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SuperNOVAS: src/coords.c File Reference

int ecl2equ (double jd_tt, enum novas_equator_type coord_sys, enum novas_accuracy accuracy, double elon, double elat, double *restrict ra, double *restrict dec) short ecl2equ_vec (double jd_tt, enum novas_equator_type coord_sys, enum novas_accuracy accuracy, const double *in, double *out) short equ2ecl (double jd_tt, enum novas_equator_type coord_sys, enum novas_accuracy accuracy, double ra, double dec, double *restrict elon, double *restrict elat) short equ2ecl_vec (double jd_tt, enum novas_equator_type coord_sys, enum novas_accuracy accuracy, const double *in, double *out) int equ2gal (double ra, double dec, double *restrict glon, double *restrict glat) int equ2hor (double jd_ut1, double ut1_to_tt, enum novas_accuracy accuracy, double xp, double yp, const on_surface *restrict location, double ra, double dec, enum novas_refraction_model ref_option, double *restrict zd, double *restrict az, double *restrict rar, double *restrict decr) int gal2equ (double glon, double glat, double *restrict ra, double *restrict dec) int hor_to_itrs (const on_surface *restrict location, double az, double za, double *restrict itrs) int itrs_to_hor (const on_surface *restrict location, const double *restrict itrs, double *restrict az, double *restrict za)

Date: Created on Mar 5, 2025

Various transformations between different coordinate systems

◆ ecl2equ() int ecl2equ ( double jd_tt, enum novas_equator_type coord_sys, enum novas_accuracy accuracy, double elon, double elat, double *restrict ra, double *restrict dec )

Convert ecliptic longitude and latitude to right ascension and declination. To convert GCRS ecliptic coordinates (mean ecliptic and equinox of J2000.0), set 'coord_sys' to NOVAS_GCRS_EQUATOR(2); in this case the value of 'jd_tt' can be set to anything, since J2000.0 is assumed. Otherwise, all input coordinates are dynamical at'jd_tt'.

Parameters: jd_tt [day] Terrestrial Time (TT) based Julian date. (Unused if 'coord_sys' is NOVAS_GCRS_EQUATOR[2]) coord_sys The astrometric reference system of the coordinates. If 'coord_sys' is NOVAS_GCRS_EQUATOR(2), the input GCRS coordinates are converted to J2000 ecliptic coordinates. accuracy NOVAS_FULL_ACCURACY (0) or NOVAS_REDUCED_ACCURACY (1) elon [deg] Ecliptic longitude in degrees, referred to specified ecliptic and equinox of date. elat [deg] Ecliptic latitude in degrees, referred to specified ecliptic and equinox of date. [out] ra [h] Right ascension in hours, referred to specified equator and equinox of date. [out] dec [deg] Declination in degrees, referred to specified equator and equinox of date.

Returns: 0 if successful, or else 1 if the value of 'coord_sys' is invalid.

See also: ecl2equ_vec(); equ2ecl()

Since: 1.0

Author: Attila Kovacs

References ecl2equ_vec().

◆ ecl2equ_vec()

Converts an ecliptic position vector to an equatorial position vector. To convert ecliptic coordinates (mean ecliptic and equinox of J2000.0) to GCRS RA and dec to, set 'coord_sys' to NOVAS_GCRS_EQUATOR(2); in this case the value of 'jd_tt' can be set to anything, since J2000.0 is assumed. Otherwise, all input coordinates are dynamical at 'jd_tt'.

Parameters: jd_tt [day] Terrestrial Time (TT) based Julian date. (Unused if 'coord_sys' is NOVAS_GCRS_EQUATOR[2]) coord_sys The astrometric reference system type of the coordinates accuracy NOVAS_FULL_ACCURACY (0) or NOVAS_REDUCED_ACCURACY (1) in Position vector, referred to specified ecliptic and equinox of date. [out] out Position vector, referred to specified equator and equinox of date. It can be the same vector as the input.

Returns: 0 if successful, -1 if either vector argument is NULL or the accuracy is invalid, or else 1 if the value of 'coord_sys' is invalid.

See also: ecl2equ(); equ2ecl_vec()

References e_tilt(), frame_tie(), J2000_TO_ICRS, mean_obliq(), NOVAS_FULL_ACCURACY, NOVAS_GCRS_EQUATOR, NOVAS_MEAN_EQUATOR, NOVAS_REDUCED_ACCURACY, and NOVAS_TRUE_EQUATOR.

