Table of Contents

EncDotNet.S100.Datasets.S125

Library for reading and portraying IHO S-125 (Marine Aids to Navigation) datasets.

S-125 supersedes the AtoN (Aids to Navigation) feature classes from S-57 / S-101 with a stand-alone S-100-based product specification covering lights, buoys, beacons, daymarks, AIS aids, and other aids to navigation.

Features

  • Parse S-125 GML datasets (S-100 Part 10b encoding using the S-100 GML 5.0 profile)
  • Extract concrete AtoN features (Landmark, LateralBuoy, CardinalBeacon, LightSectored, VirtualAISAidToNavigation, …) and information types (AtonStatusInformation, SpatialQuality)
  • Preserve information bindings (xlink:href / informationRef) so the XSLT portrayal rules can resolve cross-references
  • Project to the S-100 Part 9 FeatureXML neutral form (Dataset/Features/* plus Dataset/InformationTypes/*) consumed by the S-125 portrayal catalogue
  • XSLT-based portrayal via the S-125 Portrayal Catalogue (AtoN status indications, data coverage)
  • AtoN symbology (buoys, beacons, topmarks, daymarks, landmarks, lights and light sectors, AIS aids, navigation lines, recommended tracks) via the bundled S-101 Portrayal Catalogue's Lua rules — see Portrayal

Overview

Key types:

  • S125Dataset — root model containing parsed features, information types, and dataset identification. ReadMetadata() (plus static ReadMetadata(path) / ReadMetadata(stream)) is the phased-loading "peek" path (issue #460): it returns a DatasetMetadata with the declared spec and the raw WGS-84 extent folded from feature geometry (null when the dataset carries only geometry-less container features), skipping the XSLT portrayal pipeline.
  • S125Feature — a geographic feature with type code, geometry, simple/complex attributes, and information references. Implements IS100Feature.
  • S125InformationType — an information type instance (e.g. AtonStatusInformation). Implements IS100InformationType.
  • S125InformationReference — a feature → information-type association captured from xlink:href / informationRef attributes.
  • S125ComplexAttribute — a complex attribute group with sub-attribute values. Implements IS100ComplexAttribute.
  • S100GeometryType — shared enum (from EncDotNet.S100.Core) describing the geometry primitive type of a feature.
  • S125FeatureXmlSource — IFeatureXmlSource adapter that projects an S125Dataset into the synthesized Dataset/Features/* shape that S-125 XSLT rules match against.
  • Feature geometry reaches the renderers through the shared FeatureGeometryProvider<TFeature> (IFeatureGeometryProvider, from EncDotNet.S100.Core), which the dataset processor builds over the parsed features.
  • S125PortrayalCatalogue — IVectorPortrayalCatalogue implementation that loads XSLT rules, symbols, line styles, area fills, and color palettes.
  • S125AtonPortrayalProjection / S125AtonLuaDataProvider / S125AtonLuaRuleExecutor — portray the aids themselves with the bundled S-101 AtoN Lua rules (see Portrayal).
  • S125Feature.AttributeTree — the feature's attributes as an ordered, lossless tree (repeated values such as multi-colour colour, nested complexes such as sectorCharacteristics/lightSector); Attributes / ComplexAttributes are flat last-value views.

Portrayal

What the S-125 specification provides

S-125 does not define symbology for the aids themselves. Its portrayal is deliberately limited to flagging AtoN status changes on top of the ENC's own AtoN symbols:

