@s57-parser/s57

IHO S-57 (Edition 3.1) electronic navigational chart parser: feature and spatial records, chain-node topology, incremental updates (.001, .002, ...), typed features and GeoJSON conversion.

Zero dependencies besides @s57-parser/iso8211. ESM only. Node.js 18+, Bun, browsers.

npm install @s57-parser/s57

Parse a cell and convert to GeoJSON

import { readFileSync } from 'node:fs';
import { parseS57, toGeoJSON } from '@s57-parser/s57';

const read = (path: string) => {
  const b = readFileSync(path);
  return b.buffer.slice(b.byteOffset, b.byteOffset + b.byteLength) as ArrayBuffer;
};

const dataset = parseS57(read('US5MA12M.000'));
dataset.name;               // 'US5MA12M.000'
dataset.cscl;               // 25000 (compilation scale 1:25 000)
dataset.features.length;    // 2406
dataset.spatialRecords.size // 4678

const geojson = toGeoJSON(dataset);
// Feature properties: RCID, OBJL, PRIM, GRUP, AGEN/FIDN/FIDS and every
// attribute as ATTL_<code>, e.g. { OBJL: 75, ATTL_75: '1', ATTL_107: '2', ... }

In the browser, pass await (await fetch(url)).arrayBuffer() instead.

Only some object classes? toGeoJSON(dataset, [75, 129]) keeps LIGHTS and SOUNDG.

Geometry: points and isolated nodes become Point (soundings MultiPoint), edges are chained through their connected nodes into LineString, and areas into closed Polygon rings with holes. Areas cut by the data limit or with masked edges get an _outline property with only the edges that should be stroked (S-52).

Apply updates

import { parseS57, applyUpdate } from '@s57-parser/s57';

const ds = parseS57(read('US5MA19M.000'));
applyUpdate(ds, read('US5MA19M.001')); // mutates and returns ds
applyUpdate(ds, read('US5MA19M.002'));
ds.name; // 'US5MA19M.002'

Supported: record insert/delete/modify (RUIN) for feature and vector records, attribute changes and deletions, FSPC/VRPC/SGCC pointer and coordinate splices. Apply updates in sequence; update numbers are not checked.

Typed features

import { typedFeatures, filterByClass } from '@s57-parser/s57';

const typed = typedFeatures(ds.features);
for (const light of filterByClass(typed, 'LIGHTS')) {
  // light: Light, with litchr, sigper, siggrp, colour, sectr1, sectr2, ...
  console.log(light.rcid, light.name, light.litchr, light.sigper);
}
for (const area of filterByClass(typed, 'DEPARE')) {
  console.log(area.drval1, area.drval2); // numbers, metres
}

15 interfaces cover 19 object classes: DEPARE, DEPCNT, SOUNDG, COALNE, LNDARE, LIGHTS, BCNCAR, BCNLAT, BOYCAR, BOYLAT, BOYSAW, BOYSPP, OBSTRN, WRECKS, UWTROC, RESARE, BRIDGE, LNDMRK, ACHARE.

Attribute codes and names: S57_ATTRIBUTES (code → { acronym, name, valueType }), ATTL_BY_ACRONYM, ATTL.DRVAL1, ...

API

| Export | | |--------|---| | parseS57(buffer) | Parse a base cell (.000) into an S57Dataset | | applyUpdate(dataset, buffer) | Apply an update file in place | | toGeoJSON(dataset, objl?) | GeoJSON FeatureCollection | | typedFeature(f), typedFeatures(fs), filterByClass(fs, cls) | Typed access | | spatialKey(rcnm, rcid) | Key into dataset.spatialRecords | | GeomPrimitive, SpatialType, OBJL, ATTL, S57_ATTRIBUTES, ATTL_BY_ACRONYM | Constants |

Text attributes are decoded byte by byte (ASCII / ISO 8859-1). National text in UCS-2 (lexical level 2, e.g. NOBJNM) is not converted yet.

Part of s57-parser. MIT licence.