flightgear/Simulator/Time/fg_time.cxx

// fg_time.cxx -- 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.
//
// $Id$


#ifdef HAVE_CONFIG_H
#  include <config.h>
#endif

#include <Include/compiler.h>

#ifdef FG_HAVE_STD_INCLUDES
#  include <cmath>
#  include <cstdio>
#  include <cstdlib>
#  include <ctime>
#else
#  include <math.h>
#  include <stdio.h>
#  include <stdlib.h>
#  include <time.h>
#endif

#ifdef HAVE_SYS_TIMEB_H
#  include <sys/timeb.h> // for ftime() and struct timeb
#endif
#ifdef HAVE_UNISTD_H
#  include <unistd.h>    // for gettimeofday()
#endif
#ifdef HAVE_SYS_TIME_H
#  include <sys/time.h>  // for get/setitimer, gettimeofday, struct timeval
#endif

#include <Debug/logstream.hxx>
#include <Astro/sky.hxx>
#include <Astro/solarsystem.hxx>
#include <FDM/flight.hxx>
#include <Include/fg_constants.h>
#include <Main/options.hxx>
#include <Time/light.hxx>

#include "fg_time.hxx"


#define DEGHR(x)        ((x)/15.)
#define RADHR(x)        DEGHR(x*RAD_TO_DEG)

// #define MK_TIME_IS_GMT 0         // default value
// #define TIME_ZONE_OFFSET_WORK 0  // default value


fgTIME cur_time_params;


// Force an update of the sky and lighting parameters
static void local_update_sky_and_lighting_params( void ) {
    // fgSunInit();
    SolarSystem::theSolarSystem->rebuild();
    cur_light_params.Update();
    fgSkyColorsInit();
}


// Initialize the time dependent variables
void fgTimeInit(fgTIME *t) {
    FG_LOG( FG_EVENT, FG_INFO, "Initializing Time" );

    t->gst_diff = -9999.0;

    FG_LOG( FG_EVENT, FG_DEBUG, 
	    "time offset = " << current_options.get_time_offset() );

    t->warp = current_options.get_time_offset();
    t->warp_delta = 0;

    t->pause = current_options.get_pause();
}


// 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 = (int)(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 sidereal 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;

    FG_LOG( FG_EVENT, FG_DEBUG, "  gst => " << 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);
}


// Fix up timezone if using ftime()
long int fix_up_timezone( long int timezone_orig ) {
#if !defined( HAVE_GETTIMEOFDAY ) && defined( HAVE_FTIME )
    // ftime() needs a little extra help finding the current timezone
    struct timeb current;
    ftime(&current);
    return( current.timezone * 60 );
#else
    return( timezone_orig );
#endif
}


// Return time_t for Sat Mar 21 12:00:00 GMT
//
// I believe the mktime() has a SYSV vs. BSD behavior difference.
//
// The BSD style mktime() is nice because it returns its result
// assuming you have specified the input time in GMT
//
// The SYSV style mktime() is a pain because it returns its result
// assuming you have specified the input time in your local timezone.
// Therefore you have to go to extra trouble to convert back to GMT.
//
// If you are having problems with incorrectly positioned astronomical
// bodies, this is a really good place to start looking.

time_t get_start_gmt(int year) {
    struct tm mt;

    // For now we assume that if daylight is not defined in
    // /usr/include/time.h that we have a machine with a BSD behaving
    // mktime()
#   if !defined(HAVE_DAYLIGHT)
#       define MK_TIME_IS_GMT 1
#   endif

    // timezone seems to work as a proper offset for Linux & Solaris
#   if defined( __linux__ ) || defined( __sun__ ) 
#       define TIMEZONE_OFFSET_WORKS 1
#   endif

    mt.tm_mon = 2;
    mt.tm_mday = 21;
    mt.tm_year = year;
    mt.tm_hour = 12;
    mt.tm_min = 0;
    mt.tm_sec = 0;
    mt.tm_isdst = -1; // let the system determine the proper time zone

#   if defined( MK_TIME_IS_GMT )
    return ( mktime(&mt) );
#   else // ! defined ( MK_TIME_IS_GMT )

    long int start = mktime(&mt);

    FG_LOG( FG_EVENT, FG_DEBUG, "start1 = " << start );
    // the ctime() call can screw up time progression on some versions
    // of Linux
    // fgPrintf( FG_EVENT, FG_DEBUG, "start2 = %s", ctime(&start));
    FG_LOG( FG_EVENT, FG_DEBUG, "(tm_isdst = " << mt.tm_isdst << ")" );

    timezone = fix_up_timezone( timezone );

