1 // sunpos.c (taken 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.)
12 // Copyright (C) 1989, 1990, 1993, 1994, 1995 Kirk Lauritz Johnson
14 // Parts of the source code (as marked) are:
15 // Copyright (C) 1989, 1990, 1991 by Jim Frost
16 // Copyright (C) 1992 by Jamie Zawinski <jwz@lucid.com>
18 // Permission to use, copy, modify and freely distribute xearth for
19 // non-commercial and not-for-profit purposes is hereby granted
20 // without fee, provided that both the above copyright notice and this
21 // permission notice appear in all copies and in supporting
24 // The author makes no representations about the suitability of this
25 // software for any purpose. It is provided "as is" without express or
28 // THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
29 // INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS,
30 // IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, INDIRECT
31 // OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
32 // LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
33 // NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
34 // CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
37 // (Log is kept at end of this file)
48 #include <Astro/orbits.hxx>
49 #include <Include/fg_constants.h>
50 #include <Main/views.hxx>
51 #include <Math/fg_geodesy.h>
52 #include <Math/mat3.h>
53 #include <Math/polar.h>
54 #include <Math/vector.h>
55 #include <Scenery/scenery.h>
57 #include "fg_time.hxx"
65 * the epoch upon which these astronomical calculations are based is
66 * 1990 january 0.0, 631065600 seconds since the beginning of the
67 * "unix epoch" (00:00:00 GMT, Jan. 1, 1970)
69 * given a number of seconds since the start of the unix epoch,
70 * DaysSinceEpoch() computes the number of days since the start of the
71 * astronomical epoch (1990 january 0.0)
74 #define EpochStart (631065600)
75 #define DaysSinceEpoch(secs) (((secs)-EpochStart)*(1.0/(24*3600)))
78 * assuming the apparent orbit of the sun about the earth is circular,
79 * the rate at which the orbit progresses is given by RadsPerDay --
80 * FG_2PI radians per orbit divided by 365.242191 days per year:
83 #define RadsPerDay (FG_2PI/365.242191)
86 * details of sun's apparent orbit at epoch 1990.0 (after
87 * duffett-smith, table 6, section 46)
89 * Epsilon_g (ecliptic longitude at epoch 1990.0) 279.403303 degrees
90 * OmegaBar_g (ecliptic longitude of perigee) 282.768422 degrees
91 * Eccentricity (eccentricity of orbit) 0.016713
94 #define Epsilon_g (279.403303*(FG_2PI/360))
95 #define OmegaBar_g (282.768422*(FG_2PI/360))
96 #define Eccentricity (0.016713)
99 * MeanObliquity gives the mean obliquity of the earth's axis at epoch
100 * 1990.0 (computed as 23.440592 degrees according to the method given
101 * in duffett-smith, section 27)
103 #define MeanObliquity (23.440592*(FG_2PI/360))
105 /* static double solve_keplers_equation(double); */
106 /* static double sun_ecliptic_longitude(time_t); */
107 static void ecliptic_to_equatorial(double, double, double *, double *);
108 static double julian_date(int, int, int);
109 static double GST(time_t);
112 * solve Kepler's equation via Newton's method
113 * (after duffett-smith, section 47)
116 static double solve_keplers_equation(double M) {
122 delta = E - Eccentricity*sin(E) - M;
123 if (fabs(delta) <= 1e-10) break;
124 E -= delta / (1 - Eccentricity*cos(E));
132 /* compute ecliptic longitude of sun (in radians) (after
133 * duffett-smith, section 47) */
135 static double sun_ecliptic_longitude(time_t ssue) {
136 // time_t ssue; // seconds since unix epoch
141 D = DaysSinceEpoch(ssue);
145 if (N < 0) N += FG_2PI;
147 M_sun = N + Epsilon_g - OmegaBar_g;
148 if (M_sun < 0) M_sun += FG_2PI;
150 E = solve_keplers_equation(M_sun);
151 v = 2 * atan(sqrt((1+Eccentricity)/(1-Eccentricity)) * tan(E/2));
153 return (v + OmegaBar_g);
158 /* convert from ecliptic to equatorial coordinates (after
159 * duffett-smith, section 27) */
161 static void ecliptic_to_equatorial(double lambda, double beta,
162 double *alpha, double *delta) {
163 /* double lambda; ecliptic longitude */
164 /* double beta; ecliptic latitude */
165 /* double *alpha; (return) right ascension */
