if (document.images) {
// create all global variables for image preloading.
	var legOn = new Array(); 
	var legOff = new Array();
	var legTxt = new Array();
	var gLegDescDefault = new Image();
	gLegDescDefault.src = "/lewisandclark/images/legnav_desc_select.gif";	// default value, reset on each page
// preload the intro 
		legOn[0] = new Image();
		legOff[0] = new Image();
		legTxt[0] = new Image();
		legOn[0].src = "/lewisandclark/images/legnav_on_intro.gif";
		legOff[0].src = "/lewisandclark/images/legnav_off_intro.gif";
		legTxt[0].src = "/lewisandclark/images/legnav_desc_0.gif";
// attempt to preload all other images for this page
	for (var i = 1; i <= 22; i++) {
		legOn[i] = new Image();
		legOff[i] = new Image();
		legTxt[i] = new Image();
		legOn[i].src = "/lewisandclark/images/legnav_on_" + i + ".gif";
		legOff[i].src = "/lewisandclark/images/legnav_off_" + i + ".gif";
		legTxt[i].src = "/lewisandclark/images/legnav_desc_" + i + ".gif";
	}
}

function swapImage(strElement, objImage) {	
// this function swaps the image identified by strElement for a new one preloaded as objImage
	if (document.images && objImage && objImage.src && objImage.src != "") {
		if (document.images[strElement]) {
			document.images[strElement].src = objImage.src
		}
	}
}

function actLeg(leg) {
// function handles mouseover effects for journey legs given state s
// assumes leg images named "leg_N" and "legDesc_N"
	legImg = "leg_" + leg;
	legDescImg = "legDesc";
	swapImage(legImg, legOn[leg]);
	swapImage(legDescImg, legTxt[leg]);
}

function deactLeg(leg) {
// function handles mouseover effects for journey legs given state s
// assumes leg images named "leg_N"
	legImg = "leg_" + leg;
	legDescImg = "legDesc";
	swapImage(legImg, legOff[leg]);
	swapImage(legDescImg, gLegDescDefault);
}