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improve time
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@tiagohm
tiagohm committed Dec 26, 2024
1 parent 68c4a84 commit 9676640
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Showing 2 changed files with 58 additions and 8 deletions.
23 changes: 23 additions & 0 deletions src/time.test.ts
View file
Original file line number Diff line number Diff line change
Expand Up @@ -118,6 +118,10 @@ test('ut1', () => {
expect(tcg(t)).toMatchTime(time(2459130, 0.000813870140404485, Timescale.TCG, false))
expect(tdb(t)).toMatchTime(time(2459130, 0.000802709826729233, Timescale.TDB, false))
expect(tcb(t)).toMatchTime(time(2459130, 0.001050568932858317, Timescale.TCB, false))

expect(t.extra?.ut1MinusUtc).not.toBeUndefined()
expect(t.extra?.ut1MinusTai).not.toBeUndefined()
expect(t.extra?.tdbMinusTt).not.toBeUndefined()
})

test('utc', () => {
Expand All @@ -132,6 +136,9 @@ test('utc', () => {
expect(tcg(t)).toMatchTime(time(2459130, 0.000811881499790694, Timescale.TCG, false))
expect(tdb(t)).toMatchTime(time(2459130, 0.000800721186116808, Timescale.TDB, false))
expect(tcb(t)).toMatchTime(time(2459130, 0.001048580292215058, Timescale.TCB, false))

expect(t.extra?.ut1MinusUtc).not.toBeUndefined()
expect(t.extra?.tdbMinusTt).not.toBeUndefined()
})

test('tai', () => {
Expand All @@ -146,6 +153,10 @@ test('tai', () => {
expect(tcg(t)).toMatchTime(time(2459130, 0.00038364075875147, Timescale.TCG, false))
expect(tdb(t)).toMatchTime(time(2459130, 0.000372480445371678, Timescale.TDB, false))
expect(tcb(t)).toMatchTime(time(2459130, 0.000620339544829971, Timescale.TCB, false))

expect(t.extra?.ut1MinusUtc).not.toBeUndefined()
expect(t.extra?.ut1MinusTai).not.toBeUndefined()
expect(t.extra?.tdbMinusTt).not.toBeUndefined()
})

test('tt', () => {
Expand All @@ -160,6 +171,9 @@ test('tt', () => {
expect(tcg(t)).toMatchTime(time(2459130, 0.000011140758491864, Timescale.TCG, false))
expect(tdb(t)).toMatchTime(time(2459130, -0.000000019554632113, Timescale.TDB, false))
expect(tcb(t)).toMatchTime(time(2459130, 0.000247839539050494, Timescale.TCB, false))

expect(t.extra?.ut1MinusUtc).not.toBeUndefined()
expect(t.extra?.tdbMinusTt).not.toBeUndefined()
})

test('tcg', () => {
Expand All @@ -174,6 +188,9 @@ test('tcg', () => {
expect(tcg(t)).toMatchTime(time(2459130, 0, Timescale.TCG, false))
expect(tdb(t)).toMatchTime(time(2459130, -0.000011160313116326, Timescale.TDB, false))
expect(tcb(t)).toMatchTime(time(2459130, 0.000236698780393541, Timescale.TCB, false))

expect(t.extra?.ut1MinusUtc).not.toBeUndefined()
expect(t.extra?.tdbMinusTt).not.toBeUndefined()
})

test('tdb', () => {
Expand All @@ -188,6 +205,9 @@ test('tdb', () => {
expect(tcg(t)).toMatchTime(time(2459130, 0.00001116031312399, Timescale.TCG, false))
expect(tdb(t)).toMatchTime(time(2459130, 0, Timescale.TDB, false))
expect(tcb(t)).toMatchTime(time(2459130, 0.00024785909368291, Timescale.TCB, false))

expect(t.extra?.ut1MinusUtc).not.toBeUndefined()
expect(t.extra?.tdbMinusTt).not.toBeUndefined()
})

test('tcb', () => {
Expand All @@ -202,6 +222,9 @@ test('tcb', () => {
expect(tcg(t)).toMatchTime(time(2459130, -0.000236698776886034, Timescale.TCG, false))
expect(tdb(t)).toMatchTime(time(2459130, -0.000247859089839806, Timescale.TDB, false))
expect(tcb(t)).toMatchTime(time(2459130, 0, Timescale.TCB, false))

expect(t.extra?.ut1MinusUtc).not.toBeUndefined()
expect(t.extra?.tdbMinusTt).not.toBeUndefined()
})

