# Underwater GPS recv data

**URL:** <https://discuss.bluerobotics.com/t/underwater-gps-recv-data/2297>\
**Category:** Blue Robotics Software\
**Tags:** positioning\
**Created:** [March 12, 2018, 10:33am UTC](https://discuss.bluerobotics.com/t/underwater-gps-recv-data/2297 "2018-03-12T10:33:44Z")\
**Posts on this page:** 3\
**Page:** 2

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**Author:** ![Obert94](https://avatars.discourse-cdn.com/v4/letter/o/ba9def/32.png) [@Obert94](https://discuss.bluerobotics.com/u/Obert94)\
**Post date:** [June 1, 2018, 6:54am UTC](https://discuss.bluerobotics.com/t/underwater-gps-recv-data/2297/21 "2018-06-01T06:54:54Z")

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Hi Jacob, we are comparing the accelerometer (from the onboard imu) with the gps values (From the Waterlink underwater gps system).  
To get the values we use  
gps = autopilot.recv\_match(type=‘LOCAL\_POSITION\_NED’,blocking=True)  
imu = autopilot.recv\_match(type=‘RAW\_IMU’,blocking=True)  
then I get imu.xacc and gps.x from the python robot.

while measuring I draw the ROV through the water (I have tried with motor input, with same result). When plotting the accelerometer data and gps values it is seen, that accelerometer responds before the gps.

 ![GPSDelay](https://us1.discourse-cdn.com/flex019/uploads/bluerobotics/original/2X/9/956fb5bfcb32fa2324df15abb8a310a8db26d9f0.png)  
Time is in seconds, Position is in meter.

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**Author:** ![jwalser](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.bluerobotics.com/jwalser/32/2234_2.png) [@jwalser](https://discuss.bluerobotics.com/u/jwalser)\
**Post date:** [June 11, 2018, 6:42pm UTC](https://discuss.bluerobotics.com/t/underwater-gps-recv-data/2297/22 "2018-06-11T18:42:54Z")

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Try plotting the GPS\_RAW\_INT position, the local\_position\_ned is fused position. There is a [parameter for gps delay lag](https://www.ardusub.com/operators-manual/full-parameter-list.html#ek2gpsdelay-gps-measurement-delay-msec), though if it is more than a second or so, there is probably a larger issue somewhere else in the system that needs to be addressed.

Also, doesn’t it make sense for the position to lag the acceleration? You need to accelerate for some time to build up appreciable velocity and be displaced. Though again, maybe this is too much lag.

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**Author:** ![Schmalelab](https://avatars.discourse-cdn.com/v4/letter/s/ed8c4c/32.png) [@Schmalelab](https://discuss.bluerobotics.com/u/Schmalelab)\
**Post date:** [July 15, 2019, 7:54pm UTC](https://discuss.bluerobotics.com/t/underwater-gps-recv-data/2297/23 "2019-07-15T19:54:57Z")

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Hello Jacob,

We are using the Under Water GPS with and without the BlueROV2. With that we are looking for compilable position and time data. Does the GPS unit store data? Or do we need to write a script? Please in any case can you help?

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