122 lines
6.1 KiB
Markdown
122 lines
6.1 KiB
Markdown
# MQTT API
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The program is both an MQTT **subscriber** (remote control) and **publisher** (status + capture events). The
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MQTT channel is the `MqttControlChannel` implementation of `IControlChannel`
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([src/mqtt/MqttControlChannel.cpp](../src/mqtt/MqttControlChannel.cpp), Eclipse Paho C++). It is used only when
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MQTT is enabled; otherwise a `NullControlChannel` runs (publishes dropped, auto-sweep mode). All topics are
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namespaced by tower name:
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```
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GGS/FWT/<tower_name>/...
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```
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`<tower_name>` comes from `config.ini` (`General.tower_name`). All messages use **QoS 1**. Published messages
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are **retained**.
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## Connection
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- Broker URI is assembled from `Network.zkms_server_ip` + `Network.mqtt_port` as `tcp://<host>:<port>`
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(`NetworkConfig::brokerUri`), and logged on every connect and connect failure. Two escape hatches, so
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existing configs keep working: a `zkms_server_ip` containing `://` is passed through verbatim, and one
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already of the form `host:port` keeps that port. In both cases `mqtt_port` is ignored. Client ID = the
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tower name.
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- Auth: `mqtt_user` / `mqtt_pw` (preferring `$FGC_MQTT_USER`/`$FGC_MQTT_PW`); `clean_session = true`,
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keep-alive 20 s, `set_automatic_reconnect(true)`.
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- Connect timeout 5 s. On connection loss Paho auto-reconnects; the channel re-subscribes on reconnect.
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- **The program no longer exits if MQTT is unavailable** — it logs a warning and continues in degraded mode.
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Use `--no-mqtt` to disable MQTT entirely (null channel).
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## Subscribed topics (inbound — remote control)
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Subscribed on (re)connect; handled in `MqttControlChannel::message_arrived()`
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([src/mqtt/MqttControlChannel.cpp](../src/mqtt/MqttControlChannel.cpp)).
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| Topic | Payload | Parsed as | Effect |
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|-------|---------|-----------|--------|
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| `GGS/FWT/<tower>/target_HDG` | integer heading as string, e.g. `"137"` | validated with `stoi`, stored as **string** | Sets the yaw target used in ControlCode 1 (converted to encoder counts via `[Motor]`) |
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| `GGS/FWT/<tower>/ControlCode` | integer as string, `"0"` or `"1"` | `stoi` → int | Selects the capture mode (see below) |
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Invalid (non-integer) payloads are caught and logged; the previous value is kept.
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The main loop consumes these via `get_sub_data()`, which returns a snapshot and **clears the "available"
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flags** so each update is acted on once (`MqttControlChannel::poll()`).
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### ControlCode semantics
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| ControlCode | Behaviour ([CaptureScheduler](../src/core/CaptureScheduler.cpp)) |
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|-------------|---------------------------------------------------|
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| `0` | **Automatic sweep.** Walk the scan grid front to back, then start over: `MOVE` to the next `(yaw,pitch)` waypoint, wait for standstill, trigger cameras. |
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| `1` | **Directed.** `MOVE` yaw to `target_HDG` (pitch held), wait for standstill, trigger. |
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When a ControlCode message arrives, the program echoes the current code back on the StatusCode topic.
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## Published topics (outbound)
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| Topic | When | Payload | QoS / Retain |
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|-------|------|---------|--------------|
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| `GGS/FWT/<tower>/StatusCode` | At startup (`"0"`); whenever a ControlCode message is received (echoes the code) | integer as string | 1 / retained |
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| `GGS/FWT/<tower>/CamEvent` | After each image is saved | JSON object (below) | 1 / retained |
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### CamEvent payload
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Built by `MqttControlChannel::publishCamEvent` from a `CamEvent`:
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```json
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{ "fwt":"ExampleTower", "cam":"RGB", "hdg":1373, "pit":300, "time":1719312345678 }
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```
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| Field | Type | Meaning |
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|-------|------|---------|
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| `fwt` | string | Tower name (`config.ini` `tower_name`) |
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| `cam` | string | Camera label: `RGB`, `ACR`, or `NIR` (by camera index) |
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| `hdg` | int | Gimbal yaw heading **× 10** (one decimal place encoded as integer) at capture time, from the **yaw encoder** |
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| `pit` | int | Gimbal pitch elevation **× 10** at capture time, from the **IMU** — elevation relative to gravity, i.e. true pointing angle |
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| `time` | int | Capture timestamp, Unix epoch **milliseconds** (matches the `.jxl` filename) |
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> The `time` value is the same Unix-ms timestamp used as the image filename, so a consumer can locate the file
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> for a given event: `<RGB|ACR|NIR>/<time>.jxl`.
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**`pit` is measured against gravity, `hdg` against the encoder.** The two axes come from
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different sources deliberately. The pitch encoder only measures the axis relative to the
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gimbal's own base, so a leaning mast is invisible to it; the IMU measures against gravity
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and therefore reports the elevation the imagery is actually pointing at. Yaw stays on the
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encoder because IMU yaw drifts and depends on the heading reset and XKF profile, whereas
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encoder yaw is calibrated against the IMU by `gimbal calib` and then holds.
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Two consequences for consumers:
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- **`pit` no longer agrees with the commanded waypoint by construction.** Commanding `+10.0`
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and receiving `pit: 104` is correct — the residual is real tilt, not error. Before this
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change both came off the same encoder scale and agreed trivially.
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- **Archives spanning the change contain two different measurements** in this field: an axis
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angle before it, a true elevation after. If the mast is level the two agree; if it leans,
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they differ by the lean.
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If the IMU is disabled (`[Features] enable_imu = false`), `pit` falls back to the encoder as
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before. If the IMU is enabled but has no fresh sample, it also falls back — and logs a
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warning saying so, once per outage, since that mixes the two measurements in one field.
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Both `hdg` and `pit` are sampled **when the frame arrives**, not when its JPEG XL encode
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finishes, so a slow encode or a backed-up queue cannot attribute a later pose to earlier
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pixels.
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## Topic summary
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```
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subscribe: GGS/FWT/<tower>/target_HDG (int heading)
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GGS/FWT/<tower>/ControlCode (0 = auto sweep, 1 = directed)
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publish: GGS/FWT/<tower>/StatusCode (echoed control code)
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GGS/FWT/<tower>/CamEvent (JSON: fwt, cam, hdg×10, pit×10, time-ms)
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```
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## Local testing
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Point `zkms_server_ip` at a local broker and exercise the topics with Mosquitto:
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```bash
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mosquitto_sub -t 'GGS/FWT/ExampleTower/#' -v # watch everything for the tower
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mosquitto_pub -t 'GGS/FWT/ExampleTower/ControlCode' -m '0'
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mosquitto_pub -t 'GGS/FWT/ExampleTower/target_HDG' -m '180'
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```
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