A JavaScript module for accurately calculating the parameters of the geomagnetic field incl. declination (variation), and inclination (dip) using the World Magnetic Model (currently WMM2020, valid from 2020-2025). It is adapted from magvar by Darren Yeates (https://github.com/dpyeates/magvar)

Compiled versions (both minified and not) are located in dist/.

<script src="{yourjspath}/geomag.min.js"></script>

These versions expose a geomag global.

npm install geomag

For bundling (e.g., with Rollup) you can then import the ES6 module via

import * as geomag from 'geomag'

or directly use it in the browser via

import * as geomag from 'node_modules/geomag/dist/geomag-es.js'

import * as geomag from 'geomag';

const field = geomag.field(latitude, longitude);
// or const field = geomag.field(latitude, longitude, altitude);
const { 
    declination,
    inclination,
    intensity,
    northIntensity,
    eastIntensity,
    verticalIntensity,
    horizontalIntensity,
} = field;

latitude is the geographic latitude (WGS 84) in degrees (-90 to 90, north is positive, south negative).

longitude is the geographic longitude (WGS 84) in degrees (-180 to 180, east is positive, west negative).

altitude is the altitude in km above sea level. The parameter is optional and defaults to 0 if not provided.

declination is the angle in degrees between magnetic north and true north in the horizontal plane. Positive values correspond to magnetic north pointing eastward from true north.

inclination is the angle in degrees of the magnetic field lines with respect to the horizontal plane. Positive values correspond to the field pointing downward.

intensity, northIntensity, eastIntensity, verticalIntensity, and horizontalIntensity are the intensities in nT of the geomagnetic fields - total magnitude, north-pointing component, east-pointing component, vertical component, and horizontal component, respectively.

The package provides type definitions in dist/geomag.d.ts.

geomag is freely distributable under the terms of the MIT license.