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precession.c
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precession.c
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// hskymon from HDS OPE file Editor
// New SkyMonitor for Subaru Gen2
// precession.c --- imported from libnova
//
// 2012.10.22 A.Tajitsu
/*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*
* Copyright (C) 2000 - 2005 Liam Girdwood
*/
#include <math.h>
#include <libnova/precession.h>
#include <libnova/utility.h>
#ifdef HAVE_LIBsunmath
#include <sunmath.h>
#endif
// fixed missing *l functions
#ifndef HAVE_COSL
#define cosl cos
#endif
#ifndef HAVE_SINL
#define sinl sin
#endif
#ifndef HAVE_ACOSL
#define acosl acos
#endif
#ifndef HAVE_ASINL
#define asinl asin
#endif
#ifndef HAVE_ATAN2L
#define atan2l atan2
#endif
/*
** Precession
*/
/*! \fn void ln_get_equ_prec (struct ln_equ_posn * mean_position, double JD, struct ln_equ_posn * position)
* \param mean_position Mean object position
* \param JD Julian day
* \param position Pointer to store new object position.
*
* Calculate equatorial coordinates with the effects of precession for a given Julian Day.
* Uses mean equatorial coordinates and is
* only for initial epoch J2000.0
*/
/* Equ 20.3, 20.4 pg 126
*/
void ln_get_equ_prec (struct ln_equ_posn * mean_position, double JD, struct ln_equ_posn * position)
{
long double t, t2, t3, A, B, C, zeta, eta, theta, ra, dec, mean_ra, mean_dec;
/* change original ra and dec to radians */
mean_ra = ln_deg_to_rad (mean_position->ra);
mean_dec = ln_deg_to_rad (mean_position->dec);
/* calc t, zeta, eta and theta for J2000.0 Equ 20.3 */
t = (JD - JD2000) / 36525.0;
t *= 1.0 / 3600.0;
t2 = t * t;
t3 = t2 *t;
zeta = 2306.2181 * t + 0.30188 * t2 + 0.017998 * t3;
eta = 2306.2181 * t + 1.09468 * t2 + 0.041833 * t3;
theta = 2004.3109 * t - 0.42665 * t2 - 0.041833 * t3;
zeta = ln_deg_to_rad (zeta);
eta = ln_deg_to_rad (eta);
theta = ln_deg_to_rad (theta);
/* calc A,B,C equ 20.4 */
A = cosl (mean_dec) * sinl (mean_ra + zeta);
B = cosl (theta) * cosl (mean_dec) * cosl (mean_ra + zeta) - sinl (theta) * sinl (mean_dec);
C = sinl (theta) * cosl (mean_dec) * cosl (mean_ra + zeta) + cosl (theta) * sinl (mean_dec);
ra = atan2l (A,B) + eta;
/* check for object near celestial pole */
if (mean_dec > (0.4 * M_PI) || mean_dec < (-0.4 * M_PI)) {
/* close to pole */
dec = acosl (sqrt(A * A + B * B));
if (mean_dec < 0.)
dec *= -1; /* 0 <= acos() <= PI */
} else {
/* not close to pole */
dec = asinl (C);
}
/* change to degrees */
position->ra = ln_range_degrees (ln_rad_to_deg (ra));
position->dec = ln_rad_to_deg (dec);
}
/*! \fn void ln_get_equ_prec2 (struct ln_equ_posn * mean_position, double fromJD, double toJD, struct ln_equ_posn * position);
*
* \param mean_position Mean object position
* \param fromJD Julian day (start)
* \param toJD Julian day (end)
* \param position Pointer to store new object position.
*
* Calculate the effects of precession on equatorial coordinates, between arbitary Jxxxx epochs.
* Use fromJD and toJD parameters to specify required Jxxxx epochs.
*/
/* Equ 20.2, 20.4 pg 126 */
void ln_get_equ_prec2 (struct ln_equ_posn * mean_position, double fromJD, double toJD, struct ln_equ_posn * position)
{
long double t, t2, t3, A, B, C, zeta, eta, theta, ra, dec, mean_ra, mean_dec, T, T2;
/* change original ra and dec to radians */
mean_ra = ln_deg_to_rad (mean_position->ra);
mean_dec = ln_deg_to_rad (mean_position->dec);
/* calc t, T, zeta, eta and theta Equ 20.2 */
T = ((long double) (fromJD - JD2000)) / 36525.0;
T *= 1.0 / 3600.0;
t = ((long double) (toJD - fromJD)) / 36525.0;
t *= 1.0 / 3600.0;
T2 = T * T;
t2 = t * t;
t3 = t2 *t;
zeta = (2306.2181 + 1.39656 * T - 0.000139 * T2) * t + (0.30188 - 0.000344 * T) * t2 + 0.017998 * t3;
eta = (2306.2181 + 1.39656 * T - 0.000139 * T2) * t + (1.09468 + 0.000066 * T) * t2 + 0.018203 * t3;
theta = (2004.3109 - 0.85330 * T - 0.000217 * T2) * t - (0.42665 + 0.000217 * T) * t2 - 0.041833 * t3;
zeta = ln_deg_to_rad (zeta);
eta = ln_deg_to_rad (eta);
theta = ln_deg_to_rad (theta);
/* calc A,B,C equ 20.4 */
A = cosl (mean_dec) * sinl (mean_ra + zeta);
B = cosl (theta) * cosl (mean_dec) * cosl (mean_ra + zeta) - sinl (theta) * sinl (mean_dec);
C = sinl (theta) * cosl (mean_dec) * cosl (mean_ra + zeta) + cosl (theta) * sinl (mean_dec);
ra = atan2l (A,B) + eta;
/* check for object near celestial pole */
if (mean_dec > (0.4 * M_PI) || mean_dec < (-0.4 * M_PI)) {
/* close to pole */
dec = acosl (sqrt(A * A + B * B));
if (mean_dec < 0.)
dec *= -1; /* 0 <= acos() <= PI */
} else {
/* not close to pole */
dec = asinl (C);
}
/* change to degrees */
position->ra = ln_range_degrees (ln_rad_to_deg (ra));
position->dec = ln_rad_to_deg (dec);
}
/*! \fn void ln_get_ecl_prec (struct ln_lnlat_posn * mean_position, double JD, struct ln_lnlat_posn * position)
* \param mean_position Mean object position
* \param JD Julian day
* \param position Pointer to store new object position.
*
* Calculate ecliptical coordinates with the effects of precession for a given Julian Day.
* Uses mean ecliptical coordinates and is
* only for initial epoch J2000.0
* \todo To be implemented.
*/
/* Equ 20.5, 20.6 pg 128
*/
void ln_get_ecl_prec (struct ln_lnlat_posn * mean_position, double JD, struct ln_lnlat_posn * position)
{
}