Eager Eagle‘It’s the perfect place’: London Underground hosts tests for ‘quantum compass’ that could replace GPS
maniacal_gaffEven a perfect sensor will accumulate errors in the nav solution over time because there’s no such thing as a perfect gravity model. No free-running INS will ever replace GPS long term. This shit is so frustrating to see in the press.
Especially since, to calculate current location, it needs an input of initial location (i.e. it needs GPS coordinates to begin with so it can track direction and velocity relative to that initial position). You can’t replace something you depend upon.
the initial location doesn’t need to be GPS, just a known anchor location. Which is trivial to implement in the case of trains, since stations don’t move that drastically.
“Fixed” ground points move a surprising amount. The local ground can shift, and of course whole continents are constantly drifting.
surely these are things that should be considered, but they move in relation to what? And is this surprising amount of any significance for tens or hundreds of miles of rail?
In relation to all other points of interest, which are themselves all moving.
It’s not really relevant for rail, no, but not because of inaccuracy and drift, but because the trains are on fixed paths already. Inertial navigation and dead reckoning are accurate enough to get from station to station, and each station can have local markers, even something as simple as a reflector at the end of the platform.
But they’re not developing it just for rail. It would be incredibly valuable for submarines and mining, for example.