1 /**************************************************************************
2 * fg_time.c -- data structures and routines for managing time related stuff.
4 * Written by Curtis Olson, started August 1997.
6 * Copyright (C) 1997 Curtis L. Olson - curt@infoplane.com
8 * This program is free software; you can redistribute it and/or
9 * modify it under the terms of the GNU General Public License as
10 * published by the Free Software Foundation; either version 2 of the
11 * License, or (at your option) any later version.
13 * This program is distributed in the hope that it will be useful, but
14 * WITHOUT ANY WARRANTY; without even the implied warranty of
15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16 * General Public License for more details.
18 * You should have received a copy of the GNU General Public License
19 * along with this program; if not, write to the Free Software
20 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
23 * (Log is kept at end of this file)
24 **************************************************************************/
33 #include <sys/time.h> /* for gettimeofday() */
34 #include <unistd.h> /* for gettimeofday() */
38 #include "../constants.h"
39 #include "../Flight/flight.h"
40 #include "../Time/fg_time.h"
43 #define DEGHR(x) ((x)/15.)
44 #define RADHR(x) DEGHR(x*RAD_TO_DEG)
47 struct fgTIME cur_time_params;
50 /* Initialize the time dependent variables */
52 void fgTimeInit(struct fgTIME *t) {
53 t->gst_diff = -9999.0;
57 /* given a date in months, mn, days, dy, years, yr, return the
58 * modified Julian date (number of days elapsed since 1900 jan 0.5),
59 * mjd. Adapted from Xephem. */
61 double cal_mjd (int mn, double dy, int yr) {
62 static double last_mjd, last_dy;
64 static int last_mn, last_yr;
68 if (mn == last_mn && yr == last_yr && dy == last_dy) {
74 y = (yr < 0) ? yr + 1 : yr;
80 if (yr < 1582 || (yr == 1582 && (mn < 10 || (mn == 10 && dy < 15)))) {
89 c = (long)((365.25*y) - 0.75) - 694025L;
91 c = (long)(365.25*y) - 694025L;
96 mjd = b + c + d + dy - 0.5;
107 /* given an mjd, return greenwich mean siderial time, gst */
109 double utc_gst (double mjd) {
111 double day = floor(mjd-0.5)+0.5;
112 double hr = (mjd-day)*24.0;
115 T = ((int)(mjd - 0.5) + 0.5 - J2000)/36525.0;
116 x = 24110.54841 + (8640184.812866 + (0.093104 - 6.2e-6 * T) * T) * T;
118 gst = (1.0/SIDRATE)*hr + x;
120 printf("gst => %.4f\n", gst);
126 /* given Julian Date and Longitude (decimal degrees West) compute and
127 * return Local Sidereal Time, in decimal hours.
129 * Provided courtesy of ecdowney@noao.edu (Elwood Downey)
132 double sidereal_precise (double mjd, double lng) {
136 /* printf ("Current Lst on JD %13.5f at %8.4f degrees West: ",
139 /* convert to required internal units */
142 /* compute LST and print */
144 lst = gst - RADHR (lng);
145 lst -= 24.0*floor(lst/24.0);
146 /* printf ("%7.4f\n", lst); */
153 /* return a courser but cheaper estimate of sidereal time */
154 double sidereal_course(struct tm *gmt, time_t now, double lng) {
155 time_t start, start_gmt;
158 double diff, part, days, hours, lst;
168 printf("COURSE: GMT = %d/%d/%2d %d:%02d:%02d\n",
169 gmt->tm_mon, gmt->tm_mday, gmt->tm_year,
170 gmt->tm_hour, gmt->tm_min, gmt->tm_sec);
174 mt.tm_year = gmt->tm_year;
182 daylight = mt.tm_isdst;
183 gettimeofday(&tv, &tz);
184 timezone = tz.tz_minuteswest * 60;
187 if ( daylight > 0 ) {
189 } else if ( daylight < 0 ) {
190 printf("OOOPS, big time problem in fg_time.c, no daylight savings info.\n");
193 offset = -(timezone / 3600 - daylight);
195 printf("Raw time zone offset = %ld\n", timezone);
196 printf("Daylight Savings = %d\n", daylight);
