MAX-M10M - Integration manual
Configuration item
Description
CFG-NAVSPG-INFIL_NCNOTHRS,
CFG-NAVSPG-INFIL_CNOTHRS
A navigation solution will only be attempted if there is at least the given number of
satellites with signals at least as strong as the given threshold.
Table 9: Navigation input filter parameters
If the receiver has only three satellites for calculating a position, the navigation algorithm uses a
constant altitude to compensate for the missing fourth satellite. This is called a 2D fix. The constant
altitude value is taken from the last successful 3D fix using a minimum of four available satellites.
u-blox receivers do not calculate any navigation solution with fewer than three satellites.
2.2.3 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
(for example, 2D, 3D ).
Where a fix has been achieved, the fix is checked to determine whether it is 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 be 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 as valid should not 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 it is recommended to use the
UBX-NAV-PVT message.
2.2.4 Odometer filters
2.2.4.1 Speed (3D) low-pass filter
The CFG-ODO-OUTLPVEL configuration item activates a speed (3D) low-pass filter. The output of
the speed low-pass filter is available in the UBX-NAV-VELNED message (
speed
field). The filtering
level can be set via the CFG-ODO-VELLPGAIN configuration item and must be between 0 (heavy low-
pass filtering) and 255 (weak low-pass filtering).
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.
2.2.4.2 Course over ground low-pass filter
The CFG-ODO-OUTLPCOG configuration item activates 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
2D) low-pass filter is available 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 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 8 m/s or higher, no course over ground low-pass
filtering is performed.
UBX-22038241 - R02
2 Receiver configuration
Page 16 of 92
C1-Public
