# Collision Avoidance Behavior Mining Model Considering Encounter Scenarios
## 1 Introduction
### Literature Review  
#### 1.2.1 Related Research on the Division of Ship Encounter Scenarios  
The COLREGs in Articles 13, 14, and 15 classify encounter scenarios between vessels under the condition of mutual visibility into three categories: overtaking, head-on, and crossing scenarios. However, no specific quantitative criteria are provided to determine the exact boundaries of these encounter scenarios. In the study of ship-to-ship collision risks, determining the encounter scenario of vessels and assessing the type of encounter are crucial steps. Consequently, many experts and scholars have attempted to further subdivide these three situations based on the COLREGs and have redefined and supplemented the identification models for different encounter scenarios as outlined in the regulations. One classic method for classifying encounter situations is based on the relative bearing model, as shown in Figure 1a. [PERSON] and [PERSON] [8] analyzed 236 expert questionnaires to establish a classification diagram based on the bearing angle, with the model divided into the ranges of 5-67.5\({}^{\circ}\), 112.5-210\({}^{\circ}\), and 247.5-355\({}^{\circ}\). Although this model has garnered widespread attention, it is clearly limited when relying solely on the position of the target vessel relative to the ship's bow angle to classify encounter types. As illustrated in Figure 1b, defining the situation solely based on the target vessel's bow angle range leads to the conclusion that target vessels 1 and 2 and the ship should form a head-on encounter and target vessels 3 and 4 and the ship should form a crossing encounter. However, it is evident that target vessels 1 and 4 should constitute an overtaking situation.  
Many scholars in the maritime field have improved models for vessel encounter scenario identification based on the COLREGs. [PERSON] et al. [9], in their study of collision avoidance methods for unmanned surface vehicles (USVs), divided encounter situations into six regions to ensure that the avoidance maneuvers of the vessel comply with the requirements of the COLREGs. First, the encounter situations were classified according to the relative bearing (bow angle) between the vessels. Then, they explained that the types of encounter situations (such as head-on, crossing, or overtaking) are determined by the heading angles of the two encountering vessels. Finally, different collision avoidance decisions were made based on the collision types. [PERSON] et al. [10], in their research on intelligent collision avoidance systems for ships, divided the ship's bearing angle into ranges of 22.5-90\({}^{\circ}\), 112.5-150\({}^{\circ}\), 210-247.5\({}^{\circ}\), and 270-337.5\({}^{\circ}\), adding fuzzy regions for crossing and overtaking situations to complement the COLREGs. [PERSON] et al. [11] classified the ship's bearing angles into the following ranges: 5-85\({}^{\circ}\), 95-175\({}^{\circ}\), 185-211\({}^{\circ}\), 265-275\({}^{\circ}\), and 329-355\({}^{\circ}\). They divided the collision avoidance regions I to X into ten zones,allowing for a smooth transition between fuzzy collision avoidance decisions. [PERSON] et al. [12], based on AIS data, extracted vessel encounter locations and corresponding actual avoidance behaviors. They combined the requirements of the COLREGs and support vector classification to construct a bearing angle division diagram for ship encounters. The encounter bearing angles they classified were 2-5\({}^{\circ}\), 44-107\({}^{\circ}\), 203-257\({}^{\circ}\), and 306-355\({}^{\circ}\).