#include #include "moonpos.hxx" #undef E /* * the epoch upon which these astronomical calculations are based is * 1990 january 0.0, 631065600 seconds since the beginning of the * "unix epoch" (00:00:00 GMT, Jan. 1, 1970) * * given a number of seconds since the start of the unix epoch, * DaysSinceEpoch() computes the number of days since the start of the * astronomical epoch (1990 january 0.0) */ #define EpochStart (631065600) #define DaysSinceEpoch(secs) (((secs)-EpochStart)*(1.0/(24*3600))) /* * assuming the apparent orbit of the moon about the earth is circular, * the rate at which the orbit progresses is given by RadsPerDay -- * FG_2PI radians per orbit divided by 365.242191 days per year: */ #define RadsPerDay (FG_2PI/365.242191) /* * details of moon's apparent orbit at epoch 1990.0 (after * duffett-smith, table 6, section 46) * * Epsilon_g (ecliptic longitude at epoch 1990.0) 279.403303 degrees * OmegaBar_g (ecliptic longitude of perigee) 282.768422 degrees * Eccentricity (eccentricity of orbit) 0.016713 */ #define Epsilon_g (279.403303*(FG_2PI/360)) #define OmegaBar_g (282.768422*(FG_2PI/360)) #define Eccentricity (0.016713) /* * MeanObliquity gives the mean obliquity of the earth's axis at epoch * 1990.0 (computed as 23.440592 degrees according to the method given * in duffett-smith, section 27) */ #define MeanObliquity (23.440592*(FG_2PI/360)) /* static double solve_keplers_equation(double); */ /* static double moon_ecliptic_longitude(time_t); */ static void ecliptic_to_equatorial(double, double, double *, double *); static double julian_date(int, int, int); static double GST(time_t); /* * solve Kepler's equation via Newton's method * (after duffett-smith, section 47) */ /* static double solve_keplers_equation(double M) { double E; double delta; E = M; while (1) { delta = E - Eccentricity*sin(E) - M; if (fabs(delta) <= 1e-10) break; E -= delta / (1 - Eccentricity*cos(E)); } return E; } */ /* compute ecliptic longitude of moon (in radians) (after * duffett-smith, section 47) */ /* static double moon_ecliptic_longitude(time_t ssue) { // time_t ssue; // seconds since unix epoch double D, N; double M_moon, E; double v; D = DaysSinceEpoch(ssue); N = RadsPerDay * D; N = fmod(N, FG_2PI); if (N < 0) N += FG_2PI; M_moon = N + Epsilon_g - OmegaBar_g; if (M_moon < 0) M_moon += FG_2PI; E = solve_keplers_equation(M_moon); v = 2 * atan(sqrt((1+Eccentricity)/(1-Eccentricity)) * tan(E/2)); return (v + OmegaBar_g); } */ /* convert from ecliptic to equatorial coordinates (after * duffett-smith, section 27) */ static void ecliptic_to_equatorial(double lambda, double beta, double *alpha, double *delta) { /* double lambda; ecliptic longitude */ /* double beta; ecliptic latitude */ /* double *alpha; (return) right ascension */ /* double *delta; (return) declination */ double sin_e, cos_e; double sin_l, cos_l; sin_e = sin(MeanObliquity); cos_e = cos(MeanObliquity); sin_l = sin(lambda); cos_l = cos(lambda); *alpha = atan2(sin_l*cos_e - tan(beta)*sin_e, cos_l); *delta = asin(sin(beta)*cos_e + cos(beta)*sin_e*sin_l); } /* computing julian dates (assuming gregorian calendar, thus this is * only valid for dates of 1582 oct 15 or later) (after duffett-smith, * section 4) */ static double julian_date(int y, int m, int d) { /* int y; year (e.g. 19xx) */ /* int m; month (jan=1, feb=2, ...) */ /* int d; day of month */ int A, B, C, D; double JD; /* lazy test to ensure gregorian calendar */ if (y < 1583) { FG_LOG( FG_EVENT, FG_ALERT, "WHOOPS! Julian dates only valid for 1582 oct 15 or later" ); } if ((m == 1) || (m == 2)) { y -= 1; m += 