Pure Go IGRF (International Geomagnetic Reference Field). This is based on the existing C implementation. This package computes values for the geomagnetic field and secular variation for a given set of coordinates and date.

• lat geodetic latitude (WGS84 latitude) in decimal degrees, valid values -90.0 < lat < 90.0;
• lon geodetic longitude (WGS84 longitude) in decimal degrees, valid values -180.0 < lon < 180.0;
• alt geodetic altitude above mean sea level in km (-1.00 to 600.00);
• date decimal date, starting from 1900.00.

The output is of type type IGRFresults struct. Fields are:

The SV values are computed by subtracting the values for the desired input date from corresponding values one year later.

Unlike in C implementation, this software calculates values near geographic poles, e.g. for latitudes higher than 89.999 and -89.999. This is the same approach the reference FORTRAN implementaion does have. Be adviced that near pole values are much less accurate.

There are far more than 1000+ unittests and results are compared against those generated from FORTRAN. SV values are not covered with tests due to the initial low accuracy of FORTRAN values. For most values these tolerances are used (whichever is higher):

• relative tolerance: 0.005
• absolute tolerance: 0.15
• absolute tolerance for declination and inclination: 0.005

Near pole values are tested with relaxed accuracies. Since FORTRAN rounds almost all values, except D and I, actual results are of much higher accuracy.

• Add "github.com/proway2/go-igrf/igrf" to your import clause.

package main

import (
	"fmt"
	"github.com/proway2/go-igrf/igrf"
)

func main() {
	igrf_data := igrf.New()
	res, err := igrf_data.IGRF(46.9, 39.9, 0.0, 2021.5)
	fmt.Println(res, err)
}

• Run go mod tidy, this brings the latest version. Fix the version at go.mod if you need a different one.

• Alken, P., Thébault, E., Beggan, C.D. et al. International Geomagnetic Reference Field: the thirteenth generation. Earth Planets Space 73, 49 (2021). https://doi.org/10.1186/s40623-020-01288-x

• Implementation is based on geomag70.c. License information.