GPS

Overview

GPS time is the standard by which all GPS satellites and GPS-enabled devices coordinate their positions. It is a simple count of seconds from midnight on January 6th, 1980.

When converted into the Gregorian calendar, it drifts ahead by a second every now and then as it does not follow leap seconds found in other timekeeping standards.

Info

GPS became available to the public in 2000 CE.

Accuracy

This clock is considered to be perfectly accurate, as it's a simple calculation from Unix.

Source

Common Source

Wikipedia article

Primary Sources

Leap Second website

Epoch Converter website

Calculation

Calculating the current GPS time requires starting with the GPS epoch. and subtracting it from the current datetime.

gpsEpoch = new Date("1980-01-06T00:00:00Z").getTime();
// Calculate total time difference in seconds
let gpsTime = Math.floor((currentDateTime - gpsEpoch) / 1000);

After that, the leap seconds that have already passed need to be added.

const GPSleapSeconds = [
    "1981-06-30T23:59:59Z",
    "1982-06-30T23:59:59Z",
    "1983-06-30T23:59:59Z",
    "1985-06-30T23:59:59Z",
    "1987-12-31T23:59:59Z",
    "1989-12-31T23:59:59Z",
    "1990-12-31T23:59:59Z",
    "1992-06-30T23:59:59Z",
    "1993-06-30T23:59:59Z",
    "1994-06-30T23:59:59Z",
    "1995-12-31T23:59:59Z",
    "1997-06-30T23:59:59Z",
    "1998-12-31T23:59:59Z",
    "2005-12-31T23:59:59Z",
    "2008-12-31T23:59:59Z",
    "2012-06-30T23:59:59Z",
    "2015-06-30T23:59:59Z",
    "2016-12-31T23:59:59Z"
];

// Calculate how many leap seconds have occurred before the currentDateTime
let leapSecondsCount = 0;
GPSleapSeconds.forEach(leapSecond => {
    if (new Date(leapSecond).getTime() <= currentDateTime) {
        leapSecondsCount++;
    }
});

// Add leap seconds to account for the growing difference between GPS and UTC.
gpsTime += leapSecondsCount;