ZED-F9P-Integration Manual
UBX-18010802 - R02
4 Receiver description Page 55 of 114
Advance Information
Important: Users are recommended to check the gnssFixOK flag in the UBX-NAV-PVT or the
NMEA valid flag. Fixes not marked valid should not normally be used.
UBX-NAV-STATUS message also reports whether a fix is valid in the gpsFixOK flag. These
messages have only been retained for backwards compatibility and users are recommended to use
the UBX-NAV-PVT message in preference.
The CFG-NAVSPG-OUTFIL_TDOP and CFG-NAVSPG-OUTFIL_TACC configuration items also
define TDOP and time accuracy values that are used in order to establish whether a fix is regarded
as locked to GNSS or not, and as a consequence of this, which time pulse setting has to be used.
Fixes that do not meet both criteria will be regarded as unlocked to GNSS, and the corresponding
time pulse settings of CFG-TP-* configuration group will be used to generate a time pulse.
4.9.3.1 Speed (3-D) Low-pass filter
The CFG-ODO-OUTLPVEL configuration item offers the possibility to activate a speed (3D) low-
pass filter. The output of the speed low-pass filter is published in the UBX-NAV-VELNED message
(speed field). The filtering level can be set via the CFG-ODO-VELLPGAIN configuration item and
must be comprised between 0 (heavy low-pass filtering) and 255 (weak low-pass filtering).
Strictly speaking, the internal filter gain is computed as a function of speed. Therefore, the
level as defined in the CFG-ODO-VELLPGAIN configuration item defines the nominal filtering
level for speeds below 5m/s.
4.9.3.2 Course over ground low-pass filter
The CFG-ODO-OUTLPCOG configuration item offers the possibility to activate a course over ground
low-pass filter when the speed is below 8m/s. The output of the course over ground (also named
heading of motion 2-D) low-pass filter is published in the UBX-NAV-PVT message (headMot field),
UBX-NAV-VELNED message (heading field), NMEA-RMC message (cog field) and NMEA-VTG
message (cogt field). The filtering level can be set via the CFG-ODO-COGLPGAIN configuration item
and must be comprised between 0 (heavy low-pass filtering) and 255 (weak low-pass filtering).
The filtering level as defined in the CFG-ODO-COGLPGAIN configuration item defines the
filter gain for speeds below 8m/s. If the speed is higher than 8m/s, no course over ground low-
pass filtering is performed.
4.9.3.3 Low-speed course over ground filter
The CFG-ODO-USE_COG activates this feature and the CFG-ODO-COGMAXSPEED, CFG-ODO-
COGMAXPOSACC configuration items offer the possibility to configure a low-speed course over
ground filter (also named heading of motion 2D). This filter derives the course over ground from
position at very low speed. The output of the low-speed course over ground filter is published in
the UBX-NAV-PVT message (headMot field), UBX-NAV- VELNED message (heading field), NMEA-
RMC message (cog field) and NMEA-VTG message (cogt field). If the low-speed course over ground
filter is not activated or inactive, then the course over ground is computed as described in section
Freezing the Course Over Ground.
4.9.4 Static hold
Static Hold Mode allows the navigation algorithms to decrease the noise in the position output
when the velocity is below a pre-defined "Static Hold Threshold". This reduces the position wander
caused by environmental factors such as multi-path and improves position accuracy especially in
stationary applications. By default, static hold mode is disabled.
If the speed drops below the defined "Static Hold Threshold", the Static Hold Mode will be activated.
Once Static Hold Mode has been entered, the position output is kept static and the velocity is set to
zero until there is evidence of movement again. Such evidence can be velocity, acceleration, changes
of the valid flag (e.g. position accuracy estimate exceeding the Position Accuracy Mask, see also
section Navigation Output Filters), position displacement, etc.
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