+++ /dev/null
-// moonpos.cxx (basically, this is a slightly modified version of the
-// 'sunpos.cxx' file, adapted from XEarth)
-//
-// kirk johnson
-// july 1993
-//
-// code for calculating the position on the earth's surface for which
-// the moon is directly overhead (adapted from _practical astronomy
-// with your calculator, third edition_, peter duffett-smith,
-// cambridge university press, 1988.)
-//
-// Copyright (C) 1989, 1990, 1993, 1994, 1995 Kirk Lauritz Johnson
-//
-// Parts of the source code (as marked) are:
-// Copyright (C) 1989, 1990, 1991 by Jim Frost
-// Copyright (C) 1992 by Jamie Zawinski <jwz@lucid.com>
-//
-// Permission to use, copy, modify and freely distribute xearth for
-// non-commercial and not-for-profit purposes is hereby granted
-// without fee, provided that both the above copyright notice and this
-// permission notice appear in all copies and in supporting
-// documentation.
-//
-// The author makes no representations about the suitability of this
-// software for any purpose. It is provided "as is" without express or
-// implied warranty.
-//
-// THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
-// INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS,
-// IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, INDIRECT
-// OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
-// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
-// NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
-// CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
-//
-// $Id$
-
-
-#ifdef HAVE_CONFIG_H
-# include <config.h>
-#endif
-
-#include <simgear/compiler.h>
-
-#ifdef SG_HAVE_STD_INCLUDES
-# include <cmath>
-# include <cstdio>
-# include <ctime>
-#else
-# include <math.h>
-# include <stdio.h>
-# include <time.h>
-#endif
-
-#include <simgear/constants.h>
-#include <simgear/debug/logstream.hxx>
-#include <simgear/ephemeris/ephemeris.hxx>
-#include <simgear/math/point3d.hxx>
-#include <simgear/math/polar3d.hxx>
-#include <simgear/math/sg_geodesy.hxx>
-#include <simgear/math/vector.hxx>
-#include <simgear/timing/sg_time.hxx>
-
-#include <Main/globals.hxx>
-#include <Main/viewer.hxx>
-#include <Scenery/scenery.hxx>
-#include <Time/light.hxx>
-
-#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 --
- * SG_2PI radians per orbit divided by 365.242191 days per year:
- */
-
-#define RadsPerDay (SG_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*(SGD_2PI/360))
-#define OmegaBar_g (282.768422*(SGD_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*(SGD_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, SG_2PI);
- if (N < 0) N += SG_2PI;
-
- M_moon = N + Epsilon_g - OmegaBar_g;
- if (M_moon < 0) M_moon += SG_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) {
- SG_LOG( SG_EVENT, SG_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 - (SGD_2PI/24)*GST(ssue);
- if (tmp < -SGD_PI) {
- do tmp += SGD_2PI;
- while (tmp < -SGD_PI);
- } else if (tmp > SGD_PI) {
- do tmp -= SGD_2PI;
- while (tmp < -SGD_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 - (SG_2PI/24)*GST(ssue);
- tmp = alpha - (SGD_2PI/24)*gst;
- if (tmp < -SGD_PI) {
- do tmp += SGD_2PI;
- while (tmp < -SGD_PI);
- } else if (tmp > SGD_PI) {
- do tmp -= SGD_2PI;
- while (tmp < -SGD_PI);
- }
-
- *lon = tmp;
- *lat = delta;
-}
-
-
-// update the cur_time_params structure with the current moon position
-void fgUpdateMoonPos( void ) {
- sgVec3 nup, nmoon;
- Point3D rel_moonpos;
- double dot, east_dot;
- double moon_gd_lat, sl_radius;
-
- // vector in cartesian coordinates from current position to the
- // postion on the earth's surface the moon is directly over
- sgVec3 to_moon;
-
- // surface direction to go to head towards moon
- sgVec3 surface_to_moon;
-
- FGLight *l = (FGLight *)(globals->get_subsystem("lighting"));
- SGTime *t = globals->get_time_params();
- FGViewer *v = globals->get_current_view();
-
- SG_LOG( SG_EVENT, SG_INFO, " Updating Moon position" );
-
- double moon_l;
- fgMoonPositionGST(t->getGst(), &moon_l, &moon_gd_lat);
- l->set_moon_lon(moon_l);
-
- sgGeodToGeoc(moon_gd_lat, 0.0, &sl_radius, &moon_l);
- l->set_moon_gc_lat(moon_l);
-
- Point3D p = Point3D( l->get_moon_lon(), l->get_moon_gc_lat(), sl_radius );
- l->set_moonpos( sgPolarToCart3d(p) );
-
- SG_LOG( SG_EVENT, SG_INFO, " t->cur_time = " << t->get_cur_time() );
- SG_LOG( SG_EVENT, SG_INFO,
- " Moon Geodetic lat = " << moon_gd_lat
- << " Geocentric lat = " << l->get_moon_gc_lat() );
-
- // update the sun light vector
- sgSetVec4( l->moon_vec(), l->get_moonpos().x(),
- l->get_moonpos().y(), l->get_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_world_up() );
- sgSetVec3( nmoon, l->get_moonpos().x(),
- l->get_moonpos().y(), l->get_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->set_moon_angle( acos( sgScalarProductVec3( nup, nmoon ) ) );
- SG_LOG( SG_EVENT, SG_INFO, "moon angle relative to current location = "
- << l->get_moon_angle() );
-
- // calculate vector to moon's position on the earth's surface
- Point3D vp( v->get_view_pos()[0],
- v->get_view_pos()[1],
- v->get_view_pos()[2] );
- rel_moonpos = l->get_moonpos()-(vp + globals->get_scenery()->get_center());
- sgSetVec3( to_moon, rel_moonpos.x(), rel_moonpos.y(), rel_moonpos.z() );
- // printf( "Vector to moon = %.2f %.2f %.2f\n",
- // to_moon[0], to_moon[1], to_moon[2]);
-
- // 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_world_up(), v->get_view_pos(),
- to_moon, surface_to_moon );
- sgNormalizeVec3(surface_to_moon);
- // 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->set_moon_rotation( acos(dot) );
- } else {
- l->set_moon_rotation( -acos(dot) );
- }
- // cout << " Sky needs to rotate = " << angle << " rads = "
- // << angle * SGD_RADIANS_TO_DEGREES << " degrees." << endl;
-}
-
-
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