Java 已知两个坐标经纬度以及两个坐标方向（应该是方向角度数）求两点相交得交点经纬度

这个问题需要用到一些基本的地理学知识和公式，以下是一个简单的 Java 实现：

public class IntersectionPoint {
    // 地球半径，单位为米
    private static final double EARTH_RADIUS = 6378137;

    // 计算两点间的距离，返回单位为米
    private static double distance(double lat1, double lng1, double lat2, double lng2) {
        double radLat1 = Math.toRadians(lat1);
        double radLat2 = Math.toRadians(lat2);
        double a = radLat1 - radLat2;
        double b = Math.toRadians(lng1) - Math.toRadians(lng2);
        double s = 2 * Math.asin(Math.sqrt(Math.pow(Math.sin(a / 2), 2)
                + Math.cos(radLat1) * Math.cos(radLat2) * Math.pow(Math.sin(b / 2), 2)));
        return s * EARTH_RADIUS;
    }

    // 计算方向角，返回值为角度数
    private static double direction(double lat1, double lng1, double lat2, double lng2) {
        double dx = Math.cos(Math.toRadians(lat2)) * Math.sin(Math.toRadians(lng2 - lng1));
        double dy = Math.cos(Math.toRadians(lat1)) * Math.sin(Math.toRadians(lat2)) -
                Math.sin(Math.toRadians(lat1)) * Math.cos(Math.toRadians(lat2)) *
                        Math.cos(Math.toRadians(lng2 - lng1));
        double angle = Math.atan2(dx, dy);
        return (Math.toDegrees(angle) + 360) % 360;
    }

    // 计算交点坐标，返回值为经纬度数组
    private static double[] intersection(double lat1, double lng1, double dir1,
                                         double lat2, double lng2, double dir2) {
        double d = distance(lat1, lng1, lat2, lng2);
        double radDir1 = Math.toRadians(dir1);
        double radDir2 = Math.toRadians(dir2);
        double radLat1 = Math.toRadians(lat1);
        double radLat2 = Math.toRadians(lat2);
        double radLng1 = Math.toRadians(lng1);
        double radLng2 = Math.toRadians(lng2);
        double x = Math.sin(radDir1) * Math.cos(radDir2) * Math.sin(radLat2 - radLat1);
        double y = Math.sin(radDir1) * Math.cos(radDir2) * Math.cos(radLat2 - radLat1) * Math.sin(radLng2 - radLng1);
        double z = Math.cos(radDir1) * Math.sin(radDir2) * Math.sin(radLat2 - radLat1) * Math.cos(radLng2 - radLng1);
        double a = Math.pow(x, 2) + Math.pow(y, 2) + Math.pow(z, 2);
        double b = 2 * EARTH_RADIUS * (x * (radLng2 - radLng1) + y * (radLat2 - radLat1) + z * (Math.PI / 2 - radLat2));
        double c = Math.pow(EARTH_RADIUS, 2) * Math.pow(d, 2) - Math.pow(x * EARTH_RADIUS * (radLng2 - radLng1), 2) -
                Math.pow(y * EARTH_RADIUS * (radLat2 - radLat1), 2) - Math.pow(z * EARTH_RADIUS * (Math.PI / 2 - radLat2), 2);
        double delta = Math.pow(b, 2) - 4 * a * c;
        if (delta < 0) {
            return null;
        }
        double t = (-b + Math.sqrt(delta)) / (2 * a);
        double lat = Math.asin(Math.sin(radLat1) * Math.cos(t) + Math.cos(radLat1) * Math.sin(t) * Math.cos(radDir1));
        double lng = radLng1 + Math.atan2(Math.sin(t) * Math.sin(radDir1) * Math.sin(radLat1),
                Math.cos(t) - Math.sin(radLat1) * Math.sin(lat));
        return new double[]{Math.toDegrees(lat), Math.toDegrees(lng)};
    }

    public static void main(String[] args) {
        double lat1 = 39.9042;
        double lng1 = 116.4074;
        double dir1 = 30;
        double lat2 = 31.2304;
        double lng2 = 121.4737;
        double dir2 = 220;
        double[] intersection = intersection(lat1, lng1, dir1, lat2, lng2, dir2);
        if (intersection == null) {
            System.out.println("No intersection point.");
        } else {
            System.out.printf("Intersection point: (%f, %f)\n", intersection[0], intersection[1]);
        }
    }
}

以上代码假设输入的经纬度为 WGS84 坐标系下的经纬度，计算结果也是 WGS84 坐标系下的经纬度。如果需要用其他坐标系，需要进行转换。