Hello, I'm not really using therion yet (there were always other people who draw the caves ;-) but that will change propably. a) I try to get an overlay of the centreline on a scanned topographical map but I always get an error ( test.th [47] -- number expected -- end) but I don't know where to insert more numbers examplecode: surface bitmap ur.png [1 11 211065.0 2139614.0 6310 4474 237623.0 2158455.0 meters] grid-units meters grid 211000.0 2139000.0 20000.0 15000.0 2 2 10.0 10.0 10.0 10.0 end surface b) at loops: is the standard error for the measurement devices included when the loops are closed? IE when more than one GPS measurements (with high errors are used to fix the cave)? Thanks for any help Wolfgang