This is parallax.c in view mode; [Download] [Up]
#include <stdio.h>
#include <math.h>
#include "astro.h"
/* given true ha and dec, tha and tdec, the geographical latitude, phi, the
* height above sea-level (as a fraction of the earths radius, 6378.16km),
* ht, and the equatorial horizontal parallax, ehp, find the apparent
* ha and dec, aha and adec allowing for parallax.
* all angles in radians. ehp is the angle subtended at the body by the
* earth's equator.
*/
ta_par (tha, tdec, phi, ht, ehp, aha, adec)
double tha, tdec, phi, ht, ehp;
double *aha, *adec;
{
static double last_phi, last_ht, rsp, rcp;
double rp; /* distance to object in Earth radii */
double ctha;
double stdec, ctdec;
double tdtha, dtha;
double caha;
/* avoid calcs involving the same phi and ht */
if (phi != last_phi || ht != last_ht) {
double cphi, sphi, u;
cphi = cos(phi);
sphi = sin(phi);
u = atan(9.96647e-1*sphi/cphi);
rsp = (9.96647e-1*sin(u))+(ht*sphi);
rcp = cos(u)+(ht*cphi);
last_phi = phi;
last_ht = ht;
}
rp = 1/sin(ehp);
ctha = cos(tha);
stdec = sin(tdec);
ctdec = cos(tdec);
tdtha = (rcp*sin(tha))/((rp*ctdec)-(rcp*ctha));
dtha = atan(tdtha);
*aha = tha+dtha;
caha = cos(*aha);
range (aha, 2*PI);
*adec = atan(caha*(rp*stdec-rsp)/(rp*ctdec*ctha-rcp));
}
#ifdef NEEDIT
/* given the apparent ha and dec, aha and adec, the geographical latitude, phi,
* the height above sea-level (as a fraction of the earths radius, 6378.16km),
* ht, and the equatorial horizontal parallax, ehp, find the true ha and dec,
* tha and tdec allowing for parallax.
* all angles in radians. ehp is the angle subtended at the body by the
* earth's equator.
* uses ta_par() iteratively: find a set of true ha/dec that converts back
* to the given apparent ha/dec.
*/
at_par (aha, adec, phi, ht, ehp, tha, tdec)
double aha, adec, phi, ht, ehp;
double *tha, *tdec;
{
double nha, ndec; /* ha/dec corres. to current true guesses */
double eha, edec; /* error in ha/dec */
/* first guess for true is just the apparent */
*tha = aha;
*tdec = adec;
while (1) {
ta_par (*tha, *tdec, phi, ht, ehp, &nha, &ndec);
eha = aha - nha;
edec = adec - ndec;
if (fabs(eha)<1e-6 && fabs(edec)<1e-6)
break;
*tha += eha;
*tdec += edec;
}
}
#endif
These are the contents of the former NiCE NeXT User Group NeXTSTEP/OpenStep software archive, currently hosted by Netfuture.ch.