function regiokaartOverlay () {
	var viewportwidth;
	var viewportheight;

	if (typeof window.innerWidth != 'undefined')
	{
		viewportwidth = window.innerWidth,
		viewportheight = window.innerHeight			
	}
	else if	(	typeof document.documentElement != 'undefined'
				&& typeof document.documentElement.clientWidth != 'undefined'
				&& document.documentElement.clientWidth != 0
			)
	{
		viewportwidth = document.documentElement.clientWidth,
		viewportheight = document.documentElement.clientHeight
	}
	else
	{
		viewportwidth = document.getElementsByTagName('body')[0].clientWidth,
		viewportheight = document.getElementsByTagName('body')[0].clientHeight
	}

	document.getElementById('regiokaart_overlay').style.visibility = 'visible';
	document.getElementById('regiokaart_background').style.visibility = 'visible';
	document.getElementById('gooien').style.visibility = 'visible';
	
	document.getElementById('regiokaart_overlay').style.width = viewportwidth + 'px';
	document.getElementById('regiokaart_overlay').style.height = viewportheight + 'px';
	document.getElementById('regiokaart_background').style.width = viewportwidth + 'px';
	document.getElementById('regiokaart_background').style.height = viewportheight + 'px';
	document.getElementById('gooien').style.top = (viewportheight - 600) / 2 + 'px';
	document.getElementById('gooien').style.left = (viewportwidth - 1000) / 2 + 'px';
	
}

function closeRegiokaartOverlay () {
	document.getElementById('regiokaart_overlay').style.visibility = 'hidden';
	document.getElementById('regiokaart_background').style.visibility = 'hidden';
	document.getElementById('gooien').style.visibility = 'hidden';
}