Thalias Relay · Project Document CTR-WEB-001

Contour.

Parametric CAD in the browser. Drawn, dimensioned, and machined from a single tab.

Project Thalias Relay

Revision A — 2026-11-09

Units mm · deg

Status Live

Sheet 1 of 1

Scale 1 : 1, always

Definition

Noun · from the Italian contorno, an outline

contour /ˈkɒn.tʊər/

noun.

The outline of a solid; the edge you can trace where a surface turns away from the light.
A line on a drawing or map joining points that share one value — height, pressure, temperature.
Here: a CAD program named for both — it takes the outline seriously, and it keeps every value exact.

Browser CAD that feels like Shapr3D, with a real B-rep kernel — accurate enough for CNC shops and 3D printing.

Specification

As built · not as promised

Kernel	Open CASCADE Technology 8.0, compiled to WebAssembly. A production B-rep kernel — the same class of geometry engine behind industrial CAD — not a mesh approximation of one.
Solver	PlaneGCS geometric constraint solver. Sketches report their degrees of freedom, conflicts, and redundancies; a sketch is never silently half-solved.
Document	Feature-history JSON is the source of truth. The model is a list of operations that can be replayed, edited, and re-solved — the 3D view is a consequence of the document, never the other way round.
Interaction	Direct manipulation. Push and pull faces by their arrows; drag an edge to grow a fillet or chamfer. Type a number mid-drag when the hand is not precise enough.
Previews	Real kernel results, never faked. What follows your cursor while you drag is the kernel’s own answer for that value — there is no stand-in geometry anywhere in the program.
Exports	STEP AP214 by default, AP242 on request — and every export is re-imported and volume-checked before it is handed over. Hand-rolled 3MF for printing.
Runs	Entirely in the browser. Kernel, solver, and document live on your machine; there is no server in the loop and nothing to upload.

Principles

Working rules · enforced in review

The kernel is never approximated.If a result did not come out of the geometry engine, it does not go on the screen.
A preview is a result, not a guess.Drag feedback is computed, not theatre. When the kernel is still working, the last true answer stays up.
State is exposed, not hidden.Degrees of freedom, invalid features, stale measurements — the program says what it knows and what it doesn’t.
The document outranks the picture.Features, parameters, and references are the model. Rendering is downstream and disposable.
Nothing silently retargets.An edit that cannot find the face or edge it was made on stops and says so. It never lands on a neighbour.
Accuracy is the feature.Exports are verified against the source solid. A file that measures wrong is a defect, not a rounding error.

Status

Checked 2026-11-09

Live now, in active development. Contour opens in a browser tab and is ready to model: sketch with a real constraint solver, extrude and revolve, push and pull faces, fillet and chamfer by dragging edges, measure, and export verified STEP.

Development is continuous — the current build carries a session-based kernel core, so edits re-solve only what changed and drag previews land as true kernel results. Expect it to move quickly, and expect the numbers on this page to be re-measured as it does.

Run it

Launch Contour → contour-5by.pages.dev Source on GitHub ↗

Rev	Date	Description	By
A	2026-11-09	Initial release of this sheet. App live on Cloudflare Pages; session-core build current.	Thalias Relay

Colophon

Imprint