julian
411572511d
Captures this session's back-and-forth as a new concept page
[[lane-presence-and-anpr-entry]] and cross-links it:
- BUILT: advisory lane busy/free booth lights (LaneStatus + WS), with the
measured camera limits behind the 30s timeout (no leave signal; movement-
driven re-fire; notificationRecurrence locked to "beginning" — ISAPI flip
silently reverts).
- PLANNED: the ANPR "bridge" — explicitly a small apps/server HANDLER (~40
lines), NOT a new service/container. On a camera vehicle event: snapshot ->
ANPR -> high-confidence match -> debounce -> emitRead{kind:"plate"}, then
the existing subscription match/dispatch/gate admits the subscriber. Both
directions, opt-in (config.anpr), plate never the sole authority.
- Records the decisions (high confidence floor, debounce-for-correctness)
and the REJECTED ideas (continuous livestream / per-car queue tracking /
make-model) with why, plus the open hardware question (booth-PC test).
Updates subscription.md (plate matching is built; the live source is this
bridge) and lpr-camera.md (the two consumers of the vehicle event).
Claude-Session: https://claude.ai/code/session_01Xcm6ikLgGoCxxHrxtjkk5V
115 lines
7.3 KiB
Markdown
115 lines
7.3 KiB
Markdown
---
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type: concept
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tags: [parking, camera, anpr, subscription, lane, vision]
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sources: []
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updated: 2026-06-22
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status: open
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---
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# Lane Presence & ANPR Subscriber Entry
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Two related things a camera's vehicle detection feeds, worked out over a long field session
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(2026-06-22, see [[lpr-camera]] for the camera-side saga + the corrected "it was the undrawn
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detection area" conclusion):
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1. **Lane busy/free** — BUILT. An advisory barrier light on the booth.
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2. **ANPR subscriber entry** — PLANNED. A subscriber's plate, read from the lane camera, drives
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their entry/exit through the EXISTING [[subscription]] flow. The "bridge" below.
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The camera (Hik `DS-2CD1043G2-LIU`) only emits `VMD` events with `eventState=active` and a
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`targetType` of `vehicle`/`human` — a coarse **presence** signal, never an identity. Everything
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here is built on that, and on the camera's hard limits.
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## What the camera actually gives us (measured)
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- **Push only, no poll.** No ISAPI endpoint reports "is a car in the zone now"; the only live source
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is the event push. We tried to force a steadier signal by flipping `notificationRecurrence`
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`beginning → recurring` via ISAPI — the firmware **accepts the PUT but silently reverts** (locked to
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`beginning` on this value line). So: notify-once-at-motion-start is all we get.
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- **No leave signal.** The camera never sends an `inactive`/end event. Confirmed by config
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(`notificationRecurrence: beginning`) AND a controlled in/out test.
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- **Re-fire is MOVEMENT-driven, not steady.** Controlled test (call out enter/leave, correlate to the
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event log): while a car MOVES, `active` repeats ~1–3 s apart; while it sits MOTIONLESS, gaps stretch
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to ~15–25 s. Crucially the camera has **~no dwell lag** — it goes silent within ~1 s of the car
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leaving (last event 16:15:17 vs car-left ~16:15:30).
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## 1. Lane busy/free (BUILT)
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`apps/server/src/lane-status.ts` (`LaneStatus`) + the hik-alarm handler + the booth WS. A `vehicle`
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`active` event on a camera bound to entry/exit marks THAT lane busy and arms an auto-clear timer; the
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booth shows two barrier lights beside the scan input (green=free, red=busy). **Advisory only — gates
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nothing** (never blocks a ticket or opens a barrier; the standing rule).
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- **"Free" is timeout-driven** (no leave signal). The TTL must exceed the still-car gap (~25 s) or a
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parked car flickers free — so `LANE_BUSY_TTL_MS` default is **30 s** (started at a guessed 90 s,
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briefly 5 s, then set to 30 s from the measured data). The camera's lack of dwell lag means 30 s
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also clears promptly after departure.
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- A `both`-direction camera marks both lanes. Pushed over the existing `/api/ws` (kind `lane-status`).
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## 2. ANPR subscriber entry — THE BRIDGE (PLANNED, not built)
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> **"Bridge" = a HANDLER FUNCTION in `apps/server` (≈40 lines, e.g. `anpr-entry.ts`). NOT a new
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> service / container / app.** It is in-process glue that calls things that ALREADY exist.
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The goal (narrowed deliberately — see Rejected below): **a subscriber's plate, read by the lane
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camera, admits them through the same gated flow a QR/card scan uses.** Scope was cut to subscribers
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ONLY — no queue segmentation, no per-car tracking, no make/model, no ticket-button gating.
