1 // moonpos.cxx (basically, this is a slightly modified version of the 'sunpos.cxx' file, adapted from XEarth)
6 // code for calculating the position on the earth's surface for which
7 // the moon is directly overhead (adapted from _practical astronomy
8 // with your calculator, third edition_, peter duffett-smith,
9 // cambridge university press, 1988.)
11 // Copyright (C) 1989, 1990, 1993, 1994, 1995 Kirk Lauritz Johnson
13 // Parts of the source code (as marked) are:
14 // Copyright (C) 1989, 1990, 1991 by Jim Frost
15 // Copyright (C) 1992 by Jamie Zawinski <jwz@lucid.com>
17 // Permission to use, copy, modify and freely distribute xearth for
18 // non-commercial and not-for-profit purposes is hereby granted
19 // without fee, provided that both the above copyright notice and this
20 // permission notice appear in all copies and in supporting
23 // The author makes no representations about the suitability of this
24 // software for any purpose. It is provided "as is" without express or
27 // THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
28 // INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS,
29 // IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, INDIRECT
30 // OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
31 // LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
32 // NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
33 // CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
36 // (Log is kept at end of this file)
43 #include "Include/compiler.h"
44 #ifdef FG_HAVE_STD_INCLUDES
55 //#include <Astro/orbits.hxx>
56 #include <Astro/solarsystem.hxx>
57 #include <Debug/logstream.hxx>
58 #include <Include/fg_constants.h>
59 #include <Main/views.hxx>
60 #include <Math/fg_geodesy.hxx>
61 #include <Math/mat3.h>
62 #include <Math/point3d.hxx>
63 #include <Math/polar3d.hxx>
64 #include <Math/vector.hxx>
65 #include <Scenery/scenery.hxx>
67 #include "fg_time.hxx"
68 #include "moonpos.hxx"
70 extern SolarSystem *solarSystem;
76 * the epoch upon which these astronomical calculations are based is
77 * 1990 january 0.0, 631065600 seconds since the beginning of the
78 * "unix epoch" (00:00:00 GMT, Jan. 1, 1970)
80 * given a number of seconds since the start of the unix epoch,
81 * DaysSinceEpoch() computes the number of days since the start of the
82 * astronomical epoch (1990 january 0.0)
85 #define EpochStart (631065600)
86 #define DaysSinceEpoch(secs) (((secs)-EpochStart)*(1.0/(24*3600)))
89 * assuming the apparent orbit of the moon about the earth is circular,
90 * the rate at which the orbit progresses is given by RadsPerDay --
91 * FG_2PI radians per orbit divided by 365.242191 days per year:
94 #define RadsPerDay (FG_2PI/365.242191)
97 * details of moon's apparent orbit at epoch 1990.0 (after
98 * duffett-smith, table 6, section 46)
100 * Epsilon_g (ecliptic longitude at epoch 1990.0) 279.403303 degrees
101 * OmegaBar_g (ecliptic longitude of perigee) 282.768422 degrees
102 * Eccentricity (eccentricity of orbit) 0.016713
105 #define Epsilon_g (279.403303*(FG_2PI/360))
106 #define OmegaBar_g (282.768422*(FG_2PI/360))
107 #define Eccentricity (0.016713)
110 * MeanObliquity gives the mean obliquity of the earth's axis at epoch
111 * 1990.0 (computed as 23.440592 degrees according to the method given
112 * in duffett-smith, section 27)
114 #define MeanObliquity (23.440592*(FG_2PI/360))
116 /* static double solve_keplers_equation(double); */
117 /* static double moon_ecliptic_longitude(time_t); */
118 static void ecliptic_to_equatorial(double, double, double *, double *);
119 static double julian_date(int, int, int);
120 static double GST(time_t);
123 * solve Kepler's equation via Newton's method
124 * (after duffett-smith, section 47)
