Vector Sensor Reference Manual 96
constant is 2.0 seconds of smoothing. Increasing the time constant will increase the level of
heading smoothing.
The following command is used to adjust the heading time constant.
$JATT,HRTAU,hrtau<CR><LF>
Where ‘hrtau’ is the new time constant that falls within the range of 0.0 to 3600.0 seconds.
Depending on the expected dynamics of the vessel, you may wish to adjust this parameter. For
instance, if the vessel is very large and is not able to turn quickly, increasing this time is reasonable.
The resulting heading would have reduced ‘noise’, resulting in consistent values with time.
However, artificially increasing this value such that it does not agree with a more dynamic vessel
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.
6.8.13 $JATT,COGTAU
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.
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
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