船舶导航避险场景危险沉船数据
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船舶导航应用中，对当前船舶一定范围内的危险沉船进行自动识别，可在海图中标记出现，并对船舶进行文字提醒，可减少船舶在航行中的事故发生率。危险沉船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，WKT格式由两部分组成，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。在实际应用中，航行船舶可看作一个点，list的经纬度点组成一个面，根据点和面的位置关系算法判断点是否在面的内部，具体为设面的顶点依次为A1，A2…An，要判断的点为P，那么分别计算向量PA1叉乘向量PA2，向量PA2叉乘向量PA3，…，向量PA(n-1)叉乘向量PAn，向量PAn叉乘向量PA1，如果这些叉乘的结果都同向的话，那么这个点就在多边形的内部。结合船舶航行的角度和速度，从所有数据中计算出对船舶存在影响的危险沉船数据。
In ship navigation applications, automatically identifying dangerous shipwrecks within a certain range of the current vessel, marking them on nautical charts, and sending text alerts to the vessel can reduce the accident rate during navigation. The coordinates and radius in the dangerous shipwreck data belong to geom data, which are mainly processed. The data is stored in WKT (Well-Known Text) format, which consists of two parts: one part describes the type of spatial geometric object and coordinate system information (e.g., LINESTRING (x1 y1, x2 y2, ..., xn yn)), and the other part is the sequence of coordinate points of the spatial geometric object. The system identifies the object type of the current WKT through enumeration matching of coordinate types, then performs secondary processing on the contained spatial information according to the object type, and generates a longitude and latitude list data after processing cases such as points, lines, polygons, multi-lines, and multi-polygons. In practical applications, a navigating vessel can be regarded as a point, and the longitude and latitude points in the list form a polygon. The algorithm for the positional relationship between a point and a polygon is used to determine whether the point is inside the polygon. Specifically, suppose the vertices of the polygon are A1, A2…An in sequence, and the point to be judged is P. Then calculate the cross product of vector PA1 and vector PA2, the cross product of vector PA2 and vector PA3, ..., the cross product of vector PA(n-1) and vector PAn, and the cross product of vector PAn and vector PA1. If all these cross product results are in the same direction, then the point is inside the polygon. Combined with the navigation angle and speed of the vessel, the dangerous shipwreck data that poses a threat to the vessel is calculated from all the data.