127 static double solve_keplers_equation(double M) {
133 delta = E - Eccentricity*sin(E) - M;
134 if (fabs(delta) <= 1e-10) break;
135 E -= delta / (1 - Eccentricity*cos(E));
143 /* compute ecliptic longitude of moon (in radians) (after
144 * duffett-smith, section 47) */
146 static double moon_ecliptic_longitude(time_t ssue) {
147 // time_t ssue; // seconds since unix epoch
152 D = DaysSinceEpoch(ssue);
156 if (N < 0) N += FG_2PI;
158 M_moon = N + Epsilon_g - OmegaBar_g;
159 if (M_moon < 0) M_moon += FG_2PI;
161 E = solve_keplers_equation(M_moon);
162 v = 2 * atan(sqrt((1+Eccentricity)/(1-Eccentricity)) * tan(E/2));
164 return (v + OmegaBar_g);
169 /* convert from ecliptic to equatorial coordinates (after
170 * duffett-smith, section 27) */
172 static void ecliptic_to_equatorial(double lambda, double beta,
173 double *alpha, double *delta) {
174 /* double lambda; ecliptic longitude */
175 /* double beta; ecliptic latitude */
176 /* double *alpha; (return) right ascension */
177 /* double *delta; (return) declination */
182 sin_e = sin(MeanObliquity);
183 cos_e = cos(MeanObliquity);
187 *alpha = atan2(sin_l*cos_e - tan(beta)*sin_e, cos_l);
188 *delta = asin(sin(beta)*cos_e + cos(beta)*sin_e*sin_l);
192 /* computing julian dates (assuming gregorian calendar, thus this is
193 * only valid for dates of 1582 oct 15 or later) (after duffett-smith,
196 static double julian_date(int y, int m, int d) {
197 /* int y; year (e.g. 19xx) */
198 /* int m; month (jan=1, feb=2, ...) */
199 /* int d; day of month */
204 /* lazy test to ensure gregorian calendar */
206 FG_LOG( FG_EVENT, FG_ALERT,
207 "WHOOPS! Julian dates only valid for 1582 oct 15 or later" );
210 if ((m == 1) || (m == 2)) {
217 C = (int)(365.25 * y);
218 D = (int)(30.6001 * (m + 1));
220 JD = B + C + D + d + 1720994.5;
226 /* compute greenwich mean sidereal time (GST) corresponding to a given
227 * number of seconds since the unix epoch (after duffett-smith,
229 static double GST(time_t ssue) {
230 /* time_t ssue; seconds since unix epoch */
239 JD = julian_date(tm->tm_year+1900, tm->tm_mon+1, tm->tm_mday);
240 T = (JD - 2451545) / 36525;
242 T0 = ((T + 2.5862e-5) * T + 2400.051336) * T + 6.697374558;
245 if (T0 < 0) T0 += 24;
247 UT = tm->tm_hour + (tm->tm_min + tm->tm_sec / 60.0) / 60.0;
249 T0 += UT * 1.002737909;
251 if (T0 < 0) T0 += 24;
257 /* given a particular time (expressed in seconds since the unix
258 * epoch), compute position on the earth (lat, lon) such that moon is
259 * directly overhead. (lat, lon are reported in radians */
261 void fgMoonPosition(time_t ssue, double *lon, double *lat) {
262 /* time_t ssue; seconds since unix epoch */
263 /* double *lat; (return) latitude */
264 /* double *lon; (return) longitude */
270 /* lambda = moon_ecliptic_longitude(ssue); */
271 /* ecliptic_to_equatorial(lambda, 0.0, &alpha, &delta); */
272 //ecliptic_to_equatorial (solarPosition.lonMoon, 0.0, &alpha, &delta);
274 /* **********************************************************************
275 * NOTE: in the next function, each time the moon's position is updated, the
276 * the moon's longitude is returned from solarSystem->moon. Note that the
277 * moon's position is updated at a much higher frequency than the rate at
278 * which the solar system's rebuilds occur. This is not a problem, however,
279 * because the fgMoonPosition we're talking about here concerns the changing
280 * position of the moon due to the daily rotation of the earth.
281 * The ecliptic longitude, however, represents the position of the moon with
282 * respect to the stars, and completes just one cycle over the course of a
283 * year. Its therefore pretty safe to update the moon's longitude only once
284 * every ten minutes. (Comment added by Durk Talsma).
