Martin, Picking points from GoogleEarth works very well. Thank you for the suggestion. I found a very useful tool here :
http://www.gpsvisualizer.com/elevation By simply importing the .kml file of the cave centreline data (lat-long), this online tool will create a list of coordinates including the ground altitude at each point from one of it's datasets. Very easy to use and copy-paste the data back into therion as fixed stations. I imagine it would be easy to extract a full DTM surface grid using this tool. Bruce, Your suggestion worked great. It is a little odd when used in extended projection, but seems correct in elevation projection. I do have a bit of a problem in exporting to pdf, and this may be me missing something more fundamental in how survey/maps are structured and therion builds up the plot : When I just plot centreline data, I can see cave centreline and the new ground surface centreline for the complete cave length. When I include a single cave scrap, I no longer see any centreline data outside this single scrap. Is there a way to over-ride this behaviour or alternatively how should I structure my survey/map objects to avoid this? Thanks to all for your help, Steve
