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| # DSO's Datetime Library for Satellite Geodesy | ||
| ----------------------------------------------- | ||
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| ## Installation | ||
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| Source code is ISO C++17. Compilation should be trivial using any C++ compiler | ||
| supporting the c++17 standard (option `-std=c++17` in [gcc](https://gcc.gnu.org/) | ||
| and [clang](https://clang.org/)). | ||
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| The source code also makes use of several C++20 features, and is compliant with the | ||
| C++20 standard, however using this is optional. | ||
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| Prerequisites: | ||
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| * A modern C++ compiler, | ||
| * [cmake](https://cmake.org/) for building | ||
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| Installation steps: | ||
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| * clone the project: `git clone https://github.com/DSOlab/ggdatetime.git`, | ||
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| * go to the root directory, ``cd ggdatetime` | ||
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| * use [cmake](https://cmake.org/) to build the library and executables, e.g. | ||
| ``` | ||
| $> cmake -S . -B build -DCMAKE_BUILD_TYPE=Release | ||
| $> cmake --build build --target all --config Release -- -j4 | ||
| # optionally run tests | ||
| $> ctest --test-dir build | ||
| ## Install, system-wide (needs root) | ||
| $> cd build && sudo make install | ||
| ``` | ||
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| ### Compilation Options | ||
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| #### `ALLOW_DT_INTEGRAL_MATH` | ||
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| This option will allow (some) selected operations between DateTime fundamental | ||
| types and integral numbers. For example, the following snippet would be valid: | ||
| ``` | ||
| Modified_julian_day mjd (123); | ||
| mjd += 1; | ||
| // Now mjd's internal member, will have a value of 124. | ||
| ``` | ||
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| #### Build in DEBUG mode | ||
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| You can easily change to building the DEBUG version, e.g. | ||
| ``` | ||
| $> cmake -S . -B build -G "Unix Makefiles" -DCMAKE_BUILD_TYPE=Debug | ||
| $> cmake --build build --target all --config Debug -- -j4 | ||
| ``` | ||
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| ## Fundamental Date and Time Classes | ||
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| To preserve type-safety, the library goes on to define a series of classes to | ||
| represent dates and time, i.e. | ||
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| ### Time Integral Types | ||
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| * dso::hours | ||
| * dso::minutes | ||
| * dso::seconds | ||
| * dso::milliseconds, i.e. $$10^{-3} sec$$ | ||
| * dso::microseconds, i.e. $$10^{-6} sec$$ | ||
| * dso::nanoseconds, i.e. $$10^{-9} sec$$ | ||
| * dso::picoseconds, i.e. $$10^{-12} sec$$ | ||
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| ### Time Fractional Types | ||
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| * dso::FractionalSeconds | ||
| * dso::FractionalDays | ||
| * dso::FractionalYears | ||
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| ### Date Integral Types | ||
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| * dso::year | ||
| * dso::month | ||
| * dso::gps_week | ||
| * dso::day_of_month | ||
| * dso::day_of_year | ||
| * dso::modified_julian_day | ||
| * dso::ymd_date, i.e. a calendar date | ||
| * dso::ydoy_date, i.e. a date represented as Year and Day-of-Year | ||
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| ## Representing Datetime Instances | ||
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| In order to represent datetime instances, i.e. **epochs**, we have to make a | ||
| distinction between **contunuous** and **non-continuous** time scales. For example, | ||
| UTC is a non-continuous time scale, since every now and then leap seconds are | ||
| introdiced. | ||
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| ### Epochs in Continuous Time-Scales | ||
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| In continuous time scales (e.g. TT, TAI, etc, ...) an epoch can be represented | ||
| in two ways: | ||
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| * using a dso::TwoPartDate (or its alias name dso::MjdEpoch); this way of representing | ||
| an epoch, includes storage of two numerics: an integral part, which is actually the | ||
| day as Modified Julian Day and a floating point part which represents the seconds of day. | ||
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| * using the template class dso::datetime (or its alias name dso::Datetime) which | ||
