[Robotgroup] Triangulation

[Robo Al]

Does anybody know any links or reference material
about non GPS triangulation?

I would like to play with something within these
requirements:

* open and closed spaces around 150'x100' max size (ie.
  a yard or inside a house)
* accurate to within 1 to 3 centimeters
* inexpensive. Hopefully sub $40 for parts.
* A computer or fast uC will be available to do the
  calculations so the $40 is just for sensors and I/O
  interfacing to the computer.

I would imagine setting 3 or 4 radio beacons within my
fence posts, but I'm afraid I just don't know enough
about radio triangulation.

Thanks,

Alberto