Mavlink LOCAL_POSITION_NED not publishing

[jayparikh (Jay)]

Hello,
I’m trying to read local position data from ArduSub for autonomy but it’s not publishing. I’m using cube orange, jetson nano and communicating using serial telem1 port. I do see the message GPS: No GPS fix, does the Ardusub require GPS fix for publishing data?

Thank you for helping!

Jay Parikh

[tony-white]

Hi Jay!
Unfortunately, GPS signals do not penetrate water! You can fit your vehicle with a GPS that will work if the antenna is exposed to the sky, but otherwise you need another means of locating the vehicle. This is usually done with acoustics - via either a DVL, USBL, or Underwater GPS. Checkout our guide to sonar tech for more info!

[jayparikh (Jay)]

Hi Anthony,

Is there any way I can get position estimate using IMU/ Gyro data?

[tony-white]

Hi Jay -
You could develop your own code to integrate the filtered output from the IMU, but I wouldn’t expect it to perform very well. This is a common question on our forums:

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Hi Magnus, You can get the rough position from inertial data only. Keep in mind that it will drift quite a bit. @jaxxzer has spent some time testing this and has some videos on Youtube of the BlueROV reacting to position changes with only inertial sensing. I’ll point him towards this post. -Rusty

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@mseskar, I will point out that what you are trying to do will probably not work well. The imu data from the autopilot board is not suitable (precise) for dead reckoning. Here is some more information:

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Just a quick note on top of Eliot’s precious comments. You can do positioning with only IMUs generally but the IMUs you need to be looking for are starting at least 20 times of a Pixhawk in price and much bigger in size. So in theory possible but with the current ArduSub ecosystem not. Resources are vastly available to search for it.

Such techniques usually require hardware that is an order of magnitude more expensive and precise. Cheaper and easier to use acoustic based solutions!

[jayparikh (Jay)]

Thank you Anthony!