mirror of https://github.com/XEphem/XEphem.git
266 lines
6.2 KiB
C
266 lines
6.2 KiB
C
/* mars moon info */
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <errno.h>
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#include <math.h>
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#include "astro.h"
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#include "bdl.h"
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static int use_bdl (double JD, char *dir, MoonData md[M_NMOONS]);
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static void moonradec (double msize, MoonData md[M_NMOONS]);
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static void moonSVis (Obj *sop, Obj *mop, MoonData md[M_NMOONS]);
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static void moonEVis (MoonData md[M_NMOONS]);
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static void moonPShad (Obj *sop, Obj *mop, MoonData md[M_NMOONS]);
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static void moonTrans (MoonData md[M_NMOONS]);
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/* moon table and a few other goodies and when it was last computed */
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static double mdmjd = -123456;
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static MoonData mmd[M_NMOONS] = {
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{"Mars", NULL},
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{"Phobos", "I"},
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{"Deimos", "II"},
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};
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static double sizemjd;
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/* These values are from the Explanatory Supplement.
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* Precession degrades them gradually over time.
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*/
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#define POLE_RA degrad(317.61)
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#define POLE_DEC degrad(52.85)
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/* get mars info in md[0], moon info in md[1..M_NMOONS-1].
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* if !dir always use bruton model.
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* if !mop caller just wants md[] for names
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* N.B. we assume sop and mop are updated.
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*/
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void
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marsm_data (
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double Mjd, /* mjd */
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char dir[], /* dir in which to look for helper files */
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Obj *sop, /* Sun */
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Obj *mop, /* mars */
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double *sizep, /* mars's angular diam, rads */
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double *polera, double *poledec,/* pole location */
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MoonData md[M_NMOONS]) /* return info */
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{
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double JD, dmag;
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/* always copy back at least for name */
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memcpy (md, mmd, sizeof(mmd));
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/* pole */
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if (polera) *polera = POLE_RA;
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if (poledec) *poledec = POLE_DEC;
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/* nothing else if repeat call or just want names */
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if (Mjd == mdmjd || !mop) {
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if (mop) {
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*sizep = sizemjd;
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}
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return;
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}
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JD = Mjd + MJD0;
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/* planet in [0] */
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md[0].ra = mop->s_ra;
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md[0].dec = mop->s_dec;
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md[0].mag = get_mag(mop);
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md[0].x = 0;
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md[0].y = 0;
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md[0].z = 0;
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md[0].evis = 1;
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md[0].svis = 1;
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/* size is straight from mop */
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*sizep = degrad(mop->s_size/3600.0);
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/* from Pasachoff/Menzel: brightest @ .6 AU */
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dmag = 5.0*log10(mop->s_edist + 0.4);
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md[1].mag = 11.8 + dmag;
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md[2].mag = 12.9 + dmag;
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/* get moon x,y,z from BDL if possible */
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if (!dir || use_bdl (JD, dir, md) < 0) {
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int i;
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for (i = 1; i < M_NMOONS; i++)
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md[i].x = md[i].y = md[i].z = 0.0;
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fprintf (stderr, "No mars model available\n");
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}
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/* set visibilities */
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moonSVis (sop, mop, md);
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moonPShad (sop, mop, md);
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moonEVis (md);
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moonTrans (md);
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/* fill in moon ra and dec */
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moonradec (*sizep, md);
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/* save */
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mdmjd = Mjd;
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sizemjd = *sizep;
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memcpy (mmd, md, sizeof(mmd));
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}
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/* hunt for BDL file in dir[] and use if possible.
