| HEG BRep Component Identifier — integration brief | |
| What it is | |
| A self-contained Windows folder (~2.1 GB unpacked) that runs an ML classifier for STEP-format CAD parts. Given a STEP file path, it returns a component label (elbow, tee, pipe, miscellaneous, plus a subtype for elbows/tees). | |
| It is not a DLL. It's a local HTTP service that runs as a child process of our viewer. The classifier is a PyTorch model behind a FastAPI server. The whole Python stack — interpreter, OCC kernel, torch, model weights — is bundled inside the folder. No Python install required on the user's machine. | |
| Architecture | |
| ┌──────────────────────────┐ ┌──────────────────────────────┐ | |
| │ Our C# 3D Viewer │ spawn child + stdout │ heg_brep_service.bat │ | |
| │ (parent process) │ ───────────────────────► │ (our launcher) │ | |
| │ │ │ └─► python.exe │ | |
| │ On viewer startup: │ read line: │ └─► FastAPI server │ | |
| │ - Process.Start(bat) │ ◄───────────────────────│ on 127.0.0.1 │ | |
| │ - read "READY port=N" │ "READY port=51571" │ :random_port │ | |
| │ │ │ │ | |
| │ On user click: │ POST /classify │ Loads models once at │ | |
| │ - HttpClient.PostAsync │ ───────────────────────► │ startup. Per-request: │ | |
| │ - JSON body │ ◄─────────────────────── │ STEP → OCC features → │ | |
| │ {step_path: "..."} │ JSON response │ GNN classifier → JSON │ | |
| │ │ │ │ | |
| │ On viewer exit: │ POST /shutdown │ │ | |
| │ - StopAsync() │ ───────────────────────► │ Graceful exit │ | |
| └──────────────────────────┘ └──────────────────────────────┘ | |
| Two key properties: | |
| One process per viewer instance. Service lifetime == viewer lifetime. | |
| Loopback only. Binds to 127.0.0.1, never exposed to the network. No firewall prompts. | |
| The API contract | |
| Endpoint Method Body Returns | |
| /health GET — {"status":"ok","models_loaded":true,"device":"cpu","uptime_sec":...} | |
| /classify POST {"step_path":"C:\\full\\path.step"} classification JSON (below) | |
| /classify_batch POST {"step_paths":["...","..."]} {"results":[...]} | |
| /shutdown POST — {"status":"shutting_down"} (service exits ~200ms later) | |
| Successful /classify response: | |
| { | |
| "status": "ok", | |
| "final_label": "4_tee_wf", | |
| "final_conf": 0.9997, | |
| "route": "tee", | |
| "pass1_argmax": "tee", "pass1_conf": 1.0, | |
| "pass2_argmax": "4_tee_wf", "pass2_predicted": "4_tee_wf", "pass2_conf": 0.9997, | |
| "step_path": "C:\\...\\part.step", | |
| "npz_path": "C:\\Users\\...\\AppData\\Local\\Temp\\heg_brep_npz_xxx\\part.npz" | |
| } | |
| Error responses (HTTP 200 with an error status field, not HTTP 4xx — so the C# code branches on status): | |
| {"step_path": "...", "status": "extraction_failed", "error": "Bodies which are not closed are not supported"} | |
| {"step_path": "...", "status": "inference_failed", "error": "..."} | |
| {"step_path": "...", "status": "error", "error": "step_path not found"} | |
| Label space | |
| Pass-1 (parent classifier): elbow / tee / pipe / miscellaneous | |
| Pass-2 elbow subtypes: 1_elbow_wf / 2_elbow_pef / 3_elbow_sf / 8_elbow_misc | |
| Pass-2 tee subtypes: 4_tee_wf / 5_tee_pef / 6_tee_sf / 9_tee_misc | |
| Pipe / miscellaneous: final_label is random (no specialist for these families). Use pass1_argmax if you need the parent label. | |
| *_wf = welded fitting, *_pef / *_sf = other manufacturing subtypes, *_misc = within-family unclassified. | |
| What you need to implement in C# | |
| There's a working reference client in dist/heg_brep_dist/csharp_sample/ (~150 lines). It targets .NET 6 but works on .NET Framework 4.7.2+ with no changes. Usage: | |
| var client = new HegBrepClient(); | |
| // At viewer startup (or lazily on first identify request — your call): | |
