Various transformations between different coordinate systems used in astronomy, such as equatorial, ecliptic, Galactic, or local horizontal coordinate systems. More...

Functions
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.

short	ecl2equ_vec (double jd_tt, enum novas_equator_type coord_sys, enum novas_accuracy accuracy, const double in, double out)
	Converts an ecliptic position vector to an equatorial position vector.

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.

short	equ2ecl_vec (double jd_tt, enum novas_equator_type coord_sys, enum novas_accuracy accuracy, const double in, double out)
	Converts an equatorial position vector to an ecliptic position vector.

int	equ2gal (double ra, double dec, double restrict glon, double restrict glat)
	Converts ICRS right ascension and declination to galactic longitude and latitude.

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

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.

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.

int	novas_e2h_offset (double dra, double ddec, double pa, double restrict daz, double restrict del)
	Converts coordinate offsets, from the local equatorial system to local horizontal offsets.

double	novas_epa (double ha, double dec, double lat)
	Returns the Parallactic Angle (PA) calculated for an RA/Dec location of the sky at a given sidereal time.

int	novas_h2e_offset (double daz, double del, double pa, double restrict dra, double restrict ddec)
	Converts coordinate offsets, from the local horizontal system to local equatorial offsets.

double	novas_hpa (double az, double el, double lat)
	Returns the Parallactic Angle (PA) calculated for a horizontal Az/El location of the sky.

int	novas_los_to_xyz (const double los, double lon, double lat, double xyz)
	Converts a 3D line-of-sight vector (δφ, δθ δr) to a rectangular equatorial (δx, δy, δz) vector.

int	novas_uvw_to_xyz (const double uvw, double ha, double dec, double xyz)
	Converts equatorial u,v,w projected (absolute or relative) coordinates to rectangular telescope x,y,z coordinates (in ITRS) to for a specified line of sight.

int	novas_xyz_to_los (const double xyz, double lon, double lat, double los)
	Converts a 3D rectangular equatorial (δx, δy, δz) vector to a polar (δφ, δθ δr) vector along a line-of-sight.

int	novas_xyz_to_uvw (const double xyz, double ha, double dec, double uvw)
	Converts rectangular telescope x,y,z (absolute or relative) coordinates (in ITRS) to equatorial u,v,w projected coordinates for a specified line of sight.

Detailed Description

Various transformations between different coordinate systems used in astronomy, such as equatorial, ecliptic, Galactic, or local horizontal coordinate systems.

This module also provides functions otherwise relating to the observer locations.

For Earth-based geodetic locations, the module provides a set of functions to convert between various (local) coordinate systems. For example, calculating parallactic angles (a.k.a. vertical position angle or VPA), for converting between horizontal and equatorial offsets, and various functions for converting equatorial vectors to a line-of-sight, or u, v, w coordinate bases, and vice-versa.

Date: Created on Mar 5, 2025

Author: Attila Kovacs and G. Kaplan

See also: frames.c, transform.c

Function Documentation

◆ 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.

Since: 1.0

Author: Attila Kovacs

See also: ecl2equ_vec(), equ2ecl()

References ecl2equ_vec().

◆ ecl2equ_vec()

short ecl2equ_vec	(	double	jd_tt,
		enum novas_equator_type	coord_sys,
		enum novas_accuracy	accuracy,
		const double *	in,
		double *	out )

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()

short equ2ecl_vec	(	double	jd_tt,
		enum novas_equator_type	coord_sys,
		enum novas_accuracy	accuracy,
		const double *	in,
		double *	out )

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 )

Deprecated: You should use the frame-based novas_app_to_hor() instead, or else the more explicit (less ambiguous) tod_to_itrs() followed by itrs_to_hor(), and possibly following it with an atmospheric refraction correction if appropriate.

Transforms topocentric (TOD) apparent 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.

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, e.g. from IERS Bulletin A. If you have defined pole offsets to be incorporated into the TOD input coordinates (pre-IAU2000 method) via `cel_pole()`, then you should set this to 0.
	yp	[arcsec] Conventionally-defined y coordinate of celestial intermediate pole with respect to ITRS reference pole, e.g. from IERS Bulletin A. If you have defined pole offsets to be incorporated into the TOD input coordinates (pre-IAU2000 method) via `cel_pole()`, then you should set this to 0.
	location	Geodetic (ITRF / GRS80) observer location on Earth
	ra	[h] Topocentric apparent (TOD) right ascension of object of interest, referred to true equator and equinox of date.
	dec	[deg] Topocentric apparent (TOD) declination of object of interest, referred to true equator and equinox of date.
	ref_option	Refraction model to use. E.g., 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.

Since: 1.0

Author: Attila Kovacs

See also: equ2gal()

◆ 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	Geodetic (ITRF / GRS80) observer location on Earth
	az	[deg] astrometric (unrefracted) azimuth angle at observer location [0:360]. It may be NULL if not required.
	za	[deg] astrometric (unrefracted) 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.

