ZED-F9T-Integration Manual
Configuration item Description
CFG-NAVSPG-FIXMODE By default, the receiver calculates a 3D position fix if possible but reverts to 2D
position if necessary (auto 2D/3D). The receiver can be forced to only calculate 2D (2D
only) or 3D (3D only) positions.
CFG-NAVSPG-CONSTR_ALT, CFG-
NAVSPG-CONSTR_ALTVAR
The fixed altitude is used if fixMode is set to 2D only. A variance greater than zero
must also be supplied.
CFG-NAVSPG-INFIL_MINELEV Minimum elevation of a satellite above the horizon in order to be used in the
navigation solution. Low elevation satellites may provide degraded accuracy, due to
the long signal path through the atmosphere.
CFG-NAVSPG-INFIL_NCNOTHRS,
CFG-NAVSPG-INFIL_CNOTHRS
A navigation solution will only be attempted if there are at least the given number of
SVs with signals at least as strong as the given threshold.
Table 13: Navigation input filter parameters
3.1.7.3 Navigation output filters
The result of a navigation solution is initially classified by the fix type (as detailed in the fixType
field of UBX-NAV-PVT message). This distinguishes between failures to obtain a fix at all ("No Fix")
and cases where a fix has been achieved, which are further subdivided into specific types of fixes
(e.g. 2D, 3D, dead reckoning).
The ZED-F9T firmware does not support the dead reckoning position fix type.
Where a fix has been achieved, a check is made to determine whether the fix should be classified as
valid or not. A fix is only valid if it passes the navigation output filters as defined in CFG-NAVSPG-
OUTFIL. In particular, both PDOP and accuracy values must lie below the respective limits.
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.
3.1.7.3.1 Speed (3D) 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 5 m/s.
3.1.7.3.2 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 8 m/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 8 m/s. If the speed is higher than 8 m/s, no course over ground
low-pass filtering is performed.
3.1.7.3.3 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
UBX-19005590 - R01
3 Receiver functionality Page 17 of 80
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