#   if defined( TIMEZONE_OFFSET_WORKS )
    FG_LOG( FG_EVENT, FG_DEBUG, 
	    "start = " << start << ", timezone = " << timezone );
    return( start - timezone );
#   else // ! defined( TIMEZONE_OFFSET_WORKS )

    daylight = mt.tm_isdst;
    if ( daylight > 0 ) {
	daylight = 1;
    } else if ( daylight < 0 ) {
	FG_LOG( FG_EVENT, FG_WARN, 
		"OOOPS, problem in fg_time.cxx, no daylight savings info." );
    }

    long int offset = -(timezone / 3600 - daylight);

    FG_LOG( FG_EVENT, FG_DEBUG, "  Raw time zone offset = " << timezone );
    FG_LOG( FG_EVENT, FG_DEBUG, "  Daylight Savings = " << daylight );
    FG_LOG( FG_EVENT, FG_DEBUG, "  Local hours from GMT = " << offset );
    
    long int start_gmt = start - timezone + (daylight * 3600);
    
    FG_LOG( FG_EVENT, FG_DEBUG, "  March 21 noon (CST) = " << start );

    return ( start_gmt );
#   endif // ! defined( TIMEZONE_OFFSET_WORKS )
#   endif // ! defined ( MK_TIME_IS_GMT )
}

static char*
format_time( const struct tm* p, char* buf )
{
    sprintf( buf, "%d/%d/%2d %d:%02d:%02d", 
	     p->tm_mon, p->tm_mday, p->tm_year,
	     p->tm_hour, p->tm_min, p->tm_sec);
    return buf;
}

// return a courser but cheaper estimate of sidereal time
double sidereal_course(fgTIME *t, double lng) {
    struct tm *gmt;
    time_t start_gmt, now;
    double diff, part, days, hours, lst;
    char tbuf[64];

    gmt = t->gmt;
    now = t->cur_time;
    start_gmt = get_start_gmt(gmt->tm_year);

    FG_LOG( FG_EVENT, FG_DEBUG, "  COURSE: GMT = " << format_time(gmt, tbuf) );
    FG_LOG( FG_EVENT, FG_DEBUG, "  March 21 noon (GMT) = " << start_gmt );

    diff = (now - start_gmt) / (3600.0 * 24.0);
    
    FG_LOG( FG_EVENT, FG_DEBUG, 
	    "  Time since 3/21/" << gmt->tm_year << " GMT = " << 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;
    }

    FG_LOG( FG_EVENT, FG_DEBUG,
	    "  days = " << days << "  hours = " << hours << "  lon = " 
	    << lng << "  lst = " << lst );

    return(lst);
}


// Update time variables such as gmt, julian date, and sidereal time
void fgTimeUpdate(FGInterface *f, fgTIME *t) {
    double gst_precise, gst_course;

    FG_LOG( FG_EVENT, FG_DEBUG, "Updating time" );

    // get current Unix calendar time (in seconds)
    t->warp += t->warp_delta;
    t->cur_time = time(NULL) + t->warp;
    FG_LOG( FG_EVENT, FG_DEBUG, 
	    "  Current Unix calendar time = " << t->cur_time 
	    << "  warp = " << t->warp << "  delta = " << t->warp_delta );

    if ( t->warp_delta ) {
	// time is changing so force an update
	local_update_sky_and_lighting_params();
    }

    // get GMT break down for current time
    t->gmt = gmtime(&t->cur_time);
    FG_LOG( FG_EVENT, FG_DEBUG, 
	    "  Current GMT = " << 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;
    FG_LOG( FG_EVENT, FG_DEBUG, "  Current Julian Date = " << 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.
      FG_LOG( FG_EVENT, FG_INFO, "  First time, doing precise gst" );
      t->gst = gst_precise = sidereal_precise(t->mjd, 0.00);
      gst_course = sidereal_course(t, 0.00);
      t->gst_diff = gst_precise - gst_course;

      t->lst =
	  sidereal_course(t, -(f->get_Longitude() * RAD_TO_DEG)) + t->gst_diff;
    } else {
	// course + difference should drift off very slowly
	t->gst = sidereal_course(t, 0.00) + t->gst_diff;
	t->lst = sidereal_course(t, -(f->get_Longitude() * RAD_TO_DEG)) + 
	    t->gst_diff;
    }
    FG_LOG( FG_EVENT, FG_DEBUG,
	    "  Current lon=0.00 Sidereal Time = " << t->gst );
    FG_LOG( FG_EVENT, FG_DEBUG,
	    "  Current LOCAL Sidereal Time = " << t->lst << " (" 
	    << sidereal_precise(t->mjd, -(f->get_Longitude() * RAD_TO_DEG)) 
	    << ") (diff = " << t->gst_diff << ")" );
}