Ryan Malloy
3915d1784f
An existing product called PG Orbit (a mobile PostgreSQL client) creates a naming conflict. pg_orrery — a database orrery built from Keplerian parameters and SQL instead of brass gears. Build system: control file, Makefile, Dockerfile, docker init script. C source: GUC prefix, PG_FUNCTION_INFO_V1 symbol, header guards, ereport prefixes, comments across ~30 files including vendored SGP4. SQL: all 5 install/migration scripts, function name pg_orrery_ephemeris_info. Tests: 9 SQL suites, 8 expected outputs, standalone DE reader test. Documentation: CLAUDE.md, README.md, DESIGN.md, Starlight site infra, 36 MDX pages, OG renderer, logo SVG, docker-compose, agent threads. All 13 regression suites pass. Docs site builds (37 pages).
221 lines
6.6 KiB
C
221 lines
6.6 KiB
C
/*
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* astro_math.h -- Shared astronomical math for pg_orrery
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*
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* Static inline functions used by star_funcs.c, kepler_funcs.c,
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* and future planet/moon observation code.
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*
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* Using static inline preserves the project convention of no
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* cross-translation-unit symbol coupling.
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*/
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#ifndef PG_ORRERY_ASTRO_MATH_H
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#define PG_ORRERY_ASTRO_MATH_H
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#include <math.h>
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#include "types.h"
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#define DEG_TO_RAD (M_PI / 180.0)
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#define RAD_TO_DEG (180.0 / M_PI)
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#define ARCSEC_TO_RAD (M_PI / (180.0 * 3600.0))
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/* Pre-computed obliquity trig (IAU 1976, OBLIQUITY_J2000 = 0.40909280422232897 rad).
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* Avoids recomputing cos/sin on every frame rotation call. */
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#define COS_OBLIQUITY_J2000 0.91748206206918181
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#define SIN_OBLIQUITY_J2000 0.39777715593191371
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/*
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* Greenwich Mean Sidereal Time from Julian date.
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* Vallado, "Fundamentals of Astrodynamics", Eq. 3-47.
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* Returns angle in radians.
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*/
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static inline double
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gmst_from_jd(double jd)
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{
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double t_ut1 = (jd - 2451545.0) / 36525.0;
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double gmst = 67310.54841
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+ (876600.0 * 3600.0 + 8640184.812866) * t_ut1
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+ 0.093104 * t_ut1 * t_ut1
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- 6.2e-6 * t_ut1 * t_ut1 * t_ut1;
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gmst = fmod(gmst * M_PI / 43200.0, 2.0 * M_PI);
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if (gmst < 0.0)
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gmst += 2.0 * M_PI;
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return gmst;
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}
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/*
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* IAU 1976 precession: rotate J2000 equatorial to mean equatorial of date.
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*
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* Source: Lieske (1979), A&A 73, 282.
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* Three angles zeta_A, z_A, theta_A define the precession rotation.
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* Valid within ~1 arcsecond for several centuries around J2000.
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*/
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static inline void
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precess_j2000_to_date(double jd, double ra_j2000, double dec_j2000,
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double *ra_date, double *dec_date)
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{
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double T, T2, T3;
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double zeta_A, z_A, theta_A;
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double cos_dec, sin_dec, cos_ra_zeta, sin_ra_zeta;
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double cos_theta, sin_theta;
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double A, B, C;
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T = (jd - J2000_JD) / 36525.0;
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T2 = T * T;
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T3 = T2 * T;
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/* Precession angles in arcseconds (Lieske 1979) */
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zeta_A = (2306.2181 + 1.39656 * T - 0.000139 * T2) * T
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+ (0.30188 - 0.000344 * T) * T2 + 0.017998 * T3;
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z_A = (2306.2181 + 1.39656 * T - 0.000139 * T2) * T
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+ (1.09468 + 0.000066 * T) * T2 + 0.018203 * T3;
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theta_A = (2004.3109 - 0.85330 * T - 0.000217 * T2) * T
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- (0.42665 + 0.000217 * T) * T2 - 0.041833 * T3;
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/* Arcseconds to radians */
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zeta_A *= ARCSEC_TO_RAD;
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z_A *= ARCSEC_TO_RAD;
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theta_A *= ARCSEC_TO_RAD;
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/* Direct formula: R3(-z_A) R2(theta_A) R3(-zeta_A) applied to (ra, dec) */
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cos_dec = cos(dec_j2000);
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sin_dec = sin(dec_j2000);
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cos_ra_zeta = cos(ra_j2000 + zeta_A);
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sin_ra_zeta = sin(ra_j2000 + zeta_A);
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cos_theta = cos(theta_A);
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sin_theta = sin(theta_A);
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A = cos_dec * sin_ra_zeta;
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B = cos_theta * cos_dec * cos_ra_zeta - sin_theta * sin_dec;
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C = sin_theta * cos_dec * cos_ra_zeta + cos_theta * sin_dec;
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*dec_date = asin(C);
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*ra_date = atan2(A, B) + z_A;
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if (*ra_date < 0.0)
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*ra_date += 2.0 * M_PI;
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if (*ra_date >= 2.0 * M_PI)
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*ra_date -= 2.0 * M_PI;
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}
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/*
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* Equatorial (hour angle, declination) to horizontal (azimuth, elevation).