285 ************************************************************************/
287 ecliptic_to_equatorial( SolarSystem::theSolarSystem->getMoon()->getLon(),
288 0.0, &alpha, &delta );
289 tmp = alpha - (FG_2PI/24)*GST(ssue);
292 while (tmp < -FG_PI);
293 } else if (tmp > FG_PI) {
295 while (tmp < -FG_PI);
303 /* given a particular time expressed in side real time at prime
304 * meridian (GST), compute position on the earth (lat, lon) such that
305 * moon is directly overhead. (lat, lon are reported in radians */
307 static void fgMoonPositionGST(double gst, double *lon, double *lat) {
308 /* time_t ssue; seconds since unix epoch */
309 /* double *lat; (return) latitude */
310 /* double *lon; (return) longitude */
316 /* lambda = moon_ecliptic_longitude(ssue); */
317 /* ecliptic_to_equatorial(lambda, 0.0, &alpha, &delta); */
318 //ecliptic_to_equatorial (solarPosition.lonMoon, 0.0, &alpha, &delta);
319 ecliptic_to_equatorial( SolarSystem::theSolarSystem->getMoon()->getLon(),
320 SolarSystem::theSolarSystem->getMoon()->getLat(),
323 // tmp = alpha - (FG_2PI/24)*GST(ssue);
324 tmp = alpha - (FG_2PI/24)*gst;
327 while (tmp < -FG_PI);
328 } else if (tmp > FG_PI) {
330 while (tmp < -FG_PI);
338 // update the cur_time_params structure with the current moon position
339 void fgUpdateMoonPos( void ) {
343 MAT3vec nup, nmoon, v0, surface_to_moon;
344 Point3D p, rel_moonpos;
345 double dot, east_dot;
346 double moon_gd_lat, sl_radius;
349 l = &cur_light_params;
350 t = &cur_time_params;
353 FG_LOG( FG_EVENT, FG_INFO, " Updating Moon position" );
355 // (not sure why there was two)
356 // fgMoonPosition(t->cur_time, &l->moon_lon, &moon_gd_lat);
357 fgMoonPositionGST(t->gst, &l->moon_lon, &moon_gd_lat);
359 fgGeodToGeoc(moon_gd_lat, 0.0, &sl_radius, &l->moon_gc_lat);
361 p = Point3D( l->moon_lon, l->moon_gc_lat, sl_radius );
362 l->fg_moonpos = fgPolarToCart3d(p);
364 FG_LOG( FG_EVENT, FG_INFO, " t->cur_time = " << t->cur_time );
365 FG_LOG( FG_EVENT, FG_INFO,
366 " Moon Geodetic lat = " << moon_gd_lat
367 << " Geocentric lat = " << l->moon_gc_lat );
369 // I think this will work better for generating the moon light vector
370 l->moon_vec[0] = l->fg_moonpos.x();
371 l->moon_vec[1] = l->fg_moonpos.y();
372 l->moon_vec[2] = l->fg_moonpos.z();
373 MAT3_NORMALIZE_VEC(l->moon_vec, ntmp);
374 MAT3_SCALE_VEC(l->moon_vec_inv, l->moon_vec, -1.0);
376 // make sure these are directional light sources only
377 l->moon_vec[3] = 0.0;
378 l->moon_vec_inv[3] = 0.0;
380 // printf(" l->moon_vec = %.2f %.2f %.2f\n", l->moon_vec[0], l->moon_vec[1],
383 // calculate the moon's relative angle to local up
384 MAT3_COPY_VEC(nup, v->get_local_up());
385 nmoon[0] = l->fg_moonpos.x();
386 nmoon[1] = l->fg_moonpos.y();
387 nmoon[2] = l->fg_moonpos.z();
388 MAT3_NORMALIZE_VEC(nup, ntmp);
389 MAT3_NORMALIZE_VEC(nmoon, ntmp);
391 l->moon_angle = acos(MAT3_DOT_PRODUCT(nup, nmoon));
392 // printf(" MOON ANGLE relative to current location = %.3f rads.\n",
395 // calculate vector to moon's position on the earth's surface
396 rel_moonpos = l->fg_moonpos - (v->get_view_pos() + scenery.center);
397 v->set_to_moon( rel_moonpos.x(), rel_moonpos.y(), rel_moonpos.z() );
398 // printf( "Vector to moon = %.2f %.2f %.2f\n",
399 // v->to_moon[0], v->to_moon[1], v->to_moon[2]);
401 // make a vector to the current view position
402 Point3D view_pos = v->get_view_pos();
403 MAT3_SET_VEC(v0, view_pos.x(), view_pos.y(), view_pos.z());
405 // Given a vector from the view position to the point on the
406 // earth's surface the moon is directly over, map into onto the
407 // local plane representing "horizontal".
