Seacraft ENC3 Inertial navigation unit?

[Texasguy]

So, it compensates for current (which the ENC3 does not)?

Not sure how it can compensate against the current. Same as any boat can only see the speed only against the water (without GPS like solutions).

 

[scubaozy]

Not sure how it can compensate against the current. Same as any boat can only see the speed only against the water (without GPS like solutions).

Like dead reckoning, you will input wind direction and strength. In this case current.

 

[211ratsbud]

Im in the St Lawrence/1000 Islands Region, if anyone would like to demo or just check out an ENC I have several Future 1000's and a Ghost we can get you on. There is some minor post dive correction you can do in the laptop software.

Also if you think about mapping a cave and you travel two directions, and the cave has flow you can interpolate the offset tracks.

It produces several types of files.

 

[stuartv]

Not sure how it can compensate against the current. Same as any boat can only see the speed only against the water (without GPS like solutions).

Because the post I responded to said it's an INS system. I think that means Inertial Navigation System.

If it's an inertial system, that means it can tell when it starts to move. For example, when a current pushes it, the inertial unit would detect that acceleration and know, based on how long the acceleration continues, the direction and speed the unit is moving. Then, if it does not detect any new acceleration, it would track the path by Velocity times Time.

That's what inertial sensors do, right?

It just has to start with a known, fixed point. I.e. I believe you would just have to start it (calibrate it?) in a spot where it is not moving.

The ENC3 does not do that. Thus why it cannot compensate for current. And why I asked if the SINAPSI system does compensate for current - i.e. really IS an inertial system.

 

[211ratsbud]

*delete"

 

[scubaozy]

Because the post I responded to said it's an INS system. I think that means Inertial Navigation System.

If it's an inertial system, that means it can tell when it starts to move. For example, when a current pushes it, the inertial unit would detect that acceleration and know, based on how long the acceleration continues, the direction and speed the unit is moving. Then, if it does not detect any new acceleration, it would track the path by Velocity times Time.

That's what inertial sensors do, right?

It just has to start with a known, fixed point. I.e. I believe you would just have to start it (calibrate it?) in a spot where it is not moving.

The ENC3 does not do that. Thus why it cannot compensate for current. And why I asked if the SINAPSI system does compensate for current - i.e. really IS an inertial system.

My understanding is ins extrapolates based on previous estimated position, thus even tiny errors will end up being magnified making the track increasingly inaccurate perhaps even useless if you do not have constant actual position input. On land, this is done by gps input to correct the positions but uw you will not have this.
"To get a rough idea, this means that, for a single, uncorrected accelerometer, the cheapest (at 100 mg) loses its ability to give 50-meter accuracy after around 10 seconds, while the best accelerometer (at 10 µg) loses its 50-meter accuracy after around 17 minutes."

 

[Valyngar]

Getting this system soon, so I will post in few months how good it is.

 

[stuartv]

My understanding is ins extrapolates based on previous estimated position, thus even tiny errors will end up being magnified making the track increasingly inaccurate perhaps even useless if you do not have constant actual position input. On land, this is done by gps input to correct the positions but uw you will not have this.
"To get a rough idea, this means that, for a single, uncorrected accelerometer, the cheapest (at 100 mg) loses its ability to give 50-meter accuracy after around 10 seconds, while the best accelerometer (at 10 µg) loses its 50-meter accuracy after around 17 minutes."

Which brings us back to the point I was making: It's not really an Inertial Navigation System, is it?

If it is, what makes it so?

Also, if you have GPS input to correct actual position every 50 meters, why would you need inertial guidance at all?

 

[scubaozy]

Which brings us back to the point I was making: It's not really an Inertial Navigation System, is it?

If it is, what makes it so?

Also, if you have GPS input to correct actual position every 50 meters, why would you need inertial guidance at all?

You must have a position fix, at least for the start point. Be it gps or and other radio or any other form. I remember reading some missiles like tomahawk using image comparison to figure out and correct their position during ins navigation.. I am pretty sure military submarines using INS also listen so acoustical signals to correct their position.
I think it does have most of the sensors to build an INS but only the implementer of the system will be able to answer whether it qualifies as one. In my view you can build one, and drift problem can be reduced as well if someone takes the time. I do not see in the videos that they are being guided from waypoint to waypoint, so, to me it looks like simple dead reckoning is how it is implemented. Probably they use the additional speed sensor because they do not use accelerometer to detect the speed (thus no drift problem to solve) but then w/o that, it will not detect the current.
My Garmin DC has also all the needed sensors. It can figure out when I am walking cycling or running. Someone took the time to fuse the sensor inputs and filter them for those actions. Result is not perfect but usable. So theoretically it should be possible to write a ins app for it as well.

 

[Jai Bar]

It is an inertial navigation system by dead reckoning, and as such is prone to some error depending on the currents and distance travelled from the last GPS fix / entry point. For non-overhead environment they have an additional antenna (or small GPS receiver) that can be sent to surface to get an accurate GPS fix and correct for drifting etc.

I amused myself with a similar concept many years ago (something similar to this Underwater GPS (sorta)) , and at the time the GPS (inside a small transparent box) was crappy and with high surf it could take a while to get a fix. When I towed the box throghout the dive and downloading the tracks to a PC, I could see that there were lots of gaps in the data, for example when a wave passing and the box getting immersed it was losing connectivity for 2-3 minutes. Probably today one can just used some old smartphone for similar purposes- jump it to surface in order to get a fix and bring it back to have a look at the screen...