C语言实现GPS星历转换实用程序

/**********************************************************************
  NOTE TO ALL USERS:

  This file contains 6 main() programs and 12 C functions. 
  Before compiling with a C compiler, this file should be split into
  6 files; each having one main program and two C functions.  The six
  files are separated by equal signs (========== name =============).


 **********************************************************************/

/*============================= GPS_YD.C ===============================*/
#include <stdio.h>
#include <math.h>
#define JAN61980 44244
#define JAN11901 15385
#define SEC_PER_DAY 86400.0
void gps_to_ydhms(long gps_week, double sec_of_week,
              long *year, long *yday, long *hour, long *minute, double *second);
void ydhms_to_gps(long year, long yday, long hour, long minute, double second,
              long *gps_week, double *sec_of_week);
/*++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++*/
void main()
{
long gps_week, year, yday, hour, minute;
double sec_of_week, second;

gps_week = 633; sec_of_week = 241000.0;

gps_to_ydhms(gps_week, sec_of_week, &year, &yday, &hour, &minute, &second);

printf("%ld %lf %ld %ld %ld %ld %lf\n",
       gps_week, sec_of_week, year, yday, hour, minute, second);
ydhms_to_gps(year, yday, hour, minute, second, &gps_week, &sec_of_week);
printf("%ld %lf %ld %ld %ld %ld %lf\n",
       gps_week, sec_of_week, year, yday, hour, minute, second);
}
/*------------------------------------------------------------------------
 * gps_to_ydhms                                                          *
 *                                                                       *
 * Input: gps_week, sec_of_week                                          *
 *                                                                       *
 * Output: year, yday, hour, minute, second                              *
 *                                                                       *
 * Author: Benjamin W. Remondi                      Date: November 1999  *
 *-----------------------------------------------------------------------*/
void gps_to_ydhms(long gps_week, double sec_of_week,
      long *year, long *yday, long *hour, long *minute, double *second)
{
long mjd, days_fr_jan1_1901;
double fmjd;
long delta_yrs, num_four_yrs, years_so_far, days_left;

mjd = gps_week*7 + sec_of_week/SEC_PER_DAY + JAN61980;
fmjd = fmod(sec_of_week, SEC_PER_DAY)/SEC_PER_DAY;

days_fr_jan1_1901 = mjd - JAN11901;
num_four_yrs = days_fr_jan1_1901/1461;
years_so_far = 1901 + 4*num_four_yrs;
days_left = days_fr_jan1_1901 - 1461*num_four_yrs;
delta_yrs = days_left/365 - days_left/1460;