1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
|
/**
* @file
*
* @date Created on Jan 29, 2025
* @author Attila Kovacs
*
* Example file for using the time-related functions of the SuperNOVAS C/C++ library
*
* Link with
*
* ```
* -lsupernovas
* ```
*/
#if __STDC_VERSION__ < 201112L
# define _POSIX_C_SOURCE 199309 ///< struct timespec
#endif
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <novas.h> ///< SuperNOVAS functions and definitions
// Below are some Earth orientation values. Here we define them as constants, but they may
// of course be variables. They should be set to the appropriate values for the time
// of observation based on the IERS Bulletins...
#define LEAP_SECONDS 37 ///< [s] current leap seconds from IERS Bulletin C
#define DUT1 0.048 ///< [s] current UT1 - UTC time difference from IERS Bulletin A
#define POLAR_DX 230.0 ///< [mas] Earth polar offset x, e.g. from IERS Bulletin A.
#define POLAR_DY -62.0 ///< [mas] Earth polar offset y, e.g. from IERS Bulletin A.
int main() {
// SuperNOVAS variables --------------------------------------------------->
// Astronomical time data for SuperNOVAS
novas_timespec time1 = NOVAS_TIMESPEC_INIT, time2 = NOVAS_TIMESPEC_INIT, time3 = NOVAS_TIMESPEC_INIT;
// Calculated quantities -------------------------------------------------->
enum novas_timescale scale; // astronomical timescale
double jd; // [day] Julian days
long ijd; // [day] integer part of Julian Day
double fjd; // [day] fractional part of Julian Day.
double dt; // [s] time difference
int year, month, day; // broken-down date components
double hours; // broken-down time-of-day component
char timestamp[40]; // String timestamp, at leat 29 characters.
// Other used quantities -------------------------------------------------->
struct timespec unix_time;
// -------------------------------------------------------------------------
// 1.a. Simple dates from strings...
// Use a UTC string date-time specification in YMD format
// (It could also be TAI, or GPS, or TDB...)
novas_set_str_time(NOVAS_UTC, "2025-01-29T18:09:29.333+0200", LEAP_SECONDS, DUT1, &time1);
// -------------------------------------------------------------------------
// 1.b. Dates from strings more generally...
// - Parse a date/time string in YMD format -- there is a fait bit of
// flexibility on how the components are separated, but they must be year,
// month, day, then optionally time and possibly time zone also. For
// example:
jd = novas_date("2025-01-29T18:09:29.333+0200");
// Alternatively, you could use a string time that also contains a timescale
// specification:
jd = novas_date_scale("2025-01-29 18:09:29.333+0200 TAI", &scale);
// - Next, convert that date to an astronomical time of a specific time
// scale. Let's say the above date was on the TAI... (It could be UTC, or
// GPS, or TDB...)
novas_set_time(NOVAS_TAI, jd, LEAP_SECONDS, DUT1, &time1);
// -------------------------------------------------------------------------
// 1.c. Dates from broken-down time
// - Use year, month, day, and time-of-day, e.g. 1974-01-31 23:30
// The date is in the astronomical calendar of date (as opposed to a fixed
jd = novas_jd_from_date(NOVAS_ASTRONOMICAL_CALENDAR, 1974, 1, 31, 23.5);
// - Next, convert that date to an astronomical time of a specific time
// scale. Let's say the above date was on the TAI... (It could be UTC, or
// GPS, or TDB...)
novas_set_time(NOVAS_TAI, jd, LEAP_SECONDS, DUT1, &time2);
// -------------------------------------------------------------------------
// 1.d. UNIX time
// We'll set unix_time to current time, but it could be a UNIX timestamp...
#if __STDC_VERSION__ >= 201112L || defined(_MSC_VER)
timespec_get(&unix_time, TIME_UTC);
#else
clock_gettime(CLOCK_REALTIME, &unix_time);
#endif
// Use the UNIX time (seconds + nanoseconds) to define astrometric time
novas_set_unix_time(unix_time.tv_sec, unix_time.tv_nsec, LEAP_SECONDS, DUT1, &time3);
// -------------------------------------------------------------------------
// 1.e. Current time
// Use the current UNIX time to set astronomical time
novas_set_current_time(LEAP_SECONDS, DUT1, &time3);
// -------------------------------------------------------------------------
// 2. Extract specific timescales from the astronomical time
// - Get a TDB-based JD date for time1
jd = novas_get_time(&time1, NOVAS_TDB);
// - Or for higher precision, get a split JD...
fjd = novas_get_split_time(&time1, NOVAS_TDB, &ijd);
printf("Split date is %ld / %.9f", ijd, fjd);
// -------------------------------------------------------------------------
// 3. Measure time difference
// - Difference in Earth-based time measures (UTC, GPS, TAI, TT)
dt = novas_diff_time(&time1, &time2);
printf(" UTC Time difference is %.6f days\n", dt / NOVAS_DAY);
// - Difference in TCG -- time progresses differently outside of Earth gravity
dt = novas_diff_tcg(&time1, &time2);
printf(" TCG Time difference is %.6f days\n", dt / NOVAS_DAY);
// - Difference in TCB -- time progresses differently outside of Earth gravity
dt = novas_diff_tcb(&time1, &time2);
printf(" TDB Time difference is %.6f days\n", dt / NOVAS_DAY);
// -------------------------------------------------------------------------
// 4. Offset time
// - Add 5.31 seconds to time1. We can put the result in a different time data
// or we can overwrite the input (as we'll do here).
novas_offset_time(&time1, 5.31, &time1);
// -------------------------------------------------------------------------
// 5. Print time
// - Print an UTC-based ISO timestamp to a string
novas_iso_timestamp(&time1, timestamp, sizeof(timestamp));
printf(" Offset time is: %s\n", timestamp);
// - Print a timestamp in a specific time measure, e.g. GPS time
novas_timestamp(&time1, NOVAS_GPS, timestamp, sizeof(timestamp));
printf(" in TDB : %s\n", timestamp);
// -------------------------------------------------------------------------
// 6. Get Calendar date in specific calendar
// - Get a Broken down date, say in the Julian/Roman calendar
novas_jd_to_date(jd, NOVAS_ROMAN_CALENDAR, &year, &month, &day, &hours);
return 0;
}
|