408 map_vec_onto_cur_surface_plane( v->get_local_up(), v0, v->get_to_moon(),
410 MAT3_NORMALIZE_VEC(surface_to_moon, ntmp);
411 v->set_surface_to_moon( surface_to_moon[0], surface_to_moon[1],
412 surface_to_moon[2] );
413 // printf("Surface direction to moon is %.2f %.2f %.2f\n",
414 // v->surface_to_moon[0], v->surface_to_moon[1], v->surface_to_moon[2]);
415 // printf("Should be close to zero = %.2f\n",
416 // MAT3_DOT_PRODUCT(v->local_up, v->surface_to_moon));
418 // calculate the angle between v->surface_to_moon and
419 // v->surface_east. We do this so we can sort out the acos()
420 // ambiguity. I wish I could think of a more efficient way ... :-(
421 east_dot = MAT3_DOT_PRODUCT( surface_to_moon, v->get_surface_east() );
422 // printf(" East dot product = %.2f\n", east_dot);
424 // calculate the angle between v->surface_to_moon and
425 // v->surface_south. this is how much we have to rotate the sky
426 // for it to align with the moon
427 dot = MAT3_DOT_PRODUCT( surface_to_moon, v->get_surface_south() );
428 // printf(" Dot product = %.2f\n", dot);
429 if ( east_dot >= 0 ) {
430 l->moon_rotation = acos(dot);
432 l->moon_rotation = -acos(dot);
434 // printf(" Sky needs to rotate = %.3f rads = %.1f degrees.\n",
435 // angle, angle * RAD_TO_DEG); */
440 // Revision 1.1 1999/03/22 12:08:57 curt
443 // Revision 1.19 1999/01/07 20:25:37 curt
444 // Portability changes and updates from Bernie Bright.
446 // Revision 1.18 1998/12/09 18:50:36 curt
447 // Converted "class fgVIEW" to "class FGView" and updated to make data
448 // members private and make required accessor functions.
450 // Revision 1.17 1998/11/09 23:41:53 curt
451 // Log message clean ups.
453 // Revision 1.16 1998/11/07 19:07:14 curt
454 // Enable release builds using the --without-logging option to the configure
455 // script. Also a couple log message cleanups, plus some C to C++ comment
458 // Revision 1.15 1998/10/18 01:17:24 curt
461 // Revision 1.14 1998/10/17 01:34:32 curt
464 // Revision 1.13 1998/10/16 00:56:12 curt
465 // Converted to Point3D class.
467 // Revision 1.12 1998/09/15 04:27:50 curt
468 // Changes for new astro code.
470 // Revision 1.11 1998/08/12 21:13:22 curt
471 // Optimizations by Norman Vine.
473 // Revision 1.10 1998/07/22 21:45:39 curt
474 // fg_time.cxx: Removed call to ctime() in a printf() which should be harmless
475 // but seems to be triggering a bug.
476 // light.cxx: Added code to adjust fog color based on moonrise/moonset effects
477 // and view orientation. This is an attempt to match the fog color to the
478 // sky color in the center of the screen. You see discrepancies at the
479 // edges, but what else can be done?
480 // moonpos.cxx: Caculate local direction to moon here. (what compass direction
481 // do we need to face to point directly at moon)
483 // Revision 1.9 1998/07/08 14:48:39 curt
484 // polar3d.h renamed to polar3d.hxx
486 // Revision 1.8 1998/05/02 01:53:18 curt
487 // Fine tuning mktime() support because of varying behavior on different
490 // Revision 1.7 1998/04/30 12:36:05 curt
491 // C++-ifying a couple source files.
493 // Revision 1.6 1998/04/28 01:22:18 curt
494 // Type-ified fgTIME and fgVIEW.
496 // Revision 1.5 1998/04/26 05:10:05 curt
497 // "struct fgLIGHT" -> "fgLIGHT" because fgLIGHT is typedef'd.
499 // Revision 1.4 1998/04/25 22:06:34 curt
500 // Edited cvs log messages in source files ... bad bad bad!
