPC_H*.C Gas/pressure variants Specific gas fill and pressure combinations
SpecMAT_*.C SpecMAT Different pad geometry; scintillator variants available
GADGET_II.C GADGET-II Cylindrical TPC variant
FRIB_TPC_v*.C FRIB TPC

Macro Anchors

Use real macros, not isolated snippets, when tracing behavior:

  • macro/examples/run_sim.C
  • macro/tests/AT-TPC/run_sim_attpc.C

Those show the surrounding FairRunSim setup, run->SetMaterials("media.geo"), and the other modules commonly registered with the TPC geometry such as AtCave, AtMagnet, and AtPipe.

Variant Selection

There is no single geometry file that is clearly canonical across the tree.

Different workflows use different files:

  • unpacking and display macros often use ATTPC_v1.2.root
  • older example simulation macros use ATTPC_v1.1.root
  • the AT-TPC integration test uses ATTPC_He1bar.root

When editing a workflow, trust the specific macro or test in that workflow over generic prose.

Materials

run->SetMaterials("media.geo") supplies material definitions used by geometry generation and simulation setup.

Common modifications to geometry/media.geo:

  • Gas composition: update the AtTPC_Gas entry — change density, atomic composition, and weight fractions
  • Window materials: modify the entrance window material entry
  • Add a material: append a new block following the existing format; the file header documents the required fields (ncomp, aw, an, dens, wm, sensflag, fldflag, fld, epsil)

If media.geo changes, regenerate any geometry outputs that depend on it.

Geometry vs Mapping

Keep these separate:

  • transport geometry: AtDetectors/AtTpc, geometry/*.C, simulation macros
  • pad mapping and display-plane geometry: AtMap/, visualization, decoder/mapping setup

If the task mentions pad geometry or lookup tables, start in AtMap/, not AtDetectors/AtTpc.

Navigation Order

  1. Find the macro, task, or test that names the geometry file.
  2. Check whether that .root file already exists in geometry/.
  3. Inspect AtDetectors/AtTpc/AtTpc.cxx for the runtime load path.
  4. Inspect the matching geometry generator macro in geometry/ if the asset must change.
  5. Branch into AtMap/ only if the task is really about pad mapping rather than transport geometry.