var popWin = null    // use this when referring to pop-up window
var winCount = 0
var winName = "popWin"

function openPopWin(winURL, winWidth, winHeight, winFeatures, winLeft, winTop)
{
  var d_winLeft = 20  // default, pixels from screen left to window left
  var d_winTop = 20   // default, pixels from screen top to window top
  winName = "popWin" + winCount++ //unique name for each pop-up window
  closePopWin()           // close any previously opened pop-up window
  
  if (openPopWin.arguments.length >= 4)  // any additional features? 
  {
    winFeatures = "," + winFeatures
  }
  else
  {
    winFeatures = ""
  }
  
  if (openPopWin.arguments.length == 6)  // location specified
  {
    winFeatures += getLocation(winWidth, winHeight, winLeft, winTop)
  }
  else
  {
    winFeatures += getLocation(winWidth, winHeight, d_winLeft, d_winTop)
  }
  
  popWin = window.open(winURL, winName, "width=" + winWidth + ",height=" + winHeight + winFeatures)
}

function closePopWin()    // close pop-up window if it is open
{
  if (navigator.appName != "Microsoft Internet Explorer" 
      || parseInt(navigator.appVersion) >=4) //do not close if early IE
    if(popWin != null) if(!popWin.closed) popWin.close() 
}

function getLocation(winWidth, winHeight, winLeft, winTop)
{
  var winLocation = ""
  
  if (winLeft < 0)
  {
    winLeft = screen.width - winWidth + winLeft
  }
  
  if (winTop < 0)
  {
    winTop = screen.height - winHeight + winTop
  }
  
  if (winTop == "cen")
  {
    winTop = (screen.height - winHeight)/2 - 20
  }
  
  if (winLeft == "cen")
  {
    winLeft = (screen.width - winWidth)/2
  }
  
  if (winLeft>0 & winTop>0)
  {
    winLocation =  ",screenX=" + winLeft + ",left=" + winLeft + ",screenY=" + winTop + ",top=" + winTop
  }
  else
  {
    winLocation = ""
  }
    
  return winLocation
}