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flightgear/Time/fg_time.c
curt 273bd9bc6e Transform scenery coordinates earlier in pipeline when scenery is being 
created, not when it is being loaded.  Precalculate normals for each node
as average of the normals of each containing polygon so Garoude shading is
now supportable.
1997-11-14 00:26:49 +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) + 43200;
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 1.9 1997/11/14 00:26:50 curt
/* Transform scenery coordinates earlier in pipeline when scenery is being
/* created, not when it is being loaded. Precalculate normals for each node
/* as average of the normals of each containing polygon so Garoude shading is
/* now supportable.
/*
* 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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