//Switches the class of an element between 2 predefined css classes
function SwitchLayer(class1, class2, layerID)
{
  if(layerID_2 === undefined) { layerID_2 = null; }
  if(layerID_3 === undefined) { layerID_3 = null; }
  
  var switchLayer = document.getElementById(layerID);
  
  if(switchLayer.className == class1)
  {
    switchLayer.className = class2;
  }
  else
  {
    switchLayer.className = class1;
  }
}