util.c File Reference

Various commonly used routines used throughout the SuperNOVAS library. More...

Functions
double	d_light (const double *pos_src, const double *pos_body)
	Returns the difference in light-time, for a star, between the barycenter of the solar system and the observer (or the geocenter) (Usage A).
PROTECTED void	novas_debug (enum novas_debug_mode mode)
	Enables or disables reporting errors and traces to the standard error stream.
double	novas_equ_sep (double ra1, double dec1, double ra2, double dec2)
	Returns the angular separation of two equatorial locations on a sphere.
enum novas_debug_mode	novas_get_debug_mode ()
	Returns the current, thread-local, mode for reporting errors encountered (and traces).
double	novas_norm_ang (double angle)
	Returns the normalized angle in the [0:2π) range.
double	novas_sep (double lon1, double lat1, double lon2, double lat2)
	Returns the angular separation of two locations on a sphere.
double	novas_vlen (const double *restrict v)
	(for internal use only) Calculates the length of a 3-vector
int	radec2vector (double ra, double dec, double dist, double *restrict pos)
	Converts equatorial spherical coordinates to a vector (equatorial rectangular coordinates).
int	spin (double angle, const double *in, double *out)
	Transforms a vector from one coordinate system to another with same origin and axes rotated about the z-axis.
short	vector2radec (const double *restrict pos, double *restrict ra, double *restrict dec)
	Converts an vector in equatorial rectangular coordinates to equatorial spherical coordinates.

Variables
int	novas_inv_max_iter = 100
	Maximum number of iterations for convergent inverse calculations.

Detailed Description

Various commonly used routines used throughout the SuperNOVAS library.

Date

Created on Mar 6, 2025

Author

G. Kaplan and Attila Kovacs

Function Documentation

d_light()

double d_light	(	const double *	pos_src,
		const double *	pos_body )

Returns the difference in light-time, for a star, between the barycenter of the solar system and the observer (or the geocenter) (Usage A).

Alternatively (Usage B), this function returns the light-time from the observer (or the geocenter) to a point on a light ray that is closest to a specific solar system body. For this purpose, 'pos_src' is the position vector toward observed object, with respect to origin at observer (or the geocenter); 'pos_body' is the position vector of solar system body, with respect to origin at observer (or the geocenter), components in AU; and the returned value is the light time to point on line defined by 'pos' that is closest to solar system body (positive if light passes body before hitting observer, i.e., if 'pos_body' is within 90 degrees of 'pos_src').

NOTES:

1. This function is called by novas_geom_posvel(), novas_sky_pos(), or place()

Parameters

pos_src	Position vector towards observed object, with respect to the SSB (Usage A), or relative to the observer / geocenter (Usage B).
pos_body	[AU] Position of observer relative to SSB (Usage A), or position of intermediate solar-system body with respect to the observer / geocenter (Usage B).

Returns

[day] Difference in light time to observer, either relative to SSB (Usage A) or relative intermediate solar-system body (Usage B); or else NAN if either of the input arguments is NULL.

See also

novas_sky_pos(), novas_geom_posvel()

References novas_vlen().

novas_debug()

PROTECTED void novas_debug

(

enum novas_debug_mode

mode

)

Enables or disables reporting errors and traces to the standard error stream.

Parameters

mode	NOVAS_DEBUG_OFF (0; or <0), NOVAS_DEBUG_ON (1), or NOVAS_DEBUG_EXTRA (2; or >2).

Since

1.0

Author

Attila Kovacs

See also

novas_get_debug_mode()

References NOVAS_DEBUG_EXTRA.

novas_equ_sep()

double novas_equ_sep	(	double	ra1,
		double	dec1,
		double	ra2,
		double	dec2 )

Returns the angular separation of two equatorial locations on a sphere.

Parameters

ra1	[h] right ascension of first location
dec1	[deg] declination of first location
ra2	[h] right ascension of second location
dec2	[deg] declination of second location

Returns

[deg] the angular separation of the two locations.

