Link Search Menu Expand Document
OCCTSwiftScripts

Engineering analysis

A DFM-style workflow for three headless verbs: check wall thickness against a manufacturing floor, confirm clearance and flag interference between mating bodies, and heal imported geometry that arrives non-watertight. All three verbs are pure read-then-write — they take BREPs from disk and emit JSON on stdout.

Full flag and return-value details: Engineering analysis reference.

1. Wall-thickness check

check-thickness UV-grid samples each face and casts an inward ray to the opposite wall. Use --sampling-density fine (16×16 per face) for a casting or injection-mould submission; coarse (4×4) for a quick sanity pass on large bodies.

occtkit check-thickness housing.brep \
    --min-acceptable 1.5 \
    --sampling-density fine

{
  "minThickness": 1.1,
  "maxThickness": 4.8,
  "meanThickness": 2.9,
  "thinRegions": [
    {
      "centerPoint": [10.5, 20.3, 5.1],
      "thickness": 1.1,
      "faceRefs": ["face[3]"]
    }
  ],
  "samples": 256
}

minThickness: 1.1 is below the 1.5 mm floor. The thinRegions array gives the world-space centerPoint and faceRefs for every flagged sample — take those coordinates back to your modeller to thicken the wall at face[3].

2. Clearance and interference check

analyze-clearance runs all pairwise gap checks in one call. Pass --min-clearance to tag every pair whose gap falls below a design rule; when two solids overlap, interferenceVolume reports the volume of the intersection.

occtkit analyze-clearance shaft.brep housing.brep bearing.brep \
    --min-clearance 0.1

{
  "pairs": [
    {
      "a": "shaft.brep",
      "b": "housing.brep",
      "minDistance": 0.05,
      "intersects": false,
      "belowMinClearance": true,
      "contacts": [
        { "fromPoint": [10.0, 0.0, 5.0], "toPoint": [10.05, 0.0, 5.0], "distance": 0.05 }
      ],
      "interferenceVolume": null
    },
    {
      "a": "shaft.brep",
      "b": "bearing.brep",
      "minDistance": 0.0,
      "intersects": true,
      "belowMinClearance": true,
      "contacts": [],
      "interferenceVolume": 2.3
    },
    {
      "a": "housing.brep",
      "b": "bearing.brep",
      "minDistance": 0.8,
      "intersects": false,
      "belowMinClearance": false,
      "contacts": [],
      "interferenceVolume": null
    }
  ]
}

The shaft–bearing pair has intersects: true and interferenceVolume: 2.3 mm³ — a real clash that needs fixing. The shaft–housing gap of 0.05 mm is within spec tolerance but tagged belowMinClearance: true because it is under the 0.1 mm design rule. Add --no-contacts to suppress point details and speed up large assemblies.

3. Heal imported geometry

Geometry imported from STEP or IGES often arrives with free edges, small slivers, or invalid orientation. Run heal to apply OCCT ShapeFix and write a repaired BREP, then compare the before/after snapshots to confirm the repair.

Before heal — snapshot the raw import:

occtkit check-thickness imported.brep --sampling-density coarse

{ "minThickness": null, "maxThickness": null, "meanThickness": null,
  "thinRegions": [], "samples": 0 }

No samples returned: the shape is not watertight, so inward rays escape without hitting an opposite wall.

Heal:

occtkit heal imported.brep --output imported_healed.brep --tolerance 0.01

{
  "outputPath": "/tmp/imported_healed.brep",
  "before": {
    "faceCount": 24, "edgeCount": 72,
    "freeEdgeCount": 3, "smallEdgeCount": 2, "smallFaceCount": 1,
    "selfIntersectionCount": 0, "isValid": false
  },
  "after": {
    "faceCount": 24, "edgeCount": 72,
    "freeEdgeCount": 0, "smallEdgeCount": 0, "smallFaceCount": 0,
    "selfIntersectionCount": 0, "isValid": true
  },
  "fixes": {
    "smallEdgesFixed": 2, "smallFacesFixed": 1,
    "freeEdgesClosed": 3, "selfIntersectionsResolved": 0
  },
  "warnings": []
}

isValid: true and freeEdgeCount: 0 in the after snapshot confirm the shell is closed. fixes.freeEdgesClosed: 3 accounts for all three violations from the before snapshot.

After heal — re-run the thickness check:

occtkit check-thickness imported_healed.brep \
    --min-acceptable 1.5 \
    --sampling-density fine

The healed BREP now returns real thickness statistics, and you can feed it straight into analyze-clearance alongside mating parts.

What next?