| depends on a template parameter \p T. This parameter denotes the precision in which | ||
| the datetime is 'measured' and it can be any of the [Time Integral Types](#time-integral-types) | ||
| that are multiples of seconds. E.g., you can have a `dso::datetime<dso::milliseconds> t(...)`. | ||
| In this way, it is guaranteed that the specified accuracy will be preserved, since | ||
| no floating point math are involved when e.g. adding or subtracting second multiples. | ||
| Note however that precision is lost if you add a 'more accurate' subdivision of | ||
| seconds to a leeser one, e.g. | ||
| ``` | ||
| dso::datetime<dso::milliseconds> t(...); | ||
| t.add_seconds(picoseconds(1)); | ||
| ``` | ||
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| ### Epochs in Continuous Time-Scales aka UTC | ||
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| ## Leap Seconds | ||
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| Leap seconds are introduced as necessary to keep UT1-UTC in the $$\pm 0^{s}.9$$. | ||
| Because on the average the solar day is now 1-2 ms longer than the nominal | ||
| 86,400 SI seconds, accumulating to 1s over a period of 18 months to a few years, | ||
| leap seconds are in practice always positive ([see SOFA](#sofa_ts)). Each time | ||
| a leap second is introduced, the offset $\Delta$AT = TAI - UTC changes by exactly 1s. | ||
| Insertion of leap seconds, make UTC a non-continuous time scale, which should be | ||
| handled-specially-(see-[Epochs-in-Continuous-Time-Scales-aka-UTC](#epochs-in-continuous-time-scales-aka-utc)). | ||
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| > [!CAUTION] | ||
| > **Latest leap second considered in datetime library occured at: 2017/01/01** | ||
| ## Bibliography | ||
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| 1. <a id="sofa_ts"></a> International Astronomical Union, Standards of Fundamental Astronomy, SOFA Time Scale and Calendar Tools, Document revision 1.63, 2023 |
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| #include "calendar.hpp" | ||
| #include <random> | ||
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| using namespace dso; | ||
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| constexpr const int MIN_MJD = 41317 - 5; | ||
| constexpr const int MAX_MJD = 57754 + 5; | ||
| constexpr const std::array<ymd_date, 28> changes = {{ | ||
| ymd_date{year(1972), month(1), day_of_month(1)}, | ||
| ymd_date{year(1972), month(7), day_of_month(1)}, | ||
| ymd_date{year(1973), month(1), day_of_month(1)}, | ||
| ymd_date{year(1974), month(1), day_of_month(1)}, | ||
| ymd_date{year(1975), month(1), day_of_month(1)}, | ||
| ymd_date{year(1976), month(1), day_of_month(1)}, | ||
| ymd_date{year(1977), month(1), day_of_month(1)}, | ||
| ymd_date{year(1978), month(1), day_of_month(1)}, | ||
| ymd_date{year(1979), month(1), day_of_month(1)}, | ||
| ymd_date{year(1980), month(1), day_of_month(1)}, | ||
| ymd_date{year(1981), month(7), day_of_month(1)}, | ||
| ymd_date{year(1982), month(7), day_of_month(1)}, | ||
| ymd_date{year(1983), month(7), day_of_month(1)}, | ||
| ymd_date{year(1985), month(7), day_of_month(1)}, | ||
| ymd_date{year(1988), month(1), day_of_month(1)}, | ||
| ymd_date{year(1990), month(1), day_of_month(1)}, | ||
| ymd_date{year(1991), month(1), day_of_month(1)}, | ||
| ymd_date{year(1992), month(7), day_of_month(1)}, | ||
| ymd_date{year(1993), month(7), day_of_month(1)}, | ||
| ymd_date{year(1994), month(7), day_of_month(1)}, | ||
| ymd_date{year(1996), month(1), day_of_month(1)}, | ||
| ymd_date{year(1997), month(7), day_of_month(1)}, | ||
| ymd_date{year(1999), month(1), day_of_month(1)}, | ||
| ymd_date{year(2006), month(1), day_of_month(1)}, | ||
| ymd_date{year(2009), month(1), day_of_month(1)}, | ||
| ymd_date{year(2012), month(7), day_of_month(1)}, | ||
| ymd_date{year(2015), month(7), day_of_month(1)}, | ||
| ymd_date{year(2017), month(1), day_of_month(1)}, | ||
| }}; | ||
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| int main() { | ||
| for (const auto &d : changes) { | ||
| const modified_julian_day mjd(d); | ||
| assert(mjd.is_leap_insertion_day() == 0); | ||
| const modified_julian_day mjdm1 = mjd - modified_julian_day(1); | ||
| assert(mjdm1.is_leap_insertion_day() == 1); | ||
| const modified_julian_day mjdm2 = mjd - modified_julian_day(2); | ||
| assert(mjdm1.is_leap_insertion_day() == 0); | ||
| const modified_julian_day mjdp1 = mjd + modified_julian_day(1); | ||
| assert(mjdp1.is_leap_insertion_day() == 0); | ||
| } | ||
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| constexpr const modified_julian_day mjd{std::get<0, ymd_date, 28>(changes)}; | ||
| static_assert(mjd.is_leap_insertion_day() == 0); | ||
| constexpr const modified_julian_day mjdm1{mjd - modified_julian_day(1)}; | ||
| static_assert(mjdm1.is_leap_insertion_day() == 1); | ||
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| return 0; | ||
| } |