1 // sunpos.cxx (adapted from XEarth)
5 // code for calculating the position on the earth's surface for which
6 // the sun is directly overhead (adapted from _practical astronomy
7 // with your calculator, third edition_, peter duffett-smith,
8 // cambridge university press, 1988.)
10 // Copyright (C) 1989, 1990, 1993, 1994, 1995 Kirk Lauritz Johnson
12 // Parts of the source code (as marked) are:
13 // Copyright (C) 1989, 1990, 1991 by Jim Frost
14 // Copyright (C) 1992 by Jamie Zawinski <jwz@lucid.com>
16 // Permission to use, copy, modify and freely distribute xearth for
17 // non-commercial and not-for-profit purposes is hereby granted
18 // without fee, provided that both the above copyright notice and this
19 // permission notice appear in all copies and in supporting
22 // The author makes no representations about the suitability of this
23 // software for any purpose. It is provided "as is" without express or
26 // THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
27 // INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS,
28 // IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, INDIRECT
29 // OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
30 // LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
31 // NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
32 // CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
35 // (Log is kept at end of this file)
46 //#include <Astro/orbits.hxx>
47 #include <Astro/solarsystem.hxx>
48 #include <Include/fg_constants.h>
49 #include <Main/views.hxx>
50 #include <Math/fg_geodesy.hxx>
51 #include <Math/mat3.h>
52 #include <Math/point3d.hxx>
53 #include <Math/polar3d.hxx>
54 #include <Math/vector.hxx>
55 #include <Scenery/scenery.hxx>
57 #include "fg_time.hxx"
60 extern SolarSystem *solarSystem;
66 * the epoch upon which these astronomical calculations are based is
67 * 1990 january 0.0, 631065600 seconds since the beginning of the
68 * "unix epoch" (00:00:00 GMT, Jan. 1, 1970)
70 * given a number of seconds since the start of the unix epoch,
71 * DaysSinceEpoch() computes the number of days since the start of the
72 * astronomical epoch (1990 january 0.0)
75 #define EpochStart (631065600)
76 #define DaysSinceEpoch(secs) (((secs)-EpochStart)*(1.0/(24*3600)))
79 * assuming the apparent orbit of the sun about the earth is circular,
80 * the rate at which the orbit progresses is given by RadsPerDay --
81 * FG_2PI radians per orbit divided by 365.242191 days per year:
84 #define RadsPerDay (FG_2PI/365.242191)
87 * details of sun's apparent orbit at epoch 1990.0 (after
88 * duffett-smith, table 6, section 46)
90 * Epsilon_g (ecliptic longitude at epoch 1990.0) 279.403303 degrees
91 * OmegaBar_g (ecliptic longitude of perigee) 282.768422 degrees
92 * Eccentricity (eccentricity of orbit) 0.016713
95 #define Epsilon_g (279.403303*(FG_2PI/360))
96 #define OmegaBar_g (282.768422*(FG_2PI/360))
97 #define Eccentricity (0.016713)
100 * MeanObliquity gives the mean obliquity of the earth's axis at epoch
101 * 1990.0 (computed as 23.440592 degrees according to the method given
102 * in duffett-smith, section 27)
104 #define MeanObliquity (23.440592*(FG_2PI/360))
106 /* static double solve_keplers_equation(double); */
107 /* static double sun_ecliptic_longitude(time_t); */
108 static void ecliptic_to_equatorial(double, double, double *, double *);
109 static double julian_date(int, int, int);
110 static double GST(time_t);
113 * solve Kepler's equation via Newton's method
114 * (after duffett-smith, section 47)
117 static double solve_keplers_equation(double M) {
123 delta = E - Eccentricity*sin(E) - M;
