Reconstruction graph

Swift only — the reconstruct_* tools require the Swift occtmcp-server.

This recipe walks the annotate-and-persist layer over an attributed reconstruction graph. OCCTMCP exposes topology as nodes addressed <kind>:<index> (e.g. face:3) and lets an LLM write per-node reconstruct.* attributes: decisions, fit overrides, and instance membership. The fitting engine lives in OCCTReconstruct; reconstruct_force_fit records an override attribute — it does not re-fit.

See the Reconstruction graph reference for full parameter tables.

1. Start a session

Call reconstruct_get_graph with a bodyId to open a session. The returned sessionId is the handle for every subsequent call.

{ "bodyId": "scan_part" }

{
  "sessionId": "scan_part",
  "topologyCounts": { "face": 12, "edge": 30, "vertex": 20 },
  "annotatedNodes": [],
  "instanceClusters": []
}

The graph has 12 faces, 30 edges, and 20 vertices — all unannotated so far. Resume an existing session by passing sessionId instead of bodyId.

2. Annotate a node’s decision

Use reconstruct_set_decision to record who made a fit decision and whether it is accepted. Supply at least one of decidedBy or accepted.

{
  "sessionId": "scan_part",
  "node": "face:3",
  "decidedBy": "human",
  "accepted": true
}

{
  "sessionId": "scan_part",
  "node": "face:3",
  "updated": {
    "reconstruct.decidedBy": "human",
    "reconstruct.accepted": true
  }
}

Repeat for each node you want to annotate. A subsequent reconstruct_get_graph call (with sessionId) will list all annotated nodes.

3. Override a surface type

If a face was fitted as plane but you know it should be cylinder, record the override with reconstruct_force_fit. This writes reconstruct.forcedSurfaceType onto the node; the OCCTReconstruct engine honours it on its next pass.

{
  "sessionId": "scan_part",
  "node": "face:5",
  "surfaceType": "cylinder"
}

{
  "sessionId": "scan_part",
  "node": "face:5",
  "forcedSurfaceType": "cylinder"
}

Valid values for surfaceType: plane, cylinder, cone, sphere, torus.

4. Confirm a congruence cluster

When you identify a set of nodes that form one part definition (congruent instances), call reconstruct_confirm_instances. Every listed node is tagged with the clusterId and the confirmed flag.

{
  "sessionId": "scan_part",
  "clusterId": "flange_boss",
  "nodes": ["face:2", "face:6", "face:9"],
  "confirmed": true
}

{
  "sessionId": "scan_part",
  "clusterId": "flange_boss",
  "nodes": ["face:2", "face:6", "face:9"],
  "confirmed": true
}

Pass "confirmed": false to reject a cluster the engine proposed.

5. Persist the session

reconstruct_export_session writes a byte-stable JSON snapshot. The default path is <output_dir>/reconstruct/<sessionId>.session.json.

{ "sessionId": "scan_part" }

{
  "sessionId": "scan_part",
  "path": "/Users/you/Library/Mobile Documents/com~apple~CloudDocs/OCCTSwiftScripts/output/reconstruct/scan_part.session.json"
}

The snapshot is byte-stable: the same session state always produces identical bytes, so it is safe to checksum or diff across saves. Pass an optional path to write elsewhere.

6. Reload a session

reconstruct_import_session reads a snapshot file back into memory and returns the full graph state. Use this after a server restart or to hand off a session between runs.

{
  "path": "/Users/you/Library/Mobile Documents/com~apple~CloudDocs/OCCTSwiftScripts/output/reconstruct/scan_part.session.json"
}

{
  "sessionId": "scan_part",
  "topologyCounts": { "face": 12, "edge": 30, "vertex": 20 },
  "annotatedNodes": [
    {
      "node": "face:3",
      "attributes": {
        "reconstruct.decidedBy": "human",
        "reconstruct.accepted": true
      }
    },
    {
      "node": "face:5",
      "attributes": {
        "reconstruct.forcedSurfaceType": "cylinder"
      }
    }
  ],
  "instanceClusters": [
    { "clusterId": "flange_boss", "nodes": ["face:2", "face:6", "face:9"], "confirmed": true }
  ]
}

sessionId defaults to the file stem (scan_part here); pass an explicit sessionId to assign a different handle.