Enumerations
enum	novas_nutation_direction { NUTATE_TRUE_TO_MEAN = -1 , NUTATE_MEAN_TO_TRUE }
	Direction constant for nutation(), between mean and true equatorial coordinates. More...

enum	novas_wobble_direction { WOBBLE_ITRS_TO_TIRS = 0 , WOBBLE_TIRS_TO_ITRS , WOBBLE_ITRS_TO_PEF , WOBBLE_PEF_TO_ITRS }
	Direction constants for polar wobble corrections via the wobble() function. 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	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.

int	novas_hor_to_app (const novas_frame restrict frame, double az, double el, RefractionModel ref_model, enum novas_reference_system sys, double restrict ra, double *restrict dec)
	Converts an observed azimuth and elevation coordinate to right ascension (R.A.) and declination coordinates expressed in the coordinate system of choice.

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.

int	wobble (double jd_tt, enum novas_wobble_direction direction, double xp, double yp, const double in, double out)
	Corrects a vector in the ITRS (rotating Earth-fixed system) for polar motion, and also corrects the longitude origin (by a tiny amount) to the Terrestrial Intermediate Origin (TIO).

Detailed Description

Enumeration Type Documentation

◆ novas_nutation_direction

enum novas_nutation_direction

Direction constant for nutation(), between mean and true equatorial coordinates.

See also: nutation()

Enumerator

NUTATE_TRUE_TO_MEAN

Change from true equator to mean equator (i.e.

undo wobble corrections). You may use any non-zero value as well.

NUTATE_MEAN_TO_TRUE

Change from mean equator to true equator (i.e. apply wobble corrections)

◆ novas_wobble_direction

enum novas_wobble_direction

Direction constants for polar wobble corrections via the wobble() function.

See also: novas_app_to_hor(), novas_hor_to_app(), wobble(), NOVAS_WOBBLE_DIRECTIONS

Enumerator
WOBBLE_ITRS_TO_TIRS	use for wobble() to change from ITRS (Earth-fixed) to TIRS (pseudo Earth-fixed). It includes TIO longitude correction. Since 1.4
WOBBLE_TIRS_TO_ITRS	use for wobble() to change from TIRS (pseudo Earth-fixed) to ITRS (Earth-fixed). It includes TIO longitude correction. Since 1.4
WOBBLE_ITRS_TO_PEF	use for wobble() to change from ITRS (Earth-fixed) Pseudo Earth Fixed (PEF). It does not include TIO longitude correction. Otherwise, it's the same as WOBBLE_ITRS_TO_TIRS
WOBBLE_PEF_TO_ITRS	use for wobble() to change from Pseudo Earth Fixed (PEF) to ITRS (Earth-fixed). It does not include TIO longitude correction. Otherwise, it's the same as WOBBLE_TIRS_TO_ITRS

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()

◆ 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_hor_to_app()

int novas_hor_to_app	(	const novas_frame *restrict	frame,
		double	az,
		double	el,
		RefractionModel	ref_model,
		enum novas_reference_system	sys,
		double *restrict	ra,
		double *restrict	dec )

Converts an observed azimuth and elevation coordinate to right ascension (R.A.) and declination coordinates expressed in the coordinate system of choice.

The observer must be located on the surface of Earth, or else the call will return with an error. The caller may optionally supply a refraction model of choice to calculate an appropriate elevation angle that includes a refraction correction for Earth's atmosphere. If no such model is provided, the provided elevation value will be assumed to be an astrometric elevation without a refraction correction.

Parameters

	frame	Observer frame, defining the time and place of observation (on Earth).
	az	[deg] Observed azimuth angle. It may be NULL if not required.
	el	[deg] Observed elevation angle. It may be NULL if not required.
	ref_model	An appropriate refraction model, or NULL to assume unrefracted elevation. Depending on the refraction model, you might want to make sure that the weather parameters were set when the observing frame was defined.
	sys	Astronomical coordinate system in which the output is R.A. and declination values are to be calculated.
[out]	ra	[h] Calculated apparent right ascension (R.A.) coordinate
[out]	dec	[deg] Calculated apparent declination coordinate

Returns: 0 if successful, or else an error from itrs_to_tod() or itrs_to_cirs(), or -1 (errno will indicate the type of error).

Since: 1.1

Author: Attila Kovacs

See also: novas_app_to_hor(); novas_app_to_geom(), novas_standard_refraction(), novas_optical_refraction(), novas_radio_refraction(), novas_wave_refraction()

References novas_timespec::fjd_tt, hor_to_itrs(), novas_timespec::ijd_tt, NOVAS_AIRBORNE_OBSERVER, NOVAS_CIRS, NOVAS_GCRS, NOVAS_ICRS, NOVAS_ITRS, NOVAS_J2000, NOVAS_MOD, NOVAS_OBSERVER_ON_EARTH, NOVAS_REFRACT_OBSERVED, NOVAS_TIRS, NOVAS_TOD, spin(), vector2radec(), wobble(), WOBBLE_ITRS_TO_PEF, and WOBBLE_ITRS_TO_TIRS.

