[time-nuts] Systron Donner IMU/GPS and/or Jupiter Pico

Jim Lux jimlux at earthlink.net
Fri Feb 6 08:16:07 EST 2015


I have a colleague who's using the Systron-Donner  MMQ IMU/GPS unit, and 
he's wondering if there's a way to get "integer seconds" out of it.  It 
uses a Jupiter Pico GPS, I believe, and one of the messages provides 
Seconds of Week GPS time, as well as UTC seconds and UTC day, month, year.

So here's the question.. he needs "seconds from epoch" (like TAI time), 
and it's moderately straightforward to convert D/M/Y to get midnight 
time from epoch and then add the seconds.

The question comes up of whether there's a clever fast algorithm (in C) 
to get "Week time" so he can add GPS seconds of week to midnight of week 
start.

Or alternately, does anyone know what the leap second behavior of this 
unit is, and he can just use the UTC.

And in fact, as I sit here before my morning coffee, this brings up an 
interesting leap second question: if you did a "calculate midnight time 
in seconds and add seconds of day (or week)", what do you do for that 
calculation..

Is the midnight time for the midnight after the leap 86401 greater than 
the midnight time before leap?  That makes calculating seconds of 
midnight a bit tricky, because it's not just "year epoch + month epoch + 
day of month*86400"


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