$loginUrl = 'https://geodata.nationaalgeoregister.nl/kadastralekaartv3/ows?outputformat=application/json&request=GetFeature&service=WFS&typenames=kadastralekaartv3:perceel&version=2.0.0&cql_filter=kadastraleGemeenteCode%20=%27VAN00%27%20AND%20sectie%20=%20%27B%27%20AND%20perceelnummer%20=%273857%27';
$agent= 'Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 1.0.3705; .NET CLR 1.1.4322)';

$ch = curl_init();
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_URL,$loginUrl);
curl_setopt($ch, CURLOPT_USERAGENT, $agent);
$result=curl_exec($ch);
curl_close($ch);
$json = json_decode($result, true);

$grootte = $json->features[0]->geometry->properties->kadastralegrootte;
echo "$grootte";