Write a spec from a drawing

A drawing says what a part must be. A spec says the same as claims the engine can decide: one callout, one matcher, one expectation. The claims come from the drawing; the measurements come from the model.

Map the callouts

Python spells each matcher in snake case with the same keys as keyword arguments: to_have_circular_hole_pattern(count=6, holeDiameter=5, boltCircleDiameter=45, axis="z"). Every feature row needs a STEP export; three rows need care:

• Holes. toHaveCircularHole decides diameter, axis, centre and through; it has no depth field, so a depth callout stays a requirement the spec reports as unsupported.
• Wall thickness. The engine measures the exact minimum of a complete box or a right cylinder only (admitted geometry); a bored plate is neither, so the claim refuses with GEOSPEC_UNSUPPORTED_EVIDENCE. Keep the callout and report it as unsupported.
• Mass. density in g/mm³ gives grams. Without it the claim refuses on every subject.

Take the tolerance from the drawing

A tolerance block of ±0.1 becomes tolerance: 0.1 on the claims it covers; a claim without one is held to 0.02 mm (Set tolerances and budgets). A limit such as "2 min" is a strict comparison, greaterThanOrEqual, with no tolerance. The tolerance never moves to make a claim pass: a failure at the drawing's tolerance is a model that misses the drawing.

The plate

The drawing in words: a 40 × 40 × 20 mm aluminium plate, origin at the centre of its bottom face, Ø10 bore on centre along z. Its volume is 40 × 40 × 20 less π × 5² × 20, or 30429.2 mm³; at 0.0027 g/mm³ that is 82.16 g, centre of mass [0, 0, 10].

const part = await loadModel({ source: 'plate-with-through-bore.step', format: 'step' });

expectGeo(part)
  .toHaveBoundingBox({ size: { x: 40, y: 40, z: 20 } });
expectGeo(part)
  .toHaveCircularHole({ diameter: 10, axis: 'z', center: { x: 0, y: 0 } });
expectGeo(part)
  .toHaveVolume({ value: 30429.2 });
expectGeo(part)
  .toHaveMass({ value: 82.16, density: 0.0027 });
expectGeo(part)
  .toHaveCenterOfMass({ point: [0, 0, 10] });

import { readFile } from 'node:fs/promises';import { expectGeo } from 'geospec';import { createModelLoader } from 'geospec/model';import { Engine } from 'geospec-engine/node';const engine = new Engine();const loadModel = createModelLoader({ engine, readSource: async (source) => new Uint8Array(await readFile(source as string)) });const part = await loadModel({ source: 'plate-with-through-bore.step', format: 'step' });expectGeo(part)  .toHaveBoundingBox({ size: { x: 40, y: 40, z: 20 } });expectGeo(part)  .toHaveCircularHole({ diameter: 10, axis: 'z', center: { x: 0, y: 0 } });expectGeo(part)  .toHaveVolume({ value: 30429.2 });expectGeo(part)  .toHaveMass({ value: 82.16, density: 0.0027 });expectGeo(part)  .toHaveCenterOfMass({ point: [0, 0, 10] });await loadModel.dispose();engine.close();

All five pass. Set x to 41, or diameter to 12, and that claim fails with the measured value in its diagnostic; the drawing's number then comes from the model.

As a file, give each callout its own test: a failed or refused claim ends the test it is in, so one test per callout keeps every verdict visible. GeoSpec for agents runs a spec from a shell.

Variations

A mesh export. On a GLB of the part the size, volume, mass and centre rows still answer; the bore row refuses with GEOSPEC_UNSUPPORTED_EVIDENCE. Read a refusal says what to change.

A range on the drawing. "30400 to 30500 mm³" is toHaveVolume({ value: { greaterThan: 30400, lessThan: 30500 } }), in Python to_have_volume(value={"greaterThan": 30400, "lessThan": 30500}); the comparisons are strict and carry no tolerance.

A part with no drawing. Query analyzeBrep to list the holes, patterns, chamfers and fillets the model carries, then write claims from the requirement, not the inventory. A claim copied from the measurement passes on every model, including a wrong one.