test('location', () => {
Expand Down
43 changes: 35 additions & 8 deletions src/time.ts
View file
Original file line number Diff line number Diff line change
Expand Up @@ -27,6 +27,11 @@ export interface TimeExtra {
tdb?: Time
tcb?: Time

ut1MinusUtc?: number
ut1MinusTai?: number
taiMinusUtc?: number
tdbMinusTt?: number

gast?: Angle
gmst?: Angle
era?: Angle
Expand Down Expand Up @@ -212,6 +217,10 @@ function extra(target: Time, source?: Time, extra?: Partial<TimeExtra>) {

if (source.location) target.location = source.location
} else if (extra) {
if (extra.ut1MinusUtc) target.extra.ut1MinusUtc = extra.ut1MinusUtc
if (extra.ut1MinusTai) target.extra.ut1MinusTai = extra.ut1MinusTai
if (extra.taiMinusUtc) target.extra.taiMinusUtc = extra.taiMinusUtc
if (extra.tdbMinusTt) target.extra.tdbMinusTt = extra.tdbMinusTt
if (extra.gast) target.extra.gast = extra.gast
if (extra.gmst) target.extra.gmst = extra.gmst
if (extra.era) target.extra.era = extra.era
Expand Down Expand Up @@ -438,26 +447,32 @@ export function equationOfOrigins(time: Time): Mat3 {

// Computes UT1 - UTC in seconds at time.
export const ut1MinusUtc: TimeDelta = (time) => {
if (time.extra?.ut1MinusUtc) return time.extra.ut1MinusUtc

// https://github.com/astropy/astropy/blob/71a2eafd6c09f1992f8b4132e6e40ba68a675bde/astropy/time/core.py#L2554
// Interpolate UT1-UTC in IERS table
const d = delta(time)
let dt = delta(time)

// If we interpolated using UT1, we may be off by one
// second near leap seconds (and very slightly off elsewhere)
if (time.scale === Timescale.UT1) {
const a = eraUt1Utc(time.day, time.fraction, d)
const a = eraUt1Utc(time.day, time.fraction, dt)
// Calculate a better estimate using the nearly correct UTC
return delta({ day: a[0], fraction: a[1], scale: Timescale.UTC })
dt = delta({ day: a[0], fraction: a[1], scale: Timescale.UTC })
}

return d
extra(time, undefined, { ut1MinusUtc: dt })

return dt
}

// Computes TDB - TT in seconds at time.
export const tdbMinusTt: TimeDelta = (time) => {
const { day, fraction, scale } = time

if (scale === Timescale.TDB || scale === Timescale.TT) {
if (time.extra?.tdbMinusTt) return time.extra.tdbMinusTt

// First go from the current input time (which is either
// TDB or TT) to an approximate UT1. Since TT and TDB are
// pretty close (few msec?), assume TT. Similarly, since the
Expand All @@ -468,12 +483,18 @@ export const tdbMinusTt: TimeDelta = (time) => {
// Subtract 0.5, so UT is fraction of the day from midnight
const ut = normalize(a[0] - 0.5, a[1]).fraction

let dt = 0

if (time.location) {
const [x, y, z] = itrs(time.location)
return eraDtDb(day, fraction, ut, time.location.longitude, Math.hypot(x, y), z)
dt = eraDtDb(day, fraction, ut, time.location.longitude, Math.hypot(x, y), z)
} else {
return eraDtDb(day, fraction, ut)
dt = eraDtDb(day, fraction, ut)
}

extra(time, undefined, { tdbMinusTt: dt })

return dt
}

return 0
Expand All @@ -496,14 +517,20 @@ export const tdbMinusTtByFairheadAndBretagnon1990: TimeDelta = (time) => {

// Computes TAI - UTC in seconds at time.
export const taiMinusUtc: TimeDelta = (time) => {
if (time.extra?.taiMinusUtc) return time.extra.taiMinusUtc
const cal = eraJdToCal(time.day, time.fraction)
return eraDat(cal[0], cal[1], cal[2], cal[3])
const dt = eraDat(cal[0], cal[1], cal[2], cal[3])
extra(time, undefined, { taiMinusUtc: dt })
return dt
}

// Computes UT1 - TAI in seconds at time.
export const ut1MinusTai: TimeDelta = (time) => {
if (time.extra?.ut1MinusTai) return time.extra.ut1MinusTai
const cal = eraJdToCal(time.day, time.fraction)
const dat = eraDat(cal[0], cal[1], cal[2], cal[3])
const dut1 = (time.ut1MinusUtc ?? ut1MinusUtc)(time)
return dut1 - dat
const dt = dut1 - dat
extra(time, undefined, { ut1MinusTai: dt })
return dt
}

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