blomkaal,

Thanks for that image, it helps a lot. I've actually printed it off so I can look at it while modelling.

Falott,
Thank you for the very informative post, I'm not sure if I actually understand it all but it certainly helps . . I obviously have a lot to learn.

I'm going to do some searches on the web on methods to use. Still not sure what method is going to suit me best.

Cheers
Paul