船舶导航场景海事航标（AIS虚拟航标）数据

船舶导航应用中，用户可根据其当前经纬度位置来查找所处海区的所有AIS虚拟航标数据，可以帮助用户进行航线规划，确定船舶位置和航向，使船舶沿航道和预定航线安全航行，保障船舶航行安全。AIS虚拟航标数据中的坐标和半径为geom数据，主要对geom数据进行加工处理，数据存储为WKT格式，一部分描述空间几何对象的类型和坐标系信息（例：LINESTRING (x1 y1, x2 y2, ..., xn yn)），另一部分则是空间几何对象的坐标点的序列，系统通过坐标类型的枚举匹配识别出当前WKT的对象类型，然后根据对象类型对其包含的空间信息进行二次处理，根据点、线、面、多线、多面等情况进行处理后生成经纬度列表数据list，根据射线法判断两个面是否相交，射线法主要思想是从一个点（通常是多边形的重心）发出一条射线，然后计算这条射线穿过多边形的边数。如果穿过的边数为奇数，则这个点在多边形内部；反之则在多边形外部，最后将list划分至对应的海区，船舶在导航过程中，根据其当前经纬度位置来判断所处海区，并将海区中所有的海事航标在海图上显示。

In ship navigation applications, users can query all AIS virtual aid to navigation data of the current sea area based on their current latitude and longitude coordinates. This functionality assists users in route planning, confirming vessel position and heading, enabling safe navigation along fairways and pre-planned routes, and ensuring maritime navigation safety. The coordinates and radius in AIS virtual aid to navigation data constitute the geom data. Core processing mainly targets this geom data, which is stored in Well-Known Text (WKT) format. A WKT string consists of two parts: one describing the type of spatial geometric object and coordinate system information (e.g., LINESTRING (x1 y1, x2 y2, ..., xn yn)), and the other being the sequence of coordinate points of the spatial geometric object. The system identifies the object type of the current WKT string through enumeration matching of coordinate types, then performs secondary processing on the contained spatial information based on the object type. After processing cases such as points, lines, polygons, multi-lines and multi-polygons, a latitude-longitude list is generated. The ray-casting algorithm is used to determine whether two polygons intersect. The core idea of the ray-casting algorithm is to emit a ray from a point (usually the centroid of the polygon) and count the number of edges of the polygon that the ray intersects. If the number of intersecting edges is odd, the point is inside the polygon; otherwise, it is outside the polygon. Finally, the generated latitude-longitude list is assigned to the corresponding sea area. During the navigation process, the vessel determines its current sea area based on its current latitude and longitude coordinates, and displays all maritime aids to navigation in that sea area on the nautical chart.