Underwater digital magnetic compass with trackback?

[dmaziuk]

If dead reckoning actually worked on this planet, its inhabitants wouldn't have spent all this time and money building multiple satellite networks dedicated to aid in navigation. Anyone's welcome to buy a $50 raspberry pi, an $40 berryIMU and build themselves a digital magnetic compass with trackback for under a hundred bucks. Some posters in this thread are actually qualified to do so, too, like I'm sure there are a couple of people at DiveNav.

 

[Lorenzoid]

If dead reckoning actually worked on this planet, its inhabitants wouldn't have spent all this time and money building multiple satellite networks dedicated to aid in navigation. Anyone's welcome to buy a $50 raspberry pi, an $40 berryIMU and build themselves a digital magnetic compass with trackback for under a hundred bucks. Some posters in this thread are actually qualified to do so, too, like I'm sure there are a couple of people at DiveNav.

Yep. I've voiced interest in such an underwater inertial navigation device before and have been hoping for years that someone would commercialize one.

But as far as the implication in the original post that underwater navigation can be accomplished with any useful accuracy by some device that doesn't use inertial sensing but rather uses only "magnetic" (compass) sensing--I just do not believe that is possible.

 

[gr8jab]

An underwater INS is totally plausible and reasonable. It is simply an adaptation of current industrial INS technology. Doing a quick search online, I found two devices that were capable of the job. They include internal gyros, accelerometers, and pressure transducer. Additionally, they have all the built in signal processing to resolve position and orientation needed for navigation. Upon detailed inspection, there are only two problems that need resolved:

1. The internal software is calibrated for AIR pressure. I'm sure that it would not be difficult for the manufacturer to have an 'underwater' mode with 'depth' instead of 'altitude' calculated.

2. I'm not sure of the volume price, but the development kits are between $1K and $2K.

Considering such things were a pipe-dream just a few years ago, I'm guessing that improvements in technology and competition will quickly make such sensors more powerful and cheaper. I would bet that SCUBA INS will be affordable and available, maybe in the luxury dive computer price range, in the next 5-10 years. It would help if there were another underwater market (with more money) that would drive the innovation and allow the SCUBA community to piggy-back.

Here are the links to the two devices I found:

Vectornav

MicroStrain

 

[dmaziuk]

Yep. I've voiced interest in such an underwater inertial navigation device before and have been hoping for years that someone would commercialize one. But as far as the implication in the original post that underwater navigation can be accomplished with any useful accuracy by some device that doesn't use inertial sensing but rather uses only "magnetic" (compass) sensing--I just do not believe that is possible.

Last I looked wikipedia had reasonable articles on dead reckoning and inertial navigation that explain very clearly why it's not good enough on its own. Read if interested. The sensors may have gotten much better in the last decade but if you're jumping off a boat being pushed by the wind one way, gradually descending into a current going a different way and doing a drift dive for an hour... even if you take gps fixes (~$50 to add a gps module to your $100 Pi+IMU device) at the start & the end of the dive, good luck trying to resolve the difference and back-calculate a reasonable path.


Might be interesting to actually try but I get enough of this hardware & software crap at work to also do it in my free time. I'd rather go diving.

 

[stuartv]

Last I looked wikipedia had reasonable articles on dead reckoning and inertial navigation that explain very clearly why it's not good enough on its own. Read if interested. The sensors may have gotten much better in the last decade but if you're jumping off a boat being pushed by the wind one way, gradually descending into a current going a different way and doing a drift dive for an hour... even if you take gps fixes (~$50 to add a gps module to your $100 Pi+IMU device) at the start & the end of the dive, good luck trying to resolve the difference and back-calculate a reasonable path.


Might be interesting to actually try but I get enough of this hardware & software crap at work to also do it in my free time. I'd rather go diving.

Well, since I'm an Einstein and a genius and all, I went ahead and looked it up. I found these:

https://en.wikipedia.org/wiki/Inertial_navigation_system

https://en.wikipedia.org/wiki/Dead_reckoning

The first one says, in part:

Recent advances in the construction of microelectromechanical systems (MEMS) have made it possible to manufacture small and light inertial navigation systems. These advances have widened the range of possible applications to include areas such as human and animal motion capture.
An inertial navigation system includes at least a computer and a platform or module containing accelerometers, gyroscopes, or other motion-sensing devices. The INS is initially provided with its position and velocity from another source (a human operator, a GPS satellite receiver, etc.), and thereafter computes its own updated position and velocity by integrating information received from the motion sensors. The advantage of an INS is that it requires no external references in order to determine its position, orientation, or velocity once it has been initialized.

Apparently, being an Einstein and a genius isn't working well enough for me, though, because it seems like this is saying that it would be feasible nowadays to do inertial guidance using a reasonably small handheld consumer device. And that it wouldn't be affected by drifting in a current.

And my genius is seriously failing me on understanding how a drifting boat has anything to do with the OP's question about wanting to get back to an anchor line.

 

[paulw]

These people have been talking about doing what you want and more for a long time:

Navimate - GPS for Divers

 

[rmssetc]

So, a GPS works on the surface. What about a waterproof GPS receiver, attached to a dive buoy (flag)? The floating GPS receiver would have an RF or acoustical transmitter, communicating with a wrist/console mounted receiver. The receiver worn by the diver could easy be integrated with a digital depth gauge to provide 3D navigation.

Cheap, proven, compact, readily available technology.

Disadvantages: unusable at depth beyond the reel, with overhead obstructions, kelp, etc. Some error (30~50% of the diver's depth, depending on current & wind) if there's any vertical offset between the positions of the diver & the floating GPS.

If there was an easily retractable SMB-type-device, then the diver could get sporadic location readings while remaining submerged, without continuously pulling a float. With this system, you wouldn't even need to get continuous readings...simply store an initial point, do your dive, float the GPS receiver, and get a display that points back to the starting location.

 

[Bob DBF]

If dead reckoning actually worked on this planet, its inhabitants wouldn't have spent all this time and money building multiple satellite networks dedicated to aid in navigation. .

All the time and money spent on GPS development and deployment was to accurately target missiles on the USSR. The side effect years later was the civilian use, and that now someone who can't read a map, or navigate, can get from point a to point b.


Bob

 

[dmaziuk]

All the time and money spent on GPS development and deployment was to accurately target missiles on the USSR. The side effect years later was the civilian use, and that now someone who can't read a map, or navigate, can get from point a to point b. Bob

USSR spent the equivalent amounts on GLONASS to accurately target missiles on the USA. Who is EU planning to target with Galileo? Those warmongering yuropeans...

 

[KenGordon]

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.

The trouble is noise. These MEMS devices are maybe 99% correct +/- a bit. Thus the error expands very quickly. For relative motion that isn't a big deal, but if you want a closed loop then the chances of getting back to the beginning are small. You'd be lucky to be able to do a couple of 10ft displacements and back and know you were in the same place.