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flightgear/Time/fg_time.c
curt d06ebf220e Misc. tweaks.
1997-10-25 03:30:02 +00:00

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/**************************************************************************
* fg_time.c -- data structures and routines for managing time related stuff.
*
* Written by Curtis Olson, started August 1997.
*
* Copyright (C) 1997 Curtis L. Olson - curt@infoplane.com
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation; either version 2 of the
* License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*
* $Id$
* (Log is kept at end of this file)
**************************************************************************/
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#ifdef WIN32
#include <sys/time.h> /* for gettimeofday() */
#include <unistd.h> /* for gettimeofday() */
#endif
#include "fg_time.h"
#include "../constants.h"
#include "../Flight/flight.h"
#include "../Time/fg_time.h"
#define DEGHR(x) ((x)/15.)
#define RADHR(x) DEGHR(x*RAD_TO_DEG)
struct fgTIME cur_time_params;
/* Initialize the time dependent variables */
void fgTimeInit(struct fgTIME *t) {
t->gst_diff = -9999.0;
}
/* given a date in months, mn, days, dy, years, yr, return the
* modified Julian date (number of days elapsed since 1900 jan 0.5),
* mjd. Adapted from Xephem. */
double cal_mjd (int mn, double dy, int yr) {
static double last_mjd, last_dy;
double mjd;
static int last_mn, last_yr;
int b, d, m, y;
long c;
if (mn == last_mn && yr == last_yr && dy == last_dy) {
mjd = last_mjd;
return(mjd);
}
m = mn;
y = (yr < 0) ? yr + 1 : yr;
if (mn < 3) {
m += 12;
y -= 1;
}
if (yr < 1582 || (yr == 1582 && (mn < 10 || (mn == 10 && dy < 15)))) {
b = 0;
} else {
int a;
a = y/100;
b = 2 - a + a/4;
}
if (y < 0) {
c = (long)((365.25*y) - 0.75) - 694025L;
} else {
c = (long)(365.25*y) - 694025L;
}
d = 30.6001*(m+1);
mjd = b + c + d + dy - 0.5;
last_mn = mn;
last_dy = dy;
last_yr = yr;
last_mjd = mjd;
return(mjd);
}
/* given an mjd, return greenwich mean siderial time, gst */
double utc_gst (double mjd) {
double gst;
double day = floor(mjd-0.5)+0.5;
double hr = (mjd-day)*24.0;
double T, x;
T = ((int)(mjd - 0.5) + 0.5 - J2000)/36525.0;
x = 24110.54841 + (8640184.812866 + (0.093104 - 6.2e-6 * T) * T) * T;
x /= 3600.0;
gst = (1.0/SIDRATE)*hr + x;
printf("gst => %.4f\n", gst);
return(gst);
}
/* given Julian Date and Longitude (decimal degrees West) compute and
* return Local Sidereal Time, in decimal hours.
*
* Provided courtesy of ecdowney@noao.edu (Elwood Downey)
*/
double sidereal_precise (double mjd, double lng) {
double gst;
double lst;
/* printf ("Current Lst on JD %13.5f at %8.4f degrees West: ",
mjd + MJD0, lng); */
/* convert to required internal units */
lng *= DEG_TO_RAD;
/* compute LST and print */
gst = utc_gst (mjd);
lst = gst - RADHR (lng);
lst -= 24.0*floor(lst/24.0);
/* printf ("%7.4f\n", lst); */
/* that's all */
return (lst);
}
/* return a courser but cheaper estimate of sidereal time */
double sidereal_course(struct tm *gmt, time_t now, double lng) {
time_t start, start_gmt;
struct tm mt;
long int offset;
double diff, part, days, hours, lst;
#ifdef WIN32
int daylight;
long int timezone;
struct timeval tv;
struct timezone tz;
#endif
printf("COURSE: GMT = %d/%d/%2d %d:%02d:%02d\n",
gmt->tm_mon, gmt->tm_mday, gmt->tm_year,
gmt->tm_hour, gmt->tm_min, gmt->tm_sec);
mt.tm_mon = 2;
mt.tm_mday = 21;
mt.tm_year = gmt->tm_year;
mt.tm_hour = 12;
mt.tm_min = 0;
mt.tm_sec = 0;
start = mktime(&mt);
#ifdef WIN32
daylight = mt.tm_isdst;
gettimeofday(&tv, &tz);
timezone = tz.tz_minuteswest * 60;
#endif
