source: Sophya/trunk/SophyaExt/XephemAstroLib/marsmoon.c@ 3995

/* mars moon info */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <math.h>

#include "astro.h"
#include "bdl.h"

static int use_bdl (double JD, char *dir, MoonData md[M_NMOONS]);
static void moonradec (double msize, MoonData md[M_NMOONS]);
static void moonSVis (Obj *sop, Obj *mop, MoonData md[M_NMOONS]);
static void moonEVis (MoonData md[M_NMOONS]);
static void moonPShad (Obj *sop, Obj *mop, MoonData md[M_NMOONS]);
static void moonTrans (MoonData md[M_NMOONS]);

/* moon table and a few other goodies and when it was last computed */
static double mdmjd = -123456;
static MoonData mmd[M_NMOONS] = {
    {"Mars", NULL},
    {"Phobos", "I"},
    {"Deimos", "II"},
};
static double sizemjd;

/* These values are from the Explanatory Supplement.
 * Precession degrades them gradually over time.
 */
#define POLE_RA         degrad(317.61)
#define POLE_DEC        degrad(52.85)


/* get mars info in md[0], moon info in md[1..M_NMOONS-1].
 * if !dir always use bruton model.
 * if !mop caller just wants md[] for names
 * N.B. we assume sop and mop are updated.
 */
void
marsm_data (
double Mjd,                     /* mjd */
char dir[],                     /* dir in which to look for helper files */
Obj *sop,                       /* Sun */
Obj *mop,                       /* mars */
double *sizep,                  /* mars's angular diam, rads */
double *polera, double *poledec,/* pole location */
MoonData md[M_NMOONS])          /* return info */
{
        double JD, dmag;

        /* always copy back at least for name */
        memcpy (md, mmd, sizeof(mmd));

        /* pole */
        if (polera) *polera = POLE_RA;
        if (poledec) *poledec = POLE_DEC;

        /* nothing else if repeat call or just want names */
        if (Mjd == mdmjd || !mop) {
            if (mop) {
                *sizep = sizemjd;
            }
            return;
        }
        JD = Mjd + MJD0;

        /* planet in [0] */
        md[0].ra = mop->s_ra;
        md[0].dec = mop->s_dec;
        md[0].mag = get_mag(mop);
        md[0].x = 0;
        md[0].y = 0;
        md[0].z = 0;
        md[0].evis = 1;
        md[0].svis = 1;

        /* size is straight from mop */
        *sizep = degrad(mop->s_size/3600.0);

        /* from Pasachoff/Menzel: brightest @ .6 AU */
        dmag = 5.0*log10(mop->s_edist + 0.4);
        md[1].mag = 11.8 + dmag;
        md[2].mag = 12.9 + dmag;

        /* get moon x,y,z from BDL if possible */
        if (!dir || use_bdl (JD, dir, md) < 0) {
            int i;
            for (i = 1; i < M_NMOONS; i++)
                md[i].x = md[i].y = md[i].z = 0.0;
            fprintf (stderr, "No mars model available\n");
        }

        /* set visibilities */
        moonSVis (sop, mop, md);
        moonPShad (sop, mop, md);
        moonEVis (md);
        moonTrans (md);

        /* fill in moon ra and dec */
        moonradec (*sizep, md);

        /* save */
        mdmjd = Mjd;
        sizemjd = *sizep;
        memcpy (mmd, md, sizeof(mmd));
}

/* hunt for BDL file in dir[] and use if possible.
 * return 0 if ok, else -1
 */
static int
use_bdl (
double JD,              /* julian date */
char dir[],             /* directory */
MoonData md[M_NMOONS])  /* fill md[1..NM-1].x/y/z for each moon */
{
#define MRAU    .00002269       /* Mars radius, AU */
        double x[M_NMOONS], y[M_NMOONS], z[M_NMOONS];
        char buf[1024];
        FILE *fp;
        char *fn;
        int i;

        /* check ranges and appropriate data file */
        if (JD < 2451179.50000)         /* Jan 1 1999 UTC */
            return (-1);
        if (JD < 2455562.5)             /* Jan 1 2011 UTC */
            fn = "mars.9910";
        else if (JD < 2459215.5)        /* Jan 1 2021 UTC */
            fn = "mars.1020";
        else
            return (-1);