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* All angles in radians.
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* Azimuth convention: 0=N, pi/2=E, pi=S, 3*pi/2=W.
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*/
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static inline void
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equatorial_to_horizontal(double ha, double dec, double lat,
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double *az, double *el)
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{
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double sin_lat = sin(lat);
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double cos_lat = cos(lat);
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double sin_dec = sin(dec);
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double cos_dec = cos(dec);
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double cos_ha = cos(ha);
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double y, x;
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*el = asin(sin_lat * sin_dec + cos_lat * cos_dec * cos_ha);
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y = -cos_dec * sin(ha);
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x = cos_lat * sin_dec - sin_lat * cos_dec * cos_ha;
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*az = atan2(y, x);
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if (*az < 0.0)
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*az += 2.0 * M_PI;
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}
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/*
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* Ecliptic J2000 to equatorial J2000.
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* Simple rotation around X-axis by -obliquity.
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*
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* NOT safe for aliased (in-place) calls: ecl and equ must not overlap.
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* Writing equ[1] before reading ecl[1] for equ[2] produces wrong results
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* when ecl == equ. The vendored sgp4/sdp4.c has separate in-place versions
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* that use a temp variable; do not confuse the two.
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*/
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static inline void
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ecliptic_to_equatorial(const double *ecl, double *equ)
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{
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equ[0] = ecl[0];
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equ[1] = ecl[1] * COS_OBLIQUITY_J2000 - ecl[2] * SIN_OBLIQUITY_J2000;
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equ[2] = ecl[1] * SIN_OBLIQUITY_J2000 + ecl[2] * COS_OBLIQUITY_J2000;
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}
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/*
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* Equatorial J2000 to ecliptic J2000.
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* Rotation around X-axis by +obliquity.
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*
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* NOT safe for aliased (in-place) calls: equ and ecl must not overlap.
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* Same ordering hazard as ecliptic_to_equatorial() above.
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*/
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static inline void
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equatorial_to_ecliptic(const double *equ, double *ecl)
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{
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ecl[0] = equ[0];
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ecl[1] = equ[1] * COS_OBLIQUITY_J2000 + equ[2] * SIN_OBLIQUITY_J2000;
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ecl[2] = -equ[1] * SIN_OBLIQUITY_J2000 + equ[2] * COS_OBLIQUITY_J2000;
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}
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/*
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* Cartesian to spherical: (x, y, z) -> (ra, dec, dist).
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* ra in [0, 2*pi), dec in [-pi/2, pi/2], dist in same units as input.
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*/
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static inline void
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cartesian_to_spherical(const double *xyz, double *ra, double *dec, double *dist)
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{
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*dist = sqrt(xyz[0] * xyz[0] + xyz[1] * xyz[1] + xyz[2] * xyz[2]);
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*dec = asin(xyz[2] / *dist);
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*ra = atan2(xyz[1], xyz[0]);
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if (*ra < 0.0)
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*ra += 2.0 * M_PI;
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}
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/*
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* Geocentric observation pipeline (shared by all observation functions).
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*
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* Takes geocentric ecliptic J2000 position in AU, observer location,
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* and Julian date. Converts through equatorial, precesses to date,
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* and computes topocentric az/el.
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*
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* This is the canonical path:
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* ecliptic J2000 -> equatorial J2000 -> precess to date ->
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* sidereal time -> hour angle -> az/el
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*/
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static inline void
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observe_from_geocentric(const double geo_ecl_au[3], double jd,
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const pg_observer *obs, pg_topocentric *result)
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{
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double geo_equ[3];
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double ra_j2000, dec_j2000, geo_dist;
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double ra_date, dec_date;
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double gmst_val, lst, ha;
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double az, el;
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/* Ecliptic J2000 -> equatorial J2000 */
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ecliptic_to_equatorial(geo_ecl_au, geo_equ);
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/* Cartesian -> spherical */
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cartesian_to_spherical(geo_equ, &ra_j2000, &dec_j2000, &geo_dist);
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/* Precess J2000 -> date */
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precess_j2000_to_date(jd, ra_j2000, dec_j2000, &ra_date, &dec_date);
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/* Hour angle and az/el */
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gmst_val = gmst_from_jd(jd);
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lst = gmst_val + obs->lon;
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ha = lst - ra_date;
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equatorial_to_horizontal(ha, dec_date, obs->lat, &az, &el);
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result->azimuth = az;
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result->elevation = el;
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result->range_km = geo_dist * AU_KM;
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result->range_rate = 0.0; /* no velocity computation yet */
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}
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#endif /* PG_ORRERY_ASTRO_MATH_H */
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