166 /* double *delta; (return) declination */
170 sin_e = sin(MeanObliquity);
171 cos_e = cos(MeanObliquity);
173 *alpha = atan2(sin(lambda)*cos_e - tan(beta)*sin_e, cos(lambda));
174 *delta = asin(sin(beta)*cos_e + cos(beta)*sin_e*sin(lambda));
178 /* computing julian dates (assuming gregorian calendar, thus this is
179 * only valid for dates of 1582 oct 15 or later) (after duffett-smith,
182 static double julian_date(int y, int m, int d) {
183 /* int y; year (e.g. 19xx) */
184 /* int m; month (jan=1, feb=2, ...) */
185 /* int d; day of month */
190 /* lazy test to ensure gregorian calendar */
192 printf("WHOOPS! Julian dates only valid for 1582 oct 15 or later\n");
195 if ((m == 1) || (m == 2)) {
202 C = (int)(365.25 * y);
203 D = (int)(30.6001 * (m + 1));
205 JD = B + C + D + d + 1720994.5;
211 /* compute greenwich mean sidereal time (GST) corresponding to a given
212 * number of seconds since the unix epoch (after duffett-smith,
214 static double GST(time_t ssue) {
215 /* time_t ssue; seconds since unix epoch */
224 JD = julian_date(tm->tm_year+1900, tm->tm_mon+1, tm->tm_mday);
225 T = (JD - 2451545) / 36525;
227 T0 = ((T + 2.5862e-5) * T + 2400.051336) * T + 6.697374558;
230 if (T0 < 0) T0 += 24;
232 UT = tm->tm_hour + (tm->tm_min + tm->tm_sec / 60.0) / 60.0;
234 T0 += UT * 1.002737909;
236 if (T0 < 0) T0 += 24;
242 /* given a particular time (expressed in seconds since the unix
243 * epoch), compute position on the earth (lat, lon) such that sun is
244 * directly overhead. (lat, lon are reported in radians */
246 void fgSunPosition(time_t ssue, double *lon, double *lat) {
247 /* time_t ssue; seconds since unix epoch */
248 /* double *lat; (return) latitude */
249 /* double *lon; (return) longitude */
255 /* lambda = sun_ecliptic_longitude(ssue); */
256 /* ecliptic_to_equatorial(lambda, 0.0, &alpha, &delta); */
257 ecliptic_to_equatorial (solarPosition.lonSun, 0.0, &alpha, &delta);
259 tmp = alpha - (FG_2PI/24)*GST(ssue);
262 while (tmp < -FG_PI);
263 } else if (tmp > FG_PI) {
265 while (tmp < -FG_PI);
273 // update the cur_time_params structure with the current sun position
274 void fgUpdateSunPos( void ) {
278 MAT3vec nup, nsun, v0;
279 double sun_gd_lat, sl_radius;
282 l = &cur_light_params;
283 t = &cur_time_params;
286 printf(" Updating Sun position\n");
288 fgSunPosition(t->cur_time, &l->sun_lon, &sun_gd_lat);
289 fgSunPosition(t->cur_time, &l->sun_lon, &sun_gd_lat);
291 fgGeodToGeoc(sun_gd_lat, 0.0, &sl_radius, &l->sun_gc_lat);
293 l->fg_sunpos = fgPolarToCart(l->sun_lon, l->sun_gc_lat, sl_radius);
295 printf( " t->cur_time = %ld\n", t->cur_time);
296 printf( " Sun Geodetic lat = %.5f Geocentric lat = %.5f\n",
297 sun_gd_lat, l->sun_gc_lat);
299 // I think this will work better for generating the sun light vector
300 l->sun_vec[0] = l->fg_sunpos.x;
301 l->sun_vec[1] = l->fg_sunpos.y;
302 l->sun_vec[2] = l->fg_sunpos.z;
303 MAT3_NORMALIZE_VEC(l->sun_vec, ntmp);
304 MAT3_SCALE_VEC(l->sun_vec_inv, l->sun_vec, -1.0);
306 // make sure these are directional light sources only
308 l->sun_vec_inv[3] = 0.0;
310 printf(" l->sun_vec = %.2f %.2f %.2f\n", l->sun_vec[0], l->sun_vec[1],
313 // calculate the sun's relative angle to local up
314 MAT3_COPY_VEC(nup, v->local_up);
315 nsun[0] = l->fg_sunpos.x;
316 nsun[1] = l->fg_sunpos.y;
317 nsun[2] = l->fg_sunpos.z;
318 MAT3_NORMALIZE_VEC(nup, ntmp);
319 MAT3_NORMALIZE_VEC(nsun, ntmp);
321 l->sun_angle = acos(MAT3_DOT_PRODUCT(nup, nsun));
322 printf(" SUN ANGLE relative to current location = %.3f rads.\n",
325 // calculate vector to sun's position on the earth's surface
326 v->to_sun[0] = l->fg_sunpos.x - (v->view_pos.x + scenery.center.x);
327 v->to_sun[1] = l->fg_sunpos.y - (v->view_pos.y + scenery.center.y);
328 v->to_sun[2] = l->fg_sunpos.z - (v->view_pos.z + scenery.center.z);
329 // printf( "Vector to sun = %.2f %.2f %.2f\n",
330 // v->to_sun[0], v->to_sun[1], v->to_sun[2]);
332 // make a vector to the current view position
333 MAT3_SET_VEC(v0, v->view_pos.x, v->view_pos.y, v->view_pos.z);
335 // Given a vector from the view position to the point on the
336 // earth's surface the sun is directly over, map into onto the
337 // local plane representing "horizontal".
