I downloaded a TIFF image from USGS Earth Explorer from which I determined the contour lines and saved them in a shape file (*.shp) (see tutorial http://www.qgistutorials.com/en/docs/working_with_terrain.html). How can I convert the contour lines into XYZ points (simple CSV file or similar) for use as surface elevations in FEFLOW (groundwater modelling). THanks and best regards