Since

1.3

Author

Attila Kovacs

See also

novas_sep(), novas_sun_angle(), novas_moon_angle()

References novas_sep().

novas_get_debug_mode()

enum novas_debug_mode novas_get_debug_mode

(

)

Returns the current, thread-local, mode for reporting errors encountered (and traces).

Returns

The current debug mode in the calling thread.

Since

1.0

Author

Attila Kovacs

See also

novas_debug()

novas_norm_ang()

double novas_norm_ang

(

double

angle

)

Returns the normalized angle in the [0:2π) range.

Parameters

angle

[rad] an angle in radians.

Returns

[rad] the normalized angle in the [0:2π) range.

Since

1.0

Author

Attila Kovacs

References TWOPI.

novas_sep()

double novas_sep	(	double	lon1,
		double	lat1,
		double	lon2,
		double	lat2 )

Returns the angular separation of two locations on a sphere.

Parameters

lon1	[deg] longitude of first location
lat1	[deg] latitude of first location
lon2	[deg] longitude of second location
lat2	[deg] latitude of second location

Returns

[deg] the angular separation of the two locations.

Since

1.3

Author

Attila Kovacs

See also

novas_equ_sep(), novas_sun_angle(), novas_moon_angle()

novas_vlen()

double novas_vlen

(

const double *restrict

v

)

(for internal use only) Calculates the length of a 3-vector

Parameters

v	Pointer to a 3-component (x, y, z) vector. The argument cannot be NULL

Returns

the length of the vector

Since

1.0

Author

Attila Kovacs

See also

novas_vdot(), novas_vdist()

radec2vector()

int radec2vector	(	double	ra,
		double	dec,
		double	dist,
		double *restrict	pos )

Converts equatorial spherical coordinates to a vector (equatorial rectangular coordinates).

Parameters

	ra	[h] Right ascension (hours).
	dec	[deg] Declination (degrees).
	dist	[AU] Distance (AU)
[out]	pos	[AU] Position 3-vector, equatorial rectangular coordinates (AU).

Returns

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

See also

vector2radec(), starvectors()

spin()

int spin	(	double	angle,
		const double *	in,
		double *	out )

Transforms a vector from one coordinate system to another with same origin and axes rotated about the z-axis.

REFERENCES:

1. Kaplan, G. H. et. al. (1989). Astron. Journ. 97, 1197-1210.

Parameters

	angle	[deg] Angle of coordinate system rotation, positive counterclockwise when viewed from +z, in degrees.
	in	Input position vector.
[out]	out	Position vector expressed in new coordinate system rotated about z by 'angle'. It can be the same vector as the input.

Returns

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

References TWOPI.

vector2radec()

short vector2radec	(	const double *restrict	pos,
		double *restrict	ra,
		double *restrict	dec )

Converts an vector in equatorial rectangular coordinates to equatorial spherical coordinates.

REFERENCES:

1. Kaplan, G. H. et. al. (1989). Astron. Journ. 97, 1197-1210.

Parameters

	pos	Position 3-vector, equatorial rectangular coordinates.
[out]	ra	[h] Right ascension in hours [0:24] or NAN if the position vector is NULL or a null-vector. It may be NULL if notrequired.
[out]	dec	[deg] Declination in degrees [-90:90] or NAN if the position vector is NULL or a null-vector. It may be NULL if not required.

Returns

0 if successful, -1 of any of the arguments are NULL, or 1 if all input components are 0 so 'ra' and 'dec' are indeterminate, or else 2 if both x and y are zero, but z is nonzero, and so 'ra' is indeterminate.

See also

radec2vector()

Variable Documentation

novas_inv_max_iter

int novas_inv_max_iter = 100

Maximum number of iterations for convergent inverse calculations.

Most iterative inverse functions should normally converge in a handful of iterations. In some pathological cases more iterations may be required. This variable sets an absolute maximum for the number of iterations in order to avoid runaway (zombie) behaviour. If inverse functions fail to converge, they will return a value indicating an error, and errno should be set to ECANCELED.

Since

1.1