A Japanese team of researchers are working on a positioning system using muons, which could be used in places where GPS signals can’t be received (such as underwater or underground).
The article discusses many of the challenges and reasons why it currently isn’t ready for practical applications. But it certainly is a very interesting technology.
They say they are working on the real-time calculation, as well as the accuracy. It’s pretty early days for this still, so I imagine quite a few advances to come, and it may well supplement what we have right now, rather than being a standalone navigation system.
It would make sense that eventually you could do both real-time and after-the-fact calculations depending on whether real-time communications is available. Presumably it will depend on the specific application