        /* open */
        (void) sprintf (buf, "%s/%s", dir, fn);
        fp = fopen (buf, "r");
        if (!fp) {
            fprintf (stderr, "%s: %s\n", fn, strerror(errno));
            return (-1);
        }

        /* use it */
        if ((i = read_bdl (fp, JD, x, y, z, buf)) < 0) {
            fprintf (stderr, "%s: %s\n", fn, buf);
            fclose (fp);
            return (-1);
        }
        if (i != M_NMOONS-1) {
            fprintf (stderr, "%s: BDL says %d moons, code expects %d", fn,
                                                                i, M_NMOONS-1);
            fclose (fp);
            return (-1);
        }

        /* copy into md[1..NM-1] with our scale and sign conventions */
        for (i = 1; i < M_NMOONS; i++) {
            md[i].x =  x[i-1]/MRAU;     /* we want mars radii +E */
            md[i].y = -y[i-1]/MRAU;     /* we want mars radii +S */
            md[i].z = -z[i-1]/MRAU;     /* we want mars radii +front */
        }

        /* ok */
        fclose (fp);
        return (0);
}

/* given mars loc in md[0].ra/dec and size, and location of each moon in 
 * md[1..NM-1].x/y in mars radii,find ra/dec of each moon in md[1..NM-1].ra/dec.
 */
static void
moonradec (
double msize,           /* mars diameter, rads */
MoonData md[M_NMOONS])  /* fill in RA and Dec */
{
        double mrad = msize/2;
        double mra = md[0].ra;
        double mdec = md[0].dec;
        int i;

        for (i = 1; i < M_NMOONS; i++) {
            double dra  = mrad * md[i].x;
            double ddec = mrad * md[i].y;
            md[i].ra  = mra + dra;
            md[i].dec = mdec - ddec;
        }
}

/* set svis according to whether moon is in sun light */
static void
moonSVis(
Obj *sop,               /* SUN */
Obj *mop,               /* mars */
MoonData md[M_NMOONS])
{
        double esd = sop->s_edist;
        double eod = mop->s_edist;
        double sod = mop->s_sdist;
        double soa = degrad(mop->s_elong);
        double esa = asin(esd*sin(soa)/sod);
        double   h = sod*mop->s_hlat;
        double nod = h*(1./eod - 1./sod);
        double sca = cos(esa), ssa = sin(esa);
        int i;

        for (i = 1; i < M_NMOONS; i++) {
            MoonData *mdp = &md[i];
            double xp =  sca*mdp->x + ssa*mdp->z;
            double yp =  mdp->y;
            double zp = -ssa*mdp->x + sca*mdp->z;
            double ca = cos(nod), sa = sin(nod);
            double xpp = xp;
            double ypp = ca*yp - sa*zp;
            double zpp = sa*yp + ca*zp;
            int outside = xpp*xpp + ypp*ypp > 1.0;
            int infront = zpp > 0.0;
            mdp->svis = outside || infront;
        }
}

/* set evis according to whether moon is geometrically visible from earth */
static void
moonEVis (MoonData md[M_NMOONS])
{
        int i;

        for (i = 1; i < M_NMOONS; i++) {
            MoonData *mdp = &md[i];
            int outside = mdp->x*mdp->x + mdp->y*mdp->y > 1.0;
            int infront = mdp->z > 0.0;
            mdp->evis = outside || infront;
        }
}

/* set pshad and sx,sy shadow info */
static void
moonPShad(
Obj *sop,             /* SUN */
Obj *mop,             /* mars */
MoonData md[M_NMOONS])
{
        int i;

        for (i = 1; i < M_NMOONS; i++) {
            MoonData *mdp = &md[i];
            mdp->pshad = !plshadow (mop, sop, POLE_RA, POLE_DEC, mdp->x,
                                          mdp->y, mdp->z, &mdp->sx, &mdp->sy);
        }
}

/* set whether moons are transiting */
static void
moonTrans (MoonData md[M_NMOONS])
{
        int i;

        for (i = 1; i < M_NMOONS; i++) {
            MoonData *mdp = &md[i];
            mdp->trans = mdp->z > 0 && mdp->x*mdp->x + mdp->y*mdp->y < 1;
        }
}


/* For RCS Only -- Do Not Edit */
static char *rcsid[2] = {(char *)rcsid, "@(#) $RCSfile: marsmoon.c,v $ $Date: 2009-07-16 10:34:37 $ $Revision: 1.6 $ $Name: not supported by cvs2svn $"};