6 * code for calculating the position on the earth's surface for which
7 * the sun is directly overhead (adapted from _practical astronomy
8 * with your calculator, third edition_, peter duffett-smith,
9 * cambridge university press, 1988.)
13 * Copyright (C) 1989, 1990, 1993, 1994, 1995 Kirk Lauritz Johnson
15 * Parts of the source code (as marked) are:
16 * Copyright (C) 1989, 1990, 1991 by Jim Frost
17 * Copyright (C) 1992 by Jamie Zawinski <jwz@lucid.com>
19 * Permission to use, copy, modify and freely distribute xearth for
20 * non-commercial and not-for-profit purposes is hereby granted
21 * without fee, provided that both the above copyright notice and this
22 * permission notice appear in all copies and in supporting
25 * The author makes no representations about the suitability of this
26 * software for any purpose. It is provided "as is" without express or
29 * THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
30 * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS,
31 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, INDIRECT
32 * OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
33 * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
34 * NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
35 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
38 * (Log is kept at end of this file)
50 #include <Astro/orbits.hxx>
51 #include <Include/fg_constants.h>
52 #include <Main/views.hxx>
53 #include <Math/fg_geodesy.h>
54 #include <Math/mat3.h>
55 #include <Math/polar.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 ) {
279 /* if the 4th field is 0.0, this specifies a direction ... */
280 GLfloat white[4] = { 1.0, 1.0, 1.0, 1.0 };
282 GLfloat base_sky_color[4] = {0.60, 0.60, 0.90, 1.0};
284 GLfloat base_fog_color[4] = {0.70, 0.70, 0.70, 1.0};
285 double sun_gd_lat, sl_radius, temp;
286 double x_2, x_4, x_8, x_10;
287 double light, ambient, diffuse, sky_brightness;
288 static int time_warp = 0;
290 l = &cur_light_params;
291 t = &cur_time_params;
294 printf(" Updating Sun position\n");
296 time_warp += 0; /* increase this to make the world spin real fast */
298 fgSunPosition(t->cur_time + time_warp, &l->sun_lon, &sun_gd_lat);
300 fgGeodToGeoc(sun_gd_lat, 0.0, &sl_radius, &l->sun_gc_lat);
302 l->fg_sunpos = fgPolarToCart(l->sun_lon, l->sun_gc_lat, sl_radius);
304 /* printf(" Geodetic lat = %.5f Geocentric lat = %.5f\n", sun_gd_lat,
307 /* FALSE! (?> the sun position has to be translated just like
309 /* l->sun_vec_inv[0] = l->fg_sunpos.x - scenery_center.x; */
310 /* l->sun_vec_inv[1] = l->fg_sunpos.y - scenery_center.y; */
311 /* l->sun_vec_inv[2] = l->fg_sunpos.z - scenery_center.z; */
312 /* MAT3_SCALE_VEC(l->sun_vec, l->sun_vec_inv, -1.0); */
314 /* I think this will work better for generating the sun light vector */
315 l->sun_vec[0] = l->fg_sunpos.x;
316 l->sun_vec[1] = l->fg_sunpos.y;
317 l->sun_vec[2] = l->fg_sunpos.z;
318 MAT3_NORMALIZE_VEC(l->sun_vec, temp);
319 MAT3_SCALE_VEC(l->sun_vec_inv, l->sun_vec, -1.0);
321 /* make these are directional light sources only */
323 l->sun_vec_inv[3] = 0.0;
325 printf(" l->sun_vec = %.2f %.2f %.2f\n", l->sun_vec[0], l->sun_vec[1],
328 /* calculate the sun's relative angle to local up */
329 MAT3_COPY_VEC(nup, v->local_up);
330 nsun[0] = l->fg_sunpos.x;
331 nsun[1] = l->fg_sunpos.y;
332 nsun[2] = l->fg_sunpos.z;
333 MAT3_NORMALIZE_VEC(nup, temp);
334 MAT3_NORMALIZE_VEC(nsun, temp);
336 l->sun_angle = acos(MAT3_DOT_PRODUCT(nup, nsun));
337 printf(" SUN ANGLE relative to current location = %.3f rads.\n",
343 /* Revision 1.2 1998/04/24 00:52:31 curt
344 /* Wrapped "#include <config.h>" in "#ifdef HAVE_CONFIG_H"
346 /* Separated out lighting calcs into their own file.
