java 计算方位角

/**
* 计算方位角
*
* @param x1 lat1
* @param y1 lng1
* @param x2 lat2
* @param y2 lng2
* @return
*/
public static double azimuthAngle(double x1, double y1, double x2, double y2) {
double dx, dy, angle = 0;
dx = x2 - x1;
dy = y2 - y1;
if (x2 == x1) {
angle = Math.PI / 2.0;
if (y2 == y1) {
angle = 0.0;
} else if (y2 < y1) {
angle = 3.0 * Math.PI / 2.0;
}
} else if ((x2 > x1) && (y2 > y1)) {
angle = Math.atan(dx / dy);
} else if ((x2 > x1) && (y2 < y1)) {
angle = Math.PI / 2 + Math.atan(-dy / dx);
} else if ((x2 < x1) && (y2 < y1)) {
angle = Math.PI + Math.atan(dx / dy);
} else if ((x2 < x1) && (y2 > y1)) {
angle = 3.0 * Math.PI / 2.0 + Math.atan(dy / -dx);
}

return (angle * 180 / Math.PI);
}