◆ equ2ecl() short equ2ecl ( double jd_tt, enum novas_equator_type coord_sys, enum novas_accuracy accuracy, double ra, double dec, double *restrict elon, double *restrict elat )

Convert right ascension and declination to ecliptic longitude and latitude. To convert GCRS RA and dec to ecliptic coordinates (mean ecliptic and equinox of J2000.0), set 'coord_sys' to NOVAS_GCRS_EQUATOR(2); in this case the value of 'jd_tt' can be set to anything, since J2000.0 is assumed. Otherwise, all input coordinates are dynamical at 'jd_tt'.

Parameters: jd_tt [day] Terrestrial Time (TT) based Julian date. (Unused if 'coord_sys' is NOVAS_GCRS_EQUATOR[2]) coord_sys The astrometric reference system of the coordinates. If 'coord_sys' is NOVAS_GCRS_EQUATOR(2), the input GCRS coordinates are converted to J2000 ecliptic coordinates. accuracy NOVAS_FULL_ACCURACY (0) or NOVAS_REDUCED_ACCURACY (1) ra [h] Right ascension in hours, referred to specified equator and equinox of date. dec [deg] Declination in degrees, referred to specified equator and equinox of date. [out] elon [deg] Ecliptic longitude in degrees, referred to specified ecliptic and equinox of date. [out] elat [deg] Ecliptic latitude in degrees, referred to specified ecliptic and equinox of date.

Returns: 0 if successful, or else 1 if the value of 'coord_sys' is invalid.

See also: equ2ecl_vec(); ecl2equ()

References equ2ecl_vec().

◆ equ2ecl_vec()

Converts an equatorial position vector to an ecliptic position vector. To convert ICRS RA and dec to ecliptic coordinates (mean ecliptic and equinox of J2000.0), set 'coord_sys' to NOVAS_GCRS_EQUATOR(2); in this case the value of 'jd_tt' can be set to anything, since J2000.0 is assumed. Otherwise, all input coordinates are dynamical at 'jd_tt'.

Parameters: jd_tt [day] Terrestrial Time (TT) based Julian date. (Unused if 'coord_sys' is NOVAS_GCRS_EQUATOR[2]) coord_sys The astrometric reference system type of the coordinates. accuracy NOVAS_FULL_ACCURACY (0) or NOVAS_REDUCED_ACCURACY (1) in Position vector, referred to specified equator and equinox of date. [out] out Position vector, referred to specified ecliptic and equinox of date. It can be the same vector as the input. If 'coord_sys' is NOVAS_GCRS_EQUATOR(2), the input GCRS coordinates are converted to J2000 ecliptic coordinates.

Returns: 0 if successful, -1 if either vector argument is NULL or the accuracy is invalid, or else 1 if the value of 'coord_sys' is invalid.

See also: equ2ecl(); ecl2equ_vec()

References e_tilt(), frame_tie(), ICRS_TO_J2000, mean_obliq(), NOVAS_FULL_ACCURACY, NOVAS_GCRS_EQUATOR, NOVAS_MEAN_EQUATOR, NOVAS_REDUCED_ACCURACY, and NOVAS_TRUE_EQUATOR.

◆ equ2gal() int equ2gal ( double ra, double dec, double *restrict glon, double *restrict glat )

Converts ICRS right ascension and declination to galactic longitude and latitude.

REFERENCES:

Hipparcos and Tycho Catalogues, Vol. 1, Section 1.5.3.

Parameters: ra [h] ICRS right ascension in hours. dec [deg] ICRS declination in degrees. [out] glon [deg] Galactic longitude in degrees. [out] glat [deg] Galactic latitude in degrees.

Returns: 0 if successful, or -1 if either of the output pointer arguments are NULL.

See also: gal2equ()

◆ equ2hor() int equ2hor ( double jd_ut1, double ut1_to_tt, enum novas_accuracy accuracy, double xp, double yp, const on_surface *restrict location, double ra, double dec, enum novas_refraction_model ref_option, double *restrict zd, double *restrict az, double *restrict rar, double *restrict decr )

Transforms topocentric (TOD) right ascension and declination to zenith distance and azimuth. This method should not be used to convert CIRS apparent coordinates (IAU 2000 standard) – for those you should use cirs_to_itrs() followed by itrs_to_hor() instead.

It uses a method that properly accounts for polar motion, which is significant at the sub-arcsecond level. This function can also adjust coordinates for atmospheric refraction.

