class utils {

    /**
     * 计算两经纬度点之间的距离(单位：米)
     * @param {*} lat1  纬度1
     * @param {*} lng1 经度1
     * 
     * @param {*} lat2 纬度2
     * @param {*} lng2 经度2
     * @returns 
     */
     
    caculateLL(lng1, lat1, lng2 = 117.325426, lat2 = 31.794477) {
        var radLat1 = (lat1 * Math.PI) / 180.0;
        var radLat2 = (lat2 * Math.PI) / 180.0;
        var a = radLat1 - radLat2;
        var b = (lng1 * Math.PI) / 180.0 - (lng2 * Math.PI) / 180.0;
        var 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)
            )
          );
        s = s * 6378.137;
        s = Math.round(s * 10000) / 10;
        return s;
    }
}

module.exports = new utils();