GPS time system (recording the absolute number of seconds since the start of the GPS epoch at midnight on January 6th 1980)
Sometimes GPS time is given with an offset (e.g. 1000000000), in this case the 0 value corresponds to 2011/09/14 at 01:46:25 UTC.
Note also that POSIX (Unix) time is given since Jan 1st, 1970, 00:00:00 UTC.
convert to date
835734.87 6250812.50 -3.04 20 0 57560982
example of gps dataset
835734.88 6250296.85 -8.16 30 0 46351553
835734.88 6250476.48 -6.97 30 0 57559145
The gps epoch is in the sixth field, and the values are offset by 1 billion. To convert to date one can use Python.
>>> import datetime
>>> datetime.date.fromtimestamp(1315964785) #posix time of the GPS epoch including the 1 billion offset
datetime.date(2011, 9, 14)
>>> datetime.date.fromtimestamp(1315964782+57560982) # gps time of the dataset + the posix time
datetime.date(2013, 7, 11)