function openCenteredPopUp(url, title, popW, popH, params) {

    var w = screen.width, h = screen.height;
    
    var leftPos = (w - popW) / 2, topPos = (h - popH) / 2;
    
    window.open(url, title, 'width=' + popW + ',height=' + popH + ',top=' + topPos + ',left=' + leftPos + ',' + params);
}