GeoMagSharp

A C# library for geomagnetic field calculations using spherical harmonic models. GeoMag # is a port of the C++ application GeoMag 7.0 distributed by NOAA.

Installation

dotnet add package GeoMagSharp

Or via the NuGet Package Manager:

Install-Package GeoMagSharp

Quick Start

using GeoMagSharp;

// Load a coefficient file
var geoMag = new GeoMag();
geoMag.LoadModel("WMM2025.COF");

// Configure calculation
var options = new CalculationOptions
{
    Latitude = 45.0,
    Longitude = -93.0,
    StartDate = new DateTime(2025, 7, 1),
    SecularVariation = true,
    CalculationMethod = Algorithm.BGS
};
options.SetElevation(0, Distance.Unit.meter, true);

// Run calculation
geoMag.MagneticCalculations(options);

// Access results
var result = geoMag.ResultsOfCalculation[0];
Console.WriteLine($"Declination: {result.Declination.Value:F2} degrees");
Console.WriteLine($"Inclination: {result.Inclination.Value:F2} degrees");
Console.WriteLine($"Total Field: {result.TotalField.Value:F1} nT");

Async API

// Async with progress reporting and cancellation
var cts = new CancellationTokenSource();
var progress = new Progress<CalculationProgressInfo>(p =>
    Console.WriteLine($"{p.PercentComplete:F0}% - {p.StatusMessage}"));

var model = await ModelReader.ReadAsync("WMM2025.COF", progress, cts.Token);
await geoMag.MagneticCalculationsAsync(options, progress, cts.Token);
await geoMag.SaveResultsAsync("output.txt", false, cts.Token);

Supported Models

Model	Type	Source	Included
WMM	World Magnetic Model	NOAA	WMM2025.COF, WMM2015.COF
WMMHR	WMM High Resolution	NOAA	WMMHR.COF
IGRF	International Geomagnetic Reference Field	IAGA	IGRF12.COF
EMM	Enhanced Magnetic Model	NOAA	No (survey required)
BGGM	BGS Global Geomagnetic Model	BGS	No (commercial license)

Bundled coefficient files are in the coefficient/ directory. See coefficient/NOTICE.md for attribution and download links for non-bundled models.

Target Frameworks

• .NET Framework 4.8
• .NET Standard 2.0 (compatible with .NET Core 2.0+, .NET 5+)

API Overview

Core Classes

• GeoMag - Main entry point for loading models and running calculations
• ModelReader - Parses COF/DAT coefficient files into model objects
• Calculator - Low-level spherical harmonic calculation engine
• CalculationOptions - Configuration for latitude, longitude, date, elevation, etc.

Model Classes

• MagneticModelSet - A set of magnetic models (main field + secular variation)
• MagneticModelCollection - Manages multiple model sets with JSON serialization
• MagneticCalculations - Calculation results (declination, inclination, field components)

Result Properties

Each MagneticCalculations result contains MagneticValue objects with:

• Value - The calculated value
• ChangePerYear - Secular variation (when enabled)

Available components: Declination, Inclination, TotalField, HorizontalIntensity, NorthComponent, EastComponent, VerticalComponent, GridVariation.

License

MIT License - see LICENSE for details.

Bundled coefficient files are U.S. Government works in the public domain. See coefficient/NOTICE.md for full attribution.