var img_start  = "001";
var img_end    = "385";
var img_prefix = "ifgs_2010-03_";

function get_image_num(src) {
  // Stupid IE does not recognize using a negative offset,
  // so use the string length minus the chars to backup
  // How I hate Internet Explorer...
  return src.substr((src.length - 7),3);
}


function onclick_nav(dir) {
  var elem = document.getElementById("imagepane");
  var imgnum = get_image_num(elem.src);
  if(dir) {
    if (imgnum >= img_end) {
      return; // no change to image src on last image
    }
    imgnum++;
  } else {
    if (imgnum == img_start) {
        return; // on the first image
    }
    imgnum--;
  }

  var newimg = pad_image_name(imgnum,3);
  elem.src = "images/ifgs_2010-03_" + newimg + ".JPG";
  elem = document.getElementById("image_ref");
  elem.innerHTML = "Image " + newimg + " of " + img_end; 
}

function pad_image_name(str, len, pad) {
  if (typeof(len) == "undefined") {var len = 0; }
  if (typeof(pad) == "undefined") {var pad = "0"; }
  if (typeof(str) == "number") {var str = str+''; }
  if (len + 1 > str.length) {
    str = Array(len + 1 - str.length).join(pad) + str;
  }
  return str;
}