◆ 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().

◆ wobble()

int wobble	(	double	jd_tt,
		enum novas_wobble_direction	direction,
		double	xp,
		double	yp,
		const double *	in,
		double *	out )

Corrects a vector in the ITRS (rotating Earth-fixed system) for polar motion, and also corrects the longitude origin (by a tiny amount) to the Terrestrial Intermediate Origin (TIO).

The ITRS vector is thereby transformed to the Terrestrial Intermediate Reference System (TIRS), or equivalently the Pseudo Earth Fixed (PEF), based on the true (rotational) equator and TIO; or vice versa. Because the true equator is the plane orthogonal to the direction of the Celestial Intermediate Pole (CIP), the components of the output vector are referred to z and x axes toward the CIP and TIO, respectively.

NOTES:

You may obtain Earth orientation parameters from the IERS site and Bulletins. For sub-mas accuracy you should augment the (interpolated) published values for diurnal and semi-diurnal librations and the effect of ocean tides, e.g. by using novas_diurnal_eop() or novas_diurnal_eop_at_time().
Generally, this function should not be called if global pole offsets were set via cel_pole() and then used via place() or one of its variants to calculate Earth orientation corrected (TOD or CIRS) apparent coordinates. In such cases, calling wobble() would apply duplicate corrections. It is generally best to forgo using cel_pole() going forward, and instead apply Earth orinetation corrections with wobble() only when converting vectors between the Earth-fixed ITRS and TIRS frames.
The Earth orientation parameters xp, yp should be provided in the same ITRF realization as the observer location for an Earth-based observer. You can use novas_itrf_transform_eop() to convert the EOP values as necessary.

REFERENCES:

Kaplan, G. H. et. al. (1989). Astron. Journ. 97, 1197-1210.
Lambert & Bizouard (2002), Astronomy and Astrophysics 394, 317-321.
IERS Conventions 2010, Chapter 5, https://iers-conventions.obspm.fr/content/chapter5/icc5.pdf
IERS Conventions 2010, Chapter 8, https://iers-conventions.obspm.fr/content/chapter8/icc8.pdf

Parameters

	jd_tt	[day] Terrestrial Time (TT) based Julian date.
	direction	WOBBLE_ITRS_TO_TIRS (0) or WOBBLE_TIRS_TO_ITRS (1) to include corrections for the TIO's longitude (IAU 2006 method); or else WOBBLE_ITRS_TO_PEF (2) or WOBBLE_PEF_TO_ITRS (3) to correct for dx, dy but not for the TIO's longitude (old, pre IAU 2006 method). Negative values default to WOBBLE_TIRS_TO_ITRS.
	xp	[arcsec] Conventionally-defined X coordinate of Celestial Intermediate Pole with respect to ITRS pole. As measured or else the interpolated published value from IERS, possibly augmented for diurnal variations caused by librations ocean tides if precision below the milliarcsecond level is required.
	yp	[arcsec] Conventionally-defined Y coordinate of Celestial Intermediate Pole with respect to ITRS pole, in arcseconds. As measured or else the interpolated published value from IERS, possibly augmented for diurnal variations caused by librations ocean tides if precision below the milliarcsecond level is required.
	in	Input position vector, geocentric equatorial rectangular coordinates, in the original system defined by 'direction'
[out]	out	Output Position vector, geocentric equatorial rectangular coordinates, in the final system defined by 'direction'. It can be the same vector as the input.

Returns: 0 if successful, or -1 if the direction is invalid output vector argument is NULL.

See also: novas_diurnal_eop(), novas_diurnal_eop_at_time(), novas_itrf_transfor_eop()

References NOVAS_WOBBLE_DIRECTIONS, WOBBLE_ITRS_TO_PEF, WOBBLE_ITRS_TO_TIRS, and WOBBLE_TIRS_TO_ITRS.

Enumerations

Functions

Detailed Description

Enumeration Type Documentation

◆ novas_nutation_direction

◆ novas_wobble_direction

Function Documentation

◆ ecl2equ()

◆ ecl2equ_vec()

◆ equ2ecl()

◆ equ2ecl_vec()

◆ equ2gal()

◆ gal2equ()

◆ hor_to_itrs()

◆ itrs_to_hor()

◆ novas_e2h_offset()

◆ novas_epa()

◆ novas_h2e_offset()

◆ novas_hor_to_app()

◆ novas_hpa()

◆ novas_los_to_xyz()

◆ novas_uvw_to_xyz()

◆ novas_xyz_to_los()

◆ novas_xyz_to_uvw()

◆ wobble()