[philliphoff]

Summary

Items 1–3 of #49. The issue's "nice to have" items are in a separate PR.

1. Attribute classes.

• S57AttributeDefinition gains Class (S57AttributeClass: Feature, National, Spatial, Cartographic) and IsNational. The docs say national attributes go in NATF and spatial attributes in ATTV (S-57 Part 3, 4.5 and 7.6.4).
• The generator reads GDAL's Class column and writes it for non-feature attributes only, through an optional constructor parameter that defaults to Feature. It fails on an unknown class.
• The IHO and Inland ENC tables were regenerated from GDAL v3.12.0. Only the 17 non-feature IHO attributes changed; the Inland ENC table is identical.
• The AML .g.cs files are untouched. IHO attributes keep their class through the IHO base catalogue, and AML-only codes (20000 and up) default to Feature. This is documented in the XML docs and docs/reading-aml-data-sets.md.

With the existing S57ObjectCatalogue, this covers EncDotNet.S100's hand-written tables: code ↔ acronym, type (List vs Enumerated), and NATF.

2. S57ObjectCode above 160.

Correction to the issue: TS_PRH…T_TIMS aren't codes 161–167. S-57 Appendix A gives them as 136–142, and the enum already had them. The codes actually missing were:

• 161 ARCSLN, 162 ASLXIS and 163 NEWOBJ, from the Edition 3.1 supplement. The OBJL 163 in the NOAA corpus is NEWOBJ.

• the cartographic $ classes, named Cartographic + class name, since C# names can't contain $:

  Acronym	Code	Enum member
  $AREAS	500	CartographicArea
  $LINES	501	CartographicLine
  $CSYMB	502	CartographicSymbol
  $COMPS	503	CartographicCompass
  $TEXTS	504	CartographicText

  C_AREAS was avoided because the C_ prefix already means a collection class. The enum's remarks explain the mapping.

The writer's DSSI NOCR counting uses code ranges, and nothing calls Enum.IsDefined, so behaviour is unchanged. The one visible effect: codes 500–504 now print as names rather than numbers, for example in the ChartViewer's feature display.

3. Long-name helpers.

• S57LongName gets LnamLength (8), FromLnam(ReadOnlySpan<byte>), ToLnam() and TryWriteLnam(Span<byte>). The layout is AGEN, FIDN, FIDS, each little-endian.
• S57RecordName.FromLongName(S57LongName) keeps a FIDN above int.MaxValue as the int with the same bits; FeatureId is documented to match. The int properties stay int so the public API doesn't break.
• The reader's private FFPT LNAM decoder and the writer's FFPT encoding now use these helpers, so there's one implementation.

Docs: short notes in docs/reading-s57-charts.md (LNAM helpers) and docs/reading-aml-data-sets.md (attribute classes).

Left open: the ARCSLN/ASLXIS/NEWOBJ docs say "added by a supplement to S-57 Edition 3.1" without naming which one, because the supplement number couldn't be confirmed from the standards in the repo.

Standards alignment

• ISO/IEC 8211 (iso8211)
• S-57 records, topology, updates or exchange sets (s57-enc)
• Legacy chart viewer, maintenance only (chart-viewer)
• N/A: build, CI, docs or tooling only

Standard section references cited in code or docs: S-57 Part 3 4.5 and 7.6.4 (NATF/ATTV); Appendix A chapters 1 and 2 (object and attribute codes); Part 3 FFPT LNAM layout.

Tests

• Added or updated xUnit tests under tests/. They cover:
  • attribute classes
  • each new code
  • every catalogue cartographic class having a member
  • LNAM round trips at uint.MaxValue, int.MaxValue + 1 and the AGEN/FIDS limits
  • hand-built byte-order examples and wrong lengths
  • an FFPT write/read at the limits
• Test input is built in memory; no real ENC cells are committed
• dotnet test --configuration Release passes: 1052 unit tests (1 skipped, the AML real-data test) and 14 performance tests, with no budget changes. It also passes merged with the other EncDotNet.S57: attribute catalogue, object codes 161+ and long-name helpers #49 PR.

Documentation

• Updated the affected package's src/<project>/README.md
• Updated guides under docs/ if user-facing behavior changed
• New public APIs have XML doc comments
• docfx docfx.json --warningsAsErrors passes, if docs changed

Dependencies

• No new NuGet dependencies

Breaking changes

None to the binary API; dotnet pack package validation against 0.8.1 passes. Behavioral: S57ObjectCode values 161–163 and 500–504 now have names, so their ToString() is a name rather than a number.

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