Vector Sensor Reference Manual 27
could create a lag in the rate of heading change measurement with higher rates of turn. A
convenient formula for determining what the level of smoothing follows. If you are unsure on how
to set this value, it’s best to be conservative and leave it at the default setting.
hrtau (in seconds) = maximum rate of the rate of turn (in °/s
2
) / 10
You may query the Vector Sensor for the current heading rate time constant by issuing the same
command without an argument.
$JATT,HRTAU<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 2.0 seconds.
1.8.6.4 Course over Ground Time Constant
The course over ground (COG) time constant allows you to adjust the level of responsiveness of
the COG measurement provided in the $GPVTG message. The default value of this constant is
0.0 seconds of smoothing. Increasing the time constant will increase the level of COG smoothing.
The following command is used to adjust the COG time constant.
$JATT,COGTAU,cogtau<CR><LF>
Where ‘cogtau’ is the new time constant that falls within the range of 0.0 to 3600.0 seconds.
COG is computed using the primary GPS engine only, and its accuracy is dependant upon the
speed of the vessel (noise is proportional to 1/speed) and when stationary, this value is invalid.
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 needs be shorter in time, 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. 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.
cogtau (in seconds) = maximum rate of change of course (in °/s) / 10
You may query the Vector Sensor for the current heading time constant by issuing the same
command without an argument.
$JATT,COGTAU<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.
1.8.6.5 Speed Time Constant
The speed time constant allows you to adjust the level of responsiveness of the speed
measurement provided in the $GPVTG message. The default value of this parameter is 0.0
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