caveman-chartplotter

Satellite make map. Map show rocks. Rocks bad.

A simple, lightweight chart plotter for SignalK.

The whole point is to run anywhere: it's built to work on the older embedded browsers found in Navico MFDs (B&G Vulcan/Zeus, Simrad, Lowrance — Chromium 69 era), and it stays light enough for phones, tablets, and cheap boat computers. No frameworks, no build-time magic in the way — just Leaflet, a websocket, and your boat.

This is a hard fork of my anchor alarm plugin, hoekens-anchor-alarm, with all the anchoring machinery stripped out and the chart plotting kept. If you want an anchor alarm, use that one — they run happily side by side.

Features

🗺️ Charts and layers

Switch between satellite imagery, OpenStreetMap, or a blank base (for offline use or local-charts-only setups). Local raster charts served by a SignalK charts plugin appear automatically as overlays for the area you're looking at, and the optional Seascape bathymetry overlay shades water depth on capable browsers.

🛤️ Routes

Routes from your SignalK server's resources API are drawn on the chart — a green line with a dot at the start, arrows pointing the way along each leg, and a square at the end. Only routes near your current view are shown, each one gets its own checkbox in the layer control, and while you're actively navigating a route, it's the only one drawn. Routes refresh every minute, so edits made in Freeboard or any other app show up without a reload. Display is read-only (this is a chart plotter, not a route editor) and can be switched off with the "Show Routes" setting.

🧭 Course vectors

A COG/SOG predictor line extends from each vessel's bow, showing where it'll be after a set amount of travel time (5, 10, 15, 30, or 60 minutes, or off). It applies to your own boat and every AIS neighbor, and stationary vessels get no line — so a moored fleet doesn't sprout flickering vectors. The length is configurable in the settings dialog.

📍 Follow mode

Tap the home button and the viewport locks to your boat, staying highlighted green while it tracks; any drag of the map drops you back to free-pan. An optional "look ahead" biases the view toward the water in your direction of travel — scaled by speed and capped so the boat never leaves the screen — so you see more of where you're going instead of where you've been.

🛰️ Tracks & fleet

Historical tracks are color-coded (green for fresh, fading to red as they age) via the @signalk/tracks-plugin. Other AIS vessels show up too, with their own tracks and accurately-typed icons. Click a vessel for a detailed popup: name, MMSI, length, beam, distance, bearing, SOG, and COG.

⛵ Physically accurate boat icons

Give it your beam, LOA, and GPS antenna position and the boat icon is drawn to your boat's true size, rotating around the antenna location. Icons are picked by AIS ship type, or upload your own custom image from the settings dialog.

🌓 Day and night themes

A one-tap light/dark toggle, plus automatic handling of the ?mode=night / ?mode=day parameter Navico MFDs pass to embedded web apps. Dark mode dims the chrome, not your charts.

⚙️ In-map settings

Logged-in users can tweak the UI without leaving for the plugin config page. A gear button opens a settings dialog (basemap, layer toggles, route display, fleet radius, boat icon, course vector length, follow-mode look ahead) and every change applies live.

Usage

Point your browser at:

http://[signalk-server-ip-address]:[port-number]/caveman-chartplotter/

[!NOTE] You can view the app without logging in (read-only). The settings dialog appears once you log into your SignalK server — the login button lives at the top of the map and in the gear menu.

On a Navico MFD, install signalk-navico-embedder and the chartplotter shows up as a page on the console itself.

Embedding

If you want to drop the chartplotter into another app or a dashboard (Grafana, a Node-RED dashboard, an MFD page, a custom SignalK webapp, an <iframe>), one query-string parameter trims the UI down to just the map:

http://[signalk-server-ip-address]:[port-number]/caveman-chartplotter/?embedded=true

| Parameter | Values | Default | Effect | |---|---|---|---| | embedded | true / false | false | When true, hides the settings (gear) control and the login prompt, leaving a clean map. The map, boat, and fleet still update live. |

Values are compared case-insensitively; anything other than true is treated as false.

[!TIP] This pairs well with the existing ?mode=night / ?mode=day parameter (used by B&G/Navico MFDs), which forces the dark or light theme instead of following the device preference.

Recommendations

This app pairs well with some other software:

• @signalk/tracks-plugin: required for the historical tracks. I recommend a resolution of 1000ms and 86400 points, which gives you high-resolution data for the last 24 hours. If you've got the memory, you might as well use it.
• signalk-navico-embedder: puts the chartplotter on your Navico MFD as a native-feeling page.
• hoekens-anchor-alarm: this plugin's sibling — the full-featured anchor alarm this chartplotter was forked from.
• Tailscale: makes accessing SignalK remotely dead simple. Free, and a five-minute setup.

Contributing

Issues and PRs are welcome; this is an open source project and I'm happy to have company. See DEVELOPMENT.md for getting set up, and CHANGELOG.md for the full history of what's changed.