astro::delta_t Namespace Reference

Namespaces
namespace	algo1
namespace	algo2
namespace	algo3
namespace	algo4
namespace	algo5

Enumerations
enum class	Model : uint8_t {   ALGO1 , ALGO2 , ALGO3 , ALGO4 ,   ALGO5 }
	A selectable ΔT algorithm. More...

Functions
constexpr auto	compute (const Model model, const double year) -> double
	Evaluate a selected ΔT model at a decimal Gregorian year.
constexpr auto	compute (const double year) noexcept -> double
	Compute ΔT for a decimal Gregorian year using the default model.
constexpr auto	compute (const Model model, const calendar::Datetime &dt) -> double
	Evaluate a selected ΔT model at a valid calendar datetime.
constexpr auto	compute (const calendar::Datetime &dt) -> double
	Evaluate Algo 5 at a valid calendar datetime.
constexpr auto	ut1_to_tt (const Model model, const calendar::Datetime &ut1_dt) -> calendar::Datetime
	Convert UT1 to TT with one ΔT evaluation at the UT1 datetime.
constexpr auto	ut1_to_tt (const calendar::Datetime &ut1_dt) -> calendar::Datetime
	Convert a calendar::Datetime in UT1 to a new calendar::Datetime in TT.
constexpr auto	tt_to_ut1 (const Model model, const calendar::Datetime &tt_dt) -> calendar::Datetime
	Convert TT to modelled UT1 with one ΔT evaluation at the TT datetime.
constexpr auto	tt_to_ut1 (const calendar::Datetime &tt_dt) -> calendar::Datetime
	Convert a calendar::Datetime in TT to a new calendar::Datetime in UT1.

Variables
constexpr Model	DEFAULT_MODEL
	Default for operations with a selectable ΔT model; fixed-Algo5 shortcuts stay fixed.
constexpr double	ALGO1_START_JDE_TT
constexpr double	ALGO3_END_JDE_TT
constexpr double	ALGO4_END_JDE_TT

Detailed Description

This file computes ΔT (TT − UT1) and converts between the UT1 and TT time scales. The time scales (UT1, UTC, TT) and ΔT = TT − UT1 are defined in the Time Scales section of docs/DESIGN.md.

Enumeration Type Documentation

Model

enum class astro::delta_t::Model : uint8_t

strong

A selectable ΔT algorithm.

Enumerator
ALGO1
ALGO2
ALGO3
ALGO4
ALGO5

Function Documentation

compute() [1/4]

auto astro::delta_t::compute ( const calendar::Datetime & dt ) ->double

nodiscardconstexpr

Evaluate Algo 5 at a valid calendar datetime.

Returns

TT minus UT1, in seconds.

Exceptions

std::invalid_argument

If the datetime is invalid.

Note

The TT/UT1 distinction in the datetime argument is ignored.

compute() [2/4]

auto astro::delta_t::compute ( const double year ) ->double

nodiscardconstexprnoexcept

Compute ΔT for a decimal Gregorian year using the default model.

Parameters

year	The year, of double type. The year has fractional part, indicating the time elapsed in the year.

Returns

ΔT in seconds.

Algo5 is used for all finite years, with continuous joins and no upper year bound.

Example

compute(2005.99999999....) returns ΔT for the last moment of year 2005.

Example

compute(1984.0) returns ΔT for the first moment of year 1984.

Example

compute(2015.5) returns ΔT for the middle moment of year 2015 (roughly June 30/July 1).

compute() [3/4]

auto astro::delta_t::compute ( const Model model, const calendar::Datetime & dt )->double

nodiscardconstexpr

Evaluate a selected ΔT model at a valid calendar datetime.

Returns

TT minus UT1, in seconds; the sub-day fraction participates in the decimal year.

Exceptions

std::invalid_argument

If the datetime or model is invalid, or the year leaves the model's domain.

Note

The TT/UT1 distinction in the datetime argument is ignored.

compute() [4/4]

auto astro::delta_t::compute ( const Model model, const double year )->double

nodiscardconstexpr

Evaluate a selected ΔT model at a decimal Gregorian year.

Returns

TT minus UT1, in seconds.

Exceptions

std::invalid_argument

If the model is unknown or the year leaves its domain.

Note

Non-finite propagation and year limits depend on the selected model.

tt_to_ut1() [1/2]

auto astro::delta_t::tt_to_ut1 ( const calendar::Datetime & tt_dt ) ->calendar::Datetime

nodiscardconstexpr

Convert a calendar::Datetime in TT to a new calendar::Datetime in UT1.

Parameters

tt_dt

The datetime in TT.

Returns

The datetime in UT1.

Exceptions

std::invalid_argument

If the datetime is invalid or the shift leaves the representable years.

tt_to_ut1() [2/2]

auto astro::delta_t::tt_to_ut1 ( const Model model, const calendar::Datetime & tt_dt )->calendar::Datetime

nodiscardconstexpr

Convert TT to modelled UT1 with one ΔT evaluation at the TT datetime.

Parameters

model	The ΔT model.
tt_dt	The datetime in TT.

Returns

The datetime in UT1; this is a single shift, not an iterative inverse.

Exceptions

std::invalid_argument

If the datetime or model is invalid, the shift leaves the representable years, or the datetime leaves the model's domain.

ut1_to_tt() [1/2]

auto astro::delta_t::ut1_to_tt ( const calendar::Datetime & ut1_dt ) ->calendar::Datetime

nodiscardconstexpr

Convert a calendar::Datetime in UT1 to a new calendar::Datetime in TT.

Parameters

ut1_dt

The datetime in UT1.

Returns

The datetime in TT.

Exceptions

std::invalid_argument

If the datetime is invalid or the shift leaves the representable years.

ut1_to_tt() [2/2]

auto astro::delta_t::ut1_to_tt ( const Model model, const calendar::Datetime & ut1_dt )->calendar::Datetime

nodiscardconstexpr

Convert UT1 to TT with one ΔT evaluation at the UT1 datetime.

Parameters

model	The ΔT model.
ut1_dt	The datetime in UT1.

Returns

The datetime in TT.

Exceptions

std::invalid_argument

If the datetime or model is invalid, the shift leaves the representable years, or the datetime leaves the model's domain.

Variable Documentation

ALGO1_START_JDE_TT

double astro::delta_t::ALGO1_START_JDE_TT

inlineconstexpr

ALGO3_END_JDE_TT

double astro::delta_t::ALGO3_END_JDE_TT

inlineconstexpr

ALGO4_END_JDE_TT

double astro::delta_t::ALGO4_END_JDE_TT

inlineconstexpr

DEFAULT_MODEL

Model astro::delta_t::DEFAULT_MODEL

inlineconstexpr

Default for operations with a selectable ΔT model; fixed-Algo5 shortcuts stay fixed.