Leeway

A native iOS chartplotter and passage planner with offline sea charts and land-avoiding routing.
SwiftUI, MapLibre, iOS 26 (Liquid Glass) and a Rust data server. Eastern Adriatic charts built from open data.

_{A weather-routed passage, the Kornati chart, satellite with the chart on top, night colours, and the wind and tide forecast.}

A native iOS chartplotter and passage planner in the spirit of savvy navvy and Garmin plotters: SwiftUI, MapLibre, iOS 26 (Liquid Glass). One nautical chart for the whole world, with detailed offline charts for the eastern Adriatic (the Slovenian coast, Istria, Kvarner, Dalmatia, Dubrovnik and the Bay of Kotor, 13.2–19.0°E, 42.2–45.57°N).

Features

Chart

• One style everywhere: a paper-chart look for land and water worldwide (OpenMapTiles base map plus worldwide depth bands and contours from the data server), and the sharp version inside chart packs, in the same colours.
• Depth areas, contours (1, 2, 3, 5, 10 … 100 m in packs), a bold safety contour at the boat's safety depth, and spot soundings thinned by zoom.
• INT 1-style seamarks: lateral, cardinal, isolated danger, safe water and special marks, rocks by water level, wrecks, obstructions, light flares with characteristics (Fl(2)R.5s 12m 6M) and light sectors; harbours, marinas and anchorages; restricted areas, traffic separation, cables, pipelines, fish farms, seabed. OpenSeaMap symbols outside packs.
• Day, dusk and night palettes, automatic by the sun; night turns the whole app dark. Satellite base (Sentinel-2) with shallows, contours and seamarks on top.
• Tap anything: the object, its light, zones, the depth (pack grid or depth band), position, bearing and distance from the boat, the next tide; then route there, mark it, or measure from it.
• North up, heading up and course up, a compass when rotated, a capped nautical-mile scale bar, lat/lon grid.

Routing

• Shortest: the shortest path through water at least the safety depth deep (draft + under-keel clearance), clear of charted rocks, wrecks and obstructions, isolated-danger and cardinal marks, and bridges lower than the air draft + 1 m. Harbours are left through connected water.
• Fastest (weather routing): isochrones in the forecast wind with the boat's polar, tacking and gybing where it pays, with exactly the same safety checks. The planner says how much time it saves.
• Manual: straight legs; legs crossing land or shallows are drawn red.
• Every route is timed with the finest forecast wind per hour (ItaliaMeteo ICON-2I 2.2 km, then ICON-EU, then global), waves and tidal streams; a best-departure chart covers the next 3 days. Bura gusts are flagged.
• Polars: presets by boat type or import your own (tab/semicolon text, as designers and ORC certificates give them).
• GPX import and export of routes, tracks and waypoints.

Underway

• Navigation bar: next waypoint, bearing, distance, ETA, cross-track error; VMG and finish ETA; Live Activity.
• Man overboard, anchor watch with drag alarm, collision alarm from AIS (CPA/TCPA limits in settings), shallow water and off-track alarms; alarms sound with the phone on silent and notify in the background.
• AIS ships with 6-minute course vectors, a ship list sorted by closest approach, and the boat's own AIS receiver.
• Boat instruments over Wi-Fi: NMEA 0183 (TCP or UDP) depth, wind, heading and AIS from the boat's gateway.
• Logbook: recorded tracks with distance, time, average and top speed; show on the chart or export as GPX.
• Marks with symbols and notes; range and bearing tool.

Weather and more

• Wind now and the next 24 h, wind arrows over the chart with a time bar, rain radar, official MeteoAlarm warnings with their areas on the chart, tide curve with highs and lows, sun and twilight times.
• Search harbours, marinas, anchorages, bays, islands and towns (offline from the packs, online via the server).
• Offline map: saves the base map, depth and fonts around each chart pack, so the whole chart works without signal.

