Calculate center or centroid of irregular shape or polygon in php function

<?php

$polygon = array(50,50, 75,25, 100,50, 125,75, 100,100, 75,125, 50,100, 25,75);

$er = polyCenter($polygon);

print_r($er);



function polyCenter($polygon){

//echo "<pre>";print_r($polygon);echo "</pre>";

$app = array_chunk($polygon,2);

//echo "<pre>";print_r($app);echo "</pre>";

$n = count($app);

for($i=0;$i<$n;$i++){

$x+=$app[$i][0];

//echo "<br>";

$y+=$app[$i][1];

}

$x = round($x/$n); $y = round($y/$n);

return $x.":".$y;

}







?>