It seems to be steam engine time for GPS alternatives. We’ve already seen two proposals that suggest using constellations of low-flying satellites to provide greater accuracy and more resilience against signal blocking than GPS and other orbital navigation systems can provide. Now a research team in the Netherlands is developing a project called SuperGPS, which promises decimetre-level (10 cm) accuracy through the use of terrestrial transmitters connected to a fibre-optic network. They’ve built a working prototype, and published the results in Nature. More at the TU Delft news release.