⚓ An S-101 / S-57 chart engine: vector tiles, S-52 styles, PNG and PDF.
tile57 reads native IHO S-101 ENC charts — and legacy S-57 cells — and turns
them into vector tiles (MLT or MVT) with a matching MapLibre S-52 style, or renders finished
charts directly to PNG and PDF — one Zig library with a C ABI, compiled natively or to WASM.
Warning
Not for navigation. This is not a certified or tested navigation product. Do not rely on it for real-world navigation. See Known limitations.
tile57 reads native IHO S-101 ENC charts (S-100 Part 10a) and legacy
NOAA/IHO S-57 ENC cells — the format is detected from the .000 file itself —
and generates vector tiles by (z, x, y): MapLibre Tiles (MLT, the default;
MapLibre GL JS ≥ 5.12 decodes them natively) or Mapbox Vector Tiles. A native
S-101 dataset feeds the portrayal engine directly; an S-57 cell is converted to
the S-101 model first. Either way, the official IHO S-101 Portrayal Catalogue
runs in embedded Lua to produce S-52 nautical portrayal. Alongside the tiles it
emits a MapLibre GL style and the portrayal assets it references — colour
tables, line styles, and the sprite + area-fill pattern atlases — so a renderer
like MapLibre can draw a chart
directly.
It holds only its working set:
- Lazy, per-cell work. A multi-cell ENC_ROOT is indexed cheaply (band + bbox); cells are parsed and portrayed only when a requested tile needs them, then held under an LRU bound. A streaming open reads a cell's bytes on demand (and frees them on eviction), so a host holds only the working set — not the whole catalogue.
- Per-cell bakes. Each ENC cell bakes to its own PMTiles at its compilation
scale, so a bake holds one cell at a time; the runtime compositor stitches the
cells by
(z, x, y)on demand. - Pure-Zig core. The foundational format/encode packages have no libc; only the Lua portrayal + sprite rasterizer pull in C.
Both source formats converge on the same S-101 feature records — a native S-101 dataset produces them directly; an S-57 cell is adapted into them:
S-101 ENC (.000) S-57 ENC cell (.000)
│ ISO 8211 decode │ ISO 8211 decode src/iso8211/
▼ ▼
S-100 spatial + feature S-57 feature + geometry src/s57/ · src/s101/
records model
│ assemble to S-101 │ adapt S-57 → S-101 (native.zig / adapter.zig)
└──────────────┬──────────────┘
▼
S-101 feature records
│ S-101 portrayal (embedded Lua) src/portray/ + rules
▼
portrayal instruction stream src/s101/ (instructions)
│ scene generation src/scene/ (project + clip + draw calls)
▼
render Surface ──► MVT / MLT tiles (src/tiles/) + MapLibre style.json + assets
└───► PNG raster / vector PDF / terminal text (src/render/)
A native S-101 chart is read straight into the S-101 model — its in-band code
tables already carry the S-101 class and attribute names — so no conversion runs;
its .001… update files are applied on load. An S-57 cell is read into the S-57
model and adapted (a best-effort, S-65-guided step; see
limitations). The stages are separate Zig modules —
iso8211, s57, s101, tiles, render, scene, style — pure Zig with no
libc; only the Lua portrayal (portray) and the sprite rasterizer (sprite) pull
in C. See the architecture docs.
Add tile57 as a dependency, then @import("tile57"):
const tile57 = @import("tile57");
// Open an on-disk ENC_ROOT directory (or a single .000 file) as a streaming chart.
var chart = try tile57.Chart.openPath("ENC_ROOT/", null, true);
defer chart.deinit();
const bbox = chart.bounds(); // geographic extent [w, s, e, n], or null
// … render a view (chart.renderView), query features, or bake an archive …Chart renders views, queries features, and reads metadata. The runtime tile
path — bake each cell, then compose by (z, x, y) on demand — is exposed through
the C ABI. See the Zig API docs.
The same engine behind a thin C ABI (include/tile57.h).
Tiles are made one way — bake each cell to its own PMTiles, then compose on
demand — the structure tile57 bake ENC_ROOT -o out/ writes:
// out/ holds tiles/<CELL>.pmtiles (one per cell) + partition.tpart
const char *paths[] = { "out/tiles/US5MD1MC.pmtiles" };
tile57_compose_source *src = tile57_compose_open(paths, 1, "out/partition.tpart");
uint8_t *tile; size_t n;
if (tile57_compose_serve(src, z, x, y, &tile, &n) == 1) { /* decompressed MLT */
/* … hand the tile to your renderer … */
tile57_free(tile, n);
}
tile57_compose_close(src);A separate tile57_chart handle renders finished PNG/PDF views and answers
metadata + object queries; libtile57.a also exposes the MapLibre style builder
and the asset/atlas generators. See the C API docs.
The offline tool bakes charts and emits portrayal assets:
Any .000 — native S-101 or S-57 — works everywhere; the format is auto-detected.
zig build # builds zig-out/bin/tile57
tile57 bake CELL.000 -o out/ # one cell -> out/tiles/<CELL>.pmtiles + partition.tpart
tile57 bake ENC_ROOT -o out/ # whole catalogue -> per-cell tiles/ + partition.tpart
tile57 assets -o assets/ # colortables + linestyles + sprite + patterns
tile57 png ENC_ROOT --view -76.48,38.974,15 --size 1600x1200 -o chart.png
tile57 pdf ENC_ROOT --view -76.48,38.974,15 --size 1600x1200 -o chart.pdf
tile57 ascii CELL.000 --view -76.48,38.974,13 --ansi --tui # the chart in your terminal
tile57 s101 CELL.000 # inspect a native S-101 datasetThe Zig engine + CLI need only Zig 0.16:
git submodule update --init --recursive # vendored S-101 catalogue
zig build && zig build testFull instructions: docs/installation.
Docs source lives in docs/: intro,
getting started, the
Zig API, the C API,
the architecture, and the
tile schema.
This project is built with AI assistance. We encourage contributors to use AI tools for development and to contribute by providing clear requirements and/or a prototype of what they'd like rather than code. See the contributing guide.
tile57's own code is MIT © Jeremy Collins. It embeds the IHO S-101 Portrayal Catalogue (© IHO) and vendors nanosvg (zlib) + stb_image_write (public domain). NOAA ENC charts are U.S. public domain and not for navigation.