OnaPlotter

A touch-first chartplotter for sailors on a SignalK boat. One app for a 21" helm touchscreen with keyboard and mouse, an iPad in the cockpit, or a phone in a jacket pocket - same data, responsive layout, WCAG-sized tap targets.

Built on Blazor WebAssembly + Leaflet + the SignalK stream. Deploys as a SignalK webapp on a Pi, or runs standalone from any browser.

Highlights

• Standard SignalK interop. Routes, waypoints, notes, and regions round-trip through /resources/* using the documented SignalK resource shape so peer SignalK clients see them too.
• Real collision detection. CPA / TCPA projection with COLREGS crossing classification, not a proximity beeper. Moored-vessel auto-mute, per-target snooze, pulsing danger ring, red/amber crossing lines. (deep dive)
• Plugin-aware, not plugin-locked. Tide, buddy list, anchor alarm, radar - each lights up its own UI when the matching SignalK plugin is installed; missing plugins surface a clear "plugin vX.Y+ required" toast.
• Touch-first. Long-press context menu, bottom-sheet panels on phones, 44 px minimum tap targets, full keyboard parity, branded boot screen.

Features

Map

• Four-corner HUD. SOG/COG/position, wind (AWA + TWA, direction arrows, Beaufort), depth + tide countdown, heading compass. Tap a corner to expand (DMS, VMG, XTE, drift, tidal current, autopilot).
• Own-vessel track, history-plugin integration, speed-coloured.
• AIS targets with COG vector, 60 s fading trail, ship-type colour. Tap a vessel for SOG/COG/HDG/bearing/distance/CPA + MarineTraffic / VesselFinder deep-links.
• CPA danger pulse. Red ring + crossing lines for targets in the danger band; two-line vessel + CPA/TCPA label.
• Anchor watch via signalk-anchoralarm-plugin. Two-step drop + set-radius with on-map preview as you pick the chip; tide-aware grounding alarm when a tide plugin is feeding.
• MOB - one-tap drop with a pulsing red bullseye; non-snoozeable. Same treatment for SART / EPIRB.
• Route + waypoint editing. Tap-to-add, drag-to-move with dashed ghost + live Δ-distance, numbered waypoint list, undo. Reverse, save-as-copy, GPX import/export.
• Regions. Circle (radius preset 100 m / 250 m / 500 m / 1 nm / 2 nm) and polygon (numbered vertices, draggable, area readout in m² / ha / km²).
• Notes as folded-page pins.
• Tide card when environment.tide.* is published.
• Charts: any tile source SignalK exposes (raster PNG, S-57 raster, OpenSeaMap), plus OSM base, OpenSeaMap seamarks overlay, RainViewer rain radar. Chart overzoom keeps detail past native max zoom; quick-pick chips for the top stack.
• Tools: laylines to active waypoint, persistent measurement ruler (multi-segment), N↑ / C↑ / H↑ orientation cycle, race timer, legend modal.
• Cruise / Race mode preset (Settings) flips defaults and surfaces a performance card - target boat speed from your polar, optimal TWA. Mode picks defaults; every individual toggle still works in either.

Other pages

• Dashboard - speed, course, position, depth, wind, tide, polar performance at a glance.
• Gauges - circular instruments with colour zones, responsive grid.
• SailSteer - compass-rose view combining wind, heading, COG, laylines, waypoint bearing.
• Wind Rose - TWD history with a 15 m / 30 m / 1 h / 3 h window.
• History - replay the full track for any window with play / pause / step / speed and a scrub bar.
• Stats - passage stats (distance, time, max/avg SOG, ...).
• Paths - live SignalK path inventory: which paths your boat publishes, latest values, source plugin. For diagnosing "why is this gauge empty?" without leaving the app.
• Raw Stream - live delta viewer with per-path filtering.
• Settings - Theme (System / Light / Dark), Night Mode (Soft / Amber / Red), sailing mode, alarm thresholds (depth, two-tier CPA & TCPA alarm/awareness, wind shift), polar-file upload with live polar diagram.

Alarms

• Stacked banner (up to three), ordered by (severity, time-to-event, priority) - so SHALLOW at TTI=0 beats pending CPA.
• Snooze 10 min per vessel; snoozed chips show a live countdown.
• Server-side notifications: anything any plugin emits on notifications.* joins the same banner stack with appropriate severity, so plugin alerts don't get lost.
• Log button opens the last 20 alarms with dismissal reason.
• Configurable thresholds in Settings; rules: SHALLOW, CPA, WIND SHIFT, SART, ANCHOR-TIDE, ANCHOR-DRAG, DEADMAN, WAYPOINT-APPROACH.

Connection health

The top-row chip is the single source of truth: Live / Stale / Offline. WebSocket reconnects with exponential backoff (1 s -> 30 s cap). If nothing arrives for 5 s while the socket is open, the chip flips to Stale and a soft audio alarm plays; on full disconnect the alarm repeats every 3 s until recovery.

Plugins that light up features

Each is probed once and cached. Dependent UI hides when the plugin is absent.

Plugin	Lights up
signalk-anchoralarm-plugin v2.0.0+	Anchor watch, drag detection, incomplete-anchor alarm
signalk-tides-api (or any environment.tide.* publisher)	Tide card in HUD + Dashboard, anchor-tide grounding alarm
signalk-buddylist	Buddies section in Layers + star prefix on AIS labels
Mayara	Radar ARPA targets alongside AIS
signalk-flags	Country flag in AIS popups

Install on a SignalK server

pwsh ./deploy/deploy.ps1            # publish + scp to [email protected]
pwsh ./deploy/deploy.ps1 -SkipBuild # reuse the last publish output

The script wipes obj/Release + bin/Release (sidesteps stale-AOT), patches <base href> to the webapp path, and SCPs into ~/.signalk/node_modules/signalk-onaplotter/ on the target host. Restart SignalK; OnaPlotter shows up on the Webapps page. Target host and user live at the top of the script.

Non-PowerShell:

dotnet publish -c Release OnaPlotter/OnaPlotter.csproj
scp -r OnaPlotter/bin/Release/net10.0/publish/wwwroot/* \
    user@host:~/.signalk/node_modules/signalk-onaplotter/

Keyboard shortcuts (Map page)

Key	Action
F	Toggle follow-boat
O	Cycle orientation (N↑ / C↑ / H↑)
N	Toggle night mode
A	Toggle anchor watch
M	Drop MOB marker
T	Fit track in viewport
L	Toggle laylines
D	Toggle measurement (distance) mode
R	Start/stop race timer
?	Show the shortcut card
Esc	Dismiss overlays / exit measure / cancel

Double-click the map for a bearing/distance line from own-boat to the click point. Long-press or right-click for the context menu. Same actions live on the Add button in the bottom control bar.

Contributing

See AGENTS.md for architecture, design decisions, the six test surfaces, and SignalK setup for development.