Deprecated:: The name of this function does not reveal what type of equatorial coordinates it requires. To make it less ambiguous, you should use tod_to_itrs() followed by itrs_to_hor() instead, possibly following it with refract_astro() if you also want to apply optical refraction.

NOTES:

'xp' and 'yp' can be set to zero if sub-arcsecond accuracy is not needed.
The directions 'zd'= 0 (zenith) and 'az'= 0 (north) are here considered fixed in the terrestrial system. Specifically, the zenith is along the geodetic normal, and north is toward the ITRS pole.
If 'ref_option' is NOVAS_STANDARD_ATMOSPHERE (1), then 'rar'='ra' and 'decr'='dec'.

REFERENCES:

Kaplan, G. (2008). USNO/AA Technical Note of 28 Apr 2008, "Refraction as a Vector."

Parameters: jd_ut1 [day] UT1 based Julian date ut1_to_tt [s] TT - UT1 Time difference in seconds accuracy NOVAS_FULL_ACCURACY (0) or NOVAS_REDUCED_ACCURACY (1) xp [arcsec] Conventionally-defined x coordinate of celestial intermediate pole with respect to ITRS reference pole, in arcseconds. yp [arcsec] Conventionally-defined y coordinate of celestial intermediate pole with respect to ITRS reference pole, in arcseconds. location The observer location ra [h] Topocentric right ascension of object of interest, in hours, referred to true equator and equinox of date. dec [deg] Topocentric declination of object of interest, in degrees, referred to true equator and equinox of date. ref_option NOVAS_STANDARD_ATMOSPHERE (1), or NOVAS_WEATHER_AT_LOCATION (2) if to use the weather [out] zd [deg] Topocentric zenith distance in degrees (unrefracted). [out] az [deg] Topocentric azimuth (measured east from north) in degrees. [out] rar [h] Topocentric right ascension of object of interest, in hours, referred to true equator and equinox of date, affected by refraction if 'ref_option' is non-zero. (It may be NULL if not required) [out] decr [deg] Topocentric declination of object of interest, in degrees, referred to true equator and equinox of date. (It may be NULL if not required)

Returns: 0 if successful, or -1 if one of the 'zd' or 'az' output pointers are NULL.

See also: itrs_to_hor(); tod_to_itrs(); NOVAS_TOD

References EROT_GST, NOVAS_DYNAMICAL_CLASS, refract_astro(), and ter2cel().

◆ gal2equ() int gal2equ ( double glon, double glat, double *restrict ra, double *restrict dec )

Converts galactic longitude and latitude to ICRS right ascension and declination.

REFERENCES:

Hipparcos and Tycho Catalogues, Vol. 1, Section 1.5.3.

Parameters: glon [deg] Galactic longitude in degrees. glat [deg] Galactic latitude in degrees. [out] ra [h] ICRS right ascension in hours. [out] dec [deg] ICRS declination in degrees.

Returns: 0 if successful, or -1 if either of the output pointer arguments are NULL.

See also: equ2gal()

Since: 1.0

Author: Attila Kovacs

◆ hor_to_itrs() int hor_to_itrs ( const on_surface *restrict location, double az, double za, double *restrict itrs )

Converts astrometric (unrefracted) azimuth and zenith angles at the specified observer location to a unit position vector in the Earth-fixed ITRS frame.

Parameters: location Observer location on Earth az [deg] astrometric azimuth angle at observer location [0:360]. It may be NULL if not required. za [deg] astrometric zenith angle at observer location [0:180]. It may be NULL if not required. [out] itrs Unit 3-vector direction in Earth-fixed ITRS frame

Returns: 0 if successful, or else -1 if the location or the input vector is NULL.

See also: itrs_to_hor(); itrs_to_cirs(); itrs_to_tod(); refract()

Since: 1.0

Author: Attila Kovacs

◆ itrs_to_hor() int itrs_to_hor ( const on_surface *restrict location, const double *restrict itrs, double *restrict az, double *restrict za )

Converts a position vector in the Earth-fixed ITRS frame to astrometric (unrefracted) azimuth and zenith angles at the specified observer location.

Parameters: location Observer location on Earth itrs 3-vector position in Earth-fixed ITRS frame [out] az [deg] astrometric azimuth angle at observer location [0:360]. It may be NULL if not required. [out] za [deg] astrometric zenith angle at observer location [0:180]. It may be NULL if not required.

Returns: 0 if successful, or else -1 if the location or the input vector is NULL.

See also: hor_to_itrs(); cirs_to_itrs(); tod_to_itrs(); refract_astro()

Since: 1.0

Author: Attila Kovacs

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