orbital.c File Reference

Functions
int	novas_orbit_posvel (double jd_tdb, const novas_orbital *restrict orbit, enum novas_accuracy accuracy, double *restrict pos, double *restrict vel)
int	novas_set_orbsys_pole (enum novas_reference_system type, double ra, double dec, novas_orbital_system *restrict sys)

Detailed Description

Date

Created on Mar 6, 2025

Author

Attila Kovacs

Function relating to the use of orbital elements

Function Documentation

novas_orbit_posvel()

int novas_orbit_posvel	(	double	jd_tdb,
		const novas_orbital *restrict	orbit,
		enum novas_accuracy	accuracy,
		double *restrict	pos,
		double *restrict	vel
	)

Calculates a rectangular equatorial position and velocity vector for the given orbital elements for the specified time of observation.

REFERENCES:

1. https://ssd.jpl.nasa.gov/planets/approx_pos.html
2. https://en.wikipedia.org/wiki/Orbital_elements
3. https://orbitalofficial.com/
4. https://downloads.rene-schwarz.com/download/M001-Keplerian_Orbit_Elements_to_Cartesian_State_Vectors.pdf

Parameters

	jd_tdb	[day] Barycentric Dynamic Time (TDB) based Julian date
	orbit	Orbital parameters
	accuracy	NOVAS_FULL_ACCURACY (0) or NOVAS_REDUCED_ACCURACY (1).
[out]	pos	[AU] Output ICRS equatorial position vector, or NULL if not required
[out]	vel	[AU/day] Output ICRS equatorial velocity vector, or NULL if not required

Returns

0 if successful, or else -1 if the orbital parameters are NULL or if the position and velocity output vectors are the same or the orbital system is ill defined (errno set to EINVAL), or if the calculation did not converge (errno set to ECANCELED), or

See also

ephemeris()

novas_geom_posvel()

place()

make_orbital_object()

Author

Attila Kovacs

Since

1.2

References novas_inv_max_iter, and TWOPI.

novas_set_orbsys_pole()

int novas_set_orbsys_pole	(	enum novas_reference_system	type,
		double	ra,
		double	dec,
		novas_orbital_system *restrict	sys
	)

Sets the orientation of an orbital system using the RA and DEC coordinates of the pole of the Laplace (or else equatorial) plane relative to which the orbital elements are defined. Orbital parameters of planetary satellites normally include the R.A. and declination of the pole of the local Laplace plane in which the Keplerian orbital elements are referenced.

The system will become referenced to the equatorial plane, the relative obliquity is set to (90° - dec), while the argument of the ascending node ('Omega') is set to (90° + ra).

NOTES:

1. You should not expect much precision from the long-range orbital approximations for planetary satellites. For applications that require precision at any level, you should rely on appropriate ephemerides, or else on up-to-date short-term orbital elements.

Parameters

	type	Coordinate reference system in which ra and dec are defined (e.g. NOVAS_GCRS).
	ra	[h] the R.A. of the pole of the oribtal reference plane.
	dec	[deg] the declination of the pole of the oribtal reference plane.
[out]	sys	Orbital system

Returns

0 if successful, or else -1 (errno will be set to EINVAL) if the output sys pointer is NULL.

Author

Attila Kovacs

Since

1.2

See also

make_orbital_object()

References NOVAS_EQUATORIAL_PLANE.