124 if (fabs(delta) <= 1e-10) break;
125 E -= delta / (1 - Eccentricity*cos(E));
133 /* compute ecliptic longitude of sun (in radians) (after
134 * duffett-smith, section 47) */
136 static double sun_ecliptic_longitude(time_t ssue) {
137 // time_t ssue; // seconds since unix epoch
142 D = DaysSinceEpoch(ssue);
146 if (N < 0) N += FG_2PI;
148 M_sun = N + Epsilon_g - OmegaBar_g;
149 if (M_sun < 0) M_sun += FG_2PI;
151 E = solve_keplers_equation(M_sun);
152 v = 2 * atan(sqrt((1+Eccentricity)/(1-Eccentricity)) * tan(E/2));
154 return (v + OmegaBar_g);
159 /* convert from ecliptic to equatorial coordinates (after
160 * duffett-smith, section 27) */
162 static void ecliptic_to_equatorial(double lambda, double beta,
163 double *alpha, double *delta) {
164 /* double lambda; ecliptic longitude */
165 /* double beta; ecliptic latitude */
166 /* double *alpha; (return) right ascension */
167 /* double *delta; (return) declination */
172 sin_e = sin(MeanObliquity);
173 cos_e = cos(MeanObliquity);
177 *alpha = atan2(sin_l*cos_e - tan(beta)*sin_e, cos_l);
178 *delta = asin(sin(beta)*cos_e + cos(beta)*sin_e*sin_l);
182 /* computing julian dates (assuming gregorian calendar, thus this is
183 * only valid for dates of 1582 oct 15 or later) (after duffett-smith,
186 static double julian_date(int y, int m, int d) {
187 /* int y; year (e.g. 19xx) */
188 /* int m; month (jan=1, feb=2, ...) */
189 /* int d; day of month */
194 /* lazy test to ensure gregorian calendar */
196 printf("WHOOPS! Julian dates only valid for 1582 oct 15 or later\n");
199 if ((m == 1) || (m == 2)) {
206 C = (int)(365.25 * y);
207 D = (int)(30.6001 * (m + 1));
209 JD = B + C + D + d + 1720994.5;
215 /* compute greenwich mean sidereal time (GST) corresponding to a given
216 * number of seconds since the unix epoch (after duffett-smith,
218 static double GST(time_t ssue) {
219 /* time_t ssue; seconds since unix epoch */
228 JD = julian_date(tm->tm_year+1900, tm->tm_mon+1, tm->tm_mday);
229 T = (JD - 2451545) / 36525;
231 T0 = ((T + 2.5862e-5) * T + 2400.051336) * T + 6.697374558;
234 if (T0 < 0) T0 += 24;
236 UT = tm->tm_hour + (tm->tm_min + tm->tm_sec / 60.0) / 60.0;
238 T0 += UT * 1.002737909;
240 if (T0 < 0) T0 += 24;
246 /* given a particular time (expressed in seconds since the unix
247 * epoch), compute position on the earth (lat, lon) such that sun is
248 * directly overhead. (lat, lon are reported in radians */
250 void fgSunPosition(time_t ssue, double *lon, double *lat) {
251 /* time_t ssue; seconds since unix epoch */
252 /* double *lat; (return) latitude */
253 /* double *lon; (return) longitude */
259 /* lambda = sun_ecliptic_longitude(ssue); */
260 /* ecliptic_to_equatorial(lambda, 0.0, &alpha, &delta); */
261 //ecliptic_to_equatorial (solarPosition.lonSun, 0.0, &alpha, &delta);
263 /* **********************************************************************
264 * NOTE: in the next function, each time the sun's position is updated, the
265 * the sun's longitude is returned from solarSystem->sun. Note that the
266 * sun's position is updated at a much higher frequency than the rate at
267 * which the solar system's rebuilds occur. This is not a problem, however,
268 * because the fgSunPosition we're talking about here concerns the changing
269 * position of the sun due to the daily rotation of the earth.
270 * The ecliptic longitude, however, represents the position of the sun with
271 * respect to the stars, and completes just one cycle over the course of a
272 * year. Its therefore pretty safe to update the sun's longitude only once
273 * every ten minutes. (Comment added by Durk Talsma).
