GPSTime.hpp

Go to the documentation of this file.

#pragma once
 
#include <cmath>
#include <janus/janus.hpp>
#include <vulcan/time/JulianDate.hpp>
#include <vulcan/time/TimeConstants.hpp>
#include <vulcan/time/TimeScales.hpp>
 
namespace vulcan::time {
 
// =============================================================================
// GPS Week Number Utilities
// =============================================================================

inline constexpr int GPS_WEEK_ROLLOVER = 1024;

inline constexpr int GPS_CURRENT_ROLLOVER = 2;

[[nodiscard]] inline constexpr int
full_gps_week(int week_mod, int rollover_count = GPS_CURRENT_ROLLOVER) {
    return week_mod + rollover_count * GPS_WEEK_ROLLOVER;
}

template <typename Scalar>
[[nodiscard]] Scalar gps_week_to_utc_jd(int week, const Scalar &seconds_of_week,
                                        int delta_at = 37) {
    // GPS time as JD
    Scalar gps_jd = constants::time::JD_GPS_EPOCH +
                    static_cast<double>(week) * 7.0 +
                    seconds_of_week / constants::time::SECONDS_PER_DAY;
 
    // Convert GPS JD to UTC JD
    return gps_to_utc(gps_jd, delta_at);
}

template <typename Scalar>
[[nodiscard]] Scalar gps_week_to_tai_jd(int week,
                                        const Scalar &seconds_of_week) {
    Scalar gps_jd = constants::time::JD_GPS_EPOCH +
                    static_cast<double>(week) * 7.0 +
                    seconds_of_week / constants::time::SECONDS_PER_DAY;
 
    return gps_to_tai(gps_jd);
}

[[nodiscard]] inline std::pair<int, double> utc_jd_to_gps_week(double utc_jd,
                                                               int delta_at) {
    double gps_jd = utc_to_gps(utc_jd, delta_at);
    double days_since_epoch = gps_jd - constants::time::JD_GPS_EPOCH;
 
    int week = static_cast<int>(std::floor(days_since_epoch / 7.0));
    double days_into_week = days_since_epoch - week * 7.0;
    double seconds_of_week = days_into_week * constants::time::SECONDS_PER_DAY;
 
    return {week, seconds_of_week};
}

[[nodiscard]] inline std::pair<int, double>
utc_jd_to_gps_week_auto(double utc_jd) {
    int delta_at = leap_seconds_at_utc(utc_jd);
    return utc_jd_to_gps_week(utc_jd, delta_at);
}
 
// =============================================================================
// GPS-UTC Offset
// =============================================================================

[[nodiscard]] inline int gps_utc_offset(double utc_jd) {
    int delta_at = leap_seconds_at_utc(utc_jd);
    return delta_at - static_cast<int>(constants::time::TAI_GPS_OFFSET);
}

[[nodiscard]] inline constexpr int gps_utc_offset(int delta_at) {
    return delta_at - static_cast<int>(constants::time::TAI_GPS_OFFSET);
}
 
// =============================================================================
// Day of Week Utilities
// =============================================================================

enum class GpsDayOfWeek {
    Sunday = 0,
    Monday = 1,
    Tuesday = 2,
    Wednesday = 3,
    Thursday = 4,
    Friday = 5,
    Saturday = 6
};

[[nodiscard]] inline GpsDayOfWeek gps_day_of_week(double seconds_of_week) {
    int day = static_cast<int>(
        std::floor(seconds_of_week / constants::time::SECONDS_PER_DAY));
    return static_cast<GpsDayOfWeek>(day % 7);
}

[[nodiscard]] inline double gps_time_of_day(double seconds_of_week) {
    return std::fmod(seconds_of_week, constants::time::SECONDS_PER_DAY);
}
 
} // namespace vulcan::time