Since: 1.0

Author: Attila Kovacs

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

◆ 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	Geodetic (ITRF / GRS80) observer location on Earth.
	itrs	3-vector position in Earth-fixed ITRS frame
[out]	az	[deg] astrometric (unrefracted) azimuth angle at observer location [0:360]. It may be NULL if not required.
[out]	za	[deg] astrometric (unrefracted) 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.

Since: 1.0

Author: Attila Kovacs

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

◆ novas_e2h_offset()

int novas_e2h_offset	(	double	dra,
		double	ddec,
		double	pa,
		double *restrict	daz,
		double *restrict	del )

Converts coordinate offsets, from the local equatorial system to local horizontal offsets.

Converting between local flat projections and spherical coordinates usually requires a WCS projection.

REFERENCES:

Calabretta, M.R., & Greisen, E.W., (2002), Astronomy & Astrophysics, 395, 1077-1122.

Parameters

	dra	[arcsec] Projected ffset position in the apparent true-of-date R.A. direction. E.g. The projected offset between two RA coordinates at a same reference declination, is δRA = (RA2 - RA1) * cos(Dec₀).
	ddec	[arcsec] Projected offset position in the apparent true-of-date declination direction.
	pa	[deg] Parallactic Angle
[out]	daz	[arcsec] Output offset position in the local azimuth direction. It can be a pointer to one of the input coordinates, or NULL if not required.
[out]	del	[arcsec] Output offset position in the local elevation direction. It can be a pointer to one of the input coordinates, or NULL if not required.

Returns: 0

Since: 1.3

Author: Attila Kovacs

See also: novas_h2e_offset(), novas_epa()

References novas_h2e_offset().

◆ novas_epa()

double novas_epa	(	double	ha,
		double	dec,
		double	lat )

Returns the Parallactic Angle (PA) calculated for an RA/Dec location of the sky at a given sidereal time.

The PA is the angle between the local horizontal coordinate directions and the local true-of-date equatorial coordinate directions, at the given location and time. The polar wobble is not included in the calculation.

The Parallactic Angle is sometimes referrred to as the Vertical Position Angle (VPA). Both define the same quantity.

Parameters

ha	[h] Hour angle (LST - RA) i.e., the difference between the Local (apparent) Sidereal Time and the apparent (true-of-date) Right Ascension of observed source.
dec	[deg] Apparent (true-of-date) declination of observed source
lat	[deg] Geodetic latitude of observer

Returns: [deg] Parallactic Angle (PA). I.e., the clockwise position angle of the elevation direction w.r.t. the declination axis in the equatorial system. Same as the clockwise position angle of the declination direction w.r.t. the elevation axis, in the horizontal system.

Since: 1.3

Author: Attila Kovacs

See also: novas_hpa(), novas_e2h_offset()

◆ novas_h2e_offset()

int novas_h2e_offset	(	double	daz,
		double	del,
		double	pa,
		double *restrict	dra,
		double *restrict	ddec )

Converts coordinate offsets, from the local horizontal system to local equatorial offsets.

Converting between local flat projections and spherical coordinates usually requires a WCS projection.

REFERENCES:

Calabretta, M.R., & Greisen, E.W., (2002), Astronomy & Astrophysics, 395, 1077-1122.

Parameters

	daz	[arcsec] Projected offset position in the azimuth direction. The projected offset between two azimuth positions at the same reference elevation is δAz = (Az2 - Az1) * cos(El₀).
	del	[arcsec] projected offset position in the elevation direction
	pa	[deg] Parallactic Angle
[out]	dra	[arcsec] Output offset position in the local true-of-date R.A. direction. It can be a pointer to one of the input coordinates, or NULL if not required.
[out]	ddec	[arcsec] Output offset position in the local true-of-date declination direction. It can be a pointer to one of the input coordinates, or NULL if not required.

Returns: 0

Since: 1.3

Author: Attila Kovacs

See also: novas_e2h_offset(), novas_hpa()

◆ novas_hpa()

double novas_hpa	(	double	az,
		double	el,
		double	lat )

Returns the Parallactic Angle (PA) calculated for a horizontal Az/El location of the sky.

The PA is the angle between the local horizontal coordinate directions and the local true-of-date equatorial coordinate directions at the given location. The polar wobble is not included in the calculation.

The Parallactic Angle is sometimes referrred to as the Vertical Position Angle (VPA). Both define the same quantity.

Parameters

az	[deg] Azimuth angle
el	[deg] Elevation angle
lat	[deg] Geodetic latitude of observer

Returns: [deg] Parallactic Angle (PA). I.e., the clockwise position angle of the declination direction w.r.t. the elevation axis in the horizontal system. Same as the the clockwise position angle of the elevation direction w.r.t. the declination axis in the equatorial system.

Since: 1.3

Author: Attila Kovacs

See also: novas_epa(), novas_h2e_offset()

◆ novas_los_to_xyz()

int novas_los_to_xyz	(	const double *	los,
		double	lon,
		double	lat,
		double *	xyz )

Converts a 3D line-of-sight vector (δφ, δθ δr) to a rectangular equatorial (δx, δy, δz) vector.

