Hi, I am trying to digitize some analogue bathymetry charts, whereby each chart comes with the lat/long on the 4 corners. What I would like to do is to trace out the bathymetry contour lines on the charts so that I can export the lat/long information together with the corresponding depth value. How do I go about doing this? Or can someone please point me to a good Envi reference to get me started? Many thanks.