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* return 0 if ok, else -1
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*/
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static int
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use_bdl (
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double JD, /* julian date */
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char dir[], /* directory */
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MoonData md[M_NMOONS]) /* fill md[1..NM-1].x/y/z for each moon */
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{
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#define MRAU .00002269 /* Mars radius, AU */
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double x[M_NMOONS], y[M_NMOONS], z[M_NMOONS];
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char buf[1024];
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FILE *fp;
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char *fn;
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int i;
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/* check ranges and appropriate data file */
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if (JD < 2451179.50000) /* Jan 1 1999 UTC */
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return (-1);
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if (JD < 2455562.5) /* Jan 1 2011 UTC */
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fn = "mars.9910";
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else if (JD < 2459215.5) /* Jan 1 2021 UTC */
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fn = "mars.1020";
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else if (JD < 2466520.5) /* Jan 1 2041 UTC */
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fn = "mars.2040";
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else
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return (-1);
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/* open */
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(void) sprintf (buf, "%s/%s", dir, fn);
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fp = fopen (buf, "r");
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if (!fp) {
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fprintf (stderr, "%s: %s\n", fn, strerror(errno));
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return (-1);
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}
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/* use it */
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if ((i = read_bdl (fp, JD, x, y, z, buf)) < 0) {
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fprintf (stderr, "%s: %s\n", fn, buf);
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fclose (fp);
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return (-1);
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}
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if (i != M_NMOONS-1) {
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fprintf (stderr, "%s: BDL says %d moons, code expects %d", fn,
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i, M_NMOONS-1);
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fclose (fp);
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return (-1);
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}
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/* copy into md[1..NM-1] with our scale and sign conventions */
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for (i = 1; i < M_NMOONS; i++) {
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md[i].x = x[i-1]/MRAU; /* we want mars radii +E */
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md[i].y = -y[i-1]/MRAU; /* we want mars radii +S */
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md[i].z = -z[i-1]/MRAU; /* we want mars radii +front */
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}
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/* ok */
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fclose (fp);
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return (0);
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}
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/* given mars loc in md[0].ra/dec and size, and location of each moon in
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* md[1..NM-1].x/y in mars radii,find ra/dec of each moon in md[1..NM-1].ra/dec.
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*/
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static void
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moonradec (
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double msize, /* mars diameter, rads */
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MoonData md[M_NMOONS]) /* fill in RA and Dec */
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{
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double mrad = msize/2;
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double mra = md[0].ra;
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double mdec = md[0].dec;
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int i;
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for (i = 1; i < M_NMOONS; i++) {
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double dra = mrad * md[i].x;
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double ddec = mrad * md[i].y;
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md[i].ra = mra + dra;
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md[i].dec = mdec - ddec;
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}
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}
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/* set svis according to whether moon is in sun light */
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static void
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moonSVis(
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Obj *sop, /* SUN */
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Obj *mop, /* mars */
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MoonData md[M_NMOONS])
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{
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double esd = sop->s_edist;
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double eod = mop->s_edist;
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double sod = mop->s_sdist;
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double soa = degrad(mop->s_elong);
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double esa = asin(esd*sin(soa)/sod);
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double h = sod*mop->s_hlat;
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double nod = h*(1./eod - 1./sod);
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double sca = cos(esa), ssa = sin(esa);
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int i;
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for (i = 1; i < M_NMOONS; i++) {
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MoonData *mdp = &md[i];
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double xp = sca*mdp->x + ssa*mdp->z;
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double yp = mdp->y;
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double zp = -ssa*mdp->x + sca*mdp->z;
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double ca = cos(nod), sa = sin(nod);
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double xpp = xp;
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double ypp = ca*yp - sa*zp;
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double zpp = sa*yp + ca*zp;
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int outside = xpp*xpp + ypp*ypp > 1.0;
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int infront = zpp > 0.0;
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mdp->svis = outside || infront;
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}
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}
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/* set evis according to whether moon is geometrically visible from earth */
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static void
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moonEVis (MoonData md[M_NMOONS])
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{
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int i;
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for (i = 1; i < M_NMOONS; i++) {
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MoonData *mdp = &md[i];
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int outside = mdp->x*mdp->x + mdp->y*mdp->y > 1.0;
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int infront = mdp->z > 0.0;
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mdp->evis = outside || infront;
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}
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}
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/* set pshad and sx,sy shadow info */
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static void
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moonPShad(
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Obj *sop, /* SUN */
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Obj *mop, /* mars */
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MoonData md[M_NMOONS])
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{
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int i;
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for (i = 1; i < M_NMOONS; i++) {
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MoonData *mdp = &md[i];
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mdp->pshad = !plshadow (mop, sop, POLE_RA, POLE_DEC, mdp->x,
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mdp->y, mdp->z, &mdp->sx, &mdp->sy);
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}
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}
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/* set whether moons are transiting */
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static void
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moonTrans (MoonData md[M_NMOONS])
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{
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int i;
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for (i = 1; i < M_NMOONS; i++) {
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MoonData *mdp = &md[i];
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mdp->trans = mdp->z > 0 && mdp->x*mdp->x + mdp->y*mdp->y < 1;
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}
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}
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