# A Framework for the Detection of Search and Rescue Patterns Using Shapelet Classification
## 2 Related Work
### SAR Maneuvers  
This work presumes a list of SAR patterns as described in the \"U.S. Coast Guard addendum to the United States National Search and Rescue supplement NSS\" [20] which is extended with the patterns detected in Reference [13]. The list comprises the following SAR patterns:  
* **Creeping line (and parallel track)**: A creeping line pattern is constructed with the sequence of two turn left and two turn right (or two turn right and two left) with fixed size of 3 loops. The creeping line and the parallel track have very similar shapes with the only different that in the former case, the search legs are at right angles to the major axis of the search area, whereas in the latter search legs are parallel to the major axis of the search area.
* **Sector**: A Sector Search aims to cover a limited area, with the first leg usually orientated in the probable direction of the target drift. Once the length of the search legs exceed 3\(\times\) the sweep width, 'gaps' start to appear in the pattern. The pattern is constructed with a random choice of loop value between 2 to 4 and with the constant sequence of a go-straight, turn left, turn left (or go-straight, turn right, turn right) movements with a random turning value between 110 to 130 degrees. This is the most difficult SAR pattern to be constructed and the geometry, as well as the full completion of pattern is loosely achieved, without change the extensively the noise parameters and thus not succeed of making a solid randomly real sector pattern trajectory.
* **Box or Expanding square**: An expanding square pattern is a complicated movement to carry out due to the constant changes in distance and times for the search legs. Unlike the Sector Search it is not limited in the area it can cover. It is constructed with the use of turn left (or turn right) movements with incremental value of loops from 1 to 6 at most, with step 1 at every iteration. This kind of pattern has certain number of turns and a fixed turning value in order to succeed the geometry required, just like the real SAR patterns has.
* **Spiral movement**: Visually, it resembles the expanding square pattern but with a decreasing radius at each step and without performing almost orthogonal turns. The spiral movement pattern is constructed with the use of a constant turn left (or turn right) movement with a random value of turning between 45 to 80 degrees.
* **Steps**: A steps maneuver usually follows a presumed track but with orthogonal changes in direction and its main purpose is to patrol/scan a large are in the sea. The step up pattern is constructed with the use of a turn left movement with a turn right movement that follows. This pattern is better described as \"step up left\". In order to create a \"step up right\" pattern the sequence of turns is change to a turn right and then a turn left movement.  
A visualization of the aforementioned patterns is presented in Figure 1.  
In addition to the above patterns, we assume a random movement, which simulates the random trajectory of a vessel, with small or no changes at all in course and speed. It's a straight line trajectory, with small distortions because of bearing noise that simulates the trajectory of a vessel heading to its destination. It is important to clarify here that this random movement corresponds to the trajectory of a vessel in the open sea, on the move to its destination and not on the trajectory of the vessel near a port, where many bearing and speed changes may occur.  
Figure 1: The different types of search and rescue maneuvers.