SamT said:
out of interest footleg (if your not in matienzo yet) - can you import Autocad data into survex ?
Survex consists of two main programs. Cavern which crunches survey data, and reads plain text files. And Aven which is the cave viewer application. Cavern almost certainly does not directly digest autocad data. However it does understand most survey data (e.g. Tape, Compass, Clino. Tape, Compass, Depth (diving data), X,Y,Z coordinate data). So you could probably export Autocad as DXF (which is plain text) and then write a simple program to convert this into X,Y,Z station positions and connecting legs which Cavern could crunch.
The Aven viewer reads the .3d files output by Cavern, and lets you view the cave in 3D. You can output the centreline in DXF format for import into Autocad, which is what I think a lot of people do for drawing up surveys. You can also import DXF into CorelDraw I think, so this provides a way to get the centreline into these drawing packages for drawing up.
However I think Tunnel is a far better way to go because it handles the cave data much better, and deals with survey correction automatically when survey data is shifted by loop closures and other errors.