Vector Sensor Reference Manual 28
seconds of smoothing. Increasing the time constant will increase the level of speed measurement
smoothing.
The following command is used to adjust the speed time constant.
$JATT,SPDTAU,spdtau<CR><LF>
Where ‘spdtau’ is the new time constant that falls within the range of 0.0 to 3600.0 seconds.
Speed is computed using the primary GPS engine only. As with the heading time constant, the
setting of this value depends upon the expected dynamics of the vessel. If a boat is highly dynamic,
this value should be set to a lower value since the filtering window would be shorter, resulting in a
more responsive measurement. However, if a vessel is very large and has must more resistance to
change in its motion, this value can be increased to reduce measurement noise. The following
formula provides some guidance on how to set this value initially, however, we recommend that
you test how the revised value works in practice. If you are unsure what is the best value for this
setting, it’s best to be conservative and leave it at the default setting.
spdtau (in seconds) = maximum acceleration (in m/s
2
) / 10
You may query the Vector Sensor for the current heading time constant by issuing the same
command without an argument.
$JATT,SPDTAU<CR><LF>
Note - If you are unsure of the best value for this setting, it’s best to be conservative
and leave it at the default setting of 0.0 seconds.
1.8.7 Level Operation
If the Vector Sensor system will operate in a level plane (within ±10° from horizontal), an
additional constraint can be placed upon the RTK heading solution in order to reduce the RTK
search time and increase solution robustness. This feature, referred to as ‘level operation’ is
disabled by default but can be invoked using the following command.
$JATT,LEVEL,YES<CR><LF>
To turn this feature off, issue the following command.
$JATT,LEVEL,NO<CR><LF>
To determine the current status of this message, issue the following command.
$JATT,LEVEL<CR><LF>
1.8.8 Heading Compensation
You may adjust the heading output from the Vector Sensor in order to calibrate the true heading
of the Antenna Array to reflect the true heading of the vessel using the following command.
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