| await client.StartAsync(@"C:\Program Files\OurViewer\heg_brep\heg_brep_service.bat"); | |
| // When the user clicks "Identify component": | |
| var stepPath = await ExportCurrentSelectionToTempStep(); // your existing OCC export | |
| var result = await client.ClassifyAsync(stepPath); | |
| labelControl.Text = $"{result.FinalLabel} ({result.FinalConf:P1})"; | |
| // On viewer shutdown: | |
| await client.StopAsync(); | |
| The client class handles: spawning the bat, reading the READY port=N line from stdout, posting JSON, parsing responses, graceful shutdown with a Kill fallback. | |
| Performance budget | |
| Measured on a developer laptop (RTX 3050, but service runs on CPU): | |
| Event Cost | |
| Service startup 10–15 s (paid once per viewer launch) | |
| First /classify after startup ~1.0 s | |
| Subsequent /classify calls ~0.8 s (dominated by OCC feature extraction; inference itself is ~50 ms) | |
| For UX, recommend you start the service eagerly at viewer launch (hide behind splash) or lazily on first Identify click (show a "warming up..." spinner for ~10 s). | |
| Failure modes you must handle | |
| Service won't start (heg_brep_service.bat exits before READY line) → log stderr (the client forwards it to Debug.WriteLine), surface error to user, do not retry in a tight loop. | |
| STEP fails extraction ("Bodies which are not closed are not supported" is the most common one — Inventor exports sometimes hit this). Branch on status != "ok". | |
| Service hangs / takes too long — HegBrepClient has a 60-second timeout. If ClassifyAsync throws TaskCanceledException, the service is wedged. Call StopAsync() and restart. | |
| Service crashes mid-session — process exits, next ClassifyAsync will throw a connection error. Recovery: catch, call StartAsync() again, retry once. | |
| A small supervisor that restarts the service on crash (max 3 retries per session) is a reasonable addition. | |
| What's in the bundle | |
| heg_brep_dist/ | |
| ├── heg_brep_service.bat ← what you Process.Start | |
| ├── heg_brep_batch.bat ← offline regression-test tool, irrelevant for the viewer | |
| ├── README.txt ← detailed docs | |
| ├── python/ ← bundled Python 3.10 env (do not modify) | |
| ├── heg_brep/ ← our Python code | |
| ├── BRepExtractor/ ← STEP→features pipeline | |
| ├── models/ ← 3 model files (~94 MB total) | |
| └── csharp_sample/ ← HegBrepClient.cs + Program.cs (copy into your project) | |
| Installer should drop this whole folder somewhere under the viewer's install dir (e.g. Program Files\OurViewer\heg_brep\) and never modify it. Updates ship as a new folder replacement; viewer code doesn't change. | |
| Constraints / non-goals | |
| Windows x64 only. Linux / macOS / 32-bit not supported. | |
| CPU inference by default. A CUDA variant exists (separate ~2 GB bundle) if customers have NVIDIA GPUs — currently not packaged. | |
| STEP input only. Other CAD formats (IGES, JT, native Inventor/SolidWorks) would need a converter layer first. | |
| Single-threaded service. Don't fire concurrent /classify calls from multiple viewer threads — they'll serialize anyway. If you need parallelism, queue requests in C#. | |
| Questions to send back | |
| If anything in the contract is unclear, the things most worth raising before coding starts: | |
| Where in the installer layout should heg_brep_dist/ live? That determines the path you pass to StartAsync. | |
| Eager vs. lazy service startup — affects splash-screen design. | |
| How does the viewer currently export a selected solid to a STEP file? (We need a file path, not in-memory geometry, in v1.) | |
| Logging — should service stderr go to the viewer's existing log file, or to its own file alongside the bundle? |