eph_manager.c File Reference

Functions
short	ephem_close (void)
short	ephem_open (const char *ephem_name, double *jd_begin, double *jd_end, short *de_number)
int	interpolate (const double *buf, const double *t, long ncf, long na, double *position, double *velocity)
short	planet_ephemeris (const double tjd[2], enum de_planet target, enum de_planet origin, double *position, double *velocity)
int	split (double tt, double *fr)
short	state (const double *jed, enum de_planet target, double *target_pos, double *target_vel)

Variables
double *	BUFFER
	(for internal use) Array containing Chebyshev coefficients of position.
double	EM_RATIO
	(for internal use)
FILE *	EPHFILE = NULL
	(for internal use) The currently open JPL DE planetary ephemeris file
int	IPT [3][12]
	(for internal use)
double	JPLAU
	(for internal use)
short	KM
	Flag that defines physical units of the output states.
int	LPT [3]
	(for internal use)
long	NP
	(for internal use)
long	NRL
	(for internal use) Current record number buffered
long	NV
	(for internal use)
double	PC [18]
	(for internal use)
long	RECORD_LENGTH
	(for internal use)
double	SS [3]
	(for internal use)
double	TWOT
	(for internal use)
double	VC [18]
	(for internal use)

Detailed Description

Author

G. Kaplan and A. Kovacs

SuperNOVAS planetary ephemeris manager for the planet_eph_manager and planet_eph_manager_hp() functions.

This module exposes a lot of its own internal state variables globally. You probably should not access them from outside this module, but they are kept ad globals to ensure compatibility with existing NOVAS C applications that might access those values.

Based on the NOVAS C Edition, Version 3.1:

U. S. Naval Observatory
Astronomical Applications Dept.
Washington, DC
http://www.usno.navy.mil/USNO/astronomical-applications

See also

solsys2.c

Function Documentation

ephem_close()

short ephem_close

(

void

)

Closes a JPL planetary ephemeris file and frees the memory.

REFERENCES:

1. Standish, E.M. and Newhall, X X (1988). "The JPL Export Planetary Ephemeris"; JPL document dated 17 June 1988.

NOTES:

1. Includes fix for the known resource leak issue in NOVAS C 3.1.

Returns

0 if the file successfully closed or was closed already, or else EOF.

See also

ephem_open()

References BUFFER, and EPHFILE.

ephem_open()

short ephem_open	(	const char *	ephem_name,
		double *	jd_begin,
		double *	jd_end,
		short *	de_number
	)

This function opens a JPL planetary ephemeris file and sets initial values. This function must be called prior to calls to the other JPL ephemeris functions.

REFERENCES:

1. Standish, E.M. and Newhall, X X (1988). "The JPL Export Planetary Ephemeris"; JPL document dated 17 June 1988.

Parameters

	ephem_name	Name/path of the direct-access ephemeris file.
[out]	jd_begin	[day] Beginning Julian date of the ephemeris file. It may be NULL if not required.
[out]	jd_end	[day] Ending Julian date of the ephemeris file. It may be NULL if not required.
[out]	de_number	DE number of the ephemeris file opened. It may be NULL if not required.

Returns

0 if successful, or -1 if any of the arhuments is NULL, or else 1 if the file could no be opened, 2–10 if (= line + 1) if there was an error reading the header line, or 11 if the type of DE file is not supported.

See also

ephem_close()

References BUFFER, EM_RATIO, EPHFILE, IPT, JPLAU, KM, LPT, NP, NRL, NV, PC, RECORD_LENGTH, SS, TWOT, and VC.

interpolate()

int interpolate	(	const double *	buf,
		const double *	t,
		long	ncf,
		long	na,
		double *	position,
		double *	velocity
	)

Differentiates and interpolates a set of Chebyshev coefficients to give position and velocity.

