geomag.h

#ifndef GEOMAG_H
#define GEOMAG_H

#ifdef __cplusplus
extern "C" {
#endif

/** Max number of models in a file */
#define MAXMOD 30

typedef enum {
	kUnitsKilometers = 1,
	kUnitsMeters     = 2,
	kUnitsFeet       = 3
} Units;

typedef enum {
	kCoordSysGeodetic   = 1, /* WGS-84 */
	kCoordSysGeocentric = 2
} CoordinateSystem;

typedef struct {
	double d;    /** Declination of the field from the
	                 geographic north (deg). */
	double i;    /** Inclination of the field (deg). */
	double h;    /** */
	double f;    /** Total field intensity. */
	double x;    /** */
	double y;    /** */
	double z;    /** */
	double ddot; /** Annual rate of change of declination. (arc-min/yr) */
	double fdot; /** Annual rate of change of . */
	double hdot; /** Annual rate of change of . */
	double idot; /** Annual rate of change of inclination. (arc-min/yr). */
	double xdot; /** Annual rate of change of . */
	double ydot; /** Annual rate of change of . */
	double zdot; /** Annual rate of change of . */
} BField;

#define MAXDEG 13
#define MAXCOEFF (MAXDEG*(MAXDEG+2)+1) /* index starts with 1!, (from old Fortran?) */

typedef struct {
	char name[MAXMOD][9];
	double epoch[MAXMOD];  /** epoch of model. */
	double yrmin[MAXMOD];  /** Min year of model. */
	double yrmax[MAXMOD];  /** Max year of model. */
	double minyr;          /** Min year of all models. */
	double maxyr;          /** Max year of all models. */
	double altmin[MAXMOD]; /** Minimum height of each model. */
	double altmax[MAXMOD]; /** Maximum height of each model. */
	int nmodel;            /** Number of models in file */
	int max1[MAXMOD];      /** Main field coefficient. */
	int max2[MAXMOD];      /** Secular variation coefficient. */
	int max3[MAXMOD];      /** Acceleration coefficient. */
	long irec_pos[MAXMOD]; /** Record counter for header */
	double gh1[MAXMOD][MAXCOEFF]; /** Schmidt quasi-normal internal spherical harmonic coeff. */
	double gh2[MAXMOD][MAXCOEFF]; /** Schmidt quasi-normal internal spherical harmonic coeff. */
} BFieldModel;

int get_field_components(BField *const bfield,
                         BFieldModel const*const model,
                         double alt,
                         const Units altUnits,
                         const CoordinateSystem coordSys,
                         const double latitude,
                         const double longitude,
                         const double sdate);

double julday(const int month, const int day, const int year);

#ifndef TARGET_EMBEDDED
int read_model(BFieldModel *const model, const char mdfile[]);
#endif

#ifdef __cplusplus
} /* extern "C" */
#endif

#endif