  • Product Specification. S-125 Marine Aids to Navigation (AtoN), Edition 1.0.0, December 2025 (release ed1.0.0). Clause 13 Portrayal says only that "The Portrayal Catalogue is found at Annex D". Clause 1 positions S-125 as a Nautical Publication Information Overlay (NPIO) for ECDIS: "the digital equivalent of the extended list of lights".
  • Portrayal Catalogue (Annex D).
    • The release's PortrayalCatalogue.zip (XSLT) has rules only for AtoNStatusIndication, AtoNStatusInformation and DataCoverage (main.xsl dispatches to those three).
    • Its symbols are the CHNG* change symbols and QUESMRK1.
    • The Lua draft on the repository's main branch (PC/1.0.0) has the same scope plus a Default rule that draws QUESMRK1.
    • Neither has a rule for any buoy, beacon, light, daymark, landmark or AIS feature type.
    • This library bundles the release catalogue unchanged.
  • Design intent. IHO NIPWG's S-125 portrayal paper (NIPWG9-08.2A, 2022, slide 8) says:
    • S-125 is "not replacing nor duplicating actual existing AtoN symbology";
    • the status symbol is "flagging and not obscuring" the ENC symbol beneath;
    • interoperability "could be enhanced at a later stage".
  • S-98 Interoperability, Edition 2.0.0.
    • Main document §6.1.3 lists S-125 among products for future editions.
    • Annex A §15.4 mentions "suppression of S-101 navigation aids by S-125" at interoperability level 2. That is only an example of what an Interoperability Catalogue could do; no published catalogue does it.

So the specification neither ships full AtoN symbology nor defers it by reference to S-101 / S-52. It assumes an ENC is displayed underneath, and S-125 data alone portrays as status flags only.

Implementation choice: S-101 AtoN rules

On its own, that portrays a dataset of buoys and lights as an empty chart. This library therefore also portrays the aids themselves with the bundled S-101 Portrayal Catalogue's Lua rules. This is an implementation choice, not part of the S-125 specification.

  • The rules are reused as-is. The S-101 rule set covers:

    • buoy shapes and colour patterns (LateralBuoy, CardinalBuoy, …);
    • topmarks (TOPMAR02);
    • daymarks and landmarks;
    • light flares, characteristics and sector legs (LightAllAround, LightSectored, LightFlareAndDescription, LITDSN02);
    • AIS aids, navigation lines and recommended tracks.

    Both feature catalogues draw these feature types and attributes from the IHO GI Registry, so most features map one-to-one. The two catalogues share sectorCharacteristics, rhythmOfLight and the listed values for colour and shape.

  • S125AtonPortrayalProjection bridges the differences:

    • S-125 Topmark equipment features are lifted onto their structure (via the StructureEquipment parent / child roles, or co-location) as S-101's topmark complex attribute.
    • SyntheticAISAidToNavigation is portrayed as PhysicalAISAidToNavigation.
    • maximalPermittedDraught becomes maximumPermittedDraught.
    • orientation flattens to orientationValue where S-101 binds the simple attribute.
    • The pre-1.0 spellings objectName / MMSICode are read as featureName / mMSICode.
    • Features the S-125 catalogue portrays itself (AtonStatusIndication, DataCoverage) and meta / aggregation features are not projected.

  • S125AtonLuaDataProvider serves the projected features to the S-101 rules through the S-100 Part 9A host API:

    • It uses the S-101 feature catalogue for type information.
    • Point features at the same position share one synthetic point record. This reproduces S-101 structure / equipment co-location, which the light-flare direction and the stacking of light descriptions depend on.

  • S125DatasetProcessor merges the S-101 AtoN instructions with the S-125 catalogue's own output (status indications drawn over the aid) into one layer.

    • The S-101 colour palette is used for both: the S-125 colour profile uses the same S-52 tokens, and the CHNG* symbols keep their S-125 stylesheets.
    • Without a Lua engine or the S-101 catalogues, the processor falls back to the S-125 catalogue output only.

Gap: obscuredSector. S-125's obscuredSector (on LightSectored) has no S-101 counterpart and is not portrayed.

ENC display. Over an ENC that portrays the same physical aids (S-98 interplay):

  • S-125 sits on the other chart overlays plane, above the ENC's base and standard chart planes.
  • The S-101 instructions run through the same viewing-group, display-mode and display-plane filtering as an ENC. Under the mariner's ECDIS display category, S-125 aids show and hide (names and light descriptions included) exactly as the ENC's do.
  • Where S-125 and the ENC encode the same aid at the same position, the symbols and sector legs coincide. The S-125 status flags (CHNG*) then mark the ENC aid, which is the overlay the specification intends.
  • No S-98 Interoperability Catalogue suppression of either product is applied (see the Annex A example above).

