TRACKPOINT 3
OPERATION
3-24
FILTERING provides operator a choice of various combinations of averaging, filtering, threshold
settings and also limits on certain parameters. Filtering includes averaging, target velocity check-
ing, range gating, signal threshold, minimum xponder range, maximum xponder range and signal
rejection via signal quality checking. The filtering parameters are individual per target.
Averaging: The Averaging parameter is variable from 0 (off) to 10. It is independent of the Filter
Level setting in that you can select the buffer size in which to average a number of replies over (1-
10). This setting corresponds to the number of replies that are averaged along with the present
reply. The averaging routine is used in conjunction with the QF (Quality Factor) and the Filter
Level. With a high quality factor the target position is weighted heavily both on the present reply
and on the previous replies in the averaging buffer. If the present reply has a high QF and the pre-
vious reply had a low QF then the position with the high QF remains heavily weighted within the
averaging buffer. As new replies are received the high QF positions maintain their heavier weight
while the positions with lower QF’s have very little weight. The weights of the target positions are
reduced as the newer replies are received. This approach biases the target position towards the
better QF and also towards the most recent reply providing a better representation of target posi-
tion than by using a mean or average of the target positions. At the higher filter levels (8-10) the
averaging is almost linear across all replies while at the lower filter levels the weight is higher on
the most recent reply. Averaging occurs on the target's position only (X, Y or HD, BRG), not on the
displayed slant range. The slant range displayed in the status block and sent out the RS-232 is the
actual value. Because of this there may be an apparent discrepancy between the displayed posi-
tion and slant range.
Filter Level: The Filter Level setting is variable from 1 to 10. A Filter Level setting of 1-5 is rec-
ommended for most dynamic applications (e.g., ROV tracking). The higher settings of 6-10 are
appropriate for static applications such as station keeping. The parameter settings for the range
blanking gate and velocity filter “tighten up” as the Filter Level is increased with the premise that
dynamic targets such as AUV’s can change position quickly with respect to the vessel while static
targets such as a tow fish or other moored targets do not. Filter settings 6-10 cause the analog or
telemetry depth to average the last three readings. Filter settings 1-5 do not average the input
depth. Also see error code #5.
The table below shows the relationship between the range gate, velocity filter and averaging
weight Vs the Filter Level setting.
FILTER LEVEL/RANGE (blanking) GATE (Transponders & Responders Only)
If there is more than one sequential target the range blanking gate value is multiplied by the num-
ber of targets (e.g., filter level 2 with 4 targets enabled equates to a blanking gate of 80 meters
before the average target range). If the blanking gate exceeds the current range average then it is
set to a minimum (1m). The range average for each target is weighted based on the number of
good replies for that target. If there are no recorded good replies then the routine uses 100%
weight on the current value and is scaled down for up to 4 replies (e.g., if there have been 4 or
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