# GPS data not used?

**URL:** <https://discuss.bluerobotics.com/t/gps-data-not-used/11307>\
**Category:** Sonar and Acoustics\
**Tags:** water-linked, dvl, positioning, underwater-gps\
**Created:** [January 7, 2022, 10:18am UTC](https://discuss.bluerobotics.com/t/gps-data-not-used/11307 "2022-01-07T10:18:49Z")\
**Posts on this page:** 1\
**Showing post:** 12

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**Author:** ![clyde](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.bluerobotics.com/clyde/32/8563_2.png) [@clyde](https://discuss.bluerobotics.com/u/clyde)\
**Post date:** [February 1, 2024, 6:43pm UTC](https://discuss.bluerobotics.com/t/gps-data-not-used/11307/12 "2024-02-01T18:43:45Z")

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Hi, Kieron:

TL;DR AFAICT, the code is there to support USBL + DVL fusion, but getting it work well is tricky, and possibly buggy.

I ran some simulations to play around with different parameters and posted the results here: [GitHub - clydemcqueen/ardusub\_localization: Tools to run ArduSub localization experiments](https://github.com/clydemcqueen/ardusub_localization)

Inspired by the simulation results we ran a test with a BlueROV2 equipped with a WL UGPS and A50 DVL off the Seattle Aquarium dock. We never got fusion or missions to work, but we learned a lot, and we have a workaround that we hope to try soon.\*

I suspect that getting fusion to work _well_ will take some experimentation. The EKF assumes Gaussian noise, and the USBL error isn’t Gaussian in X and Y, and in fact increases as the ROV moves away from the receivers. There may also be EKF bugs to work through, including this one: [External navigation measurement noise is overwritten by GPS reported accuracy in EKF · Issue #24020 · ArduPilot/ardupilot · GitHub](https://github.com/ArduPilot/ardupilot/issues/24020)

This is high on our list for 2024, so we will keep plugging away at it. Good luck!

/Clyde

\*Since we had the UGPS antenna deployed off the dock, we weren’t really paying attention to the G2 box after we got the initial lock. It turns out there wasn’t a good view of the sky from our location, so the G2 box did not keep the fix. Log analysis revealed that the GPS\_INPUT.satellites\_visible field was always 0, and the EKF origin was never set. Thus, fusion never happened, and we could not run missions.

This is a common test environment for us, so we will try again with a modified extension that is more forgiving: [Comparing waterlinked:master...clydemcqueen:clyde\_num\_sat · waterlinked/blueos-ugps-extension · GitHub](https://github.com/waterlinked/blueos-ugps-extension/compare/master...clydemcqueen:blueos-ugps-extension:clyde_num_sat)

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