Some times when I digitise on screen, instead of coordinates
comes up as I click I get "NaN", and when I finish digitising
a get the message that only one point has been taken.
What am a doing wrong?
cheers tom 
Tom Charnock O--O
Dept Civil Engineering (~~~~)
Aston University ( __ )
Birmingham B4 7ET UK /|\ /|\
charnotw@sun.aston.ac.uk