garmin_img

A pure-Dart reader for unlocked Garmin .img map files (topographic and vector maps). It decodes the IMG container, GMP sub-maps, the TRE index (map levels, subdivisions, bounds) and RGN geometry into typed features — with no Flutter or mapsforge dependency, so you can use it with mapsforge_flutter, flutter_map, a CLI, or a server.

There is currently no other Garmin IMG reader on pub.dev.

Status

Early. Validated end-to-end against a real Bulgarian NT/GMP topo map (gmapsupp.img): the container, GMP sub-maps, TRE bounds/levels/subdivisions and polyline first-points all decode correctly and in-bounds.

Implemented:

• IMG container + GMP sub-map location
• TRE: bounding box, map levels (bits-per-coord), subdivisions
• RGN: points/POIs, polylines and polygons — full geometry (all vertices) via the bit-packed bitstream (topo contour lines, types 0x20–0x25, come through)
• LBL: labels — POI/feature names and contour elevations (8-bit & 6-bit)
• example/img2geojson.dart — dump features to GeoJSON (view in geojson.io)

Next:

• Extended types (0x10000+); non-Latin label codepages (Cyrillic)
• FAT-based subfile enumeration (streaming reads already done ✅)

Usage

import 'package:garmin_img/garmin_img.dart';

final img = await GarminImg.open('gmapsupp.img');
for (final map in img.maps) {
  print(map.bounds);                 // BBox(S=… W=… N=… E=…)
  print(map.levels);                 // [MapLevel(zoom bpc n)…]
  for (final f in map.polylines()) // decoded polyline start points
    print(f);
}

Scope

• Unlocked images only (XOR byte 0x00, "GARMIN" markers in the clear). Encrypted Garmin maps are out of scope.
• Web-Mercator / Garmin 24-bit coordinates.

License

MIT.