PHP code for forward and inverse calculation of longitude and latitude BL and Cartesian coordinates XY

<?php
	function BLtoXY($latitude, $longitude)
	{
            $_a = 6378245.0;
        $_f = 1.0 / 298.3;
        $zoneWide = 6;
        $PI = 3.14159265353846;
        $iPI = 0.0174532925199433; //3.1415926535898/180.0; 
        //ZoneWide = 6; //6度带宽 
        $ProjNo = floor($longitude / $zoneWide);
        $longitude0 = $ProjNo * $zoneWide + $zoneWide / 2;
        $longitude0 = $longitude0 * $iPI;
        $latitude0 = 0;
        $longitude1 = $longitude * $iPI; //经度转换为弧度
        $latitude1 = $latitude * $iPI; //纬度转换为弧度
        $e2 = 2 * $_f - $_f * $_f;
        $ee = $e2 * (1.0 - $e2);
        $NN = $_a / sqrt(1.0 - $e2 * sin($latitude1) * sin($latitude1));
        $T = tan($latitude1) * tan($latitude1);
        $C = $ee * cos($latitude1) * cos($latitude1);
        $A = ($longitude1 - $longitude0) * cos($latitude1);
        $M = $_a * ((1 - $e2 / 4 - 3 * $e2 * $e2 / 64 - 5 * $e2 * $e2 * $e2 / 256) * $latitude1 - (3 * $e2 / 8 + 3 * $e2 * $e2 / 32 + 45 * $e2 * $e2 * $e2 / 1024) * sin(2 * $latitude1) + (15 * $e2 * $e2 / 256 + 45 * $e2 * $e2 * $e2 / 1024) * sin(4 * $latitude1) - (35 * $e2 * $e2 * $e2 / 3072) * sin(6 * $latitude1));
        $xval = $NN * ($A + (1 - $T + $C) * $A * $A * $A / 6 + (5 - 18 * $T + $T * $T + 72 * $C - 58 * $ee) * $A * $A * $A * $A * $A / 120);
        $yval = $M + $NN * tan($latitude1) * ($A * $A / 2 + (5 - $T + 9 * $C + 4 * $C * $C) * $A * $A * $A * $A / 24 + (61 - 58 * $T + $T * $T + 600 * $C - 330 * $ee) * $A * $A * $A * $A * $A * $A / 720);
        $X0 = 1000000 * ($ProjNo + 1) + 500000;
        $Y0 = 0;
        $X = round(($xval + $X0) * 100) / 100.0;
            $Y = round(($yval + $Y0) * 100) / 100.0;
		return array($X, $Y);
	}
	$lng = $_GET["lng"];
	$lat = $_GET["lat"];
	$XY = BLtoXY($lat, $lng);
	echo json_encode($XY);
?>