function popupLayer(id) {
	if (id) {
		document.getElementById('popup'+id).style.display = 'none';
	} else {
		var elements = document.getElementsByClassName("popup");

		var number = Math.floor(Math.random()*elements.length)+1;
		document.getElementById('popup'+number).style.display = 'block';
		
		var coors = findPos(document.getElementById('kaartje'));
		var x = document.getElementById('popup'+number);
		if ((navigator.appName.indexOf("Microsoft")>-1) || (navigator.appName.indexOf("MSIE")>-1)) {
			x.style.top = coors[1]+45 + 'px';
		} else {
			x.style.top = coors[1] + 'px';
		}
		x.style.top = (document.documentElement.clientHeight/2)-(x.offsetHeight/2)+"px";
		x.style.left = (document.documentElement.clientWidth/2)-(x.offsetWidth/2)+"px";

		for (pu=1; pu<=elements.length; pu++){
			if (pu != number) {
				if (document.getElementById('popup'+pu).style.display == 'block') {
					document.getElementById('popup'+pu).style.display = 'none';
				}
			}
		}		
	}
}
function findPos(obj) {
	var curleft = curtop = 0;
	if (obj.offsetParent) {
		curleft = obj.offsetLeft
		curtop = obj.offsetTop
		while (obj = obj.offsetParent) {
			curleft += obj.offsetLeft
			curtop += obj.offsetTop
		}
	}
	return [curleft,curtop];
}