--- type: entity tags: [parking, hardware, readers, offline-first] sources: [parking-system-architecture] updated: 2026-06-15 --- # LPR Camera License-plate-recognition camera. For **casual/transient** vehicles, the **plate acts as ticket + an independent record**. (See [[parking-system-architecture]] §8, §9.) > **Superseded direction (2026-06-15):** recognition now runs **host-side** on snapshots from > ordinary Hikvision/Dahua cameras via the [[opencv-anpr-service]], **not** on a dedicated edge-AI > LPR camera — see [[vision-service]]. The edge-AI camera below is kept as the original assumption / > a fallback option, but is no longer the planned path. The host-side service also does **vehicle > verification** (anti-plate-spoofing), which an edge-LPR camera does not. - **Edge AI (original assumption)**: recognition runs **on-device**, so it keeps working with no internet — fits [[offline-first]]. - It's a **host-side** identity source: only the host sees the read; the host decides and commands the relay open (the [[uhppote-controller]] is demoted to a commanded relay for that lane). See [[entry-exit-readers]]. - Being host-in-the-loop is **good for fraud detection** — you get two independent records (the host's signed [[append-only-event-chain]] entry + the controller's remote-open event) that should reconcile one-to-one; any mismatch is an anomaly. - Mounting: within ~15° of vehicle travel at a controlled chokepoint for best reads. ## Snapshot driver (entry/exit fraud-control record) Separate from edge-AI LPR: the camera driver (`packages/devices/src/drivers/camera.ts`) does **snapshot-on-event** — the host pulls a still over HTTP when an entry/exit fires and stores it, referenced from the signed [[append-only-event-chain]] entry as an independent record. The camera **pulls, it does not push** — so it is NOT `pushesToBackend` and the setup wizard correctly hides the "Backend push IP" field for it (gated on the driver's `pushesToBackend` flag; only [[dingtian-relay]] sets it). - **Hikvision** uses **ISAPI**: `GET /ISAPI/Streaming/channels//picture` (`101` = ch1 main stream) with **HTTP Digest** auth. The "Enable Hikvision-CGI" toggle (Network → Advanced → Integration Protocol) is a *different* legacy CGI surface — **not** needed for ISAPI. - **Dahua** uses CGI: `GET /cgi-bin/snapshot.cgi?channel=` (0-based channel; the wizard's 1-based channel is decremented). **Driver / storage boundary:** the driver FETCHES the image bytes (client-side HTTP Digest in `drivers/http-digest.ts`) and returns them on `Snapshot.bytes`; **storage is the caller's job** (the future entry/exit flow stores the bytes + mints a durable `imageRef`). This keeps the device adapter free of any filesystem/blob-store dependency. `healthCheck()` is honest — it actually pulls a frame (exercising reachability + auth + path/channel in one shot), not a fake `ready/stub`. ### Verified on hardware (2026-06-15) A **Hikvision** unit ("Camera 20", MAC `94:e1:ac:…`, Hikvision OUI) at `10.0.10.121`, creds `admin` / `admin123` (Digest), TCP 80: - Initial `curl` test confirmed the ISAPI path returns a 2688×1520 JPEG (~306 KB). - The **real driver** (no longer a stub) was then run end to end against it: `healthCheck()` → `ready` (pulled a frame), `captureSnapshot()` → valid `image/jpeg`, ~322 KB, correct JPEG magic. Digest handshake works through `HttpCamera`. - Reaching it from the WSL dev box required forcing the source address (`config.localAddress`, threaded into the driver) — see [[wsl-dev-networking]] (multi-subnet source-selection trap). ## Camera PUSH — "Alarm Server" event notifications (2026-06-22) Separate from the **pull** snapshot path above: newer Hikvision firmware can **push** an event to us. Under **Event → Smart/VCA** (e.g. line crossing / intrusion / "Vehicle Detection") the unit exposes **Detection Target: Human / Vehicle** — selecting **Vehicle** + **Notify Surveillance Center**, then **Alarm Settings → Alarm Server**, makes the camera **HTTP-POST an `EventNotificationAlert`** to a URL we host on each detection. Same machine-call shape as the [[dingtian-relay]] Input Link push — no polling. - **Ingress:** `POST /api/devices/hikvision/:deviceId/event` (`apps/server/src/routes/hikvision-alarm.ts`). **Source-IP guarded** (must come from the device's configured `host`) + **optional HTTP Digest** (some firmware can't authenticate the Alarm Server call → source-IP only). NOT behind the SPA cookie/CSRF (it's a device call), exactly like the Dingtian push. - **Config:** added to the `hikvision` driver — `alarmPushEnabled` (bool), `pushUser`/`pushPassword` (optional Digest). The driver is now `pushesToBackend: true`, so first-run setup offers the backend push IP. Point the camera's Alarm Server at `http://:/api/devices/hikvision//event`. - **Discovery-first:** the endpoint is **permissive** — accepts ANY content-type as raw bytes (event XML, multipart-with-JPEG, or JSON; Hik's format varies by model/firmware), records the **verbatim body** as a `kind:"alarm"` device_event, and best-effort extracts `eventType` / `target` / `plate` / `dateTime` / `channelID`. The point of this first cut is to **see exactly what a given camera sends** (inspect via `GET /api/events` or the server log) before wiring it to the read bus. - **Not yet a barrier trigger.** It records + breadcrumbs only; it does NOT emit a `DeviceReadEvent` or open anything. A plate read is **advisory, never the sole reason** a barrier opens ([[append-only-event-chain]], [[opencv-anpr-service]]) — the entry/exit wiring is a deliberate next step once the real payload is known. If the camera emits its own plate (``), we can use it as an advisory read directly; otherwise the server hands the attached/pulled frame to the [[opencv-anpr-service|vision service]] for ANPR.