ZED-F9R-Integration manual
reporting GNSS system time or receiver local time. It is recommended to use messages that
report UTC time and other messages are retained only for backwards compatibility reasons.
3.10.3 iTOW timestamps
All the main UBX-NAV messages (and some other messages) contain an iTOW field which indicates
the GPS time at which the navigation epoch occurred. Messages with the same iTOW value can be
assumed to have come from the same navigation solution.
With Priority navigation mode enabled, iTOW can be used as an epoch collector only for
messages of the same group (e.g. priority navigation messages with the same iTOW value
can be assumed to have come from the same navigation solution).
Note that iTOW values may not be valid (i.e. they may have been generated with insufficient
conversion data) and therefore it is not recommended to use the iTOW field for any other purpose.
The original designers of GPS chose to express time/date as an integer week number
(starting with the first full week in January 1980) and a time of week (often abbreviated
to TOW) expressed in seconds. Manipulating time/date in this form is far easier for digital
systems than the more conventional year/month/day, hour/minute/second representation.
Consequently, most GNSS receivers use this representation internally, only converting to a
more conventional form at external interfaces. The iTOW field is the most obvious externally
visible consequence of this internal representation.
If reliable absolute time information is required, users are recommended to use the UBX-NAV-PVT
navigation solution message which also contains additional fields that indicate the validity (and
accuracy in UBX-NAV-PVT) of the calculated times (see also the GNSS times section below for
further messages containing time information).
3.10.4 GNSS times
Each GNSS has its own time reference for which detailed and reliable information is provided in the
messages listed in the table below.
Time reference Message
GPS time UBX-NAV-TIMEGPS
BeiDou time UBX-NAV-TIMEBDS
GLONASS time UBX-NAV-TIMEGLO
Galileo time UBX-NAV-TIMEGAL
QZSS time UBX-NAV-TIMEQZSS
UTC time UBX-NAV-TIMEUTC
Table 25: GNSS times
3.10.5 Time validity
Information about the validity of the time solution is given in the following form:
•
Time validity: Information about time validity is provided in the valid flags (e.g. validDate
and validTime flags in the UBX-NAV-PVT message). If these flags are set, the time is known
and considered valid for use. These flags are shown in table GNSS times in section GNSS times
above as well as in the UBX-NAV-PVT message.
• Time validity confirmation: Information about confirmed validity is provided in the
confirmedDate and confirmedTime flags in the UBX-NAV-PVT message. If these flags are
set, the time validity can be confirmed by using an additional independent source, meaning
that the probability of the time to be correct is very high. Note that information about time
UBX-20039643 - R06
3 Receiver functionality Page 67 of 119
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