//preload image
var collimg = new Image();
collimg.src = "collapse.png";
var expimg = new Image();
collimg.src = "expand.png";

function ShowHideLayer(boxID) {
    /* Obtain reference for the selected boxID layer and its button */
    var box = document.getElementById("box"+boxID);
    var boxbtn = document.getElementById("btn"+boxID);
    
    /* If the selected box is currently invisible, show it */
    if(box.style.display == "none" || box.style.display=="") {
        box.style.display = "block";
        boxbtn.src = "img/collapse.png";
    }
    /* otherwise hide it */
    else {
        box.style.display = "none";
        boxbtn.src = "img/expand.png";
    }
}