ENC.NET

A .NET 10 library suite and desktop application for reading, parsing, and rendering IHO S-57 Electronic Navigational Charts (ENCs).

EncDotNet implements:

• ISO/IEC 8211 — the binary container format used by S-57 for data encoding
• IHO S-57 — the International Hydrographic Organization's transfer standard for digital hydrographic data
• Nautical chart visualization — rendering ENC data on an interactive map

Projects

Project	Description
EncDotNet.Iso8211	Low-level ISO 8211 binary format parser (DDR, field definitions, subfield readers)
EncDotNet.S57	S-57 domain model — documents, features, vectors, catalogs, charts, and topology
EncDotNet.Noaa	NOAA ENC product catalog client for discovering and downloading chart data
EncDotNet.ChartViewer	Avalonia/Mapsui desktop viewer for rendering charts on an interactive map

Iso8211  →  S57  →  ChartViewer
                 →  Noaa

Getting Started

Prerequisites

• .NET 10 SDK

Build

dotnet build

Run Tests

dotnet test

Launch the Chart Viewer

dotnet run --project src/EncDotNet.ChartViewer

Sound Charts

Sound Charts is the desktop chart viewer application built with Avalonia and Mapsui. It renders S-57 ENC data on an interactive map with configurable chart layers.

Features:

• Browse and search available NOAA ENC charts
• Toggle chart layers: coastline, depth areas, depth contours, soundings, sea area, land area, buoys, lights, and more
• Configurable depth units (fathoms, meters, feet)
• Multi-scale chart display ordered by compilation scale

Launch

dotnet run --project src/EncDotNet.ChartViewer

Library Usage

Parsing ISO 8211 Files

EncDotNet.Iso8211 provides a self-contained parser for the ISO/IEC 8211 binary container format. It can read any ISO 8211 file, not just S-57 charts.

using EncDotNet.Iso8211;

// Parse a file
var document = Iso8211DocumentReader.ReadFromFile("chart.000");

// The first record is the Data Descriptive Record (DDR), which defines
// the schema (field tags, subfield names, and data types) for all
// subsequent data records.
var ddr = Iso8211DataDescriptiveRecordReader.Read(document.DataDescriptiveRecord!);

// Iterate data records
foreach (var record in document.DataRecords)
{
    foreach (var field in record.Fields)
    {
        Console.WriteLine($"Field tag: {field.Tag}  ({field.Data.Length} bytes)");

        // Use the DDR field definition to decode subfields
        var fieldDef = ddr.GetFieldDefinition(field.Tag);
        if (fieldDef is not null)
        {
            var reader = new Iso8211FieldReader(fieldDef, field.Data);

            foreach (var subfieldDef in fieldDef.SubfieldDefinitions)
            {
                if (reader.TryGetSubfield<string>(subfieldDef.Name, out var value))
                {
                    Console.WriteLine($"  {subfieldDef.Name} = {value}");
                }
            }
        }
    }
}

Reading S-57 Charts

EncDotNet.S57 builds on the ISO 8211 parser to provide a typed domain model for S-57 electronic navigational chart data.

using EncDotNet.S57;

// Parse an S-57 chart file (.000)
var document = S57DocumentReader.ReadFromFile("US5CA11M.000");

// Access data set metadata
Console.WriteLine($"Dataset: {document.DataSetIdentification?.DataSetName}");
Console.WriteLine($"Scale:   1:{document.DataSetParameters?.CompilationScale}");

// Coordinate multiplication factor — divide raw integer coordinates
// by this value to get decimal degrees (typically 10,000,000)
int comf = document.CoordinateMultiplicationFactor;

// Query features by S-57 object code
var depthAreas = document.GetFeaturesByObjectCode(S57ObjectCode.DEPARE);

foreach (var feature in depthAreas)
{
    Console.WriteLine($"Depth Area {feature.RecordName} — {feature.Primitive}");

    // Feature attributes (e.g. DRVAL1, DRVAL2 for depth range)
    foreach (var attr in feature.Attributes)
    {
        Console.WriteLine($"  ATTL {attr.AttributeCode} = {attr.Value}");
    }

    // Follow spatial pointers to geometry
    foreach (var ptr in feature.SpatialPointers)
    {
        var vector = document.GetVectorRecord(ptr.Name);

        if (vector is not null)
        {
            foreach (var coord in vector.Coordinates2D)
            {
                double lon = coord.X / (double)comf;
                double lat = coord.Y / (double)comf;
                Console.WriteLine($"  ({lat:F6}, {lon:F6})");
            }
        }
    }
}