274 ************************************************************************/
276 ecliptic_to_equatorial( SolarSystem::theSolarSystem->getSun()->getLon(),
277 0.0, &alpha, &delta );
278 tmp = alpha - (FG_2PI/24)*GST(ssue);
281 while (tmp < -FG_PI);
282 } else if (tmp > FG_PI) {
284 while (tmp < -FG_PI);
292 /* given a particular time expressed in side real time at prime
293 * meridian (GST), compute position on the earth (lat, lon) such that
294 * sun is directly overhead. (lat, lon are reported in radians */
296 static void fgSunPositionGST(double gst, double *lon, double *lat) {
297 /* time_t ssue; seconds since unix epoch */
298 /* double *lat; (return) latitude */
299 /* double *lon; (return) longitude */
305 /* lambda = sun_ecliptic_longitude(ssue); */
306 /* ecliptic_to_equatorial(lambda, 0.0, &alpha, &delta); */
307 //ecliptic_to_equatorial (solarPosition.lonSun, 0.0, &alpha, &delta);
308 ecliptic_to_equatorial( SolarSystem::theSolarSystem->getSun()->getLon(),
309 0.0, &alpha, &delta );
311 // tmp = alpha - (FG_2PI/24)*GST(ssue);
312 tmp = alpha - (FG_2PI/24)*gst;
315 while (tmp < -FG_PI);
316 } else if (tmp > FG_PI) {
318 while (tmp < -FG_PI);
326 // update the cur_time_params structure with the current sun position
327 void fgUpdateSunPos( void ) {
331 MAT3vec nup, nsun, v0;
332 Point3D p, rel_sunpos;
333 double dot, east_dot;
334 double sun_gd_lat, sl_radius;
337 l = &cur_light_params;
338 t = &cur_time_params;
341 printf(" Updating Sun position\n");
343 // (not sure why there was two)
344 // fgSunPosition(t->cur_time, &l->sun_lon, &sun_gd_lat);
345 fgSunPositionGST(t->gst, &l->sun_lon, &sun_gd_lat);
347 fgGeodToGeoc(sun_gd_lat, 0.0, &sl_radius, &l->sun_gc_lat);
349 p.setvals( l->sun_lon, l->sun_gc_lat, sl_radius );
350 l->fg_sunpos = fgPolarToCart3d(p);
352 printf( " t->cur_time = %ld\n", t->cur_time);
353 printf( " Sun Geodetic lat = %.5f Geocentric lat = %.5f\n",
354 sun_gd_lat, l->sun_gc_lat);
356 // I think this will work better for generating the sun light vector
357 l->sun_vec[0] = l->fg_sunpos.x();
358 l->sun_vec[1] = l->fg_sunpos.y();
359 l->sun_vec[2] = l->fg_sunpos.z();
360 MAT3_NORMALIZE_VEC(l->sun_vec, ntmp);
361 MAT3_SCALE_VEC(l->sun_vec_inv, l->sun_vec, -1.0);
363 // make sure these are directional light sources only
365 l->sun_vec_inv[3] = 0.0;
367 // printf(" l->sun_vec = %.2f %.2f %.2f\n", l->sun_vec[0], l->sun_vec[1],
370 // calculate the sun's relative angle to local up
371 MAT3_COPY_VEC(nup, v->local_up);
372 nsun[0] = l->fg_sunpos.x();
373 nsun[1] = l->fg_sunpos.y();
374 nsun[2] = l->fg_sunpos.z();
375 MAT3_NORMALIZE_VEC(nup, ntmp);
376 MAT3_NORMALIZE_VEC(nsun, ntmp);
378 l->sun_angle = acos(MAT3_DOT_PRODUCT(nup, nsun));
379 // printf(" SUN ANGLE relative to current location = %.3f rads.\n",
382 // calculate vector to sun's position on the earth's surface
383 rel_sunpos = l->fg_sunpos - (v->view_pos + scenery.center);
384 v->to_sun[0] = rel_sunpos.x();
385 v->to_sun[1] = rel_sunpos.y();
386 v->to_sun[2] = rel_sunpos.z();
387 // printf( "Vector to sun = %.2f %.2f %.2f\n",
388 // v->to_sun[0], v->to_sun[1], v->to_sun[2]);
390 // make a vector to the current view position
391 MAT3_SET_VEC(v0, v->view_pos.x(), v->view_pos.y(), v->view_pos.z());
393 // Given a vector from the view position to the point on the
394 // earth's surface the sun is directly over, map into onto the
395 // local plane representing "horizontal".
