Digital celestial navigation

It should be possible to construct a device that uses light sensors (digital cameras), data on star (and visible planet) position and an accurate clock to give the user their latitude and longitude. The user would point the device towards the sky, and it would capture image data. This data would be pattern-matched against expected star positions for a particular latitude and longitude, at a particular time. Such a device might serve as a useful backup to GPS in the event of failure of the GPS network.