signalk-nmea0183-logger

Signal K plugin that logs raw NMEA0183 sentences to daily log files with a built-in web viewer featuring GPS track visualization on OpenSeaMap, voyage statistics, and historical weather data.

Features

Logging

• Logs raw NMEA0183 sentences to daily files (nmea0183_YYYY-MM-DD.log)
• Optional ISO timestamp prefix per line
• Per-sentence-type filtering (enable/disable individual NMEA sentence types)
• Automatic daily file rotation
• Configurable maximum file size with automatic part splitting

AIS Throttling

• VDM throttle: Limits AIS messages to 1 per MMSI per configurable interval (default: 30s). In busy waterways this reduces AIS log volume by 90-95% while retaining all vessel tracks.
• VDO heartbeat: When GPS dedup is active, logs own-vessel AIS (VDO) once per interval (default: 180s) as transponder health check. Set to 0 to skip VDO entirely.

GPS Deduplication

• When RMC sentences are available, redundant GGA and GLL sentences are automatically skipped
• RMC contains everything needed: position, SOG, COG, date/time
• VDO (own AIS position) is throttled to a heartbeat interval rather than logged at full rate
• Significantly reduces log file size without losing any track data

File Size Management

• Configurable maximum file size (default: 50 MB)
• When exceeded, a new part file is created: nmea0183_2025-03-15_part1.log
• Protects SD cards and prevents memory issues on Raspberry Pi during log analysis

Web Viewer (Webapp)

• GPS Track: Displayed on OpenSeaMap with Leaflet.js, SOG color gradient, start/end markers
• Voyage Statistics: Distance (nm), duration, SOG avg/max, TWS avg/max, TWA avg/min/max, engine hours
• Weather Overlay: Historical weather per 2-hour interval based on average GPS position per interval, fetched from Open-Meteo (free, no API key)
• Raw Log Viewer: Syntax-highlighted NMEA sentences with filter, line limit, and auto-refresh
• Mobile-friendly layout: map → stats → weather → raw data

Architecture

• Public API on separate port (default: 3033) — no SignalK authentication required for read access
• Delete requires SignalK login (routed through authenticated SignalK router)
• SignalK Webapp entry redirects to the public API port

Installation

From npm (after publishing)

Install via the SignalK Appstore, or manually:

cd ~/.signalk
npm install signalk-nmea0183-logger
sudo systemctl restart signalk

Manual / Development

# Copy plugin to SignalK config directory
cp -r signalk-nmea0183-logger ~/.signalk/signalk-nmea0183-logger

# Add to ~/.signalk/package.json dependencies:
#   "signalk-nmea0183-logger": "file:signalk-nmea0183-logger"

# Install and restart
cd ~/.signalk
rm -f package-lock.json
npm install
sudo systemctl restart signalk

File structure

signalk-nmea0183-logger/
├── package.json
├── index.js          # Plugin + public API server
├── README.md
└── public/
    ├── index.html    # Redirect to :3033
    └── app.html      # Main webapp

Configuration

After installation, enable the plugin in SignalK Admin → Plugin Config → NMEA0183 Logger.

General

| Setting | Default | Description | |---|---|---| | Log Directory | (auto) | Path for log files. Leave empty for ~/.signalk/nmea0183-logs/ | | Public API Port | 3033 | Port for the unauthenticated read-only API and webapp | | Include ISO Timestamp | ✓ | Prefix each line with 2025-03-15T12:34:56.789Z |

Throttle & Dedup

| Setting | Default | Description | |---|---|---| | AIS Throttle (VDM) | 30 sec | Max 1 message per MMSI per interval. 0 = disabled | | GPS Dedup | ✓ | Skip GGA/GLL when RMC is available; throttle VDO | | VDO Heartbeat | 180 sec | When dedup is on: log 1 VDO per interval. 0 = skip all VDO |

File Management

| Setting | Default | Description | |---|---|---| | Max File Size | 50 MB | Start new part file when exceeded. 0 = unlimited |

Sentence Filter

Each NMEA sentence type can be individually enabled or disabled:

• Navigation: GGA, GLL, RMC, RMB, VTG, GSA, GSV, ZDA, GNS
• Compass: HDG, HDM, HDT
• Wind: MWV, MWD, VWR
• Depth: DBT, DBS, DBK, DPT
• Speed: VHW
• Waypoint / Route / AP: APB, BOD, BWC, BWR, RTE, WPL, XTE, XDR, RSA, RPM
• Environment: MTW, MTA, MMB, MDA
• AIS: VDM, VDO
• Misc: TXT, TTM, TLL

Accessing the Webapp

| URL | Description | |---|---| | http://<host>:3033/ | Recommended — webapp + API on same port, works without login | | http://<host>:3000/signalk-nmea0183-logger/ | Redirects to :3033 | | SignalK Admin → Webapps → NMEA0183 Logger | Redirects to :3033 |

API Endpoints

All endpoints on the public API port (default 3033). No authentication required.

| Method | Path | Description | |---|---|---| | GET | /api/logs | List all log files | | GET | /api/logs/:filename | Read log content (query: ?lines=200&filter=RMC) | | GET | /api/logs/:filename/stats | Voyage statistics + track + weather intervals | | GET | /api/logs/:filename/download | Download raw log file | | GET | /api/stats | Live plugin status, sentence counts, throttle stats |

Delete (requires SignalK authentication on port 3000):

| Method | Path | Description | |---|---|---| | DELETE | /plugins/signalk-nmea0183-logger/api/logs/:filename | Delete a log file |

Voyage Statistics

Parsed from logged NMEA sentences:

| Statistic | Source | Notes | |---|---|---| | Distance (nm) | RMC | Haversine formula, skips GPS jumps >10 nm | | Duration | RMC | First to last timestamp | | SOG avg/max (kn) | RMC, VTG | | | TWS avg/max (kn) | MWV (ref=T), MWD | Converted to knots from m/s or km/h | | TWA avg/min/max (°) | MWV (ref=T) | True Wind Angle | | Engine hours | RPM | Time intervals where RPM > 100, skips gaps > 1 hour |

Weather Data

• Source: Open-Meteo (free, no API key needed)
• Historical weather for past dates, forecast API for today
• Per 2-hour interval: temperature, cloud cover, weather description, wind speed/gusts (in knots)
• Position-based: uses average GPS position per 2-hour interval, so longer voyages show local weather along the route
• Fetched client-side (requires internet on the viewing device)

Estimated Log File Sizes

With default settings (AIS throttle 30s, GPS dedup on):

| Scenario | Per 24 hours | |---|---| | GPS only | ~7 MB | | GPS + wind + depth + heading | ~25 MB | | Above + AIS (busy waterway, ~100 vessels) | ~40 MB |

Without throttling, AIS in busy waterways can produce 200-500 MB/day.

Requirements

• Signal K server (tested with v2.x on OpenPlotter/Raspberry Pi)
• NMEA0183 data connection configured in SignalK
• Port 3033 (or configured port) available
• Internet on viewing device for weather data and map tiles

NMEA Sentences Used

For full functionality, these sentences should be present:

| Sentence | Required for | |---|---| | RMC | GPS track, distance, SOG, timestamps (essential) | | MWV | Wind speed (TWS) and True Wind Angle | | RPM | Engine hours calculation | | VDM | AIS vessel tracking | | VDO | Own AIS transponder health check |

License

MIT