Purpose: To give insight for the potential user on a commonly seen misunderstanding in the difference between UTC and GPS timestamps.
Last Updated: March, 2020
Customer:
I have found one issue that I am currently confused with. The timestamp recorded from COM1 of the INS is consistently 17-20 seconds fast. If I start recording at 00 seconds, the first timestamp is equal to 17+ seconds, however the location data that comes from the GPS receiver is correct for 00 seconds and not 17+ seconds. Any insights into this issue?
Inertial Labs Service Member:
Regarding the timestamps, I guess that you are comparing UTC and GPS time and the difference you see is 18 seconds. This difference is caused by leap seconds (currently there are 18 leap seconds). The UTC includes leap seconds. The INS-B timestamp is GPS time and GPS time does not include leap seconds. Currently (in Feb 2020) the GPS time is 18 seconds ahead of UTC. You should take into account the leap seconds when you perform UTC to GPS week time conversion.
You can check UTC and GPS time based on your PC clock here: leapsecond.com/java/gpsclock.htm.
Thank you!
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