Time

The Time submodule contains common time transformations such as converting between different date representations or converting a specific instant in time between different time systems.

The module also defines the Epoch class which provides the standard representation of instants in time used throughout the module.

Most of the transformations are make backend calls to the SOFA C-library functions provide the package SOFA.jl

SatelliteDynamics.caldate_to_mjd — Function

Convert a Gregorian calendar date to the equivalent Modified Julian Date representation of that time instant.

Aguments:

year::Integer Year
year::Integer Month
year::Integer Day
hour::Integer Hour
minute::Integer Minute
second::Real Seconds
nanoseconds::Real Nanoseconds

Returns:

mjd::Float64 Modified Julian Date of Epoch

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SatelliteDynamics.mjd_to_caldate — Function

Convert a Modified Julian Date to the equivalent Gregorian calendar date representation of the same instant in time.

Aguments:

mjd::Real: Modified Julian Date of Epoch

Returns:

year::Int: Year
year::Int: Month
year::Int: Day
hour::Int: Hour
minute::Int: Minute
second::Float64: Seconds
nanoseconds::Float64: Nanoseconds

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SatelliteDynamics.caldate_to_jd — Function

Convert a Gregorian calendar date to the equivalent Julian Date representation of that time instant.

Aguments:

year::Integer: Year
year::Integer: Month
year::Integer: Day
hour::Integer: Hour
minute::Integer: Minute
second::Real: Seconds
nanoseconds::Real: Nanoseconds

Returns:

mjd::Float64: Julian Date of Epoch

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SatelliteDynamics.jd_to_caldate — Function

Convert a Julian Date to the equivalent Gregorian calendar date representation of the same instant in time.

Aguments:

jd::Real: Julian Date of Epoch

Returns:

year::Int: Year
year::Int: Month
year::Int: Day
hour::Int: Hour
minute::Int: Minute
second::Float64: Seconds
microsecond::Float64: Nanoseconds

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SatelliteDynamics.elapsed_from_epoch — Function

Compute the number of elapsed seconds since a given Epoch from the day number. Can be used to compute the elapsed time since a given Julian or Modified Julian Date.

Arguments:

day_number::Real: Day number, can contain fractional days. Asummes all days are a uniform 86400.0 seconds in length.
day_epoch::Real: Modified Julian Date of Epoch

Returns:

t::Float: Number of elapsed seconds between the Provided Modified Julian date and the epoch.

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SatelliteDynamics.days_from_elapsed — Function

Computes the day number in a given time scale given the elapsed time since epoch and the epoch itself.

Assumes all days are counted using a uniform 86400.0 seconds over the time span.

Arguments:

t::Real: Elapsed seconds since the day_epoch.
day_epoch::Real: Day number of the epoch. Common values are SatelliteDynamics.MJD_ZERO (to get the Julian Day number) or SatelliteDynamics.MJD2000 (to get Modified Julian Days if reckoning time from January 1, 2000 0H)

Returns:

days::Float: Number of elapsed days in the time scale.

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SatelliteDynamics.time_system_offset — Function

Compute the offset between two time systems at a given Epoch.

The offset (in seconds) is computed as:

time_system_offset = tsys_dest - tsys_src

The value returned is the number of seconds that musted be added to the source time system given the input epoch, to get the equivalent epoch.

Conversions are accomplished using SOFA C library calls. Epoch.

Arguments:

jd::Real: Part 1 of two-part date (Julian days)
fd::Real: Part 2 of two-part date (Fractional days)
tsys_src::String: Base time system
tsys_dest::String: Destination time system

Returns:

offset::Float: Offset between soruce and destination time systems in seconds.

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SatelliteDynamics.Epoch — Type

The Epoch type represents a single instant in time. It is used throughout the SatelliteDynamics module. It is meant to provide a clear definition of moments in time and provide a convenient interface display time in various representations as well as in differrent time systems. The internal data members are also chosen such that the representation maintains nanosecond-precision in reprersenation of time and doesn't accumulate floating-point arithmetic errors larger than nanoseconds even after centuries.

Supports +, +=, -, and -= operators. Two Epoch's can be differenced to return the time difference between two Epochs. If adding a Real number it is interpreted as an offset in seconds to add to the Epoch.

The class also supports all arithmetic operators: ==, !=, <, <=, >, >=

Arguments:

year::Int Year
year::Int Month
year::Int Day
hour::Int Hour (optional)
minute::Int Minute (optional)
second::Real Seconds (optional)
nanoseconds::Real Nanoseconds (optional)
tsys::String: Time system of the epoch at initialization

The Epoch class can be also be initialized from a string. Examples of Valid String constructors are:

epc = Epoch("2018-12-20")
epc = Epoch("2018-12-20T16:22:19.0Z")
epc = Epoch("2018-12-20T16:22:19.123Z")
epc = Epoch("2018-12-20T16:22:19.123456789Z")
epc = Epoch("2018-12-20T16:22:19Z")
epc = Epoch("20181220T162219Z")
epc = Epoch("2018-12-01 16:22:19 GPS")
epc = Epoch("2018-12-01 16:22:19.0 GPS")
epc = Epoch("2018-12-01 16:22:19.123 GPS")
epc = Epoch("2018-12-01 16:22:19.123456789 GPS")

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SatelliteDynamics.caldate — Function

Return the Gregorian calendar date for a specific

Arguments: