This file contains functions for performing coordinate transformations. More...

#include <ctype.h>
#include <math.h>
#include <stdlib.h>
#include <string.h>
#include "aephem.h"

Functions
void	ae_rect_to_polar (const double rect[], double ra, double dec, double *radius)
	Convert an equatorial rectangular unit vector to ra/dec/radius. More...

void	ae_rect_to_polar_with_jd (double pp[], double jd, char ofdate, double polar[])
	Convert equatorial rectangular coordinates to polar coordinates. More...

void	ae_polar_to_rect (double ra, double dec, double radius, double rect[])
	Convert ra/dec/radius to a rectangular vector. More...

void	ae_radec_to_altaz (double last, double glat, double ra, double dec, double alt, double az)
	Convert ra/dec to alt/az. More...

void	ae_altaz_to_radec (double last, double glat, double alt, double az, double ra, double dec)
	Convert alt/az to ra/dec. More...

void	ae_radec_to_gal (double ra, double dec, double l, double b, int fk5)
	Convert ra/dec to l/b (galactic coordinates). More...

void	ae_gal_to_radec (double l, double b, double ra, double dec, int fk5)
	Convert l/b (galactic coordinates) to ra/dec. More...

void	ae_geocentric_lat (double glat, double height, double tlat, double trho)
	Calculate the geocentric latitude and the distance to the earth's centre. More...

void	ae_delta_q (double q0[], double q1[], double dra, double ddec)
	Convert change in rectangular coordinatates to change in ra/dec. More...

Detailed Description

This file contains functions for performing coordinate transformations.

Function Documentation

void ae_altaz_to_radec	(	double	last,
		double	glat,
		double	alt,
		double	az,
		double *	ra,
		double *	dec
	)

Convert alt/az to ra/dec.

Parameters

last	The local aparent sidereal time, in degrees.
glat	The geodetic latitude, in degrees.
alt	The altitude, in degrees.
az	The azimuth, in degrees.
ra	For returning the right ascension, in degrees.
dec	For returning the declination, in degrees.

References AE_DTR, ae_mod_360(), AE_RTD, and ae_zatan2().

Referenced by ae_topocentric().

void ae_delta_q	(	double	q0[],
		double	q1[],
		double *	dra,
		double *	ddec
	)

Convert change in rectangular coordinatates to change in ra/dec.

For changes greater than about 0.1 degree, the coordinates are converted directly to ra and dec and the results subtracted. For small changes, the change is calculated to first order by differentiating $tan(ra) = y/x$ to obtain

$\frac{dra}{\cos^2(ra)} = \frac{dy}{x} - \frac{y dx}{x^2},$

where

$\cos^2(ra) = \frac{1}{1 + (y/x)^2}.$

The change in declination $arcsin(z/R)$ is

$d\arcsin(u) = \frac{du}{\sqrt{1-u^2}},$

where $u = z/R.$

Parameters

q0	The initial object - earth vector.
q1	The vector after motion or aberration.
dra	The change in right ascension.
ddec	The change in declination.

References ae_zatan2().

void ae_gal_to_radec	(	double	l,
		double	b,
		double *	ra,
		double *	dec,
		int	fk5
	)

Convert l/b (galactic coordinates) to ra/dec.

Parameters

l	The galactic longitude, in degrees.
b	The galactic latitude, in degrees.
ra	For returning the right ascension, in degrees.
dec	For returning the declination, in degrees.
fk5	If non-zero, assume FK5 system (i.e., J2000 compatible); if zero, use the old FK4 (B1950 compatible) galactic pole.

References AE_DTR, ae_mod_360(), and AE_RTD.

void ae_geocentric_lat	(	double	glat,
		double	height,
		double *	tlat,
		double *	trho
	)

Calculate the geocentric latitude and the distance to the earth's centre.

This function uses the reciprocal of flattening and the earth's radius (or, more precisely, semi-major axis) from from the WGS84 definition. (See AE_FLAT and AE_R_EARTH.)

Parameters

glat	The geodetic latitude of the observer, in degrees.
height	The height of the observer above sea level, in metres.
tlat	For returning the geocentric latitude, in degrees.
trho	For returning the distance to the earth's centre, in earth radii.

References AE_DTR, AE_FLAT, AE_R_EARTH, and AE_RTD.

Referenced by aes_topocentric().

void ae_polar_to_rect	(	double	ra,
		double	dec,
		double	radius,
		double	rect[]
	)

Convert ra/dec/radius to a rectangular vector.

Parameters

ra	The right ascension, in degrees.
dec	The declination, in degrees.
radius	The radius; the units of `radius` will determine the units of the output.
rect	For returning the rectangular vector.

References AE_DTR.

Referenced by ae_coord_to_constel_index(), ae_phys_pole(), ae_subobs_point(), and aes_subobs_point().

void ae_radec_to_altaz	(	double	last,
		double	glat,
		double	ra,
		double	dec,
		double *	alt,
		double *	az
	)

Convert ra/dec to alt/az.

Parameters

last	The local aparent sidereal time, in degrees.
glat	The geodetic latitude, in degrees.
ra	The right ascension, in degrees.
dec	The declination, in degrees.
alt	For returning the altitude, in degrees.
az	For returning the azimuth, in degrees.

References AE_DTR, AE_RTD, and ae_zatan2().

Referenced by ae_topocentric().

void ae_radec_to_gal	(	double	ra,
		double	dec,
		double *	l,
		double *	b,
		int	fk5
	)

Convert ra/dec to l/b (galactic coordinates).

Parameters

ra	The right ascension, in degrees.
dec	The declination, in degrees.
l	For returning the galactic longitude, in degrees.
b	For returning the galactic latitude, in degrees.
fk5	If non-zero, assume FK5 system (i.e., J2000 compatible); if zero, use the old FK4 (B1950 compatible) galactic pole.

References AE_DTR, ae_mod_360(), and AE_RTD.

void ae_rect_to_polar	(	const double	rect[],
		double *	ra,
		double *	dec,
		double *	radius
	)

Convert an equatorial rectangular unit vector to ra/dec/radius.

Parameters

rect	An equatorial rectangular vector.
ra	For returning the right ascension, in degrees.
dec	For returning the declination, in degrees.
radius	For returning the radius. Set to NULL if you do not need this value.

References AE_RTD, and ae_zatan2().

Referenced by ae_geocentric(), ae_geocentric_from_cat(), ae_geocentric_moon_from_orbit(), and ae_subobs_point().

void ae_rect_to_polar_with_jd	(	double	pp[],
		double	jd,
		char	ofdate,
		double	polar[]
	)

Convert equatorial rectangular coordinates to polar coordinates.

This routine is similar to ae_rect_to_polar(), except that it also performs //! any necessary precession.

Parameters

pp	The equatorial rectangular coordinates.
jd	The Julian date.
ofdate	If 1, precess from J2000.0 to `jd`.
polar	For returning the polar coordinates.

References ae_epsilon(), AE_FROM_J2000, ae_precess(), AE_STR, and ae_zatan2().

Functions

Detailed Description

Function Documentation