if the accuracies reported are very low then we can do a division by
zero and this results in a constraining NaN for GPS vertical velocity
filter in NavEKF3_core::calcGpsGoodToAlign
this improves the display on the GCS when the GPS has not yet been
found. This is particularly important after a reboot, as otherwise the
GCS may display stale information from the previous boot
this detects GPS data lag, and if 5 samples in a row are lagged by
more than 50ms beyond the expected lag for the GPS then we declare the
GPS as unhealthy.
This is useful to detect users who have asked for more data from the
GPS then it can send at the baudrate that is being used. The case that
led to this path was a F9 GPS with GPS_RAW_DATA=1 at 115200 baud. In
that case the UART data is quickly lagged by over 1s
when you have a moving baseline pair of ublox GPS modules and the
rover GPS does not have full fixed RTK lock on the base GPS then we
should not use it as our primary GPS as it's position and velocity can
be badly affected by the attempts of the GPS to gain a fixed lock.
This was observed in a flight with two F9P GPS, where the GPS velocity
data from the rover GPS went way off when it lost full RTK lock. It's
status stayed at 4, so it was selected as the primary GPS
this allows for configuration of moving baseline with either uart1 or
uart2 for the RTCM data. Using uart2 requires an extra cable between
the two modules, but requires less uart bandwidth which is good when
DMA channels are low. Using uart2 also avoids the rtcmv3 parser, which
saves memory
this fixes the status reported for a UAVCAN GPS when the cable is
unplugged. It should be "NO GPS", but was instead reporting "NO
FIX". The user had no way to distinguish between not finding a CAN GPS
at all and it not getting satellites
thanks to CUAV for reporting
The NMEA GPHDT sentence can be used to determine the vehicles bearing
instead of a compass even when the vehicle is stationary. This type
of GPS is normally very expensive and does the bearing using some sort
of phase ambituity algorithm.
