I am using therion with servex 3d files using the command import GB.3d -surveys use -cs EPSG:27700 -calibrate [0 0 0 300000 100000 0] Which works fine, and generating the 3d file to check, using export model -fmt survex -o GBth.3d in the configuration file gives the same co-ordinates (with the displacement added for the national grid) as the original survex 3d file, however generating the kml file and looking at it on google earth, the entrance has moved 90 metres on a heading of 078 degrees (and I assume the rest of the cave) I have no idea where to look to fix this! Thanks Andrew (The file extern/proj4/nad/epsg gave 3 results when searched for OSGB and I have to say I did not understand the contents of the file, but got three search results gave 2 numbers that I hope are the ones to use 4277 and 27700 I went for 27700 as http://www.dnf.org/Pages/registry/CRS.asp#ETRS89 has 27700 but this is the SRID and also EPSG OP 19916 further down? trying 4277 crashes my machine with a memory unaddressable error)