Illustrator- how to scale using reference points?

[Jackson]

I'm trying to scale elevation jpgs in Illustrator and was wondering if there's a way to scale them using reference points like you can in Autocad or SU i.e. select two points on the jpg and type in the 1:1 distance I want them to be? So far I'm having to use the "draw a line the right scale length, then scale the jpg by eye until it matches" method which is slow and obviously innaccurate.

Thanks in advance,

[thinkbuild]

do you know about hotdoor cad tools? it is AMAZING - take a look:

http://hotdoor.com/index.php?content=cadtools&navcontent=cadtools

good luck!