REFERENCES:

1. Standish, E.M. and Newhall, X X (1988). "The JPL Export Planetary Ephemeris"; JPL document dated 17 June 1988.

Parameters

	buf	Array of Chebyshev coefficients of position.
	t	t[0] is fractional time interval covered by coefficients at which interpolation is desired (0 <= t[0] <= 1). t[1] is length of whole interval in input time units.
	ncf	Number of coefficients per component.
	na	Number of sets of coefficients in full array (i.e., number of sub-intervals in full interval).
[out]	position	Position array of requested object.
[out]	velocity	Velocity array of requested object.

Returns

0 if successful, or -1 if one of the input arrays or output pointer arguments is NULL.

References NP, NV, PC, TWOT, and VC.

planet_ephemeris()

short planet_ephemeris	(	const double	tjd[2],
		enum de_planet	target,
		enum de_planet	origin,
		double *	position,
		double *	velocity
	)

Retries planet position and velocity data from the JPL planetary ephemeris

(If nutations are desired, set 'target' = 13; 'center' will be ignored on that call.)

REFERENCES:

1. Standish, E.M. and Newhall, X X (1988). "The JPL Export Planetary Ephemeris"; JPL document dated 17 June 1988.

Parameters

	tjd	[day] Two-element array containing the Julian date, which may be split any way (although the first element is usually the "integer" part, and the second element is the "fractional" part). Julian date is in the TDB or "T_eph" time scale.
	target	The integer code (see above) for the planet for which coordinates are requested, e.g. DE_JUPITER.
	origin	The integer code of the planet or position relative to which coordinates are measured.
[out]	position	[AU] Position vector array of target relative to center, measured in AU.
[out]	velocity	[AU/day] Velocity vector array of target relative to center, measured in AU/day.

Returns

0 if successful, or -1 if one of the pointer arguments is NULL, or else the error returned from state().

See also

ephem_open()

References EM_RATIO, and state().

split()

int split	(	double	tt,
		double *	fr
	)

reaks up a double number into a double integer part and a fractional part.

Parameters

	tt	Input number.
[out]	fr	2-element output array; fr[0] contains integer part, fr[1] contains fractional part. For negative input numbers, fr[0] contains the next more negative integer; fr[1] contains a positive fraction.

Returns

0 if successful, or -1 if the output pointer argument is NULL.

state()

short state	(	const double *	jed,
		enum de_planet	target,
		double *	target_pos,
		double *	target_vel
	)

Reads and interpolates the JPL planetary ephemeris file.

For ease in programming, the user may put the entire epoch in jed[0] and set jed[1] = 0. For maximum interpolation accuracy, set jed[0] = the most recent midnight at or before interpolation epoch, and set jed[1] = fractional part of a day elapsed between jed[0] and epoch. As an alternative, it may prove convenient to set jed[0] = some fixed epoch, such as start of the integration and jed[1] = elapsed interval between then and epoch.

REFERENCES:

1. Standish, E.M. and Newhall, X X (1988). "The JPL Export Planetary Ephemeris"; JPL document dated 17 June 1988.

Parameters

	jed	[day] 2-element Julian date (TDB) at which interpolation is wanted. Any combination of jed[0]+jed[1] which falls within the time span on the file is a permissible epoch. See Note 1 below. target (short)
	target	The integer code (see above) for the planet for which coordinates are requested, e.g. DE_JUPITER.
[out]	target_pos	[AU] The barycentric position vector array of the requested object, in AU.
[out]	target_vel	[AU/day] The barycentric velocity vector array of the requested object, in AU/Day.

Returns

0 if successful, -1 if any of the pointer arguments is NULL, or else 1 if there was an error reading the ephemeris file, or 2 if the epoch is out of range.

References BUFFER, ephem_close(), EPHFILE, interpolate(), IPT, JPLAU, KM, NRL, RECORD_LENGTH, split(), and SS.

Variable Documentation

KM

short KM

Flag that defines physical units of the output states.

Flag that defines physical units of the output states. 1: km and km/sec; 0: AU and AU/day. Its default value is 0 (KM determines time unit for nutations. Angle unit is always radians.)