Check meshes

A mesh answers for its triangles: whether they close, whether any are degenerate or duplicated, and how many pieces they form. Mesh checks run on GLB files; neither loadModel nor load_model admits raw triangles.

1. Claim closure and integrity

const part = await loadModel({ source: 'involute-gear.glb', format: 'glb', sourceUnit: 'mm' });

expectGeo(part)
  .toBeWatertight();
expectGeo(part)
  .toHaveMeshIntegrity({
    finitePositions: true,
    degenerateTriangles: { count: 0 },
    duplicateFaces: { count: 0 },
    triangleCount: 624,
  });
expectGeo(part)
  .toHaveNoDiagnostics();

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: 'involute-gear.glb', format: 'glb', sourceUnit: 'mm' });expectGeo(part)  .toBeWatertight();expectGeo(part)  .toHaveMeshIntegrity({    finitePositions: true,    degenerateTriangles: { count: 0 },    duplicateFaces: { count: 0 },    triangleCount: 624,  });expectGeo(part)  .toHaveNoDiagnostics();await loadModel.dispose();engine.close();

The gear is a GLB mesh of 624 triangles. Set triangleCount to 600 and the integrity claim fails with GEOSPEC_MESH_INTEGRITY_MISMATCH, stating 624 triangles, which does not satisfy 600. toBeWatertight reports the edges it checked, { "irregularEdgeFraction": 0, "irregularEdges": 0, "nonManifoldEdges": 0, "openBoundaryEdges": 0, "totalEdges": 936, "watertight": true }, and toHaveNoDiagnostics reads what the loader reported at admission, errors and warnings by default, and measures no geometry.

Switch the model to the plate, a STEP part: closure passes from the exact BRep topology, and the integrity claim is refused with GEOSPEC_UNSUPPORTED_EVIDENCE, because its fields would measure a tessellation the engine made; toHaveMeshIntegrity({ watertight: true }) is the one form STEP answers.

2. Count the pieces

toHaveConnectedComponents counts closed material shells, and shells closer than toleranceMm count as one. The gear is one piece, so { count: 2 } fails with GEOSPEC_CONNECTED_COMPONENTS_MISMATCH; the count indexes every triangle, which keeps it out of the live demo. The script counts the two 10 mm cubes, 20 mm apart, of an engine fixture, packages/geospec-engine/bench/fixtures/performance-lab/generated/assembly.glb, copied next to it:

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 cubes = await loadModel({ source: 'assembly.glb', format: 'glb', sourceUnit: 'mm' });

const pieces = expectGeo(cubes).toHaveConnectedComponents({ count: 2 });
const merged = expectGeo(cubes).toHaveConnectedComponents({ count: 1, toleranceMm: 21 });
console.log(pieces.report?.status, merged.report?.status);

await loadModel.dispose();
engine.close();

$ node check.ts
passed passed

from geospec import GeoSpecEngine, expect_geo, load_model

with GeoSpecEngine(model_root="."):
    cubes = load_model(file="assembly.glb", format="glb", source_unit="mm")
    pieces = expect_geo(cubes).to_have_connected_components(count=2)
    merged = expect_geo(cubes).to_have_connected_components(count=1, toleranceMm=21)
    print(pieces.result["status"], merged.result["status"])

$ python check.py
passed passed

The second claim spans the 20 mm gap with toleranceMm: 21, so the cubes count as one. The tolerance states how close two shells may sit and still be separate parts; it is not a way to make a count pass. Set tolerances and budgets covers it.

Variations

An open mesh. Remove one triangle from a closed box mesh and the claims answer differently: closure fails with GEOSPEC_WATERTIGHT_MISMATCH, The mesh has 3 irregular edges (3 open, 0 non-manifold), so it is not a closed manifold surface.; the component count is refused with GEOSPEC_INVALID_EVIDENCE rather than guessed, because shells are counted over closed, consistently oriented triangles; the integrity claim fails on its triangle count. The open box still reports a volume, 5000 mm³ where the closed one has 6000, which is why closure comes before Check mass properties.

A STEP subject. toHaveConnectedComponents reads the exact BRep topology and passes on the plate with { count: 1 }.

The reference. The mesh reference lists every field of the four claims.