338 map_vec_onto_cur_surface_plane(v->local_up, v0, v->to_sun,
340 MAT3_NORMALIZE_VEC(v->surface_to_sun, ntmp);
341 // printf("Surface direction to sun is %.2f %.2f %.2f\n",
342 // v->surface_to_sun[0], v->surface_to_sun[1], v->surface_to_sun[2]);
343 // printf("Should be close to zero = %.2f\n",
344 // MAT3_DOT_PRODUCT(v->local_up, v->surface_to_sun));
349 // Revision 1.3 1998/04/25 20:24:03 curt
350 // Cleaned up initialization sequence to eliminate interdependencies
351 // between sun position, lighting, and view position. This creates a
352 // valid single pass initialization path.
354 // Revision 1.2 1998/04/24 00:52:31 curt
355 // Wrapped "#include <config.h>" in "#ifdef HAVE_CONFIG_H"
357 // Separated out lighting calcs into their own file.
359 // Revision 1.1 1998/04/22 13:24:07 curt
360 // C++ - ifiing the code a bit.
361 // Starting to reorginize some of the lighting calcs to use a table lookup.
363 // Revision 1.27 1998/04/03 22:12:57 curt
364 // Converting to Gnu autoconf system.
365 // Centralized time handling differences.
367 // Revision 1.26 1998/02/23 19:08:00 curt
368 // Incorporated Durk's Astro/ tweaks. Includes unifying the sun position
369 // calculation code between sun display, and other FG sections that use this
370 // for things like lighting.
372 // Revision 1.25 1998/02/09 15:07:53 curt
375 // Revision 1.24 1998/01/27 00:48:07 curt
376 // Incorporated Paul Bleisch's <bleisch@chromatic.com> new debug message
377 // system and commandline/config file processing code.
379 // Revision 1.23 1998/01/19 19:27:21 curt
380 // Merged in make system changes from Bob Kuehne <rpk@sgi.com>
381 // This should simplify things tremendously.
383 // Revision 1.22 1998/01/19 18:40:40 curt
384 // Tons of little changes to clean up the code and to remove fatal errors
385 // when building with the c++ compiler.
387 // Revision 1.21 1997/12/30 23:10:19 curt
388 // Calculate lighting parameters here.
390 // Revision 1.20 1997/12/30 22:22:43 curt
391 // Further integration of event manager.
393 // Revision 1.19 1997/12/30 20:47:59 curt
394 // Integrated new event manager with subsystem initializations.
396 // Revision 1.18 1997/12/23 04:58:40 curt
397 // Tweaked the sky coloring a bit to build in structures to allow finer rgb
400 // Revision 1.17 1997/12/15 23:55:08 curt
401 // Add xgl wrappers for debugging.
402 // Generate terrain normals on the fly.
404 // Revision 1.16 1997/12/11 04:43:57 curt
405 // Fixed sun vector and lighting problems. I thing the moon is now lit
408 // Revision 1.15 1997/12/10 22:37:55 curt
409 // Prepended "fg" on the name of all global structures that didn't have it yet.
410 // i.e. "struct WEATHER {}" became "struct fgWEATHER {}"
412 // Revision 1.14 1997/12/09 04:25:39 curt
413 // Working on adding a global lighting params structure.
415 // Revision 1.13 1997/11/25 19:25:42 curt
416 // Changes to integrate Durk's moon/sun code updates + clean up.
418 // Revision 1.12 1997/11/15 18:15:39 curt
419 // Reverse direction of sun vector, so object normals can be more normal.
421 // Revision 1.11 1997/10/28 21:07:21 curt
422 // Changed GLUT/ -> Main/
424 // Revision 1.10 1997/09/13 02:00:09 curt
425 // Mostly working on stars and generating sidereal time for accurate star
428 // Revision 1.9 1997/09/05 14:17:31 curt
429 // More tweaking with stars.
431 // Revision 1.8 1997/09/05 01:36:04 curt
432 // Working on getting stars right.
434 // Revision 1.7 1997/09/04 02:17:40 curt
437 // Revision 1.6 1997/08/27 03:30:37 curt
438 // Changed naming scheme of basic shared structures.
440 // Revision 1.5 1997/08/22 21:34:41 curt
441 // Doing a bit of reorganizing and house cleaning.
443 // Revision 1.4 1997/08/19 23:55:09 curt
444 // Worked on better simulating real lighting.
446 // Revision 1.3 1997/08/13 20:23:49 curt
447 // The interface to sunpos now updates a global structure rather than returning
448 // current sun position.
450 // Revision 1.2 1997/08/06 00:24:32 curt
451 // Working on correct real time sun lighting.
453 // Revision 1.1 1997/08/01 15:27:56 curt