gpstime

Some simple GPS time-related utilities for JavaScript.

Terms, and purpose

GPS time is measured using a "week number" (or WN) and a "time of week" (or TOW). See more information here.

GPS time started in January 1980, and does not account for leap seconds like UTC time does. There have been 17 leap seconds in UTC time since 1980, so GPS time is ahead of UTC by 17 seconds.

This library has utilities for converting UTC and GPS-relative Date objects to { wn, tow } pairs and back.

CLI Usage

gpstime also comes with a few handy CLI tools:

• current-gps-wn-tow returns the current week number and TOW.
• utc-to-wn-tow accepts a single argument, an ISO8601-formatted UTC date string, and returns the corresponding week number and TOW.
• gps-to-wn-tow accepts a single argument, an ISO8601-formatted GPS-relative date string, and returns the corresponding week number and TOW.
• wn-tow-to-utc accepts a week number and TOW, and returns an ISO8601-formatted date string representing the UTC time.
• wn-tow-to-gps accepts a week number and TOW, and returns an ISO8601-formatted date string representing the GPS-relative time.
• utc-to-gps accepts a single argument, an ISO8601-formatted UTC date string, and returns an ISO8601-formatted GPS-relative date string.
• gps-to-utc accepts a single argument, an ISO8601-formatted GPS-relative date string, and returns an ISO8601-formatted UTC date string.

Examples

$ current-gps-wn-tow
1916 327239.06999993324
$ utc-to-wn-tow 2016-09-28T18:43:25.208Z
1916 326622.2079999447
$ gps-to-wn-tow 2016-09-28T18:43:25.208Z
1916 326605.2079999447
$ utc-to-gps 2016-09-28T18:43:25.208Z
2016-09-28T18:43:42.208Z
$ utc-to-gps 2016-09-28T18:43:25.208Z
2016-09-28T18:43:42.208Z
$ gps-to-utc 2016-09-28T18:43:25.208Z
2016-09-28T18:43:08.208Z

Functions

The following functions are available:

• utcTimestampToWnTow - takes a Date object and returns GPS time as { wn, tow } dictionary.
• gpsTimestampToWnTow - takes a Date object and returns GPS time as { wn, tow } dictionary. Assumes that this object is in GPS time, without accounting for leap seconds.
• wnTowToUtcTimestamp - takes a GPS week number and TOW, and returns a Date object in UTC time, with leap-seconds accounted.
• wnTowToGpsTimestamp - takes a GPS week number and TOW, and returns a Date object in GPS-relative time, without leap-seconds accounted.
• utcTimestampToGpsTimestamp - takes a UTC timestamp and removes leap-seconds from it, returning a GPS-relative timestamp.
• gpsTimestampToUtcTimestamp - takes a GPS timestamp and adds leap-seconds from it, returning a UTC timestamp.
• currentGpsWnTow - convenience function that returns the current time as { wn, tow }.

Install

You can use these utilities programatically or via the CLI.

To install globally:

npm install -g gpstime

Or to save it to a project:

npm install --save gpstime

License

MIT license. See LICENSE file.