ZED-F9H - Integration manual
3.1.5.3 MB rover operation
In its default configuration, the ZED-F9H will attempt to provide the best heading accuracy
depending on the received correction data from a ZED-F9P base in moving base mode. It will enter
RTK float mode as soon as it receives an input stream of RTCM correction messages. Once the rover
has resolved the carrier phase ambiguities, it will enter RTK fixed mode. When in this mode, the
relative heading between base and rover can be expected to be accurate. The time period between
RTK float and RTK fixed operation is referred to as the convergence time. Note that the convergence
time is affected by multipath and satellite visibility at both rover and base station.
The ZED-F9H should receive RTCM corrections matching its GNSS signal configuration to function
optimally. The rover requires both base station observation (MSM4 or MSM7 messages) and
position message (RTCM 4072.0) in order to attempt ambiguity fixes. The rover will attempt to
provide RTK fixed operation when sufficient number of ambiguities are available. If phase lock on
sufficient number of signals cannot be maintained, the rover will drop back to RTK float mode. The
rover will continue to attempt to resolve carrier ambiguities and revert to RTK fixed mode once the
minimum number of signals has been restored.
The RTK mode that an RTK rover operates in can be configured through the CFG-NAVHPG-
DGNSSMODE configuration item. The following two RTK modes are available:
• RTK fixed: The rover will attempt to fix ambiguities whenever possible.
• RTK float: The rover will estimate the ambiguities as float but will make no attempts at fixing
them.
To provide accurate heading information RTK fixed mode should be kept.
The received correction messages stream should comply with the following:
• The reference station ID in the reference station message (RTCM 4072.0) must match that
used in the MSM observation messages. Otherwise, the rover cannot compute its position.
With a direct connection between the ZED-F9P moving base and the ZED-F9H rover this will
not be an issue. On a more complex networked communication system such as automotive or a
shipping vessel this needs to be considered.
• In order to fix GLONASS ambiguities the correction stream must contain message 1230.
Otherwise, the carrier ambiguities will be estimated as float even when set to operate in RTK
fixed mode. This will significantly degrade heading accuracy.
CFG-RTCM-DF003_IN
can be used to configure the desired reference station ID and CFG-RTCM-
DF003_IN_FILTER can be used to configure how strict the filtering should be (RELAXED is the
recommended setting).
3.1.5.3.1 Message output in MB RTK mode
When operating in MB RTK rover mode users should take note of the modified information within
the following NMEA and UBX messages:
• NMEA-GGA: The quality field will be 4 for RTK fixed and 5 for RTK float (see NMEA position fix
flags in interface description). The age of differential corrections and base station ID will be set.
• NMEA-GLL, NMEA-VTG: The posMode indicator will be D for RTK float and RTK fixed (see
NMEA position fix flags in interface description).
• NMEA-RMC, NMEA-GNS: The posMode indicator will be F for RTK float and R for RTK fixed (see
NMEA position fix flags in interface description).
• UBX-NAV-PVT: The carrSoln flag will be set to 1 for RTK float and 2 for RTK fixed.
5
CFG-RTCM-DF003_* items are supported from firmware version HDG 1.13 onwards
UBX-19030120 - R04
3 Receiver functionality
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