and users are recommended to use the UBX-NAV-PVT message in preference.
The UBX-CFG-NAV5 message also defines 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 UBX-CFG-TP5 will be used to generate a time pulse.
2.3.1 Speed (3-D) Low-pass Filter
The UBX-CFG-ODO message offers the possibility to activate a speed (3-D) 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 UBX-CFG-ODO message (velLpGain field) 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 UBX-CFG-ODO message (velLpGain field) defines the nominal filtering level for
speeds below 5m/s.
2.3.2 Course over Ground Low-pass Filter
The UBX-CFG-ODO message 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
UBX-CFG-ODO message (cogLpGain field) and must be comprised between 0 (heavy low-pass filtering) and
255 (weak low-pass filtering).
The filtering level as defined in the UBX-CFG-ODO message (cogLpGain field) 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.
2.4 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.
The UBX-CFG-NAV5 message additionally allows for configuration of distance threshold (field
staticHoldMaxDist). If the estimated position is farther away from the static hold position than this threshold,
static mode will be quit.
2.5 Low-speed Course Over Ground Filtering
The UBX-CFG-ODO message offers the possibility to activate a low-speed course over ground filter (also named
heading of motion 2-D). This filter derives the course over ground from position at very low speed. The output
of the course over ground low-speed 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 course over ground low-speed filter is not activated or inactive, then the course over ground is
computed as described in section Freezing the Course Over Ground.
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