396 map_vec_onto_cur_surface_plane(v->local_up, v0, v->to_sun,
398 MAT3_NORMALIZE_VEC(v->surface_to_sun, ntmp);
399 // printf("Surface direction to sun is %.2f %.2f %.2f\n",
400 // v->surface_to_sun[0], v->surface_to_sun[1], v->surface_to_sun[2]);
401 // printf("Should be close to zero = %.2f\n",
402 // MAT3_DOT_PRODUCT(v->local_up, v->surface_to_sun));
404 // calculate the angle between v->surface_to_sun and
405 // v->surface_east. We do this so we can sort out the acos()
406 // ambiguity. I wish I could think of a more efficient way ... :-(
407 east_dot = MAT3_DOT_PRODUCT(v->surface_to_sun, v->surface_east);
408 // printf(" East dot product = %.2f\n", east_dot);
410 // calculate the angle between v->surface_to_sun and
411 // v->surface_south. this is how much we have to rotate the sky
412 // for it to align with the sun
413 dot = MAT3_DOT_PRODUCT(v->surface_to_sun, v->surface_south);
414 // printf(" Dot product = %.2f\n", dot);
415 if ( east_dot >= 0 ) {
416 l->sun_rotation = acos(dot);
418 l->sun_rotation = -acos(dot);
420 // printf(" Sky needs to rotate = %.3f rads = %.1f degrees.\n",
421 // angle, angle * RAD_TO_DEG); */
426 // Revision 1.14 1998/10/17 01:34:32 curt
429 // Revision 1.13 1998/10/16 00:56:12 curt
430 // Converted to Point3D class.
432 // Revision 1.12 1998/09/15 04:27:50 curt
433 // Changes for new astro code.
435 // Revision 1.11 1998/08/12 21:13:22 curt
436 // Optimizations by Norman Vine.
438 // Revision 1.10 1998/07/22 21:45:39 curt
439 // fg_time.cxx: Removed call to ctime() in a printf() which should be harmless
440 // but seems to be triggering a bug.
441 // light.cxx: Added code to adjust fog color based on sunrise/sunset effects
442 // and view orientation. This is an attempt to match the fog color to the
443 // sky color in the center of the screen. You see discrepancies at the
444 // edges, but what else can be done?
445 // sunpos.cxx: Caculate local direction to sun here. (what compass direction
446 // do we need to face to point directly at sun)
448 // Revision 1.9 1998/07/08 14:48:39 curt
449 // polar3d.h renamed to polar3d.hxx
451 // Revision 1.8 1998/05/02 01:53:18 curt
452 // Fine tuning mktime() support because of varying behavior on different
455 // Revision 1.7 1998/04/30 12:36:05 curt
456 // C++-ifying a couple source files.
458 // Revision 1.6 1998/04/28 01:22:18 curt
459 // Type-ified fgTIME and fgVIEW.
461 // Revision 1.5 1998/04/26 05:10:05 curt
462 // "struct fgLIGHT" -> "fgLIGHT" because fgLIGHT is typedef'd.
464 // Revision 1.4 1998/04/25 22:06:34 curt
465 // Edited cvs log messages in source files ... bad bad bad!
467 // Revision 1.3 1998/04/25 20:24:03 curt
468 // Cleaned up initialization sequence to eliminate interdependencies
469 // between sun position, lighting, and view position. This creates a
470 // valid single pass initialization path.
