mirror of https://github.com/XEphem/XEphem.git
271 lines
6.4 KiB
C
271 lines
6.4 KiB
C
/* uranus 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[U_NMOONS]);
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static void moonradec (double usize, MoonData md[U_NMOONS]);
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static void moonSVis (Obj *sop, Obj *uop, MoonData md[U_NMOONS]);
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static void moonEVis (MoonData md[U_NMOONS]);
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static void moonPShad (Obj *sop, Obj *uop, MoonData md[U_NMOONS]);
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static void moonTrans (MoonData md[U_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 umd[U_NMOONS] = {
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{"Uranus", NULL},
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{"Ariel", "I"},
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{"Umbriel", "II"},
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{"Titania", "III"},
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{"Oberon", "IV"},
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{"Miranda", "V"},
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};
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static double sizemjd; /* size at last mjd */
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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(257.43) /* RA of Uranus' north pole */
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#define POLE_DEC degrad(-15.10) /* Dec of Uranus' north pole */
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/* get uranus info in md[0], moon info in md[1..U_NMOONS-1].
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* if !uop caller just wants md[] for names
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* N.B. we assume sop and uop are updated.
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*/
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void
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uranus_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 *uop, /* uranus */
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double *sizep, /* u angular diam, rads */
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double *polera, double *poledec, /* pole location */
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MoonData md[U_NMOONS]) /* return info */
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{
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double JD;
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/* always copy back at least for name */
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memcpy (md, umd, sizeof(umd));
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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 || !uop) {
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if (uop) {
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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 = uop->s_ra;
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md[0].dec = uop->s_dec;
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md[0].mag = get_mag(uop);
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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 uop */
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*sizep = degrad(uop->s_size/3600.0);
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/* from Pasachoff/Menzel */
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md[1].mag = 14.2;
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md[2].mag = 14.8;
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md[3].mag = 13.7;
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md[4].mag = 14.0;
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md[5].mag = 16.3;
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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 < U_NMOONS; i++)
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md[i].x = md[i].y = md[i].z = 0.0;
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fprintf (stderr, "No uranus model available\n");
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}
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/* set visibilities */
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moonSVis (sop, uop, md);
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moonPShad (sop, uop, 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 (umd, md, sizeof(umd));
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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[U_NMOONS]) /* fill md[1..NM-1].x/y/z for each moon */
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{
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#define URAU .0001597 /* Uranus radius, AU */
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double x[U_NMOONS], y[U_NMOONS], z[U_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 = "uranus.9910";
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else if (JD < 2459215.5) /* Jan 1 2021 UTC */
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fn = "uranus.1020";
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else if (JD < 2466520.5) /* Jan 1 2041 UTC */
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fn = "uranus.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 != U_NMOONS-1) {
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fprintf (stderr, "%s: BDL says %d moons, code expects %d", fn,
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i, U_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 < U_NMOONS; i++) {
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md[i].x = x[i-1]/URAU; /* we want u radii +E */
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md[i].y = -y[i-1]/URAU; /* we want u radii +S */
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md[i].z = -z[i-1]/URAU; /* we want u 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 uranus 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 ura 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 usize, /* ura diameter, rads */
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MoonData md[U_NMOONS]) /* fill in RA and Dec */
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{
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double urad = usize/2;
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double ura = md[0].ra;
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double udec = md[0].dec;
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int i;
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for (i = 1; i < U_NMOONS; i++) {
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double dra = urad * md[i].x;
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double ddec = urad * md[i].y;
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md[i].ra = ura + dra;
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md[i].dec = udec - 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 *uop, /* uranus */
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MoonData md[U_NMOONS])
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{
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double esd = sop->s_edist;
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double eod = uop->s_edist;
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double sod = uop->s_sdist;
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double soa = degrad(uop->s_elong);
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double esa = asin(esd*sin(soa)/sod);
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double h = sod*uop->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 < U_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[U_NMOONS])
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{
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int i;
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for (i = 1; i < U_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 *uop, /* uranus */
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MoonData md[U_NMOONS])
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{
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int i;
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for (i = 1; i < U_NMOONS; i++) {
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MoonData *mdp = &md[i];
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mdp->pshad = !plshadow (uop, 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[U_NMOONS])
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{
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int i;
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for (i = 1; i < U_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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