var activeLayer="G";
var acTab="tG";


function overTab(tdName)
 {
    if (acTab!=tdName)
    document.getElementById(tdName).className="overTab";
 }
 
 function outTab(tdName)
 {
   if (acTab!=tdName)
        document.getElementById(tdName).className="outTab";
 }
 
 function activeTab(tdName,layerName)
 {
 if (acTab!=tdName)
 {
     document.getElementById(tdName).className="activeTab";
     document.getElementById(acTab).className="outTab";
     acTab=tdName;
     setActiveLayer(layerName);
 }
 }
 
 function setActiveLayer(layerName)
 {
    document.getElementById(activeLayer).style.display='none';
    document.getElementById(layerName).style.display='block';
    activeLayer=layerName;
 }