s57-to-mbtiles

Convert NOAA S-57 ENC nautical charts (.000 files) into vector MBTiles for use with SignalK / Freeboard-SK.

What it does

Takes one or more ZIP archives of S-57 ENC files from NOAA and runs a five-stage pipeline:

1. Extract ZIPs into a staging area
2. GDAL (ogr2ogr) converts each ENC layer to GeoJSON
3. Consolidate per-layer GeoJSON across charts
4. tippecanoe builds vector tiles per zoom level
5. tile-join merges everything into a single .mbtiles file

The output can be served directly by signalk-charts-provider-simple and rendered by Freeboard-SK's S-57 style engine.

Quick start

Prerequisites

• Python 3 (standard library only)
• tippecanoe (native install)
• GDAL (ogr2ogr) — native install or via Docker/Podman container

See docs/INSTALL.md for platform-specific setup (macOS, Raspberry Pi).

Download charts

Get ENC ZIPs from NOAA: https://charts.noaa.gov/ENCs/ENCs.shtml

Files follow the pattern https://charts.noaa.gov/ENCs/{NAME}_ENCs.zip — by state (e.g., CT_ENCs.zip) or Coast Guard district (e.g., 01CGD_ENCs.zip).

Run

# Single state
./s57-to-mbtiles.py CT_ENCs.zip

# Multiple states, grouped by NOAA band (recommended)
./s57-to-mbtiles.py CT_ENCs.zip RI_ENCs.zip MA_ENCs.zip NY_ENCs.zip \
  --by-band -o ne-coast.mbtiles

# Reuse existing GeoJSON (skip the slow GDAL step)
./s57-to-mbtiles.py --geojson-dir ./data/geojson/band3/ --minzoom 11 --maxzoom 12

All intermediate files are stored in ./data/ and preserved between runs for resume capability.

Modes

Mode	Use case	Example
Single source	One ZIP or directory	./s57-to-mbtiles.py NY_ENCs.zip
By-band	Multi-state, auto-grouped by NOAA usage band	--by-band flag
Two-source split	Coarse + detail at a zoom boundary	--split 12
Multi-source	Explicit zoom ranges per source	--sources file1:9-11 file2:12-16
GeoJSON reuse	Skip GDAL, rebuild tiles only	--geojson-dir path/

See docs/USAGE.md for full details on all modes and CLI options.

GitHub Actions / CI

The repo includes a GitHub Actions workflow that can download ENC ZIPs from NOAA and build tiles automatically. Builds are defined in enc-sources.yaml:

active:
  - 01cgd          # just edit this list to control what gets built

Finished .mbtiles files are uploaded as GitHub Release assets. Builds run automatically on the 1st of each month (April-November) or manually from the Actions tab.

Forking

This repo is designed to be forked. Each fork maintains its own builds and releases independently.

1. Fork this repo on GitHub
2. Edit enc-sources.yaml — set your active list to the regions you need
3. Go to Actions tab and enable workflows on your fork
4. Run "Build ENC Charts" manually, or wait for the monthly schedule

The only file you need to customize is enc-sources.yaml. To prevent your local edits from showing up in git status or getting accidentally committed:

git update-index --skip-worktree enc-sources.yaml

To pull upstream code changes:

git remote add upstream https://github.com/motamman/s57Work.git
git fetch upstream
git merge upstream/main

If enc-sources.yaml conflicts on merge, keep your version — it's the one file meant to differ per fork. To undo skip-worktree (e.g., to resolve a conflict): git update-index --no-skip-worktree enc-sources.yaml

NOAA band / zoom mapping

Band	Description	Zoom levels
1	Overview	z7-8
2	General	z9-10
3	Coastal	z11-12
4	Approach	z13-14
5	Harbour	z15-16
6	Berthing	z17-18

In by-band mode each band also renders two zoom levels past its native ceiling (capped at --maxzoom), so wherever no finer chart exists the best available band still fills the deeper zooms. Band 1/2 tiles are then clipped to the district's own region, the union of its band 3+ chart footprints, because ocean-basin overview cells would otherwise put planet-wide tiles and bounds into every district file. The clip is written to a separate *.region.mbtiles file in data/tiles/; the per-band tippecanoe outputs are left untouched so resume keeps working.

Documentation

• docs/INSTALL.md — Installation guide (macOS, Raspberry Pi)
• docs/USAGE.md — Detailed usage guide with all CLI options
• docs/SOUNDG-FIX.md — Depth sounding fix writeup

License

This project is provided as-is for personal and educational use. NOAA chart data is public domain.