function openVirtualHouseTour() {
  var popl = (screen.width - 800) / 2;
  var popt = (screen.height - 425) / 2;
  windowSpec = 'left='+popl+',top='+popt+',width=800,height=425,scrollbars=no'
  window.open('virtual_house_tour.htm','vtourpopup',windowSpec);
}