怎样判断GPS坐标在电子围栏内

leafstamen

To determine whether a GPS coordinate is within an electronic fence, which is a convex polygon formed by multiple GPS coordinates, we can use the Ray Casting algorithm. The main idea is to draw a line segment from the coordinate to a point outside the polygon, and count how many edges it intersects. If the number of intersections is even, the coordinate is outside the polygon, otherwise it's inside.

This algorithm can accurately judge whether the coordinate is within the convex polygon. However, since the Earth is not a flat plane, if the GPS data in the vertices of the polygon crosses the change line (the boundary between 360 degrees and -360 degrees), it may cause problems, and may need to add or subtract in some corner data.

So, the implementation process is to traverse each edge of the polygon in turn, and determine whether the connection point of the coordinate and the edge is on the left or right of the edge vector. If it's on the right, it's considered to be intersected, otherwise it's not. When the last edge is judged, if the result is intersect, it means that the coordinate is outside the polygon, otherwise it's inside.

In conclusion, through the above algorithm, we can determine whether a GPS coordinate is within a given convex polygon (electronic fence).

leafstamen

竟然有这么神奇的算法，从这个点随便往一个方向画一条线，数这条线和围栏的变交点的个数，奇数个就是在围栏里面，偶数个就是在围栏外面。

leafstamen

amazing030 发表于 2024-3-20 16:20
很不错的办法，那问题又来了，怎么判断相交点？
(引用自4楼)

要计算的点(x,y)，假如竖着向下画线，边的两个点的x坐标一个比x大一个比x小就会相交，由于是往下画线，所以还需要再比较一下边的Y是不是有在点y下方的部分。估计搜索一下就能找到关于电子围栏的高效的并且成熟的计算方法。