geodesy.h

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/*
 * SPDX-License-Identifier: MIT
 * Copyright (c) 2026 Jeremiah van Oosten
 *
 * vgl geodesy: ellipsoids and conversions between geodetic, Earth-centred Earth-fixed (ECEF)
 * and local East-North-Up (ENU) coordinates (design document, section 7.2; FR-09).
 *
 * Angles are in radians and lengths in metres (docs/c-api.md, section 4.3). ECEF is
 * right-handed, with +Z through the north pole and +X through latitude 0, longitude 0.
 */
#ifndef VGL_GEODESY_H
#define VGL_GEODESY_H
 
#include <vgl/base.h>
 
#define VGL_PI 3.14159265358979323846
 
#define VGL_DEGREES_TO_RADIANS(degrees) ((degrees) * (VGL_PI / 180.0))
#define VGL_RADIANS_TO_DEGREES(radians) ((radians) * (180.0 / VGL_PI))
 
#define VGL_WGS84_SEMI_MAJOR_AXIS 6378137.0
#define VGL_WGS84_FLATTENING      (1.0 / 298.257223563)
 
#ifdef __cplusplus
extern "C" {
#endif
 
typedef struct vgl_ellipsoid
{
    double semi_major_axis; 
    double flattening;      
} vgl_ellipsoid;
 
typedef struct vgl_geodetic
{
    double latitude;  
    double longitude; 
    double height;    
} vgl_geodetic;
 
VGL_API vgl_result vgl_ellipsoid_wgs84_get(vgl_ellipsoid* out_ellipsoid);
 
VGL_API vgl_result vgl_ellipsoid_geodetic_to_ecef(const vgl_ellipsoid* ellipsoid,
                                                  const vgl_geodetic* geodetic,
                                                  vgl_dvec3* out_ecef);
 
VGL_API vgl_result vgl_ellipsoid_ecef_to_geodetic(const vgl_ellipsoid* ellipsoid,
                                                  const vgl_dvec3* ecef,
                                                  vgl_geodetic* out_geodetic);
 
VGL_API vgl_result vgl_ellipsoid_enu_frame_get(const vgl_ellipsoid* ellipsoid,
                                               const vgl_geodetic* origin,
                                               vgl_dmat4* out_enu_to_ecef,
                                               vgl_dmat4* out_ecef_to_enu);
 
VGL_API vgl_result vgl_earth_rotation_angle_get(double julian_date, double* out_angle);
 
VGL_API vgl_result vgl_degrees_to_radians(double degrees, double* out_radians);
 
VGL_API vgl_result vgl_radians_to_degrees(double radians, double* out_degrees);
 
#ifdef __cplusplus
}
#endif
 
#endif /* VGL_GEODESY_H */