The Monge kernel
Its own exact B-Rep kernel in Rust: what it can do, how we test it and what it cannot do yet.
What it is
The kernel is the part of the program that computes geometry. In Monge it is its own: written from scratch in Rust, it keeps the model as exact surfaces and edges (B-Rep), not as a mesh of triangles. That is why the model gives a drawing, a flat pattern and STEP without losing accuracy.
The kernel’s code is closed and all rights are reserved. There is no code from other geometry kernels in Monge; the only third-party libraries in the kernel are for serialisation and logging. The program around the kernel uses open-source libraries under MIT, Apache and BSD licences — their full list will ship with the program.
What it can do
- Solids
- Extrude, revolve, cut, patterns, sweeps and pipes along a 3D path, sheet metal with bends and flat patterns.
- Surfaces
- Plane, cylinder, cone, sphere, torus, NURBS; lofts, Coons patches, Gordon surfaces from a curve network, stitching hundreds of sheets into a solid.
- Operations
- Exact Booleans of curved solids, rolling-ball fillets, chamfers, shells, thickening, exact mirroring, direct face editing.
- Parameters
- Build history, dimensions on the model, rebuilding a part in the same solid with a single undo.
- Exchange
- STEP AP214 with exact geometry, read and write; DXF, SVG and PDF for drawings and CNC; STL, OBJ, glTF.
- Solid checks
- Every solid is checked before it is accepted: closure, orientation, topology, mesh.
Kernel test protocol
Results of the kernel exam of 25 Oct 2026 and of the full daily check. Machine: MacBook Air M4, 24 GB. Where the kernel does not cope yet, we say so.
1,130tests pass on every change; 0 failed, the whole check takes 112 s
173kernel failures from real work fixed and replayed on every check
76cases still open: 55 fillets and chamfers, 19 Booleans
- 400×400×10 plate with 1024 Ø5 holes — 1030 facespassed
Built, then every hole changed Ø5 → Ø6; a valid solid
Time: 674 / 681 msMemory: 674 MB
- Stitching 216 curved NURBS surfaces into a solidpassed
Built and stitched; gap 2·10⁻¹³ mm, no open edges
Time: 470 + 500 msMemory: 142 MB
- A 6 m boat hull from 25 sectionspassed
Smooth surface built (the previous version refused)
Time: 1.8–2.1 s
- Rebuilding a part’s history after changing dimensionspassed
All 7 steps recomputed, the volume is right
Time: 67 ms
- STEP AP214 write and readpassed
Faces, edges, vertices and volume match the original
- A Boolean on the cast wheel (562 faces)passed
A valid solid
Time: 200–700 ms
- The AI builds a part from a descriptionpassed
21 commands; one kernel refusal — the AI fixed it itself
- Chamfering every edge over filletsnot passed
Refused for now — being worked on
Tests run on the exact geometry; heavy ones in separate processes with a 600 s limit and peak memory measured. The exam: Monge 0.15.4; the full check: 0.15.20.
Failure memory
Every failed kernel operation saves itself — with its exact input solids and parameters — and becomes a test. A fixed failure is replayed on every check, so it does not come back. Fixed and guarded: 173. Open: 76, of which 55 are fillets and chamfers and 19 are Booleans.
What the kernel cannot do yet
- Chamfering every edge over existing fillets — refused.
- A corner where three filleted edges meet on a curved face, and some joins of a filleted edge with a sharp one.
- Thickening a surface with a sharp crease, like a boat hull’s chine.
- Heavy models take a lot of memory: 0.7–2 GB.
- The palette sphere is still faceted — Booleans with it fail.
How we test
A full check after every change to the kernel: all tests of the kernel, the document, materials and saved failures. The latest — 28 Oct 2026: 1,130 tests, 0 failed, 112 s.
Exams run in separate processes with a 600 s limit and peak memory measured, on the exact geometry; the mesh is only for display.
Machine: MacBook Air M4, 24 GB.
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