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Introduction

The purpose of coasting is to enable the software to maintain target tracking across multiple poor detection areas where a single track may be lost or go out of view. Using data from the real track sightings the software attempts to predict the course of a track when the radar loses visibility of the target. In this situation the software will report predicted track sightings until the target has been re-acquired by the radar at which point it will report real sightings again. Coasting is an embedded process in Witness, and can be controlled using the settings in the Tracking Parameters. This allows different coasting settings in different areas, allowing for larger coast allowances in areas where line of sight is poor or detection is sub-optimal.

Coasting Configuration

Coasting parameters can be found in Tracking Parameters settings.

In order to use coasting track, Witness has three primary settings:

Min. Coast Age: this is the age (in sightings) at which point the track will start to coast. Prior to the track reaching this number of sightings the track and will not coast and will be deleted as soon the radar loses visibility of the target.

Max. Coast Age: this is the maximum age of the track (in sightings) at which point the full amount of available coasts will be used from this point onward.

Coasts: the maximum number of coasts to use. This value sets the maximum number of consecutive predictions the software can make if it can't see the target. If this value is reached and the radar still can't see the target then the track will be deleted. 

Understanding the Coast Age

Coast Age serves one simple purpose: to allow the software to coast well established tracks for longer. So if a track is new and there is a possibility that it might be a false alarm then we do not want to keep this track alive for longer than necessary. However as the track gets older the software can be more confident it is a genuine track and therefore can coast the track for longer. The Min and Max Age work in conjunction with the Coasts limit. So the software will coast based a linear increase between min and max ages. 

For example, in the graph above, the min age has been set to 5 and the max age is 10. As the sightings increase the available number of coasts increases. So if the coast limit had been set to 4 then to calculate how many coasts would be used as the formula is:

((sightings - min age) / (max age - min age)) * max coasts

So when we have 6 sightings the value is:

((6 - 5) / (10 - 5) * 4 = 0.8 and rounded to a whole number = 1

And when we have 8 sightings:

((8 - 5) / (10 - 5) * 4 = 2.4 and rounded to a whole number = 2

And we have 10 sightings (or more):

((10 - 5) / (10 - 5) * 4 = 4

So we only use the maximum value of Coast when the sightings ≥ Max Coast Age (in this example when sightings is ≥ 10).

Maximum Coasts

Be cautious when setting the Coasts value. If the radar is located and configured correctly it should detect and track targets with very little coasting. If you set a large Coasts value then there is a possibility that you will keep a track alive artificially which can lead to confusion about where a track was actually lost or went out of sight. A typically coasting value is 3 or 4 and we would not recommend anything greater than 5 without a good reason.

Identification

Coasting tracks can be identified from normal tracks by their bright blue appearance. Coasted are tracks are not shown by default. To enable them use Highlight Coasting Tracks in the user Tracks:

Once enabled the tracks will display their costing status in real time on the PPI.

Coasts Ratio

Under the Playback tab, if a Track Query is posed, Coasts Ratio is one of the values given in the Results Panel. This metric is useful to identify the quality of tracking in specific areas or at certain ranges through an understanding of where tracks are lost and gained. The Coasts Ratio itself represents the ratio of coasting sightings to actual sighting e.g. 4:80. Fewer coasts means better tracking.

It is possible to specify which exact sightings were coasts by selecting the History icon and opening the Track Details window.

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