Coverage

Croatia and its waters, for now: the map itself is free to go anywhere, but the data server gathers AIS, the wind grid, MeteoAlarm warnings and place search for Croatia only (config::CROATIA, COUNTRIES in warnings.rs). Official coastline, sea names, traffic separation schemes, cables, pipelines and platforms come from the Croatian Hydrographic Institute's open data (tools/fetch_hhi.py, used by tools/build_vector.py). The official register of aids to navigation (Plovput) adds the lights, beacons and buoys OpenSeaMap lacks. National and nature parks, special reserves and the strict-protection sea zones come from the Bioportal data in tools/data/ (that service only answers browsers, so the snapshot is committed). Covering another country means widening those.

Architecture

Leeway app (SwiftUI + MapLibre Native)            seadata server (Rust/axum, Venvy)
 ChartStyle → MapLibre style JSON                  /v1/tiles/base, /v1/fonts      OpenFreeMap vector tiles + glyphs
  ├ base       vector  ─────────────────────────── /v1/tiles/bathy                worldwide depth (AWS Terrain → MVT)
  ├ bathy      vector  ───────────────────────────
  ├ chart-<id> pmtiles://  (pack on the phone)
  ├ satellite / openseamap / radar  raster  ────── /v1/tiles/satellite, seamark, radar
  └ live-*     GeoJSON (route, track, AIS, wind,   /v1/forecast, /v1/wind-grid    Open-Meteo, merged and cached
               underway, warnings, marks, measure) /v1/sealevel, /v1/warnings, /v1/search, /v1/ais, /v1/charts

Chart packs keep a .depth grid (routing, depth under the boat) next to the .pmtiles vector chart (drawing).

Data server

Everything external comes through server/ ("seadata"). Every user shares one cache: concurrent requests for the same data make one upstream call, forecasts persist on disk and are served while a fresh copy is fetched, tiles live in a size-capped disk cache and are served stale when a source is down, and responses carry ETags and Cache-Control for the app and Cloudflare. Per-client rate limits protect the shared upstream quotas.

Endpoint	What
GET /v1/forecast?points=lat,lon;…	Hourly wind (finest model per hour), gusts, waves, swell, currents, sea/air temperature, pressure, rain
GET /v1/wind-grid?west&south&east&north	Wind and waves on a grid (map arrows, weather routing); the sailing area is kept warm
GET /v1/sealevel?lat&lon	Sea level (tide + surge), hourly
GET /v1/warnings?west&south&east&north	MeteoAlarm warnings with their area outlines
GET /v1/search?q&lat&lon	Harbours, marinas, anchorages and names from the packs, then Photon
GET /v1/radar, /v1/tiles/radar/{t}/{z}/{x}/{y}.png	Rain radar frames (RainViewer)
GET /v1/tiles/base.json, /v1/tiles/base/{z}/{x}/{y}.pbf, /v1/fonts/…	Worldwide vector base map and label fonts
GET /v1/tiles/bathy/{z}/{x}/{y}.pbf	Worldwide depth areas (depare) and contours (depcnt)
GET /v1/tiles/satellite/{z}/{x}/{y}.jpg	Sentinel-2 cloudless 2016
GET /v1/tiles/seamark/{z}/{x}/{y}.png?skip=…	OpenSeaMap seamarks, transparent inside the given pack boxes
GET /v1/charts, /v1/charts/files/{name}?v=…	Offline chart packs
GET /v1/ais?west&south&east&north	Live vessels (needs AISSTREAM_API_KEY)
GET /v1/info, /health, /metrics	Capabilities, liveness, Prometheus counters (cache hits, upstream calls)

cd server
cargo test && cargo clippy --all-targets -- -D warnings
cargo run          # http://localhost:8790, serves the charts in Leeway/Charts

Settings are environment variables: PORT, CHARTS_DIR, CACHE_DIR, CACHE_MAX_GB (default 8), PUBLIC_URL, AISSTREAM_API_KEY, AIS_BBOX (south,west,north,east), OPEN_METEO_API_KEY (commercial plan; the free API is non-commercial), REQUIRE_CLIENT_HEADER=1, LOG_FORMAT=json, and the upstream URLs (TERRAIN_URL, SATELLITE_URL, …). It builds with Rust 1.85 (the Venvy host); .cargo/config.toml keeps the lockfile resolvable there.

