function changevis(layerId) {
	var targetElement = document.getElementById(layerId);

	if (targetElement.style.visibility == "hidden") 
	{ 
		targetElement.style.visibility = "visible"; 
	}
	else { 	
		targetElement.style.visibility = "hidden"; 
	} 
}
function showonly(layerId) {
	var targetElement = document.getElementById(layerId);

	var i;
	var numLayers = 25;

	for (i = 1; i <= numLayers; i++)
	{
		var thisLayerName = "example_" + parseInt(i);

		var thisElement = document.getElementById(thisLayerName);
		if (thisElement.style.display == "block") 
		{ 
			thisElement.style.display = "none"; 
		}
	}
	targetElement.style.display = "block"; 
}