通过两个经纬度算出方位

pragma mark - 得到角度

- (double)getAngleLat1:(double)lat1 withLng1:(double)lng1 withLat2:(double)lat2 withLng2:(double)lng2
{
    double x1 = lng1;
    double y1 = lat1;
    double x2 = lng2;
    double y2 = lat2;
    double pi = M_PI;
    double w1 = y1 / 180 * pi;
    double j1 = x1 / 180 * pi;
    double w2 = y2 / 180 * pi;
    double j2 = x2 / 180 * pi;
    double ret;
    if (j1 == j2) {
        if (w1 > w2)
            return 270; // 北半球的情况，南半球忽略
        else if (w1 < w2)
            return 90;
        else
            return -1;// 位置完全相同
    }
    ret = 4* pow(sin((w1 - w2) / 2), 2)- pow(
                                                            sin((j1 - j2) / 2) * (cos(w1) - cos(w2)),2);
    ret = sqrt(ret);
    double temp = (sin(fabs(j1 - j2) / 2) * (cos(w1) + cos(w2)));
    ret = ret / temp;
    ret = atan(ret) / pi * 180;
    if (j1 > j2){ // 1为参考点坐标
        if (w1 > w2)
            ret += 180;
        else
            ret = 180 - ret;
    } else if (w1 > w2)
        ret = 360 - ret;
    return ret;
}
#pragma mark - 得到方向
- (NSString *)getDirection:(double)jiaodu
{
    if ((jiaodu <= 10) || (jiaodu > 350))
        return @"东";
    if ((jiaodu > 10) && (jiaodu <= 80))
        return @"东北";
    if ((jiaodu > 80) && (jiaodu <= 100))
        return @"北";
    if ((jiaodu > 100) && (jiaodu <= 170))
        return @"西北";
    if ((jiaodu > 170) && (jiaodu <= 190))
        return @"西";
    if ((jiaodu > 190) && (jiaodu <= 260))
        return @"西南";
    if ((jiaodu > 260) && (jiaodu <= 280))
        return @"南";
    if ((jiaodu > 280) && (jiaodu <= 350))
        return @"东南";
    return @"";
}