ardupilot/libraries/AP_Declination/AP_Declination.h

#pragma once

#include <AP_Common/Location.h>

/*
  magnetic data derived from WMM
 */
class AP_Declination
{
public:
    /*
     * Calculates the magnetic intensity, declination and inclination at a given WGS-84 latitude and longitude.
     * Assumes a WGS-84 height of zero
     * latitude and longitude have units of degrees
     * declination and inclination are returned in degrees
     * intensity is returned in Gauss
     * Boolean returns false if latitude and longitude are outside the valid input range of +-60 latitude and +-180 longitude
    */    
    static bool get_mag_field_ef(float latitude_deg, float longitude_deg, float &intensity_gauss, float &declination_deg, float &inclination_deg);

    /*
      get earth field as a Vector3f in Gauss given a Location
     */
    static Vector3f get_earth_field_ga(const Location &loc);

    /*
      get declination in degrees for a given latitude_deg and longitude_deg
     */
    static float get_declination(float latitude_deg, float longitude_deg);
    
private:
    static const float SAMPLING_RES;
    static const float SAMPLING_MIN_LAT;
    static const float SAMPLING_MAX_LAT;
    static const float SAMPLING_MIN_LON;
    static const float SAMPLING_MAX_LON;

    static const uint32_t LAT_TABLE_SIZE = 19;
    static const uint32_t LON_TABLE_SIZE = 37;

    static const float declination_table[LAT_TABLE_SIZE][LON_TABLE_SIZE];
    static const float inclination_table[LAT_TABLE_SIZE][LON_TABLE_SIZE];
    static const float intensity_table[LAT_TABLE_SIZE][LON_TABLE_SIZE];
};