Strongly-typed data model

The EncDotNet.S100.Datasets.S125.DataModel namespace provides a read-only projection of S125Dataset into a domain-shaped object graph rooted at S125AtonDataset. Aids are exposed as typed shapes (S125Buoy, S125Beacon, S125Light, S125AisAton, S125Structure, S125Equipment) under the common IS125Aid interface. AtoN status bindings (AtoNStatus xlink → AtonStatusInformation) and equipment-on-structure relationships (parent xlink → host beacon / landmark) are resolved into navigable properties so callers can ask domain questions without walking the feature bag.

The projection is permissive — unresolved xlinks, attribute parse failures, and similar issues surface as ProjectionDiagnostic entries rather than exceptions. Only a fully empty dataset (no features and no information types) causes From(...) to throw.

Quick start (typed model)

using EncDotNet.S100.Datasets.S125;
using EncDotNet.S100.Datasets.S125.DataModel;

var dataset = S125Dataset.Open("path/to/aton.gml");
var typed = S125AtonDataset.From(dataset, out var diagnostics);

foreach (var aid in typed.Aids)
{
    var status = aid.Status?.IsOperational switch
    {
        true => "operational",
        false => "non-operational",
        null => "no status",
    };
    Console.WriteLine($"{aid.FeatureType} {aid.Id}: {status}");

    if (aid is S125AisAton ais && ais.IsVirtual)
        Console.WriteLine("  (virtual AIS — no physical presence)");

    if (aid.HostStructure is { } host)
        Console.WriteLine($"  mounted on {host.FeatureType} {host.Id}");
}

Validation

The EncDotNet.S100.Datasets.S125.Validation namespace exposes S125AtonRules.Default, a ValidationRuleSet<S125AtonDataset> of normative checks built on the typed S125AtonDataset projection. The pilot pack covers:

Rule Severity Summary
S125-R-1.1 Error Aid position lat/lon in WGS-84 ranges (S-100 Part 10b §6.2)
S125-R-1.2 Error Aid gml:id unique within the dataset
S125-R-2.1 Error AIS aid carries a 9-digit mMSICode
S125-R-3.1 Error AtonStatusInformation.changeTypes in {1..5}
S125-R-3.2 Error Status date range dateStart ≤ dateEnd
S125-R-4.1 Warning AtonAggregation / AtonAssociation binds ≥ 1 aid
S125-R-5.1 Warning AtonStatusIndication has a point geometry 
var raw = S125Dataset.Open("aids.gml");
var typed = S125AtonDataset.From(raw, out _);
var report = S125AtonRules.Validate(typed);
foreach (var f in report.Findings)
    Console.WriteLine($"{f.Severity} {f.RuleId} {f.RelatedFeatureId}: {f.Message}");

Projection-time issues (unresolved xlinks, duplicate ids) are not exposed on the typed model and so are not surfaced as rules; capture the out IReadOnlyList<ProjectionDiagnostic> from S125AtonDataset.From if you need them.

Notes

  • S-125 application schema namespace is http://www.iho.int/S125/1.0; geometry uses the S-100 GML 5.0 profile namespace http://www.iho.int/s100gml/5.0. Older sample datasets that still declare the S-100 GML 1.0 profile are read transparently.
  • Coordinate ordering in <gml:pos> / <gml:posList> follows the S-100 Part 10b convention of lat lon for EPSG:4326.
  • Renderers must tolerate geometry-less features — abstract supertypes such as AtonAggregation and AtonAssociation carry no geometry.
  • Time validity (fixedDateRange, periodicDateRange) is interpreted as UTC; do not coerce to local time at the source.

Test data

tests/datasets/S125/aton_us4va1bf.gml holds the 178 aids to navigation of NOAA ENC US4VA1BF (Chesapeake Bay entrance; US public domain), derived by tests/datasets/S125/derive-s125-from-enc.cs:

  • The ENC cell goes S-57 → S-101 (in-memory translation) → S-125 1.0.0 GML.
  • Attributes are limited to the S-125 Feature Catalogue bindings.
  • Topmarks are written as Topmark features.

It validates clean against S125AtonRules. The other aton_*.gml fixtures are small synthetic samples.

License

The bundled S-125 specification assets in EncDotNet.S100.Specifications are © IHO and used in accordance with their open-publication terms; see https://github.com/iho-ohi/S-125-Product-Specification-Development.

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