Higher-Level Chart Model

S57Chart provides indexed, strongly-typed access to features and spatial records:

using EncDotNet.S57.Charts;

var chart = S57Chart.FromFile("US5CA11M.000");

// Typed feature collections
Console.WriteLine($"Point features: {chart.PointFeatures.Length}");
Console.WriteLine($"Line features:  {chart.LineFeatures.Length}");
Console.WriteLine($"Area features:  {chart.AreaFeatures.Length}");

// Spatial record dictionaries (keyed by record name)
Console.WriteLine($"Edges:          {chart.Edges.Count}");
Console.WriteLine($"Connected nodes:{chart.ConnectedNodes.Count}");
Console.WriteLine($"Isolated nodes: {chart.IsolatedNodes.Count}");

Applying Incremental Updates

S-57 supports incremental updates distributed as .001, .002, etc. files:

var baseDoc = S57DocumentReader.ReadFromFile("chart.000");
var update  = S57DocumentReader.ReadFromFile("chart.001");

// Merge insert/delete/modify operations into the base document
var merged = baseDoc.ApplyChanges(update);

Reading an Exchange Set Catalog

Each S-57 exchange set contains a CATALOG.031 file listing all chart files and their geographic bounds:

using EncDotNet.S57.ExchangeSets;

var catalog = S57CatalogReader.ReadFromFile("ENC_ROOT/CATALOG.031");

foreach (var entry in catalog.Entries)
{
    Console.WriteLine($"{entry.FileName}");
    Console.WriteLine($"  Bounds: ({entry.SouthernmostLatitude}, {entry.WesternmostLongitude}) " +
                      $"to ({entry.NorthernmostLatitude}, {entry.EasternmostLongitude})");
}

Downloading NOAA ENC Charts

EncDotNet.Noaa queries the NOAA ENC product catalog and can be used to discover and download chart data:

using EncDotNet.Noaa;

using var client = new EncProductCatalogClient();
var catalog = await client.GetNoaaCatalogAsync();

Console.WriteLine($"Found {catalog.Cells.Count} charts");

foreach (var cell in catalog.Cells)
{
    Console.WriteLine($"{cell.Name} — Scale 1:{cell.ChartScale}");
    Console.WriteLine($"  Edition {cell.Edition}, Update {cell.UpdateNumber}");
    Console.WriteLine($"  Download: {cell.ZipfileLocation}");
}

Scripts

The scripts/ folder contains C# scripts for common operations. Run them with dotnet run:

Script	Description
DownloadCatalog.cs	Download all NOAA ENC chart .zip files to .catalog/
ExpandCatalog.cs	Unzip downloaded charts to .expanded/
ReadCatalog.cs	Benchmark ISO 8211 parsing of all .000 files
ReadCatalogS57.cs	Parse all .000 files as S-57 with diagnostics
DumpCatalog.cs	Hex dump + parsed view of a CATALOG.031 file
DumpChart.cs	Hex dump + parsed view of an ENC .000 file
BuildChartIndex.cs	Generate a JSON chart index from all catalogs

# Download all NOAA charts
dotnet run scripts/DownloadCatalog.cs

# Expand them
dotnet run scripts/ExpandCatalog.cs

# Dump a single chart
dotnet run scripts/DumpChart.cs .expanded/US5CA11M/ENC_ROOT/US5CA11M.000

Architecture

S-57 Topology

S-57 uses a chain-node topology model:

• Features reference spatial records via FSPT (Feature-to-Spatial) pointers
• Area features reference Faces, which are bounded by Edges
• Edges are polylines connecting two Connected Nodes, with interior coordinate points stored as SG2D fields
• Isolated Nodes represent standalone points or sounding clusters

Coordinate Handling

Raw coordinates in S-57 files are stored as integers. Divide by the Coordinate Multiplication Factor (COMF, typically 10,000,000) from the DSPM record to get decimal degrees. Soundings are similarly divided by the Sounding Multiplication Factor (SOMF, typically 10).

Immutable Data Model

All parsed data uses ImmutableArray<T> and ImmutableDictionary<K, V> for thread-safe, LINQ-friendly access. Records are immutable after construction.

Standards References

• IHO S-57 Edition 3.1 — Transfer Standard for Digital Hydrographic Data
• ISO/IEC 8211 — Specification for a data descriptive file
• IHO S-52 — Chart Content and Display Aspects of ECDIS

License

This project is licensed under the MIT License. See LICENSE for details.