Underwater digital magnetic compass with trackback?

[Chiung]

Uwatec neverlost

 

[stuartv]

a magnetic digital compass should be able to do this.

All compasses are magnetic. That's how they work. No compass is going to do what you want.

 

[Lorenzoid]

. . . I am looking for one with a trackback feature, where if you move, the digital needle will always point back to the anchor, or whatever. . . .

As already pointed out by others, the problem is that no compass can compensate for being moved laterally (i.e., off the line-of-sight direction of travel) by currents.

Digital compasses are magnetic and work according to the same principle as mechanical compasses with needles.

To do what you seek, something more complex than a compass would be required. Something like an inertial navigation system (gyroscopes and all that) might work. Or a system that involves a transmitter on the boat and a receiver in your hand, like the Lynx.

 

[marshallkarp]

The iphone has a built in magnetic field compass. Any able to make an app that stores the compass directional changes and distance to trackback? Might make alot of money selling the app. As far as using it underwater, there are camera housings for iphones.

 

[abscuba]

What your talking about is an inertial navigation system (INS). I used one at my day job thats hundreds of thousands of dollars. The problem with these systems is they are large not man portable and even the high dollar ones drift. The iPhone has something like this, but i imagine if it did not receive gps updates the dirt would be substantial. Systems on aircraft that have this use laser ring gyros which when put with all the systems to run them will not fit one your arm. Some one could make a lot of money if they could solve the problem but a better approve would be using acoustic beacons to determine position underwater. If you have 3 placed in different place you could make a system that was small and determine its location similar to how gps works with satellites. I believe desert star makes a system like this, but i imagine its expensive.

 

[DiveNav]

If you use a geo-referenced map, our SDC app will display the descent and the ascent points.

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Additionally, once we will have maps with POIs (Points of Interest), you will be able to use them to visualize your underwater path (we do this already in eDiving). See this link for more info.

 

[Lorenzoid]

The iphone has a built in magnetic field compass. Any able to make an app that stores the compass directional changes and distance to trackback? Might make alot of money selling the app. As far as using it underwater, there are camera housings for iphones.

Ah, so what you are suggesting is a system that takes compass readings every so many seconds (or fraction of a second) and uses the differences between successive readings to estimate the diver's route and, accordingly, the direction back to the start? To estimate the route, and thus the direction back to the start, the system would need to know how far the diver traveled between the successive readings or data points. Unlike, say, an airplane, a diver's speed can vary erratically as the diver stops to look at things, etc. I don't think this can be done with enough accuracy to guide a diver back to the boat on most recreational dives.

 

[stuartv]

The iphone has a built in magnetic field compass. Any able to make an app that stores the compass directional changes and distance to trackback? Might make alot of money selling the app. As far as using it underwater, there are camera housings for iphones.

You could do this with a smartphone app, but it would have nothing to do with the compass. It would just use the built-in 3-axis inertia sensors. Other posters have mentioned this and said that it won't work.

However, I have seen dynamometer apps for smartphones that do essentially the same thing - i.e. use the inertia sensors to measure time and acceleration in all 3 planes. They are able to produce some remarkably accurate readings for things like speed, 1/4 mile times, and (when calibrated) horsepower output.

Thus, I would say that an app like you want is probably feasible with an accuracy sufficient to get you back somewhere close to the anchor line. At least, that's my opinion without having reviewed the detailed specs on the inertia sensors in any modern smartphones.

---------- Post added August 19th, 2015 at 01:04 PM ----------

I should add, for an app like that to work. It would have to be mounted to something fixed - like your body - and stay fixed throughout your dive. If you put it on your arm, every time you moved your arm, I think it would throw off the app. Just like the dyno apps require the phone to firmly affixed to something in your car while in use.

So, while the app may be theoretically feasible, I'm not sure that it would be very useable in practice.

 

[Lorenzoid]

You could do this with a smartphone app, but it would have nothing to do with the compass. It would just use the built-in 3-axis inertia sensors. . . .

I had no idea the iPhone has 3-axis inertial sensors. Wow. If it can be utilized in an inertial navigation system, like the ones in aircraft and the like that have traditionally been based on gyroscopes, then I would be interested to learn what the impediments are to using it to track a person's movement (whether underwater or, for that matter, on land). As far as I know, there is no app that tracks a person's location based purely on inertial sensing--all tracking/navigation apps use the GPS and/or triangulation from cell towers, as far as I know. Maybe someone with more knowledge will chime in.

The possibility of inertial navigation devices for diving has been discussed here in the past--a quick Google search of SB threads reveals half a dozen or so--but perhaps it was before such technology made its way into iPhones.

 

[marshallkarp]

Ah, so what you are suggesting is a system that takes compass readings every so many seconds (or fraction of a second) and uses the differences between successive readings to estimate the diver's route and, accordingly, the direction back to the start? To estimate the route, and thus the direction back to the start, the system would need to know how far the diver traveled between the successive readings or data points. Unlike, say, an airplane, a diver's speed can vary erratically as the diver stops to look at things, etc. I don't think this can be done with enough accuracy to guide a diver back to the boat on most recreational dives.

Not even that complicated. I don't think it would need distance measurements, only compass measurements or dynamometer measurements. That's all it needs to do. My Columbia Switchback has a compass and a return to point (trackback) feature. If I startout moving to 340 degrees and hit the button, it will guide me back to 170 degrees. However, it can't account for movement, only straightline. Oh, it is not GPS.

My very uneducated guess would be to use the magnetic field compass or dynamometer information, take a reading every so often, store that information in the system RAM, somehow, and calculate the adjustment. For simplicity, I just want a triangle to point the way back to the entry waypoint.

---------- Post added August 19th, 2015 at 03:11 PM ----------

I should add, for an app like that to work. It would have to be mounted to something fixed - like your body - and stay fixed throughout your dive. If you put it on your arm, every time you moved your arm, I think it would throw off the app. Just like the dyno apps require the phone to firmly affixed to something in your car while in use.

So, while the app may be theoretically feasible, I'm not sure that it would be very useable in practice.[/QUOTE]

This whole quote is very interesting. As far as a fixed point, I'm good with some attachment to my tank or buddy's tank to do this.