ogeom

A B-rep solid modelling kernel in Rust. It does not wrap or link any other CAD kernel, and it is licensed LGPL-2.1 as a derivative work of Open CASCADE Technology, its reference kernel: see PROVENANCE.md.

• Guide: https://gilbertorconde.github.io/ogeom-rs/
• API reference: https://gilbertorconde.github.io/ogeom-rs/api/ogeom/
• Changes: CHANGELOG.md

What it does

Area	Included
Modelling	primitives, extrusions, revolutions, sweeps, lofts, booleans, fillets and chamfers, offsets and shells, drafts, face removal
Geometry	lines, conics, B-splines and NURBS, elementary and freeform surfaces, curve and surface intersection
Analysis	volume, area, mass properties, distances, validity checks, healing
Meshing	tessellation at a stated deflection, per-face meshes that agree along shared edges
Drawings	hidden line removal, sections, DXF output
Exchange	STEP (assemblies, colours, PMI, views) and IGES in both directions; STL, OBJ, PLY, glTF, 3MF, VRML, DXF, and a native format
Meshes to solids	solid_from_mesh turns a triangle mesh into a solid, merging flat regions into planar faces and rebuilding cylinders, cones, spheres, tori, extrusions, surfaces of revolution and fitted B-spline patches

Scope and completeness

The target is a complete solid-modelling kernel with its data exchange, plus turning meshes into solids. docs/SCOPE.md defines the boundary.

docs/CAPABILITIES.md records 90 named capabilities. Each verdict cites the code and tests that back it, and the build fails if the two drift apart. Rows marked partial state their limits.

PROVENANCE.md records where the code and design came from.

When the kernel cannot do something, it returns an error that says so. It does not return a guessed result.

Crates

Crate	Contents
ogeom	the public API, re-exporting everything below
ogeom-core	arenas, identity, errors, tolerances, predicates
ogeom-math	points, vectors, transforms, B-spline basis, solvers
ogeom-geom	curves and surfaces
ogeom-topo	the B-rep data model
ogeom-algo	construction, measurement, classification, mesh to solid
ogeom-mesh	tessellation
ogeom-intersect	curve and surface intersection
ogeom-bool	booleans and face removal
ogeom-heal	healing and simplification
ogeom-fillet	fillets and chamfers
ogeom-offset	offsets, shells, sweeps, lofts, drafts
ogeom-hlr	hidden line removal and drawings
ogeom-io	file formats
ogeom-doc	assemblies, colours, names, PMI

tools/ holds a command-line tool, a software renderer, benchmarks and the capability-ledger scripts. outside/ holds working code that is out of scope (constraint solving, feature recognition, picking) in a separate workspace.

Design

• A shape is a handle: a topology node, a chain of placements and an orientation. The same node can be placed many times without copying.
• Every entity keeps its own tolerance, which only grows.
• Every entity records where it came from, so references survive a rebuild.
• Every operation returns a history of what became of its inputs.

docs/DATA_MODEL.md has the details.

Building

cargo build --workspace
cargo test --workspace

The full check that CI runs (formatting, lints, tests, docs, the guide and the capability ledger):

bash tools/check.sh   # needs mdbook: cargo install mdbook --locked

In your own crate

The workspace's release profile does not reach a crate that depends on ogeom, and neither does a target CPU. Two settings in the dependent crate make the kernel faster with results the same to the bit:

# Cargo.toml of the crate that depends on ogeom
[profile.release]
lto = "thin"
codegen-units = 1

# .cargo/config.toml, where every machine it runs on has AVX2 and FMA
# (x86-64-v3: Intel Haswell, AMD Excavator and later)
[build]
rustflags = ["-C", "target-cpu=x86-64-v3"]

Without a target CPU each of the kernel's fused multiply-adds is a call into the C library rather than one instruction. Both are rounded once, so the answers do not change. Measured converting and refining a 29,003-face solid on one thread, against a dependent crate's default release build:

Settings	Instructions	CPU time
default	9.69e11	60.6 s
thin LTO, one codegen unit	9.39e11 (-3%)	57.1 s (-6%)
x86-64-v3	7.44e11 (-23%)	46.9 s (-23%)
both	7.22e11 (-26%)	45.7 s (-25%)

The refined solid, and each of mesh_corpus's fifteen parts converted back, came out the same to the bit under all four.

License

The GNU Lesser General Public License, version 2.1, and no other version: LGPL-2.1-only. The licence text is COPYING.LESSER and the GPL it refers to is COPYING.

ogeom is a derivative work of Open CASCADE Technology in the licensing sense: it was built with OCCT as its reference kernel, and it follows OCCT's public API vocabulary, data-model conventions and default tolerances. PROVENANCE.md records the full provenance and the audit behind that statement.