int DLL_FUNC calc_planet_orientation( int planet_no, int system_no, double jd,
double *matrix)
#endif
{
static int prev_planet_no = -1, prev_system_no = -1, prev_rval = 0;
static double prev_jd = -1.;
static double prev_matrix[9];
int i, rval, is_retrograde;
double pole_ra, pole_dec, omega;
if( planet_no == prev_planet_no && system_no == prev_system_no
&& jd == prev_jd)
{
memcpy( matrix, prev_matrix, 9 * sizeof( double));
return( prev_rval);
}
prev_planet_no = planet_no;
prev_system_no = system_no;
prev_jd = jd;
if( planet_no == 3) /* handle earth with "normal" precession: */
{
const double J2000 = 2451545.; /* 1.5 Jan 2000 = JD 2451545 */
const double t_cen = (jd - J2000) / 36525.;
int i;
setup_precession( matrix, 2000., 2000. + t_cen * 100.);
for( i = 3; i < 6; i++)
matrix[i] = -matrix[i];
spin_matrix( matrix, matrix + 3, green_sidereal_time( jd));
memcpy( prev_matrix, matrix, 9 * sizeof( double));
prev_rval = 0;
return( 0);
}
/* For everybody else, we use TD. Only the earth uses UT. */
/* (This correction added 5 Nov 98, after G Seronik pointed */
/* out an error in the Saturn central meridian.) */
jd += td_minus_ut( jd) / 86400.; /* correct from UT to TD */
rval = get_cospar_data_from_text_file( planet_no, system_no, jd,
&pole_ra, &pole_dec, &omega, &is_retrograde);
pole_ra *= PI / 180.;
pole_dec *= PI / 180.;
polar3_to_cartesian( matrix, pole_ra - PI / 2., 0.);
polar3_to_cartesian( matrix + 3, pole_ra - PI, PI / 2. - pole_dec);
polar3_to_cartesian( matrix + 6, pole_ra, pole_dec);
spin_matrix( matrix, matrix + 3, omega * PI / 180. + PI);
if( is_retrograde)
for( i = 3; i < 6; i++)
matrix[i] *= -1.;
memcpy( prev_matrix, matrix, 9 * sizeof( double));
prev_rval = rval;
return( rval);
}
int DLL_FUNC calc_ssat_loc( const double t, double DLLPTR *ssat,
const int sat_wanted, const long precision)
{
SAT_ELEMS elems;
ELEMENTS orbit;
double matrix[9];
const double t_years = (t - J2000) / 365.25;
if( precision == -1L) /* just checking version # */
return( 1);
if( sat_wanted < 0 || sat_wanted > PHOEBE)
return( -1);
elems.jd = t;
elems.sat_no = sat_wanted;
set_ssat_elems( &elems, &orbit);
setup_orbit_vectors( &orbit);
comet_posn_part_ii( &orbit, IGNORED_DOUBLE, elems.loc, NULL);
if( sat_wanted < RHEA) /* inner 4 satellites are returned in Saturnic */
{ /* coords so gotta rotate to B1950.0 */
rotate_vector( elems.loc, INCL0, 0);
rotate_vector( elems.loc, ASC_NODE0, 2);
}
/* After above, elems.loc is ecliptic 1950 coords */
rotate_vector( elems.loc, OBLIQUITY_1950, 0);
/* Now, elems.loc is equatorial 1950 coords */
#ifdef OUTPUT_IN_J2000
setup_precession( matrix, 1950., 2000);
precess_vector( matrix, elems.loc, ssat);
/* Now, ssats is equatorial J2000... */
rotate_vector( ssat, -OBLIQUITY_2000, 0);
/* And now, ssats is ecliptical J2000 */
#else
setup_precession( matrix, 1950., 2000. + t_years);
precess_vector( matrix, elems.loc, ssat);
/* Now, ssats is equatorial of epoch coords */
rotate_vector( ssat, -mean_obliquity( t_years / 100.), 0);
/* And now, ssats is ecliptical of epoch coords */
/* (which is what we really want anyway) */
#endif
return( 0);
}
void DLL_FUNC calc_triton_loc( const double jd, double *vect)
{
const double t_cent = (jd - J2000) / 36525.;
const double n = (359.28 + 54.308 * t_cent) * (PI / 180.);
const double t0 = 2433282.5;
const double theta = (151.401 + .57806 * (jd - t0) / 365.25) * (PI / 180.);
/* Semimajor axis is 488.49 arcseconds at one AU: */
const double semimajor = 488.49 * (PI / 180.) / 3600.;
const double longitude =
(200.913 + 61.2588532 * (jd - t0)) * (PI / 180.);
const double gamma = 158.996 * (PI / 180.);
/* Calculate longitude and latitude on invariable plane: */
const double lon_on_ip = theta + atan2( sin( longitude) * cos( gamma),
cos( longitude));
const double lat_on_ip = asin( sin( longitude) * sin( gamma));
/* Vectors defining invariable plane, expressed in B1950: */
double x_axis[3], y_axis[3], z_axis[3];
/* Vector defining Triton position in invariable plane space: */
double triton[3];
/* RA/dec of the pole: */
double ra_dec_p[2];
double matrix[9];
double vect_1950[3];
int i;
polar3_to_cartesian( triton, lon_on_ip, lat_on_ip);
ra_dec_p[0] = (298.72 * PI / 180.) + (2.58 * PI / 180.) * sin( n)
- (0.04 * PI / 180.) * sin( n + n);
ra_dec_p[1] = (42.63 * PI / 180.) - (1.90 * PI / 180.) * cos( n)
+ (0.01 * PI / 180.) * cos( n + n);
setup_precession( matrix, 1950., 2000.);
precess_ra_dec( matrix, ra_dec_p, ra_dec_p, 1);
polar3_to_cartesian( x_axis, ra_dec_p[0] + PI / 2., 0.);
polar3_to_cartesian( y_axis, ra_dec_p[0] + PI, PI / 2. - ra_dec_p[1]);
polar3_to_cartesian( z_axis, ra_dec_p[0], ra_dec_p[1]);
for( i = 0; i < 3; i++)
vect_1950[i] = semimajor * (x_axis[i] * triton[0] +
y_axis[i] * triton[1] + z_axis[i] * triton[2]);
precess_vector( matrix, vect_1950, vect);
}
