The Axiolid boundary

ifc-geometry is a bridge, not a geometry engine. This page states exactly where the responsibility transfers, because misunderstanding this boundary is the most common way to over-estimate what the crate can do.

The split

Swipe diagram horizontally

Diagram source

flowchart LR
  accTitle: Responsibility transfer from IFC records to Axiolid
  accDescr: The untyped IFC model is interpreted by ifc-geometry, which resolves IFC entities, units, placements, and mapped items into a neutral Axiolid GeometryGraph. Providers remain downstream and are not dependencies of the bridge.
  Model["ifc-model<br/>untyped record graph"] --> Bridge["ifc-geometry<br/>typed views<br/>IFC resolution<br/>units + placements"]
  Bridge --> Graph["Axiolid GeometryGraph<br/>neutral authored intent"]
  Graph -.-> Providers["Explicit downstream providers<br/>not owned by ifc-geometry"]

ifc-geometry answers: what does this IFC entity mean geometrically? Which profile, which placement, which units, which representation, which sub-shape does an IfcMappedItem reuse?

Axiolid answers: what do I compute with that meaning?

ifc-geometry's own crate documentation is explicit:

It does not triangulate, evaluate NURBS, perform booleans, or select execution providers.

That is a design commitment, not a temporary limitation. Geometry algorithms belong to a format-neutral kernel so they are not re-implemented per file format, and so the IFC crate never grows a dependency on a CPU or GPU provider. ifc-geometry/tests/no_backend_dependency.rs enforces the second half.

Consequences you must plan for

Curve representation is not curve evaluation. ifc-geometry reads an IfcBSplineCurveWithKnots into a neutral B-spline description. Producing points along it is an Axiolid concern. If you need discretised geometry — for drawing, export, or measurement — that call is downstream of this crate.

Booleans are represented, not executed. IfcBooleanResult lowers into a DAG node describing the operation and its operands. Evaluating it requires a mesh Boolean provider.

Sectioning remains downstream. Axiolid now provides a neutral MeshPlaneSection contract and a portable reference implementation over an explicit TriMesh, with bounded evidence and refusal semantics. ifc-geometry does not call it or manufacture plan representations from body geometry. An application may select an authored IFC plan representation, or explicitly lower and compile body geometry before invoking the opt-in Axiolid operation.

Axiolid is a contract kernel more than an algorithm library. Much of it defines neutral vocabulary and validated representations; a smaller portion is executable algorithms. Check Axiolid's own capability documentation rather than assuming an operation exists because a crate named after it does. Its geometry concepts guide uses interactive STL examples and equations to explain profiles, mesh orientation, tolerance, and the representation/execution distinction.

What Axiolid does provide

Verified at the revision pinned by this workspace:

• Exact and filtered geometric predicates (orient2d, incircle, insphere) with degeneracy tests — a correctness oracle.
• Polygon ring utilities: signed area and orientation.
• Ear-clipping triangulation for hole-free rings, and an Earcut-backed triangulation provider.
• Neutral values for primitives, profiles, curves, surfaces, and B-rep topology.
• Scalar reference evaluation for polynomial and rational B-spline curves and surfaces, including analytic first surface partials.
• An immutable shared geometry DAG with typed IDs.
• A mesh Boolean provider, bounded by its own mesh contract.
• A neutral mesh-plane-section contract plus portable reference implementation, with bounded evidence/refusal semantics.
• CPU context and a GPU seam — a seam, not a bundled kernel suite.

The pin

The workspace pins Axiolid crates to an exact git revision rather than a version range, so geometry behaviour is reproducible across builds:

axiolid-core = { git = "https://github.com/axiolid/kernel.git", rev = "c144808d76ebf653b2183d6895192514d1838bfd" }

Production lowering pins only representation-level crates — core, mesh, model, primitive, profile, curve, surface, and topology. axiolid-reference is a dev-only oracle used by import regressions; it does not enter the published adapter's production dependency graph.