--- 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 **Superseded direction (2026-06-15):** recognition now runs **host-side** on snapshots from 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]]). Two consumers were since designed off this same vehicle event — see **[[lane-presence-and-anpr-entry]]**: (a) BUILT — advisory lane busy/free booth lights; (b) PLANNED — the ANPR "bridge" that snapshots → ANPR → emits a `kind:"plate"` read for a SUBSCRIBER match through the existing gated flow (a small `apps/server` handler, not a service). If the camera ever emits its own `` we'd use it directly; this `DS-2CD1043G2` does not, so the server pulls the frame and hands it to the [[opencv-anpr-service|vision service]]. ### Gotchas learned the hard way (2026-06-22 field session) Several traps surfaced trying to get a real camera to push. In order of how long each cost: - **WSL rewrites the inbound source IP.** On the dev host (WSL mirrored mode), an inbound LAN packet arrives at our server with its **source rewritten to the host's own IP** (`10.0.10.203`), not the camera's. The source-IP guard then rejects every push as a mismatch. Fix: a per-device **`skipSourceIpCheck`** config flag (a Setup checkbox) that bypasses the IP guard — the signed ledger + optional Digest remain the real guards. Leave OFF on a normal LAN. - **The setup checkbox saved booleans as the STRING `"true"`.** The generic config-field form had no boolean renderer, so a `type:"boolean"` field fell through to a text input. Fixed (checkbox renderer); the server also coerces `"true"`/`1`/`yes`/`on` defensively. - **The camera's "Test" button proves almost nothing.** It does a TCP/connectivity probe and reports "service available" on ANY HTTP reply (even our 404) — it does **not** POST a real event to your URL. Only a real detection (or the ISAPI `httpHosts//test`) actually exercises the path. - **`httpBroken` latches.** Once the camera marks the host broken (from earlier failed deliveries), it stays `true` across reboots and won't retry. Clear it by **re-PUTting** the httpHost config (`PUT /ISAPI/Event/notification/httpHosts/1` with `false`). - **"Notify Surveillance Center" ≠ the HTTP Alarm Server** on some firmware (separate upload channels). Always confirm the **Arming Schedule** covers the test time, too (a silent killer). - **⭐ THE ROOT CAUSE (2026-06-22): no detection AREA drawn.** This is what actually defeated us for most of a day. On the motion/smart-detection page there's a **Draw Area** step — if **no region is drawn on the frame, the camera detects nothing, generates NO event, and therefore posts nothing** anywhere (httpHost, FTP, alarm stream all stay silent because there's no event upstream). Enabling the detection + ticking Notify Surveillance Center is **not enough** — you must draw the region. Once an area was drawn, the very first vehicle produced a clean POST. **Check this FIRST.** ### Confirmed real payload (DS-2CD1043G2-LIU, V5.8.10, 2026-06-22) What this camera actually POSTs on a motion event with a target — captured end-to-end: - **`Content-Type: multipart/form-data; boundary=boundary`**, one XML part named `MoveDetection.xml` (`Content-Type: application/xml`). A real frame/JPEG *may* be attached as a second part on other event types — our endpoint stores the readable head; splitting an image part to `snapshots` is a forward step (not needed for plain motion). - The XML is an `EventNotificationAlert` with the fields we care about: - `VMD` (Video Motion Detection) + `active` - **`vehicle`** — the camera classifies **vehicle vs human ON-DEVICE**. (Field is `targetType`, NOT `detectionTarget`.) This means simple presence + class comes for free, no vision model needed for that part. - `` with normalized `X/Y/width/height` (0–1) — the **bounding box**. - ``, `` (provenance), `` — **but the dateTime is GARBAGE** (`2032-…`) because this unit's **RTC is dead** (see below); we use our own server receive time, never the camera's. (No `` — this is a motion event, not an ANPR camera.) ### If a camera still won't push — diagnostics (read its OWN state) Only after confirming the **detection area is drawn** + arming schedule covers now + Notify Surveillance Center is on. These read the camera directly (no cooperation from our server): 1. **`netstat` on the camera (via SSH) while you trigger** — watch for an OUTBOUND line `cam:port → server:3000`. It appearing = the camera fired and is delivering (then check our `/api/devices/hikvision/alarms`). None = no event was generated (almost always: **no area drawn**). 2. **`GET /ISAPI/Event/notification/alertStream`** (Digest, needs a clean handshake) — the live event bus. NB: a `curl --digest` tap that fails the handshake returns empty and looks like "no events" — don't over-read silence here (this misled us); the netstat watch above is more reliable. 3. **SSH `showStatus` / `dmesg`** expose internal state. ⚠ **Caveat learned the hard way:** these surface scary-looking strings that are **red herrings** — `EventScribe: except`, a `diskfull` error on `Event/triggers` (on a camera with **no disk**), and `fh rtc get time error` / a 1970 clock. On our unit ALL of these were present **and the camera worked fine** once an area was drawn. The dead RTC is real (hence the bogus `dateTime`) but **harmless** to event push. **Do NOT conclude "dead camera / RMA" from these** — they are not proof of a broken event engine. > **Correction (2026-06-22):** an earlier version of this page concluded this DS-2CD1043G2-LIU was a > **defective unit needing RMA**, based on the silent alertStream + `diskfull`/`EventScribe:except` + > dead RTC surviving a full factory reset. **That was WRONG.** The camera was healthy; the real cause > was simply **no detection area drawn**, so no event was ever generated. The `diskfull`/RTC findings > were unrelated quirks (RTC genuinely dead, but it doesn't block event push). Lesson: don't > escalate to "hardware fault" while a basic config precondition (the drawn region) is unmet — and > treat vendor status-API error strings as unreliable. The pull + [[opencv-anpr-service|vision]] path > remains a valid fallback, but it was not needed here.