Underwater GPS

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seems like it works by inputting your gps coords just before you enter the water, then automatically switchs to compass mode and calculates from there? what I do not understand is how it would calculate distance ?
 
As posed, it has nothing at all to do with GPS. It is an inertial guidance system that takes a single GPS fix when you submerge. After that, it relies on forces that move me from place to place.

One question. I splash in my favorite inlet, submerge, and go absolutely neutral in the flow. There are no unbalanced forces on me whatsoever.

Can Ariadna track me?
 
GPS signals are be blocked by water, as are all but very low frequency radio waves.

Ariadna takes a GPS fix at the surface and then uses some kind of inertial navigation based on motion sensors to track the divers position under water.

There is Navimate that uses a GPS unit on the boat and sends an accoustic signal to a wrist unit that calculates position.

Navimate GPS for Divers
 
As posed, it has nothing at all to do with GPS. It is an inertial guidance system that takes a single GPS fix when you submerge. After that, it relies on forces that move me from place to place.

One question. I splash in my favorite inlet, submerge, and go absolutely neutral in the flow. There are no unbalanced forces on me whatsoever.

Can Ariadna track me?

That's one of the problems - in order to be accurate, you have to be very still when you start tracking - any drift will accumulate over time and the error will accumulate. For example, if you start drifting 20 feet per minute, you'll be off by 200 feet after 10 minutes, etc.. If you start still and accelerate to drifting 20 feet per minute then drift for 10 minutes, it should know you are 200 feet away from where you started.

You also need pretty good sensors, but the math isn't all that complex. That said, you have to track orientation of the device as well as movement of the device, and every measurement's inaccuracy accumulates over time with all the other errors. I wouldn't expect pinpoint accuracy out of a consumer product, but probably good enough for scuba diving.
 
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seems like it works by inputting your gps coords just before you enter the water, then automatically switchs to compass mode and calculates from there? what I do not understand is how it would calculate distance ?

Inertial guidance can guide a downhole motor to intercept a well drill hole, it can guide astronauts to the moon or a loitering submarine for months below the surface or a nuclear tipped warhead to it's target. Inertial systems have drift over time. N
 
As posed, it has nothing at all to do with GPS. It is an inertial guidance system that takes a single GPS fix when you submerge. After that, it relies on forces that move me from place to place.

One question. I splash in my favorite inlet, submerge, and go absolutely neutral in the flow. There are no unbalanced forces on me whatsoever.

Can Ariadna track me?
Sure. No unbalanced forces just means your current speed and direction are completely unchanged since the last force acted on you. For example, right before you became neutral it calculated you were moving at 2 m/s towards 140°. As long as no forces act on you, you'll continue drifting at 2 m/s towards 140°, and the device knows this. So no unbalanced forces = hold speed and direction.

Now this requires knowing how fast you are moving to start with. You either need to be completely motionless when starting the tracking, which is hard when a boat or you are drifting in the current at the surface, so it uses GPS to get your speed and direction until you go underwater and it has to switch to inertial tracking. This may be what you meant, since drifting on the surface also equals no unbalanced forces. So if you were to start tracking while drifting, and told it you were stationary, it wouldn't be able to track you.

Having said that, the following from their FAQ worries me that this isn't actually how they implemented it.
Q: What about sea-currents?

A: Sea currents can be compensated by activating the sea current compensation function while swimming against the current and maintaining a steady position for a few seconds. The speed and heading of the current are measured and taken into account in subsequent navigation calculations.
And
[ THE DIPS DIVER POSITION SYSTEM EXPLAINED ]
On the surface, the wrist unit uses its GPS receiver to obtain positional information. Upon submerging, where the GPS signal is not available, it relies on the navigation transmitter based on DIPS technology for navigational data. The navigation transmitter uses divers swimming motion capture sensors to measure diver's real-time position, speed, heading and distance information underwater. The resulting 3D underwater route is recorded and shown graphically in real time on the user interface as a continuous trace.

Swimming motion capture sensors? That's not how inertial tracking systems work, unless it is an inertial tracking system and a bunch of marketing BS, but for the case of an inertial tracking system I imagine the sensors would be best suited strapped on a BCD or tank, not on a leg. A video says it tracks similar to a submarine (inertial tracking system) but then says they saw that by tracking the fin movements of a dolphin they could track it's movement, and did a similar thing for SCUBA.

Bottom line, they aren't really clear how it actually works.

If it works as they claim, seems pretty impressive. They claim 2% error right now, or 10 m off after swimming 500 m.
 
Some serious mathematics required to make this work. Double integration to get direction and distance.
Eh, not particularly. Integration is fairly easy. Quality sensors are what you need, because each time you integrate (acceleration to velocity to position) the errors grow, and then they get stacked because the next integrated position is added to the previous one, and so forth.

I guess a total implementation is somewhat harder, as you have track 3 lateral axis and 3 rotational axis, but you're essentially just adding them all up to get a single sum after integrating them.
 
Inertial guidance can guide a downhole motor to intercept a well drill hole, it can guide astronauts to the moon or a loitering submarine for months below the surface or a nuclear tipped warhead to it's target. Inertial systems have drift over time. N

Apollo used a Star Tracker system integrated in to the nav system and guidance was updated by the astronauts using a sextant also integrated in to the guidance system to re allign the Inertial system periodically through the mission.
Submarines have a much more sophisticated system than can be strapped to a wrist.
 
I actually thought about doing something similar to this using an Arduino based controller and a variety of sensors. There is substantial maths involved, but not determine the motion vectors from the sensor inputs - more so to compensate for drift.

The sensors are no different to what you find in your phone, some modern gaming equipment or even your car. The difference in those devices thoughost, is that the vector tracking is usually only over a very short period of time, with a relatively high acceptable margin of error.

Once you start tracking motion vectors in 3D, error margins are multiplied exponentially very quickly, and become difficult to account for.

Any electronic componentry that currently exists in the consumer does not have the accuracy needed for a device like this, but one day I'm sure it will have..
 
https://www.shearwater.com/products/teric/

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