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Almost everything already exists; the bridge is the one missing wire:
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| Piece | Status |
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| --- | --- |
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| Camera vehicle event | ✅ [[lpr-camera]] (hik-alarm) |
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| Pull a snapshot | ✅ `snapshot.ts` (`captureSnapshot`) |
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| Read the plate | ✅ [[opencv-anpr-service]] `/analyze` (~50 ms on the DEV PC; appliance TBD) |
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| Match a plate → subscriber | ✅ `subscription-flow.ts` `match()` + `subscription_plates` (`via:"plate"`) |
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| Plate read → gated entry/exit | ✅ `read-dispatch.ts` + SubscriptionFlow (active/window/blocklist/car-count) |
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| **Emit the plate onto the read bus** | ❌ **the bridge** — today the snapshot ANPR only RECORDS the plate as advisory telemetry; it does NOT `emitRead`. hik-alarm.ts literally says "NOT a DeviceReadEvent yet". |
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**The bridge logic:** on a camera `vehicle`/`active` event from an **opt-in** camera (`config.anpr`),
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snapshot → `vision.analyze` → if a plate clears a **HIGH** confidence floor → **debounce** → emit
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`DeviceReadEvent{kind:"plate", value, deviceId}`. The existing dispatcher + flow do the rest.
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### Decisions settled with the user (2026-06-22)
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- **Both directions.** Entry- and exit-bound cameras both work; the dispatcher infers the verb from
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the camera's bound relay direction (an entry camera → entry, exit → exit). No per-read inference.
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- **High confidence required.** A barrier-driving read needs a stricter bar than the advisory-record
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floor — a NEW `VISION_ENTRY_MIN_CONFIDENCE` (≈0.85) distinct from `VISION_MIN_CONFIDENCE`. (The
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subscriber still holds their card/QR, so a near-miss read just falls back to that.)
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- **Opt-in** per camera (`config.anpr`), so a site that didn't ask for plate-entry is unaffected.
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- **Debounce is REQUIRED — for correctness, NOT CPU.** The camera re-fires ~1 Hz while a car is
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present; emitting a read every second would drive REPEAT entries (a fleet sub opens a 2nd
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occurrence; a single-car sub spams "already inside") or, on an exit camera, repeat exits
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(`sub.refused.noSession` after the first, and FIFO could phantom-close another occurrence). So the
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same plate on the same camera within ~10–15 s = ONE credential presentation.
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- NB: a direction-bound camera does NOT flip entry↔exit on repeat reads (the barrier's direction
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fixes the verb), so the earlier "flip-flop" fear was wrong — but repeat-same-direction is still
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bad. Debounce stands.
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- **Threat-model rule preserved by construction.** A plate is trivially spoofable (print it on
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paper); it must NEVER be the sole reason a barrier opens. Routing through the existing
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SubscriptionFlow means the plate is just another credential through the same gate (active / window
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/ blocklist / car-count) — not a bypass. See [[opencv-anpr-service]], [[append-only-event-chain]].
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### To validate (booth-PC test day, ~2026-06-23)
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The dev-PC ANPR is ~50 ms/frame, but that says little about the hardened **booth appliance** (likely a
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low-power CPU, possibly 5–15× slower). Real-hardware latency is the open number. The user is bringing
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the actual booth PC to test on.
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## Rejected / out of scope (and why)
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- **Vision monitors the RTSP livestream continuously** for presence — rejected: rebuilds (worse) what
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the camera already does (presence), pegs the appliance CPU 24/7, and the leave-detection heuristic
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is no cleaner than a 30 s timeout.
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- **Vision polls every ~1 s to track THE car, segment a queue, count cars, read make/model** — a
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genuinely harder need (bumper-to-bumper cars the camera can't tell apart). Set ASIDE, not dismissed:
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it needs a general vehicle DETECTOR ([[opencv-anpr-service]] is plate-only today) + "same-car-vs-new"
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logic + make/model (a third, weak, heavy model), and its viability is **gated on appliance
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inference budget we cannot measure on the dev PC**. Revisit only if real traffic + hardware justify
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it. The vision feasibility was checked: `fast_alpr` live + ready; plate-only; no vehicle/presence
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detector exists yet.
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- **Gate the entry ticket button on lane-busy** (don't print when no car) — deferred. The lane-busy
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signal supports it, but it gates a PHYSICAL action so it must FAIL-OPEN (allow when presence is
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unknown). Parked pending the user's real goal (anti-spam print vs one-ticket-per-car).
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