502 // Revision 1.3 1998/04/25 20:24:03 curt
503 // Cleaned up initialization sequence to eliminate interdependencies
504 // between moon position, lighting, and view position. This creates a
505 // valid single pass initialization path.
507 // Revision 1.2 1998/04/24 00:52:31 curt
508 // Wrapped "#include <config.h>" in "#ifdef HAVE_CONFIG_H"
510 // Separated out lighting calcs into their own file.
512 // Revision 1.1 1998/04/22 13:24:07 curt
513 // C++ - ifiing the code a bit.
514 // Starting to reorginize some of the lighting calcs to use a table lookup.
516 // Revision 1.27 1998/04/03 22:12:57 curt
517 // Converting to Gnu autoconf system.
518 // Centralized time handling differences.
520 // Revision 1.26 1998/02/23 19:08:00 curt
521 // Incorporated Durk's Astro/ tweaks. Includes unifying the moon position
522 // calculation code between moon display, and other FG sections that use this
523 // for things like lighting.
525 // Revision 1.25 1998/02/09 15:07:53 curt
528 // Revision 1.24 1998/01/27 00:48:07 curt
529 // Incorporated Paul Bleisch's <pbleisch@acm.org> new debug message
530 // system and commandline/config file processing code.
532 // Revision 1.23 1998/01/19 19:27:21 curt
533 // Merged in make system changes from Bob Kuehne <rpk@sgi.com>
534 // This should simplify things tremendously.
536 // Revision 1.22 1998/01/19 18:40:40 curt
537 // Tons of little changes to clean up the code and to remove fatal errors
538 // when building with the c++ compiler.
540 // Revision 1.21 1997/12/30 23:10:19 curt
541 // Calculate lighting parameters here.
543 // Revision 1.20 1997/12/30 22:22:43 curt
544 // Further integration of event manager.
546 // Revision 1.19 1997/12/30 20:47:59 curt
547 // Integrated new event manager with subsystem initializations.
549 // Revision 1.18 1997/12/23 04:58:40 curt
550 // Tweaked the sky coloring a bit to build in structures to allow finer rgb
553 // Revision 1.17 1997/12/15 23:55:08 curt
554 // Add xgl wrappers for debugging.
555 // Generate terrain normals on the fly.
557 // Revision 1.16 1997/12/11 04:43:57 curt
558 // Fixed moon vector and lighting problems. I thing the moon is now lit
561 // Revision 1.15 1997/12/10 22:37:55 curt
562 // Prepended "fg" on the name of all global structures that didn't have it yet.
563 // i.e. "struct WEATHER {}" became "struct fgWEATHER {}"
565 // Revision 1.14 1997/12/09 04:25:39 curt
566 // Working on adding a global lighting params structure.
568 // Revision 1.13 1997/11/25 19:25:42 curt
569 // Changes to integrate Durk's moon/moon code updates + clean up.
571 // Revision 1.12 1997/11/15 18:15:39 curt
572 // Reverse direction of moon vector, so object normals can be more normal.
574 // Revision 1.11 1997/10/28 21:07:21 curt
575 // Changed GLUT/ -> Main/
577 // Revision 1.10 1997/09/13 02:00:09 curt
578 // Mostly working on stars and generating sidereal time for accurate star
581 // Revision 1.9 1997/09/05 14:17:31 curt
582 // More tweaking with stars.
584 // Revision 1.8 1997/09/05 01:36:04 curt
585 // Working on getting stars right.
587 // Revision 1.7 1997/09/04 02:17:40 curt
590 // Revision 1.6 1997/08/27 03:30:37 curt
591 // Changed naming scheme of basic shared structures.
593 // Revision 1.5 1997/08/22 21:34:41 curt
594 // Doing a bit of reorganizing and house cleaning.
596 // Revision 1.4 1997/08/19 23:55:09 curt
597 // Worked on better simulating real lighting.
599 // Revision 1.3 1997/08/13 20:23:49 curt
600 // The interface to moonpos now updates a global structure rather than returning
601 // current moon position.
603 // Revision 1.2 1997/08/06 00:24:32 curt
604 // Working on correct real time moon lighting.
606 // Revision 1.1 1997/08/01 15:27:56 curt