//Get browser version
  var bName = navigator.appName;
  var bVer = parseInt(navigator.appVersion);
  //Drop-downs top position
  var top = 170;
 
  var NS6 = (bName == "Netscape" && bVer >= 5);
  var NS4 = (bName == "Netscape" && bVer >= 4 && bVer < 5);
  var IE4 = (bName == "Microsoft Internet Explorer" && bVer >= 4);
  if (NS4) {top=top-1;}

  function showNav(menu){
    var to_center = 0;
    switch(menu){
      case('about'):
	    top = 160;
	    to_center = 198;
	    showlayer('about', 'about', to_center, top);
		break;		
      case('infoCentre'):
	  	top = 304;
	    to_center = 198;
	    showlayer('infoCentre', 'Image15', to_center, top);
		break;
      case('publications'):
	  	top = 328;
	    to_center = 198;
	    showlayer('publications', 'Image16', to_center, top);
		break;	  
      case('education'):
	  	top = 352;
	    to_center = 198;
	    showlayer('education', 'Image17', to_center, top);
		break;
	  case('education_08'):
	  	top = 352;
	    to_center = 320;
	    showlayer('education_08', 'Image17', to_center, top);
		break;
	  case('education_09'):
	  	top = 352;
	    to_center = 320;
	    showlayer('education_09', 'Image17', to_center, top);
		break;
      //case('unitst'):
	  //	top = 386;
	  //  to_center = 198;
	  //  showlayer('unitst', 'Image18', to_center, top);
		//break;
	  case('technical'):
	    top = 376;
	  	to_center = 198;
	    showlayer('technical', 'Image19', to_center, top);
		break;
	  case('roads'):
	  	top = 400;
	    to_center = 198;
	    showlayer('roads', 'Image20', to_center, top);
		break;
	  case('structural'):
	    top = 422;
	    to_center = 198;
	    showlayer('structural', 'Image21', to_center, top);
		break;		
	  case('photofile'):
	  	top = 472;
	    to_center = 198;
	    showlayer('photofile', 'Image23', to_center, top);
		break;
    }	
  }

  function hideNav(menu){
	switch(menu){
	  case('about'):
	    hidelayer('about');
		break;
	  case('infoCentre'):
	    hidelayer('infoCentre');
		break;
	  case('publications'):
	    hidelayer('publications');
		break;
	  case('education'):
	    hidelayer('education');
		break;	
	  case('education_08'):
	    hidelayer('education_08');
		break;	
	  case('education_09'):
	    hidelayer('education_09');
		break;	  
	  case('unitst'):
	    hidelayer('unitst');
		break;  
	  case('technical'):
	    hidelayer('technical');
		break;
	  case('roads'):
	    hidelayer('roads');
		break;
	  case('structural'):
	    hidelayer('structural');
		break;
	  case('photofile'):
	    hidelayer('photofile');
		break;
    }
  }
  
  function showlayer(menu_div, menu_img, to_center, top){
    if (document.getElementById('layer_' + menu_div)){
	  //Get image position for different browsers
	  left = imgPosition(menu_img);	 
	  //Show drop-down (specify top, left)  
	  document.getElementById('layer_' + menu_div).style.top=top;
	  document.getElementById('layer_' + menu_div).style.left=left+to_center;
	  document.getElementById('layer_' + menu_div).style.visibility='visible';
	}
  } 
  
  function hidelayer(menu_div){
    if (document.getElementById('layer_' + menu_div)){
	  document.getElementById('layer_' + menu_div).style.visibility='hidden';
    }
  }

  //Get image position for different browsers
  function imgPosition(img_name){
    img = getImage(img_name);
    img_left = getImagePageLeft(img); 
    return img_left;
  }

  function getImage(name){
    if (NS4 || NS6) {    
	  return findImage(name, document);
    }
    if (IE4){
      return eval('document.all.' + name);
    }
    return null;
  }

  function findImage(name, doc) {
    var i;
    for (i = 0; i < doc.images.length; i++)
      if (doc.images[i].name == name)
        return doc.images[i];
    return null;
  }

  function getImagePageLeft(img){
    var x, obj;
    if (NS4 || NS6) {
      if (img.container != null)
        return img.container.pageX + img.x - 1;
      else
        return img.x - 1;
    }
    if (IE4) {
      x = 0;
      obj = img;
      while (obj.offsetParent != null) {
        x += obj.offsetLeft;
        obj = obj.offsetParent;
      }
      x += obj.offsetLeft;
      return x;
    }
    return -1;
  }