Parameters

	los	[arb.u.] Line-of-sight 3-vector (δφ, δθ δr).
	lon	[deg] Line-of-sight longitude.
	lat	[deg] Line-of-sight latitude.
[out]	xyz	[arb.u.] Output rectangular equatorial 3-vector (δx, δy, δz), in the same units as the input. It may be the same vector as the input.

Returns: 0 if successful, or else -1 if either vector argument is NULL (errno will be set to EINVAL).

Since: 1.3

Author: Attila Kovacs

See also: novas_xyz_to_los(), novas_uvw_to_xyz()

◆ novas_uvw_to_xyz()

int novas_uvw_to_xyz	(	const double *	uvw,
		double	ha,
		double	dec,
		double *	xyz )

Converts equatorial u,v,w projected (absolute or relative) coordinates to rectangular telescope x,y,z coordinates (in ITRS) to for a specified line of sight.

u,v,w are Cartesian coordinates (u,v) along the local equatorial R.A. and declination directions as seen from a direction on the sky (w). As such, they are effectively ITRS-based line-of-sight (LOS) coordinates.

x,y,z are Cartesian coordinates w.r.t the Greenwich meridian in the ITRS frame. The directions are x: long=0, lat=0; y: long=90, lat=0; z: lat=90.

Parameters

	xyz	[arb.u.] Absolute or relative u,v,w coordinates (double[3]).
	ha	[h] Hourangle (LST - RA) i.e., the difference between the Local (apparent) Sidereal Time and the apparent (true-of-date) Right Ascension of observed source.
	dec	[deg] Apparent (true-of-date) declination of source
[out]	uvw	[arb.u.] Converted x,y,z coordinates (double[3]) in the same unit as uvw. It may be the same vector as the input.

Returns: 0 if successful, or else -1 if either vector argument is NULL (errno will be set to EINVAL)

Since: 1.3

Author: Attila Kovacs

See also: novas_xyz_to_uvw()

References novas_los_to_xyz().

◆ novas_xyz_to_los()

int novas_xyz_to_los	(	const double *	xyz,
		double	lon,
		double	lat,
		double *	los )

Converts a 3D rectangular equatorial (δx, δy, δz) vector to a polar (δφ, δθ δr) vector along a line-of-sight.

Parameters

	xyz	[arb.u.] Rectangular equatorial 3-vector (δx, δy, δz).
	lon	[deg] Line-of-sight longitude.
	lat	[deg] Line-of-sight latitude.
[out]	los	[arb.u.] Output line-of-sight 3-vector (δφ, δθ δr), in the same units as the input. It may be the same vector as the input.

Returns: 0 if successful, or else -1 if either vector argument is NULL (errno will be set to EINVAL).

Since: 1.3

Author: Attila Kovacs

See also: novas_los_to_xyz(), novas_xyz_to_uvw()

◆ novas_xyz_to_uvw()

int novas_xyz_to_uvw	(	const double *	xyz,
		double	ha,
		double	dec,
		double *	uvw )

Converts rectangular telescope x,y,z (absolute or relative) coordinates (in ITRS) to equatorial u,v,w projected coordinates for a specified line of sight.

x,y,z are Cartesian coordinates w.r.t the Greenwich meridian, in the ITRS frame. The directions are x: long=0, lat=0; y: long=90, lat=0; z: lat=90.

u,v,w are Cartesian coordinates (u,v) along the local equatorial R.A. and declination directions as seen from a direction on the sky (w). As such, they are effectively ITRS-based line-of-sight (LOS) coordinates.

Parameters

	xyz	[arb.u.] Absolute or relative x,y,z coordinates (double[3]).
	ha	[h] Hourangle (LST - RA) i.e., the difference between the Local (apparent) Sidereal Time and the apparent (true-of-date) Right Ascension of observed source.
	dec	[deg] Apparent (true-of-date) declination of source
[out]	uvw	[arb.u.] Converted u,v,w coordinates (double[3]) in same units as xyz. It may be the same vector as the input.

Returns: 0 if successful, or else -1 if either vector argument is NULL (errno will be set to EINVAL)

Since: 1.3

Author: Attila Kovacs

See also: novas_uvw_to_xyz()

References novas_xyz_to_los().

Functions

Detailed Description

Function Documentation

◆ ecl2equ()

◆ ecl2equ_vec()

◆ equ2ecl()

◆ equ2ecl_vec()

◆ equ2gal()

◆ equ2hor()

◆ gal2equ()

◆ hor_to_itrs()

◆ itrs_to_hor()

◆ novas_e2h_offset()

◆ novas_epa()

◆ novas_h2e_offset()

◆ novas_hpa()

◆ novas_los_to_xyz()

◆ novas_uvw_to_xyz()

◆ novas_xyz_to_los()

◆ novas_xyz_to_uvw()