472 // Revision 1.2 1998/04/24 00:52:31 curt
473 // Wrapped "#include <config.h>" in "#ifdef HAVE_CONFIG_H"
475 // Separated out lighting calcs into their own file.
477 // Revision 1.1 1998/04/22 13:24:07 curt
478 // C++ - ifiing the code a bit.
479 // Starting to reorginize some of the lighting calcs to use a table lookup.
481 // Revision 1.27 1998/04/03 22:12:57 curt
482 // Converting to Gnu autoconf system.
483 // Centralized time handling differences.
485 // Revision 1.26 1998/02/23 19:08:00 curt
486 // Incorporated Durk's Astro/ tweaks. Includes unifying the sun position
487 // calculation code between sun display, and other FG sections that use this
488 // for things like lighting.
490 // Revision 1.25 1998/02/09 15:07:53 curt
493 // Revision 1.24 1998/01/27 00:48:07 curt
494 // Incorporated Paul Bleisch's <pbleisch@acm.org> new debug message
495 // system and commandline/config file processing code.
497 // Revision 1.23 1998/01/19 19:27:21 curt
498 // Merged in make system changes from Bob Kuehne <rpk@sgi.com>
499 // This should simplify things tremendously.
501 // Revision 1.22 1998/01/19 18:40:40 curt
502 // Tons of little changes to clean up the code and to remove fatal errors
503 // when building with the c++ compiler.
505 // Revision 1.21 1997/12/30 23:10:19 curt
506 // Calculate lighting parameters here.
508 // Revision 1.20 1997/12/30 22:22:43 curt
509 // Further integration of event manager.
511 // Revision 1.19 1997/12/30 20:47:59 curt
512 // Integrated new event manager with subsystem initializations.
514 // Revision 1.18 1997/12/23 04:58:40 curt
515 // Tweaked the sky coloring a bit to build in structures to allow finer rgb
518 // Revision 1.17 1997/12/15 23:55:08 curt
519 // Add xgl wrappers for debugging.
520 // Generate terrain normals on the fly.
522 // Revision 1.16 1997/12/11 04:43:57 curt
523 // Fixed sun vector and lighting problems. I thing the moon is now lit
526 // Revision 1.15 1997/12/10 22:37:55 curt
527 // Prepended "fg" on the name of all global structures that didn't have it yet.
528 // i.e. "struct WEATHER {}" became "struct fgWEATHER {}"
530 // Revision 1.14 1997/12/09 04:25:39 curt
531 // Working on adding a global lighting params structure.
533 // Revision 1.13 1997/11/25 19:25:42 curt
534 // Changes to integrate Durk's moon/sun code updates + clean up.
536 // Revision 1.12 1997/11/15 18:15:39 curt
537 // Reverse direction of sun vector, so object normals can be more normal.
539 // Revision 1.11 1997/10/28 21:07:21 curt
540 // Changed GLUT/ -> Main/
542 // Revision 1.10 1997/09/13 02:00:09 curt
543 // Mostly working on stars and generating sidereal time for accurate star
546 // Revision 1.9 1997/09/05 14:17:31 curt
547 // More tweaking with stars.
549 // Revision 1.8 1997/09/05 01:36:04 curt
550 // Working on getting stars right.
552 // Revision 1.7 1997/09/04 02:17:40 curt
555 // Revision 1.6 1997/08/27 03:30:37 curt
556 // Changed naming scheme of basic shared structures.
558 // Revision 1.5 1997/08/22 21:34:41 curt
559 // Doing a bit of reorganizing and house cleaning.
561 // Revision 1.4 1997/08/19 23:55:09 curt
562 // Worked on better simulating real lighting.
564 // Revision 1.3 1997/08/13 20:23:49 curt
565 // The interface to sunpos now updates a global structure rather than returning
566 // current sun position.
568 // Revision 1.2 1997/08/06 00:24:32 curt
569 // Working on correct real time sun lighting.
571 // Revision 1.1 1997/08/01 15:27:56 curt