198 printf("Local hours from GMT = %ld\n", offset);
200 start_gmt = start - timezone + (daylight * 3600);
202 printf("March 21 noon (CST) = %ld\n", start);
203 printf("March 21 noon (GMT) = %ld\n", start_gmt);
205 diff = (now - start_gmt) / (3600.0 * 24.0);
207 printf("Time since 3/21/%2d GMT = %.2f\n", gmt->tm_year, diff);
209 part = fmod(diff, 1.0);
211 hours = gmt->tm_hour + gmt->tm_min/60.0 + gmt->tm_sec/3600.0;
213 lst = (days - lng)/15.0 + hours - 12;
215 while ( lst < 0.0 ) {
219 printf("days = %.1f hours = %.2f lon = %.2f lst = %.2f\n",
220 days, hours, lng, lst);
226 /* Update the time dependent variables */
228 void fgTimeUpdate(struct FLIGHT *f, struct fgTIME *t) {
229 double gst_precise, gst_course;
230 static long int warp = 0;
232 /* get current Unix calendar time (in seconds) */
235 t->cur_time = time(NULL) + 4 * 60 * 60;
237 printf("Current Unix calendar time = %ld warp = %ld\n", t->cur_time, warp);
239 /* get GMT break down for current time */
240 t->gmt = gmtime(&t->cur_time);
241 printf("Current GMT = %d/%d/%2d %d:%02d:%02d\n",
242 t->gmt->tm_mon+1, t->gmt->tm_mday, t->gmt->tm_year,
243 t->gmt->tm_hour, t->gmt->tm_min, t->gmt->tm_sec);
245 /* calculate modified Julian date */
246 t->mjd = cal_mjd ((int)(t->gmt->tm_mon+1), (double)t->gmt->tm_mday,
247 (int)(t->gmt->tm_year + 1900));
249 /* add in partial day */
250 t->mjd += (t->gmt->tm_hour / 24.0) + (t->gmt->tm_min / (24.0 * 60.0)) +
251 (t->gmt->tm_sec / (24.0 * 60.0 * 60.0));
253 /* convert "back" to Julian date + partial day (as a fraction of one) */
254 t->jd = t->mjd + MJD0;
255 printf("Current Julian Date = %.5f\n", t->jd);
257 printf("Current Longitude = %.3f\n", FG_Longitude * RAD_TO_DEG);
259 /* Calculate local side real time */
260 if ( t->gst_diff < -100.0 ) {
261 /* first time through do the expensive calculation & cheap
262 calculation to get the difference. */
263 printf("First time, doing precise gst\n");
264 t->gst = gst_precise = sidereal_precise(t->mjd, 0.00);
265 gst_course = sidereal_course(t->gmt, t->cur_time, 0.00);
266 t->gst_diff = gst_precise - gst_course;
269 sidereal_course(t->gmt, t->cur_time, -(FG_Longitude * RAD_TO_DEG))
272 /* course + difference should drift off very slowly */
274 sidereal_course(t->gmt, t->cur_time, 0.00) + t->gst_diff;
276 sidereal_course(t->gmt, t->cur_time, -(FG_Longitude * RAD_TO_DEG))
279 printf("Current lon=0.00 Sidereal Time = %.3f\n", t->gst);
280 printf("Current LOCAL Sidereal Time = %.3f (%.3f) (diff = %.3f)\n", t->lst,
281 sidereal_precise(t->mjd, -(FG_Longitude * RAD_TO_DEG)),
287 /* Revision 1.10 1997/11/15 18:16:42 curt
290 * Revision 1.9 1997/11/14 00:26:50 curt
291 * Transform scenery coordinates earlier in pipeline when scenery is being
292 * created, not when it is being loaded. Precalculate normals for each node
293 * as average of the normals of each containing polygon so Garoude shading is
296 * Revision 1.8 1997/10/25 03:30:08 curt
299 * Revision 1.7 1997/09/23 00:29:50 curt
300 * Tweaks to get things to compile with gcc-win32.
302 * Revision 1.6 1997/09/20 03:34:34 curt
303 * Still trying to get those durned stars aligned properly.
305 * Revision 1.5 1997/09/16 22:14:52 curt
306 * Tweaked time of day lighting equations. Don't draw stars during the day.
308 * Revision 1.4 1997/09/16 15:50:31 curt
309 * Working on star alignment and time issues.
311 * Revision 1.3 1997/09/13 02:00:08 curt
312 * Mostly working on stars and generating sidereal time for accurate star
315 * Revision 1.2 1997/08/27 03:30:35 curt
316 * Changed naming scheme of basic shared structures.
318 * Revision 1.1 1997/08/13 21:55:59 curt