function swapCoverageImage (imageName) {
	image = document.getElementById('aerialimage');
	image.src = "images/aerialcoverage_"+ imageName +".gif";
}

function swapShowImage (imageName) {
	imageID = "aerialCoverage_" + imageName;
	cbID = "cb" + imageName;
	canbeseen = document.getElementById(imageID);
	cbObj = document.getElementById(cbID);
	if (canbeseen.style.opacity == 0) {
		setOpacity(canbeseen, 100);
		checkbox(cbObj, true);
	} else {
		setOpacity(canbeseen, 0);
		checkbox(cbObj, false);
	}
}

function setOpacity(obj, opacity) {
	opacity = (opacity == 100)?99.999:opacity;
	obj.style.filter = "alpha(opacity:"+opacity+")";
	obj.style.KHTMLOpacity = opacity/100;
	obj.style.MozOpacity = opacity/100;
	obj.style.opacity = opacity/100;
}

function checkbox(cbObj, state) {
	cbObj.checked = state;	
}

function coverageSetUp () {
	var aerials = ["highcoverage", "auckland", "bop", "gwrc", "manawatu", "manukau", "rodney", "rotorua", "waitakere", "whangarei", ""];
	for (var i=0; i < aerials.length -1; i++) { 
		imageID = "aerialCoverage_" + aerials[i];
		cbID = "cb" + aerials[i];
		image = document.getElementById(imageID);
		cbObj = document.getElementById(cbID);	
		setOpacity(image, 0);
		checkbox(cbObj, false);
	}
}