Import & heal a STEP file¶

Pull external CAD (.step / .stp) into a session, clean up the dirty geometry that legacy exporters ship, and turn it into a meshable, solver-ready model. This is the reason many people reach for apeGmsh — but remember: STEP gives you geometry only. Physical groups, mesh sizing, and meshing are still yours to define.

The recipe¶

Look before you heal: diagnose() reports the geometry's health without touching it, so you only reach for heal= when there are real slivers.

from apeGmsh import apeGmsh

g = apeGmsh(model_name="bracket")
g.begin()

# 1. Import raw, then inspect. load_step does NOT create physical groups.
g.model.io.load_step("bracket.step")          # default: highest_dim_only=True → volumes only

report = g.model.io.diagnose()                # -> ImportHealth, non-mutating
print(report)                                 # solids, dim_counts, short_edges, tiny_faces, suggested_tolerance

# 2. Heal only if slivers are present. heal="auto" is scale-aware
#    (≈ 1e-6 · bbox diagonal) — the right default across unit systems.
if report.is_suspect:
    imported = g.model.io.load_step(
        "bracket.step", heal="auto", dedupe=True   # re-import clean
    )
else:
    imported = g.model.io.load_step("bracket.step")

bodies = imported[3]                          # all imported volume tags

# 3. Name what the solver cares about — by SELECTION/QUERY, never raw tags.
g.physical.add(3, bodies, name="Steel")

base = g.model.queries.entities_in_bounding_box(
    -1e3, -1e3, -1e-3, 1e3, 1e3, 1e-3, dim=2)     # -> [(dim, tag), ...]
g.physical.add(2, [t for _, t in base], name="Fixed_Support")

# 4. (multi-body assemblies) make the interface conformal before meshing.
g.model.queries.make_conformal(dims=[3])

# 5. Size, mesh, hand the snapshot to the bridge.
g.mesh.sizing.set_size_global(max_size=5.0)
g.mesh.generation.generate(dim=3)
fem = g.mesh.queries.get_fem_data(dim=3)

g.end()

From here build OpenSees through the typed apeSees(fem) bridge and target everything by the physical-group names above ("Steel", "Fixed_Support") — never raw entity tags.

Notes / gotchas¶

heal= is one-shot import+clean. heal="auto" (== heal=True) derives a scale-aware tolerance; a float pins an absolute tolerance. A fixed absolute tolerance is meaningless across unit systems — a 1e-3 mm gap and a 1e-3 m gap differ by 1000×. Prefer "auto".
diagnose() never mutates. It scans the live OCC geometry and returns a frozen ImportHealth; is_suspect is True only when slivers (short_edges / tiny_faces) exist. A surface-only import is not flagged — shell models import that way on purpose. On a raw import apeGmsh already emits a WarnGeomImportHealth advisory for you.
dedupe=True merges coincident entities that STEP assemblies often repeat across bodies. Runs after healing when both are set.
STEP carries no physical groups. After load_step you always define your own. Need named regions to survive the CAD round-trip? Export to .msh from Gmsh, or use DXF layers (load_dxf).
Multi-body ≠ conformal. Imported bodies come in as independent solids. For a shared-node mesh across an interface, run make_conformal (or g.model.boolean.fragment) before meshing.
One kernel per session. load_step uses the OCC kernel; don't mix in geo-kernel entities or booleans between them will fail.

Import & heal a STEP file¶

The recipe¶

Notes / gotchas¶

See also¶