function switchRaster(num, schalter)
{
  var rasterLayer1 = document.getElementById("raster" + num + "_01");
  var rasterLayer2 = document.getElementById("raster" + num + "_02");
  var value = "visible";
  if(schalter == "off")
    value = "hidden";

  rasterLayer1.style.visibility = value;
  rasterLayer2.style.visibility = value;
}

currentPDFblock = 1;
lastPDFblock = 1;

function displayPDFs(numPDFBlocks, dir)
{
  currentPDFblock += dir;
  
  var prevBtnLayer = document.getElementById("pdf_back");
  if (currentPDFblock > 1)
    prevBtnLayer.style.visibility = "visible";
  else
    prevBtnLayer.style.visibility = "hidden";

  var prevBtnLayer = document.getElementById("pdf_next");
  if (currentPDFblock < numPDFBlocks)
    prevBtnLayer.style.visibility = "visible";
  else
    prevBtnLayer.style.visibility = "hidden";

  var pdfLayer = document.getElementById("pdf_" + currentPDFblock);
  pdfLayer.style.visibility = "visible";

  if(document.getElementById("pdf_" + lastPDFblock))
  {
    var lastPDFblockLayer = document.getElementById("pdf_" + lastPDFblock);
    lastPDFblockLayer.style.visibility = "hidden";
  }

  lastPDFblock = currentPDFblock;
}