## 3 Experiments and Discussions
### Time Retrieval Efficiency
The process of sorting the set of ships available for rescue by comparing the distance from the ship in distress has low arithmetic multiplexing, and a single computation consumes a lot of memory. With the increase in the amount of data, its space and time occupation will increase dramatically, so it is not conducive to searching for ships that meet the rescue conditions. The query method based on Google S2 grid encoding searches for rescue ships according to the number of overlapping bits of the 64-bit binary encoding prefix, which only needs to match the prefix of the 64-bit binary encoding, significantly reducing the complexity of the algorithm. At the same time, the encoding results remain unchanged when the ship position points change within the hierarchical range of the grid. This can make caching queries more efficient to increase the query speed of the nearby ships and achieve the rapid search of the eligible rescue ships for the subsequent rescue. In addition, when different ranges are searched according to the rescue needs, every time the range is reset, for the method of Euclidean distance, all the ship position distance data will be traversed again, which leads to low computing efficiency and large memory occupation and reduces the timeliness of ship rescue. For the method of Google S2, the one-dimensional geographic grid coding, instead of the traditional two-dimensional latitude and longitude, has uniqueness, one-dimensionality, and recursiveness [40], which eliminates the need to calculate the Euclidean distance and store the distance data when searching for the surrounding neighboring ships, achieves the representation of the three-dimensional data (latitude, longitude, and distance) with one-dimensional strings, and reduces the occupation of the memory space. According to the China Fisheries Statistical Yearbook [41], 12 provinces in China own marine fishing motorized fishing vessels. They are mainly from Guangdong, Hainan, and Fujian provinces. Guangdong Province owns 35,700 motorized fishing vessels, accounting for 22.88% of all marine fishing motorized fishing vessels. Installed with Beidou and other ship position terminals, according to 3 min or an even higher time-frequency collection of a ship's position information, each collection is marked as a record, and a ship's position record data for a day is 480. In Guangdong Province, the number of records of the ship's position for a day is 1.71 \(\times\) 10\({}^{8}\) articles. Currently, if the ship position track storage and query method based on latitude, longitude, and Haversine distance is used, the space occupation is large, and the retrieval efficiency is slow. The gridding coding not only saves memory resources but also retains spatial information, reflecting the first law of geography:\"Features with Similar Spatial Distance have Similar Spatial Relationships in Space\" [42]. The higher the prefix overlap of the grid coding, the closer the spatial distance of the ship is. The indexing efficiency of the one-dimensional indexing is significantly higher than that of the multi-dimensional, which is ensured through continuous iterative subdivision that the grid coding meets the retrieval demand in a particular range to meet the retrieval requirements, improve data processing efficiency, and reduce operating costs.