An article at NXTasy.org highlights a three-wheeled robot that moves in one dimension and detects signals from an external beacon that emits ultrasonic bursts. The robot relies on a microcontroller that runs a Kalman filter to perform and maintain spatial localization. The NXT software is implemented using the LabVIEW NXT toolkit
Details on the project can be found at http://www.convict.lu/htm/rob/ir_us.htm#Kalman