Download NOAA ENC cells

This page shows how to find U.S. ENC cells in the NOAA product catalog, download one, and open it with EncDotNet.S57. NOAA publishes its cells free of charge, so they're a convenient source of real data for development and testing.

Prerequisites

A console app that references EncDotNet.Noaa and EncDotNet.S57:

dotnet add package EncDotNet.Noaa
dotnet add package EncDotNet.S57

Internet access to charts.noaa.gov.

Find cells in the catalog

EncProductCatalogClient downloads and parses the NOAA ENC product catalog. Each Cell has a name, a compilation scale, edition and update numbers, the states, regions and Coast Guard districts it covers, its coverage polygons and the URL of its ZIP file.

using EncDotNet.Noaa;

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

Console.WriteLine($"{catalog.Cells.Count} cells, valid {catalog.Header.DateValid}");

IEnumerable<Cell> harbourCells = catalog.Cells
    .Where(c => c.States.StateList.Contains("MA") && c.ChartScale <= 25000)
    .OrderBy(c => c.Name);

foreach (Cell cell in harbourCells)
{
    Console.WriteLine($"{cell.Name}: {cell.LongName}, 1:{cell.ChartScale}, edition {cell.Edition} update {cell.UpdateNumber}");
}

The constructor takes an optional HttpClient. Pass one when your app manages its own, for example from IHttpClientFactory.

Download and open a cell

Each cell's ZIP file holds a single-cell exchange set: an ENC_ROOT folder with CATALOG.031, the base cell and any update cells. Download it, extract it, and read the cell with its updates applied:

using System.IO.Compression;
using EncDotNet.Noaa;
using EncDotNet.S57.Charts;
using EncDotNet.S57.ExchangeSets;

using var client = new EncProductCatalogClient();
EncProductCatalog catalog = await client.GetNoaaCatalogAsync();
Cell cell = catalog.Cells.First(c => c.Name == "US5MA1BO");

using var http = new HttpClient();
string zipPath = Path.Combine(Path.GetTempPath(), $"{cell.Name}.zip");
string extractPath = Path.Combine(Path.GetTempPath(), cell.Name);

await File.WriteAllBytesAsync(zipPath, await http.GetByteArrayAsync(cell.ZipfileLocation));
ZipFile.ExtractToDirectory(zipPath, extractPath, overwriteFiles: true);

string encRoot = Path.Combine(extractPath, "ENC_ROOT");
S57Chart chart = S57ExchangeSetReader.Read(encRoot).ReadChart(encRoot);

Console.WriteLine($"{cell.Name}: {chart.AreaFeatures.Count} area features at 1:{chart.CompilationScale}");

Replace US5MA1BO with a cell name from the previous step.

Download many cells

The repository's scripts/DownloadCatalog.cs and scripts/ExpandCatalog.cs download and extract every cell in the catalog. Run them from a clone of the repository:

dotnet run scripts/DownloadCatalog.cs
dotnet run scripts/ExpandCatalog.cs

The scripts write to .catalog/ and .expanded/ at the repository root, which Git ignores.

Important