Every commercial vessel on the planet uses electronic navigation charts (ENC) in S-57 format. Despite this, there has never been a working JavaScript parser for these charts. I set out to change that.
The Challenge
S-57 files use ISO 8211, a binary format from 1994. The data is stored as variable-length records with mixed binary and text fields. Coordinates are integers scaled by a multiplication factor (typically 10 million). Geometry uses chain-node topology where polygons are assembled from shared edges.
What I Built
A monorepo of 7 TypeScript packages:
@s57-parser/iso8211 - Pure ISO 8211 binary parser. The hardest bug: two binary field notations (b15 = suffix meaning signedness+bytes, B(40) = parenthesized meaning bits) that look almost identical but parse completely differently.
@s57-parser/s57 - S-57 data model. Resolves chain-node topology: each Edge references start/end ConnectedNodes via VRPT records. Different spatial record types can share the same RCID, so I use compound keys (rcnm * 100000 + rcid) to avoid collisions.
@s57-parser/s101 - Parser for the next-generation S-101 format (mandatory from 2029). Fun fact: S-101 uses ISO 8211, not GML/XML as many assume. My ISO 8211 parser handles both formats.
@s57-parser/s52-render - Canvas2D renderer implementing IHO S-52 symbology: 3 color palettes (Day/Dusk/Night), conditional depth coloring, sector light arcs, pattern fills, text labels with light characteristic abbreviations.
@s57-parser/leaflet and @s57-parser/maplibre - Plugins for the two most popular web mapping libraries.
@s57-parser/cli - CLI tool to inspect and parse S-57/S-101 files from the terminal.
Numbers
- ~5100 lines of TypeScript
- 127 tests across 8 test files
- 0 runtime dependencies (core packages)
- Parses a typical NOAA harbor chart (2320 features) in ~800ms in the browser
- 160+ S-101 feature types in the catalogue
- MIT license
Try It
Live demo (Boston Harbor, NOAA US5MA12M): https://devladpopov.github.io/s57-parser/
npm install @s57-parser/s57 @s57-parser/s52-render
Download free NOAA charts from charts.noaa.gov, drag-drop onto the demo viewer.