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 "../constants.h"
34 #include "../Flight/flight.h"
35 #include "../Time/fg_time.h"
38 #define DEGHR(x) ((x)/15.)
39 #define RADHR(x) DEGHR(x*RAD_TO_DEG)
42 struct fgTIME cur_time_params;
45 /* Initialize the time dependent variables */
47 void fgTimeInit(struct fgTIME *t) {
48 t->lst_diff = -9999.0;
52 /* given a date in months, mn, days, dy, years, yr, return the
53 * modified Julian date (number of days elapsed since 1900 jan 0.5),
54 * mjd. Adapted from Xephem. */
56 double cal_mjd (int mn, double dy, int yr) {
57 static double last_mjd, last_dy;
59 static int last_mn, last_yr;
63 if (mn == last_mn && yr == last_yr && dy == last_dy) {
69 y = (yr < 0) ? yr + 1 : yr;
75 if (yr < 1582 || (yr == 1582 && (mn < 10 || (mn == 10 && dy < 15)))) {
84 c = (long)((365.25*y) - 0.75) - 694025L;
86 c = (long)(365.25*y) - 694025L;
91 mjd = b + c + d + dy - 0.5;
102 /* given an mjd, return greenwich mean siderial time, gst */
104 double utc_gst (double mjd) {
106 double day = floor(mjd-0.5)+0.5;
107 double hr = (mjd-day)*24.0;
110 T = ((int)(mjd - 0.5) + 0.5 - J2000)/36525.0;
111 x = 24110.54841 + (8640184.812866 + (0.093104 - 6.2e-6 * T) * T) * T;
113 gst = (1.0/SIDRATE)*hr + x;
119 /* given Julian Date and Longitude (decimal degrees West) compute and
120 * return Local Sidereal Time, in decimal hours.
122 * Provided courtesy of ecdowney@noao.edu (Elwood Downey)
125 double sidereal_precise (double mjd, double lng) {
129 /* printf ("Current Lst on JD %13.5f at %8.4f degrees West: ",
132 /* convert to required internal units */
135 /* compute LST and print */
137 lst = gst - RADHR (lng);
138 lst -= 24.0*floor(lst/24.0);
139 printf ("%7.4f\n", lst);
146 /* return a courser but cheaper estimate of sidereal time */
147 double sidereal_course(struct tm *gmt, time_t now, double lng) {
148 time_t start, start_gmt;
151 double diff, part, days, hours, lst;
154 printf("COURSE: GMT = %d/%d/%2d %d:%02d:%02d\n",
155 gmt->tm_mon, gmt->tm_mday, gmt->tm_year,
156 gmt->tm_hour, gmt->tm_min, gmt->tm_sec);
160 mt.tm_year = gmt->tm_year;
167 offset = -(timezone / 3600 - daylight);
169 printf("Raw time zone offset = %ld\n", timezone);
170 printf("Daylight Savings = %d\n", daylight);
172 printf("Local hours from GMT = %ld\n", offset);
174 start_gmt = start - timezone + (daylight * 3600);
176 printf("March 21 noon (CST) = %ld\n", start);
177 printf("March 21 noon (GMT) = %ld\n", start_gmt);
179 diff = (now - start_gmt) / (3600.0 * 24.0);
181 printf("Time since 3/21/%2d GMT = %.2f\n", gmt->tm_year, diff);
183 part = fmod(diff, 1.0);
185 hours = gmt->tm_hour + gmt->tm_min/60.0 + gmt->tm_sec/3600.0;
187 lst = (days - lng)/15.0 + hours - 12;
189 while ( lst < 0.0 ) {
193 printf("days = %.1f hours = %.2f lon = %.2f lst = %.2f\n",
194 days, hours, lng, lst);
200 /* Update the time dependent variables */
202 void fgTimeUpdate(struct FLIGHT *f, struct fgTIME *t) {
203 double lst_precise, lst_course;
205 /* get current Unix calendar time (in seconds) */
206 t->cur_time = time(NULL);
207 printf("Current Unix calendar time = %ld\n", t->cur_time);
209 /* get GMT break down for current time */
210 t->gmt = gmtime(&t->cur_time);
211 printf("Current GMT = %d/%d/%2d %d:%02d:%02d\n",
212 t->gmt->tm_mon+1, t->gmt->tm_mday, t->gmt->tm_year,
213 t->gmt->tm_hour, t->gmt->tm_min, t->gmt->tm_sec);
215 /* calculate modified Julian date */
216 t->mjd = cal_mjd ((int)(t->gmt->tm_mon+1), (double)t->gmt->tm_mday,
217 (int)(t->gmt->tm_year + 1900));
219 /* add in partial day */
220 t->mjd += (t->gmt->tm_hour / 24.0) + (t->gmt->tm_min / (24.0 * 60.0)) +
221 (t->gmt->tm_sec / (24.0 * 60.0 * 60.0));
223 /* convert "back" to Julian date + partial day (as a fraction of one) */
224 t->jd = t->mjd + MJD0;
225 printf("Current Julian Date = %.5f\n", t->jd);
227 printf("Current Longitude = %.3f\n", FG_Longitude * RAD_TO_DEG);
229 /* Calculate local side real time */
230 if ( t->lst_diff < -100.0 ) {
231 /* first time through do the expensive calculation & cheap
232 calculation to get the difference. */
233 printf("First time, doing precise lst\n");
234 t->lst = lst_precise =
235 sidereal_precise(t->mjd, -(FG_Longitude * RAD_TO_DEG));
237 sidereal_course(t->gmt, t->cur_time, -(FG_Longitude * RAD_TO_DEG));
238 t->lst_diff = lst_precise - lst_course;
240 /* course + difference should drift off very slowly */
242 sidereal_course(t->gmt, t->cur_time, -(FG_Longitude * RAD_TO_DEG))
245 printf("Current Sidereal Time = %.3f (%.3f) (diff = %.3f)\n", t->lst,
246 sidereal_precise(t->mjd, -(FG_Longitude * RAD_TO_DEG)),
252 /* Revision 1.4 1997/09/16 15:50:31 curt
253 /* Working on star alignment and time issues.
255 * Revision 1.3 1997/09/13 02:00:08 curt
256 * Mostly working on stars and generating sidereal time for accurate star
259 * Revision 1.2 1997/08/27 03:30:35 curt
260 * Changed naming scheme of basic shared structures.
262 * Revision 1.1 1997/08/13 21:55:59 curt