This is eq_ecl.c in view mode; [Download] [Up]
#include <stdio.h>
#include <math.h>
#include "astro.h"
#define EQtoECL 1
#define ECLtoEQ (-1)
/* given the modified Julian date, mjd, and an equitorial ra and dec, each in
* radians, find the corresponding geocentric ecliptic latitude, *lat, and
* longititude, *lng, also each in radians.
* correction for the effect on the angle of the obliquity due to nutation is
* included.
*/
eq_ecl (mjd, ra, dec, lat, lng)
double mjd, ra, dec;
double *lat, *lng;
{
ecleq_aux (EQtoECL, mjd, ra, dec, lng, lat);
}
/* given the modified Julian date, mjd, and a geocentric ecliptic latitude,
* *lat, and longititude, *lng, each in radians, find the corresponding
* equitorial ra and dec, also each in radians.
* correction for the effect on the angle of the obliquity due to nutation is
* included.
*/
ecl_eq (mjd, lat, lng, ra, dec)
double mjd, lat, lng;
double *ra, *dec;
{
ecleq_aux (ECLtoEQ, mjd, lng, lat, ra, dec);
}
static
ecleq_aux (sw, mjd, x, y, p, q)
int sw; /* +1 for eq to ecliptic, -1 for vv. */
double mjd, x, y; /* sw==1: x==ra, y==dec. sw==-1: x==lng, y==lat. */
double *p, *q; /* sw==1: p==lng, q==lat. sw==-1: p==ra, q==dec. */
{
static double lastmjd = -10000; /* last mjd calculated */
static double seps, ceps; /* sin and cos of mean obliquity */
double sx, cx, sy, cy, ty;
if (mjd != lastmjd) {
double eps;
double deps, dpsi;
obliquity (mjd, &eps); /* mean obliquity for date */
nutation (mjd, &deps, &dpsi);
eps += deps;
seps = sin(eps);
ceps = cos(eps);
lastmjd = mjd;
}
sy = sin(y);
cy = cos(y); /* always non-negative */
if (fabs(cy)<1e-20) cy = 1e-20; /* insure > 0 */
ty = sy/cy;
cx = cos(x);
sx = sin(x);
*q = asin((sy*ceps)-(cy*seps*sx*sw));
*p = atan(((sx*ceps)+(ty*seps*sw))/cx);
if (cx<0) *p += PI; /* account for atan quad ambiguity */
range (p, 2*PI);
}
These are the contents of the former NiCE NeXT User Group NeXTSTEP/OpenStep software archive, currently hosted by Netfuture.ch.