# Near-Optimal Weather Routing by Using Improved A* Algorithm
## 4 Case Study
### Prediction of Ship's Estimated Time of Arrival
#### 4.1.1 Dataset 1: AIS Data  
AIS is a system designed to be capable of providing information about a ship to other ships and to coastal authorities. The information includes the ship location, speed, and other navigational information in real time. The IMO has recommended that vessels use the AIS to enhance the safety and security of the marine environment. Many countries and institutes carry out effective rescue activities and manage the safety of ships through continuous monitoring of AIS data, which also facilitates vessel traffic service. The AIS data are originally divided into static, dynamic, navigational, and text communication information; however, dividing them into static and dynamic information is common. The detailed composition of AIS data generally conforms with international standards [27]. The AIS data used in this study were collected from 76 ships during 2018. The static and dynamic data were collected daily for 1 year. These two types of data tables are defined by three common factors: the Maritime Mobile Service Identity (MMSI); message type and date time stamp that identify which vessel the data were collected from; and what kind of attributes the data have. The MMSI is an identifier of vessels and it enables categorization of ships on the basis of the country to which they belong. The message type is used only for information management in the database and is not directly related to ships. The date time stamp associated with information pertaining to the time at which the data were collected was Korean Central Standard Time (KST). The static AIS data consist of 11 parameters excluding these three common factors (MMSI, message type and date time stamp). The IMO number is used to distinguish ships along with the call sign, the vessel name, and the type of ship, where the call sign is used as an identifier especially for communication between ships. The dimensions A to D indicate the locations of the electronic position fixing devices from the front, back, left, and right ends of a ship. The ETA in the static AIS data only includes the information about the expected date on which the voyage is finished and not the total time required for the entire voyage. The draft (or \"draught\") is the vertical distance from the bottom of the hull to the sea surface, indicating how far the vessel extends below the surface. The static AIS information is shown in Table 2. The data depicted in Table 2 follow the order of the raw static AIS dataset and type 5 indicates the AIS message type ID related to the static and voyage data. The dynamic AIS data have different factors from the static data, as shown in Table 3. Type 1,2, and 3 indicate the AIS message IDs related to the position of the ship. First, the position of the vessel is described using the latitude and longitude coordinates. The SOG and COG are the ship's final speed and direction considering environmental disturbance such as wind and wave. The ROT describes the rotation angle per minute, which can be optionally included in the AIS dataset. The true heading indicates the direction in which the vessel is facing, not considering any external interferences. Thus, \begin{table}
\begin{tabular}{c c c c} \hline \hline
**No.** & **Parameter** & **Unit** & **Remark** \\ \hline
1 & MMSI & - & \\
2 & IMO number & - & \\
3 & Call sign & - & \\
4 & Name & - & \\
5 & Type of ship & - & Type 5 \\
6–9 & Dimension A–D & M & (Static information) \\
10 & Electronic fixing device & - & \\
11 & ETA & YYYMMDD & \\
12 & Max drought & M & \\
13 & Msg type & - & \\
14 & Date time stamp & KST & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Static AIS data configurations. there is always a slight difference between the heading and COG. If the vessel is under calm and still sea conditions with no drift, the heading and COG values are identical; if not, they are somewhat different.