Phones have had accelerometer/gyros for a while now. Problem with pinpointing one’s location is how to get a starting fix and how to deal with drift and loss of signal.
The way devices have dealt with it is to periodically confirm and baseline with a satellite fix.
If this method does away with all that, it could remove the reliance on overhead signals and those trying to jam them in hostile zones.
Pretty cool. Lots of potential.
Even 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.
But wouldn’t you scramble the precision with that? Stations can be quite big and anchoring to the station location means you already start with an offset to your location.
Depending on the accuracy over time, they could pinpoint a location while the user is sleeping and than use that as an anchor for the day.
But everything about that is speculative; let’s see where this goes first.
you’re thinking anywhere on the platform, I’m suggesting a known place near a station by which the train passes and its location - at that moment - is known.
All the system needs is a ground-truth location after a certain amount of time. GPS is just a cheap and convenient way to do it almost anywhere, but this location correction doesn’t need to be satellite-based at all.
Yeah maybe that could work. I definitely agree that there’s ways to get good anchor points. Maybe through cross-check with wireless networks even.
“replacing GPS” is a stretch, but it’s some sci-fi tech to use when GPS can’t be used
Can anyone explain how lasers are used to cool? I would prefer ELI18 but i probably need this ELI5
If you use the right color of light, then the doppler effect means that the atoms will only absorb (and be pushed by) light that they are headed towards. That means that the light will always act as a brake for the atoms and never an accelerator, so the fluid will cool. If you do this from all directions, the fluid will start to stay still in one place and get very close to absolute zero. Idk, I just read the Wikipedia article, but that is my best attempt at an ELI18
You got it pretty much on point. Shooting a laser at atoms is like shooting a machine gun at an indestructible target. If it moves towards you, you can slow it down. But preventing it from accelerating when the target is stationary is where quantum mechanics comes in. That is your explanation: The laser light only acts as a force when the light is resonant with the atom and the Doppler effect means that the resonance condition changes depending on the speed of the atoms.
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