Trying to build a function that find the center of a Polygon defined by geo coordinates

geo_barycentre.php

<?php

$coords = array(
  array('lat' => 2.125397, 'long' => 48.98255900000001),
  array('lat' => 2.205048, 'long' => 48.620747),
  array('lat' => 2.759857, 'long' => 48.769405),
  array('lat' => 2.457733, 'long' => 49.171471),
);

// premier test

$bar = array(
  'lat' => array('degre' => 0, 'decim' => 0), 
  'long' => array('degre' => 0, 'decim' => 0)
);

foreach($coords as $coord) {
  $bar['lat']['degre'] += abs($coord['lat']);
  $bar['lat']['decim'] += ($coord['lat'] - (int) $coord['lat']);
  $bar['long']['degre'] += abs($coord['long']);
  $bar['long']['decim'] += ($coord['long'] - (int) $coord['long']);
}

// @ToDo: récupérer la partie décimale de la division de la partie entière.
$barFinal = array(
  'lat' => (float)((int)($bar['lat']['degre'] / sizeof($coords)) + ($bar['lat']['decim'] / sizeof($coords))),
  'long' => (float)((int)($bar['long']['degre'] / sizeof($coords)) + ($bar['long']['decim'] / sizeof($coords))),
);

echo "initial coords :<br />";
var_dump($coords);
echo "<br />bar coords :<br />";
var_dump($barFinal);