if ( daylight > 0 ) {
daylight = 1;
} else if ( daylight < 0 ) {
printf("OOOPS, big time problem in fg_time.c, no daylight savings info.\n");
}
offset = -(timezone / 3600 - daylight);
printf("Raw time zone offset = %ld\n", timezone);
printf("Daylight Savings = %d\n", daylight);
printf("Local hours from GMT = %ld\n", offset);
start_gmt = start - timezone + (daylight * 3600);
printf("March 21 noon (CST) = %ld\n", start);
printf("March 21 noon (GMT) = %ld\n", start_gmt);
diff = (now - start_gmt) / (3600.0 * 24.0);
printf("Time since 3/21/%2d GMT = %.2f\n", gmt->tm_year, diff);
part = fmod(diff, 1.0);
days = diff - part;
hours = gmt->tm_hour + gmt->tm_min/60.0 + gmt->tm_sec/3600.0;
lst = (days - lng)/15.0 + hours - 12;
while ( lst < 0.0 ) {
lst += 24.0;
}
printf("days = %.1f hours = %.2f lon = %.2f lst = %.2f\n",
days, hours, lng, lst);
return(lst);
}
/* Update the time dependent variables */
void fgTimeUpdate(struct FLIGHT *f, struct fgTIME *t) {
double gst_precise, gst_course;
static long int warp = 0;
/* get current Unix calendar time (in seconds) */
warp += 60;
/* warp = 0; */
t->cur_time = time(NULL);
t->cur_time += warp;
printf("Current Unix calendar time = %ld warp = %ld\n", t->cur_time, warp);
/* get GMT break down for current time */
t->gmt = gmtime(&t->cur_time);
printf("Current GMT = %d/%d/%2d %d:%02d:%02d\n",
t->gmt->tm_mon+1, t->gmt->tm_mday, t->gmt->tm_year,
t->gmt->tm_hour, t->gmt->tm_min, t->gmt->tm_sec);
/* calculate modified Julian date */
t->mjd = cal_mjd ((int)(t->gmt->tm_mon+1), (double)t->gmt->tm_mday,
(int)(t->gmt->tm_year + 1900));
/* add in partial day */
t->mjd += (t->gmt->tm_hour / 24.0) + (t->gmt->tm_min / (24.0 * 60.0)) +
(t->gmt->tm_sec / (24.0 * 60.0 * 60.0));
/* convert "back" to Julian date + partial day (as a fraction of one) */
t->jd = t->mjd + MJD0;
printf("Current Julian Date = %.5f\n", t->jd);
printf("Current Longitude = %.3f\n", FG_Longitude * RAD_TO_DEG);
/* Calculate local side real time */
if ( t->gst_diff < -100.0 ) {
/* first time through do the expensive calculation & cheap
calculation to get the difference. */
printf("First time, doing precise gst\n");
t->gst = gst_precise = sidereal_precise(t->mjd, 0.00);
gst_course = sidereal_course(t->gmt, t->cur_time, 0.00);
t->gst_diff = gst_precise - gst_course;
t->lst =
sidereal_course(t->gmt, t->cur_time, -(FG_Longitude * RAD_TO_DEG))
+ t->gst_diff;
} else {
/* course + difference should drift off very slowly */
t->gst =
sidereal_course(t->gmt, t->cur_time, 0.00) + t->gst_diff;
t->lst =
sidereal_course(t->gmt, t->cur_time, -(FG_Longitude * RAD_TO_DEG))
+ t->gst_diff;
}
printf("Current lon=0.00 Sidereal Time = %.3f\n", t->gst);
printf("Current LOCAL Sidereal Time = %.3f (%.3f) (diff = %.3f)\n", t->lst,
sidereal_precise(t->mjd, -(FG_Longitude * RAD_TO_DEG)),
t->gst_diff);
}
/* $Log$
/* Revision 1.8 1997/10/25 03:30:08 curt
/* Misc. tweaks.
/*
* Revision 1.7 1997/09/23 00:29:50 curt
* Tweaks to get things to compile with gcc-win32.
*
* Revision 1.6 1997/09/20 03:34:34 curt
* Still trying to get those durned stars aligned properly.
*
* Revision 1.5 1997/09/16 22:14:52 curt
* Tweaked time of day lighting equations. Don't draw stars during the day.
*
* Revision 1.4 1997/09/16 15:50:31 curt
* Working on star alignment and time issues.
*
* Revision 1.3 1997/09/13 02:00:08 curt
* Mostly working on stars and generating sidereal time for accurate star
* placement.
*
* Revision 1.2 1997/08/27 03:30:35 curt
* Changed naming scheme of basic shared structures.
*
* Revision 1.1 1997/08/13 21:55:59 curt
* Initial revision.
*
*/
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