Deploy to Venvy (published at https://seadata.ringtwo.win through the Cloudflare tunnel):

python3 server/deploy/ship.py login   # once; keeps a 30-day session in ~/.config/venvy/
python3 server/deploy/ship.py

It uploads the code, styles and chart packs, removes files deleted locally, configures the port and environment, restarts, publishes the hostname and waits until the new process answers.

Build and test

brew install xcodegen   # once
xcodegen generate
open Leeway.xcodeproj
xcodebuild test -project Leeway.xcodeproj -scheme Leeway -destination 'platform=iOS Simulator,name=iPhone 17 Pro'

Debug builds use -O because routing processes millions of grid cells. CI builds and tests the app and the server on every push and pull request. Simulator launch arguments (Debug only): -debugRoute "45.32,14.44;44.53,14.47", -debugMode manual (or weather), -debugCenter "45.0,14.45,0.5".

Chart packs

tools/build_region.py builds an offline region from EMODnet Bathymetry (~115 m, CC BY 4.0) and OpenStreetMap coastline and seamarks (ODbL), then tools/build_vector.py turns it into the vector chart with tippecanoe (layers: land, depare, depcnt, soundg, seamark, lightsector, area, names, bridge).

brew install tippecanoe
python3 -m venv .venv && .venv/bin/pip install numpy scipy shapely pillow tifffile osmium contourpy
# OSM country extracts from download.geofabrik.de, e.g. into tools/.osm-cache/
.venv/bin/python tools/build_region.py adriatic "Eastern Adriatic" 13.2 42.2 19.0 45.57 \
    --osm croatia.osm.pbf,slovenia.osm.pbf,bosnia-herzegovina.osm.pbf,montenegro.osm.pbf
# Only the vector chart, from an existing pack:
.venv/bin/python tools/build_vector.py adriatic --osm croatia.osm.pbf,…

Code map

Area	File
Chart style (colours, layers, palettes)	Leeway/Map/ChartStyle.swift
Map view, live layers, taps	Leeway/Map/ChartMapView.swift
Seamark and marker icons	Leeway/Map/SeamarkSymbols.swift
Chart packs, depth lookup	Leeway/Model/ChartRegion.swift, Leeway/Services/ChartStore.swift
Shortest route (A*), hazard checks	Leeway/Model/Router.swift
Fastest route (isochrones), wind field	Leeway/Model/WeatherRouter.swift
Polars	Leeway/Model/Polar.swift, PolarTable.swift
Passage timing, departures	Leeway/Model/PassageSimulator.swift
Sun and twilight	Leeway/Model/Sun.swift
Data server client	Leeway/Services/Seadata.swift, MarineWeatherService.swift
Navigation, MOB, anchor watch, alarms	Leeway/Services/Underway.swift, LiveActivityController.swift
Boat instruments (NMEA 0183, AIS)	Leeway/Services/NMEA.swift
GPX, logbook, offline map	Leeway/Services/GPX.swift, LocationTracker.swift, OfflineMaps.swift
App state	Leeway/AppModel.swift
UI	Leeway/Views/* (map chrome, sheets, cards)
Data server	server/src/*
Tests	LeewayTests/*, server/src/tests.rs

Known limits

• Not for navigation. The depth data is a ~115 m survey grid. It doesn't show isolated rocks, shoals or wrecks smaller than that, and narrow passages (such as the Osor canal) are closed. The router avoids only the rocks and wrecks mapped in OSM. Outside packs, worldwide depth is coarse and automatic routing isn't available.
• Fastest routing uses the server's wind grid (0.1–0.5°) and ignores currents; passage timing then uses the full forecast.
• AIS comes from aisstream.io's volunteer receivers (gaps, positions up to a minute old) or the boat's own receiver.
• MeteoAlarm areas are matched by outline; a few countries' feeds cover land regions only.
• For a commercial release, the terms of OpenFreeMap, OpenSeaMap tiles, RainViewer, Photon and Open-Meteo (commercial plan) need checking; official ENC data would need licensing.

Next steps

More chart packs (Ionian, Tyrrhenian), currents in weather routing, a tide station database, AIS target trails, Apple Watch companion, CarPlay.