The problem is Einstein, specifically the part where if your accelerometer/gyro is moving in a current, it thinks it's standing still. (IRL it won't detect a slow enough acceleration either so you can swim into a current without that ever registering.) Up top you can get a GPS fix and use the IMU for fine-tuning your location. Without GPS you need some other point of reference and magnetic pole doesn't really cut it. Hence the need for the beacon.
Underwater digital magnetic compass with trackback?
- Thread starter marshallkarp
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marshallkarp
Contributor
I talked with a Bushnell Rep this afternoon about their GPS Trackback Device. No go here. It does have a magnetic compass feature and I was hoping if the GPS signal was lost, the magnetic compass would kick in. It does not, the trackback feature works off the GPS. I did ask about a hiker who loses the signal due to bad cloud cover, but it makes no difference, it is what it is. No plans to develop anything else. Dead end here.
I think the technology is really commonplace now. I believe that is how, for example, the controller on a Wii video game works. So, they're cheap and very compact. I don't they're accurate enough for plane and missile guidance. But, obviously, good enough for consumer applications like game controllers and smartphones.
I suspect the biggest impediments to the scuba app you really want are:
- insufficient processing power in a smartphone to track all the relevant data and produce an accurate TrackBack. It would need to track the phone's motion as well as orientation in 3D.
- relying on the smartphone's electronic compass is probably not practical - one reason being the possibility that being near a wreck could throw it off.
- I don't know how significant changes in ambient pressure would affect the inertial sensors. Depending on their design, it seems like that could possibly be a problem. Or might not. It would probably be pretty easy to test, though. Download a dyno app to your phone then take it diving. Use a measured distance underwater and swim with the app running to see if it can tell you, with any accuracy, how far you swam.
---------- Post added August 19th, 2015 at 04:22 PM ----------
So, if I get in my car and start my accelerometer monitoring app and I accelerate up to 30 MPH, it will tell me I'm going 30 MPH? But, if I'm driving the same direction as the wind is blowing, and the wind is blowing 30 MPH, my accelerometer is going to think I'm standing still? Ba ahahahahaa!!!!
I started at 30MPH and then accelerated to 30MPH? Tell me again who the genius is?
If you don't turn your smartphone on until you are underwater and drifting in a current, then, sure, it's not going to be able to tell that are actually moving and it's going to think that you are stationary. If you then grab the anchor line as you drift by and stop yourself, it's going to register that you "accelerated" in the opposite direction.
How is that relevant? If your smartphone is on before you get in, or you turn it on and mark your anchor line waypoint while you are stationary, then your smartphone is going to have the correct frame of reference and calibration to tell that, when you release the anchor line and drift away in a current, you are now going whatever speed and in a direction that is whatever orientation to the phone. Just the same as it would if you marked the anchor waypoint and swam away under your own steam. Your phone doesn't know or care whether you are moving under your own steam or being moved by a current.
Eh, when you say "170" do you really mean 160? 340 and 160 are simple "reciprocal headings"--that is, 180 degrees apart. Following a 340 degree course with your Columbia Switchback pointing the way, you arrive at your destination and hit the button, which causes it to subtract 180 from 340 and point you in the resulting direction of 160. Simply stated, it points you back in the direction you came from. This works accurately to get you back to your starting point so long as you walked in a straight line--in other words, so long as you did not deviate off course from your heading of 340. If you deviate off course, there is no way for a compass to point you back to your starting point simply by calculating a reciprocal heading. Sure, if the deviation was small--say, you take a few steps left or right now and then to avoid obstacles--then the direction it points to on the reciprocal heading may still be close enough to get you back to your starting point. However, when diving, we don't usually maintain anything close to a straight-line course because current continually pushes us off course or because we WANT to deviate so we can go look at things. In instances in which a simple reciprocal heading is really what the diver wants, a plain old compass works fine.
As far as I understand your question, you are not asking about a simple reciprocal heading, but rather how to extend the concept so that it takes into account a diver wandering about during the dive. To repeat the answer, this cannot be done with an app or anything else that relies solely on compass readings "taken every so often," "stored in RAM," etc. There is simply too much missing information for the calculation to be made with any useful accuracy.
AJ
Contributor
Looks to me you're losing yourself in solutions. The big question is: how can I get home? The solution at the surface is GPS, under water a beacon with a directional receiver. Simple as that.
:d
Bob DBF
Contributor
What the computer does is take the accelerations and non accelerations and determine where you are from where you were. The acceletrometers were quite accurate, but all the components for a unit might fit in a van since this was before integrated circuits. The GPS checks were quite close considering the accuracy of GPS at the time. Just saying that the concept works and was quite accurate, and is probably much more accurate than it was 50 years ago.
Bob
Depending on how well you can use trig. you can work out he drift from the current. sit still and measure how fast the current is. IE 20 foot a minute in the direction of 270. If you have been down 10 minutes yo have suffered a 200 ft drift. So to travel north 100 yards or 300 ft in 10 minutes. You actually went 300 ft north and 200 ft west. to then turn south and return you end up 400 ft west from your entry point because of another 200 ft off set. your return is now 300 ft south and 400 east. a return course of about 120 should get you close to the entry point. total return distance would be around 600 ft or so. My self ... I dont like currrent. at some point the return trip is no longer navagable cause its now a drift dive.
