1.傳入兩個經緯度座標，計算出兩個座標之間的角度，範圍是0-360。
// 計算方位角,正北向為0度，以順時針方向遞增
private double computeAzimuth(LatLng la1, LatLng la2) {
    double lat1 = la1.latitude, lon1 = la1.longitude, lat2 = la2.latitude,
            lon2 = la2.longitude;
    double result = 0.0;

    int ilat1 = (int) (0.50 + lat1 * 360000.0);
    int ilat2 = (int) (0.50 + lat2 * 360000.0);
    int ilon1 = (int) (0.50 + lon1 * 360000.0);
    int ilon2 = (int) (0.50 + lon2 * 360000.0);

    lat1 = Math.toRadians(lat1);
    lon1 = Math.toRadians(lon1);
    lat2 = Math.toRadians(lat2);
    lon2 = Math.toRadians(lon2);

    if ((ilat1 == ilat2) && (ilon1 == ilon2)) {
        return result;
    } else if (ilon1 == ilon2) {
        if (ilat1 > ilat2)
            result = 180.0;
    } else {
        double c = Math
                .acos(Math.sin(lat2) * Math.sin(lat1) + Math.cos(lat2)
                        * Math.cos(lat1) * Math.cos((lon2 - lon1)));
        double A = Math.asin(Math.cos(lat2) * Math.sin((lon2 - lon1))
                / Math.sin(c));
        result = Math.toDegrees(A);
        if ((ilat2 > ilat1) && (ilon2 > ilon1)) {
        } else if ((ilat2 < ilat1) && (ilon2 < ilon1)) {
            result = 180.0 - result;
        } else if ((ilat2 < ilat1) && (ilon2 > ilon1)) {
            result = 180.0 - result;
        } else if ((ilat2 > ilat1) && (ilon2 < ilon1)) {
            result += 360.0;
        }
    }
    return result;
}
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其他參考：http://blog.sina.com.cn/s/blog_658a93570101hynw.html