12; } A = y / 100; B = 2 - A + (A / 4); C = (int)(365.25 * y); D = (int)(30.6001 * (m + 1)); JD = B + C + D + d + 1720994.5; return JD; } /* compute greenwich mean sidereal time (GST) corresponding to a given * number of seconds since the unix epoch (after duffett-smith, * section 12) */ static double GST(time_t ssue) { /* time_t ssue; seconds since unix epoch */ double JD; double T, T0; double UT; struct tm *tm; tm = gmtime(&ssue); JD = julian_date(tm->tm_year+1900, tm->tm_mon+1, tm->tm_mday); T = (JD - 2451545) / 36525; T0 = ((T + 2.5862e-5) * T + 2400.051336) * T + 6.697374558; T0 = fmod(T0, 24.0); if (T0 < 0) T0 += 24; UT = tm->tm_hour + (tm->tm_min + tm->tm_sec / 60.0) / 60.0; T0 += UT * 1.002737909; T0 = fmod(T0, 24.0); if (T0 < 0) T0 += 24; return T0; } /* given a particular time (expressed in seconds since the unix * epoch), compute position on the earth (lat, lon) such that moon is * directly overhead. (lat, lon are reported in radians */ void fgMoonPosition(time_t ssue, double *lon, double *lat) { /* time_t ssue; seconds since unix epoch */ /* double *lat; (return) latitude */ /* double *lon; (return) longitude */ /* double lambda; */ double alpha, delta; double tmp; /* lambda = moon_ecliptic_longitude(ssue); */ /* ecliptic_to_equatorial(lambda, 0.0, &alpha, &delta); */ //ecliptic_to_equatorial (solarPosition.lonMoon, 0.0, &alpha, &delta); /* ********************************************************************** * NOTE: in the next function, each time the moon's position is updated, the * the moon's longitude is returned from solarSystem->moon. Note that the * moon's position is updated at a much higher frequency than the rate at * which the solar system's rebuilds occur. This is not a problem, however, * because the fgMoonPosition we're talking about here concerns the changing * position of the moon due to the daily rotation of the earth. * The ecliptic longitude, however, represents the position of the moon with * respect to the stars, and completes just one cycle over the course of a * year. Its therefore pretty safe to update the moon's longitude only once * every ten minutes. (Comment added by Durk Talsma). ************************************************************************/ ecliptic_to_equatorial( globals->get_ephem()->get_moon()->getLon(), 0.0, &alpha, &delta ); tmp = alpha - (FG_2PI/24)*GST(ssue); if (tmp < -FG_PI) { do tmp += FG_2PI; while (tmp < -FG_PI); } else if (tmp > FG_PI) { do tmp -= FG_2PI; while (tmp < -FG_PI); } *lon = tmp; *lat = delta; } /* given a particular time expressed in side real time at prime * meridian (GST), compute position on the earth (lat, lon) such that * moon is directly overhead. (lat, lon are reported in radians */ static void fgMoonPositionGST(double gst, double *lon, double *lat) { /* time_t ssue; seconds since unix epoch */ /* double *lat; (return) latitude */ /* double *lon; (return) longitude */ /* double lambda; */ double alpha, delta; double tmp; /* lambda = moon_ecliptic_longitude(ssue); */ /* ecliptic_to_equatorial(lambda, 0.0, &alpha, &delta); */ //ecliptic_to_equatorial (solarPosition.lonMoon, 0.0, &alpha, &delta); ecliptic_to_equatorial( globals->get_ephem()->get_moon()->getLon(), globals->get_ephem()->get_moon()->getLat(), &alpha, &delta ); // tmp = alpha - (FG_2PI/24)*GST(ssue); tmp = alpha - (FG_2PI/24)*gst; if (tmp < -FG_PI) { do tmp += FG_2PI; while (tmp < -FG_PI); } else if (tmp > FG_PI) { do tmp -= FG_2PI; while (tmp < -FG_PI); } *lon = tmp; *lat = delta; } // update the cur_time_params structure with the current moon position void fgUpdateMoonPos( void ) { fgLIGHT *l; FGViewer *v; sgVec3 nup, nmoon, v0, surface_to_moon; Point3D p, rel_moonpos; double dot, east_dot; double moon_gd_lat, sl_radius; l = &cur_light_params; SGTime *t = globals->get_time_params(); v = globals->get_current_view(); FG_LOG( FG_EVENT, FG_INFO, " Updating Moon position" ); // (not sure why there was two) // fgMoonPosition(t->cur_time, &l->moon_lon, &moon_gd_lat); fgMoonPositionGST(t->getGst(), &l->moon_lon, &moon_gd_lat); sgGeodToGeoc(moon_gd_lat, 0.0, &sl_radius, &l->moon_gc_lat); p = Point3D( l->moon_lon, l->moon_gc_lat, sl_radius ); l->fg_moonpos = sgPolarToCart3d(p); FG_LOG( FG_EVENT, FG_INFO, " t->cur_time = " << t->get_cur_time() ); FG_LOG( FG_EVENT, FG_INFO, " Moon Geodetic lat = " << moon_gd_lat << " Geocentric lat = " << l->moon_gc_lat ); // update the sun light vector sgSetVec4( l->moon_vec, l->fg_moonpos.x(), l->fg_moonpos.y(), l->fg_moonpos.z(), 0.0 ); sgNormalizeVec4( l->moon_vec ); sgCopyVec4( l->moon_vec_inv, l->moon_vec ); sgNegateVec4( l->moon_vec_inv ); // make sure these are directional light sources only l->moon_vec[3] = l->moon_vec_inv[3] = 0.0; // cout << " l->moon_vec = " << l->moon_vec[0] << "," << l->moon_vec[1] // << ","<< l->moon_vec[2] << endl; // calculate the moon's relative angle to local up sgCopyVec3( nup, v->get_local_up() ); sgSetVec3( nmoon, l->fg_moonpos.x(), l->fg_moonpos.y(), l->fg_moonpos.z() ); sgNormalizeVec3(nup); sgNormalizeVec3(nmoon); // cout << "nup = " << nup[0] << "," << nup[1] << "," // << nup[2] << endl; // cout << "nmoon = " << nmoon[0] << "," << nmoon[1] << "," // << nmoon[2] << endl; l->moon_angle = acos( sgScalarProductVec3( nup, nmoon ) ); cout << "moon angle relative to current location = " << l->moon_angle << endl; // calculate vector to moon's position on the earth's surface rel_moonpos = l->fg_moonpos - (v->get_view_pos() + scenery.center); v->set_to_moon( rel_moonpos.x(), rel_moonpos.y(), rel_moonpos.z() ); // printf( "Vector to moon = %.2f %.2f %.2f\n", // v->to_moon[0], v->to_moon[1], v->to_moon[2]); // make a vector to the current view position Point3D view_pos = v->get_view_pos(); sgSetVec3( v0, view_pos.x(), view_pos.y(), view_pos.z() ); // Given a vector from the view position to the point on the // earth's surface the moon is directly over, map into onto the // local plane representing "horizontal". sgmap_vec_onto_cur_surface_plane( v->get_local_up(), v0, v->get_to_moon(), surface_to_moon ); sgNormalizeVec3(surface_to_moon); v->set_surface_to_moon( surface_to_moon[0], surface_to_moon[1], surface_to_moon[2] ); // cout << "(sg) Surface direction to moon is " // << surface_to_moon[0] << "," // << surface_to_moon[1] << "," // << surface_to_moon[2] << endl; // cout << "Should be close to zero = " // << sgScalarProductVec3(nup, surface_to_moon) << endl; // calculate the angle between v->surface_to_moon and // v->surface_east. We do this so we can sort out the acos() // ambiguity. I wish I could think of a more efficient way ... :-( east_dot = sgScalarProductVec3( surface_to_moon, v->get_surface_east() ); // cout << " East dot product = " << east_dot << endl; // calculate the angle between v->surface_to_moon and // v->surface_south. this is how much we have to rotate the sky // for it to align with the moon dot = sgScalarProductVec3( surface_to_moon, v->get_surface_south() ); // cout << " Dot product = " << dot << endl; if ( east_dot >= 0 ) { l->moon_rotation = acos(dot); } else { l->moon_rotation = -acos(dot); } // cout << " Sky needs to rotate = " << angle << " rads = " // << angle * RAD_TO_DEG << " degrees." << endl; }