# Geomagnetic Field

This tutorial shows how to use the Geomagnetic Field Model.

## Introduction

Orekit provides an easy to use class for calculating the geomagnetic field of the earth. Currently there is support for two different models:

## Prerequisites

A geomagnetic field model relies on published coefficients files that are loaded on demand. There exist different formats for these files, but orekit uses a modified version, which may contain coefficients from multiple epochs inside one file.

The format of the expected model file is as follows:

```  {model name} {epoch} {nMax} {nMaxSec} {nMax3} {validity start} {validity end} {minAlt} {maxAlt} {model name} {line number}
{n} {m} {gnm} {hnm} {dgnm} {dhnm} {model name} {line number}
```

Example:

```   WMM2010  2010.00 12 12  0 2010.00 2015.00   -1.0  600.0          WMM2010   0
1  0  -29496.6       0.0      11.6       0.0                        WMM2010   1
1  1   -1586.3    4944.4      16.5     -25.9                        WMM2010   2
```

The latest coefficient files for IGRF and WMM can be found in attachment.

## Basic Use

To calculate the geomagnetic field of a specified geodetic location and altitude is pretty much straight-forward.

First retrieve the geomagnetic field model for a desired year (e.g. WMM):

```GeoMagneticField model = GeoMagneticFieldFactory.getWMM(2012.0);
```

The year has to be specified as a decimal year, which can be converted from a julian date like this:

```double year = GeoMagneticField.getDecimalYear(1, 6, 2012);
```

Finally we can calculate the magnetic field at a geodetic location (lat/lon in deg) and altitude (in km):

```GeoMagneticElements result = model.calculateField(80.0, 0.0, 100.0);
```

The result contains the seven magnetic components:

• F - Total Intensity of the geomagnetic field
• H - Horizontal Intensity of the geomagnetic field
• X - North Component of the geomagnetic field
• Y - East Component of the geomagnetic field
• Z - Vertical Component of the geomagnetic field
• I (DIP) - Geomagnetic Inclination
• D (DEC) - Geomagnetic Declination (Magnetic Variation)