348 * Revision 1.1 1998/04/22 13:24:07 curt
349 * C++ - ifiing the code a bit.
350 * Starting to reorginize some of the lighting calcs to use a table lookup.
352 * Revision 1.27 1998/04/03 22:12:57 curt
353 * Converting to Gnu autoconf system.
354 * Centralized time handling differences.
356 * Revision 1.26 1998/02/23 19:08:00 curt
357 * Incorporated Durk's Astro/ tweaks. Includes unifying the sun position
358 * calculation code between sun display, and other FG sections that use this
359 * for things like lighting.
361 * Revision 1.25 1998/02/09 15:07:53 curt
364 * Revision 1.24 1998/01/27 00:48:07 curt
365 * Incorporated Paul Bleisch's <bleisch@chromatic.com> new debug message
366 * system and commandline/config file processing code.
368 * Revision 1.23 1998/01/19 19:27:21 curt
369 * Merged in make system changes from Bob Kuehne <rpk@sgi.com>
370 * This should simplify things tremendously.
372 * Revision 1.22 1998/01/19 18:40:40 curt
373 * Tons of little changes to clean up the code and to remove fatal errors
374 * when building with the c++ compiler.
376 * Revision 1.21 1997/12/30 23:10:19 curt
377 * Calculate lighting parameters here.
379 * Revision 1.20 1997/12/30 22:22:43 curt
380 * Further integration of event manager.
382 * Revision 1.19 1997/12/30 20:47:59 curt
383 * Integrated new event manager with subsystem initializations.
385 * Revision 1.18 1997/12/23 04:58:40 curt
386 * Tweaked the sky coloring a bit to build in structures to allow finer rgb
389 * Revision 1.17 1997/12/15 23:55:08 curt
390 * Add xgl wrappers for debugging.
391 * Generate terrain normals on the fly.
393 * Revision 1.16 1997/12/11 04:43:57 curt
394 * Fixed sun vector and lighting problems. I thing the moon is now lit
397 * Revision 1.15 1997/12/10 22:37:55 curt
398 * Prepended "fg" on the name of all global structures that didn't have it yet.
399 * i.e. "struct WEATHER {}" became "struct fgWEATHER {}"
401 * Revision 1.14 1997/12/09 04:25:39 curt
402 * Working on adding a global lighting params structure.
404 * Revision 1.13 1997/11/25 19:25:42 curt
405 * Changes to integrate Durk's moon/sun code updates + clean up.
407 * Revision 1.12 1997/11/15 18:15:39 curt
408 * Reverse direction of sun vector, so object normals can be more normal.
410 * Revision 1.11 1997/10/28 21:07:21 curt
411 * Changed GLUT/ -> Main/
413 * Revision 1.10 1997/09/13 02:00:09 curt
414 * Mostly working on stars and generating sidereal time for accurate star
417 * Revision 1.9 1997/09/05 14:17:31 curt
418 * More tweaking with stars.
420 * Revision 1.8 1997/09/05 01:36:04 curt
421 * Working on getting stars right.
423 * Revision 1.7 1997/09/04 02:17:40 curt
426 * Revision 1.6 1997/08/27 03:30:37 curt
427 * Changed naming scheme of basic shared structures.
429 * Revision 1.5 1997/08/22 21:34:41 curt
430 * Doing a bit of reorganizing and house cleaning.
432 * Revision 1.4 1997/08/19 23:55:09 curt
433 * Worked on better simulating real lighting.
435 * Revision 1.3 1997/08/13 20:23:49 curt
436 * The interface to sunpos now updates a global structure rather than returning
437 * current sun position.
439 * Revision 1.2 1997/08/06 00:24:32 curt
440 * Working on correct real time sun lighting.
442 * Revision 1.1 1997/08/01 15:27:56 curt