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tile57 OpenCPN plugin

Not for navigation

This plugin and the tile57 engine behind it are coded almost entirely with AI (Claude) and human-reviewed — an experiment in implementing a large, complex specification (IHO S-52/S-101), not a certified or tested navigation product. The plugin marks its output accordingly (the "EXPERIMENTAL / NOT FOR NAVIGATION" note rides in the chart name OpenCPN shows). Do not rely on it for real-world navigation. See Known limitations.

An OpenCPN plugin that draws S-57/S-101 electronic navigational charts using tile57's live S-52 portrayal, rendered as vector geometry on the GPU.

tile57 S-57/S-101 charts rendered in OpenCPN

The plugin installs a first-class GL vector chart, not an overlay. OpenCPN discovers a tile57 chart by file mask, adds it to the chart database, and drives it like any native chart — chart bar, quilting, and scale transitions included. When OpenCPN asks the chart to draw, the plugin runs tile57's S-52 portrayal, tessellates the resulting vector primitives, caches them as per-tile GPU buffers, and composes the view — the same "bake once, compose on demand" model a web MapLibre client uses, but inside OpenCPN's own render loop.

How it fits together​

 ENC cells (.000)          OpenCPN                      tile57 engine
      │                       │                              │
  Build Charts               │                              │
  (bake up front)            │                              │
      ▼                      │   RenderRegionViewOnGL        │
 PMTiles bundles ────────────┤─────────────────────────────►│ S-52 portrayal
      │                      │   per-tile portray + labels   │ (draw callbacks)
      ▼                      │◄─────────────────────────────┤
  chart directory            │   per-tile GPU cache          │
      └──────────────────────►   composed on the GPU         │

Charts are baked to PMTiles bundles once (via the plugin's Build Charts dialog), then OpenCPN loads them like any chart directory and drives the GPU render.

  • tile57 is the chart engine: it reads S-57, adapts to the S-101 data model, runs the official IHO S-101 Portrayal Catalogue, and emits resolved draw primitives. This plugin embeds tile57 as a static library and calls it through its C ABI.
  • OpenCPN owns the canvas, the quilt, and the draw order. The plugin is a PlugInChartBaseExtended chart class; OpenCPN selects and renders it exactly as it would a native ENC.

Where to go next​

  • Building — dependencies, the tile57 static library, and the CMake build (Linux and macOS).
  • Getting Started — bake or link a chart, add it to OpenCPN, and enable OpenGL.
  • Architecture — the chart class, the bake flow, and how the plugin plugs into OpenCPN's quilted render.
  • Rendering — the tiled portray/cache/compose pipeline, the whole-view label pass, and the GPU vertex model.
  • Settings — how OpenCPN's S-52 display options (safety contour, depth shades, light descriptions, …) map onto tile57's mariner settings.
  • Known limitations — what does not work yet.