function switchIcon(layerId,imgId) {
	if(!document.getElementById){return};
	var theElement = document.getElementById(layerId);
	var theImage = document.getElementById(imgId);
	var fullimg1 = 'http://srainternational.org/sra03/expandabledivs/images/minus.gif'
	var fullimg2 = 'http://srainternational.org/sra03/expandabledivs/images/plus.gif'

	if(theImage.src.indexOf(fullimg1)!=-1){
		theImage.src=fullimg2;
	}
	else{
		theImage.src=fullimg1;
	}
	
	if (theElement.style.display == 'block') {
		theElement.style.display = 'none';
	} else {
		theElement.style.display = 'block';
	}
}