PHP calculates the distance between two points geographical coordinates

Function: Calculate the spherical distance between two points based on the pi ratio and the Earth radius coefficient and the longitude and latitude of the two point coordinates.
Get the coordinate distance of two points:

/**
 * 计算两点地理坐标之间的距离
 * @param  Decimal $longitude1 起点经度
 * @param  Decimal $latitude1  起点纬度
 * @param  Decimal $longitude2 终点经度 
 * @param  Decimal $latitude2  终点纬度
 * @param  Int     $unit       单位 1:米 2:公里
 * @param  Int     $decimal    精度 保留小数位数
 * @return Decimal
 */functiongetDistance($longitude1, $latitude1, $longitude2, $latitude2, $unit=2, $decimal=2){$EARTH_RADIUS = 6370.996; // 地球半径系数$PI = 3.1415926;

    $radLat1 = $latitude1 * $PI / 180.0;
    $radLat2 = $latitude2 * $PI / 180.0;

    $radLng1 = $longitude1 * $PI / 180.0;
    $radLng2 = $longitude2 * $PI /180.0;

    $a = $radLat1 - $radLat2;
    $b = $radLng1 - $radLng2;

    $distance = 2 * asin(sqrt(pow(sin($a/2),2) + cos($radLat1) * cos($radLat2) * pow(sin($b/2),2)));
    $distance = $distance * $EARTH_RADIUS * 1000;

    if($unit==2){
        $distance = $distance / 1000;
    }

    return round($distance, $decimal);

}

// 起点坐标$longitude1 = 113.330405;
$latitude1 = 23.147255;

// 终点坐标$longitude2 = 113.314271;
$latitude2 = 23.1323;

$distance = getDistance($longitude1, $latitude1, $longitude2, $latitude2, 1);
echo$distance.'m'; // 2342.38m$distance = getDistance($longitude1, $latitude1, $longitude2, $latitude2, 2);
echo$distance.'km'; // 2.34km?>