/*
 * precession.h -- IAU 2006 precession and simplified nutation
 *
 * Clean-room implementation from published standards:
 *   Precession: Capitaine, Wallace & Chapront (2003), A&A 412, 567
 *               (IAU 2006 polynomial expressions)
 *   Nutation:   Simplified 4-term model from fundamental arguments
 *               documented in IERS Technical Note 32, Ch. 5.
 *
 * No PostgreSQL dependencies -- pure math, suitable for standalone use.
 */

#ifndef PG_ORBIT_PRECESSION_H
#define PG_ORBIT_PRECESSION_H

/*
 * get_precession_angles_vondrak -- IAU 2006 precession angles
 *
 * Computes the four fundamental precession quantities at JDE:
 *   psi_A     -- luni-solar precession (arcsec)
 *   omega_A   -- inclination of equator on J2000 ecliptic (arcsec)
 *   chi_A     -- planetary precession (arcsec)
 *   epsilon_A -- obliquity of the ecliptic (arcsec)
 *
 * These are the IAU 2006 polynomial expressions valid to ~1 mas
 * for several centuries around J2000.  The full Vondrak (2011)
 * periodic terms are not included here; they extend validity
 * to +/-200,000 years but add sub-arcsecond corrections that
 * are negligible for our use case.
 *
 * Output is in arcseconds.
 */
void get_precession_angles_vondrak(double jde,
                                   double *epsilon_A,
                                   double *chi_A,
                                   double *omega_A,
                                   double *psi_A);

/*
 * get_nutation_angles_iau2000b -- simplified nutation
 *
 * Computes nutation in longitude (delta_psi) and nutation in
 * obliquity (delta_epsilon) using the dominant 4 lunisolar terms.
 *
 * This matches the level of nutation correction used in SGP4
 * coordinate transforms and is suitable for "what's up?" queries
 * where ~1 arcsecond accuracy is sufficient.
 *
 * Output is in arcseconds.
 */
void get_nutation_angles_iau2000b(double jde,
                                  double *delta_psi,
                                  double *delta_epsilon);

#endif /* PG_ORBIT_PRECESSION_H */