# EPH, EPV GPS values

**URL:** <https://discuss.px4.io/t/eph-epv-gps-values/32901>\
**Category:** PX4 Autopilot\
**Created:** [June 23, 2023, 10:54am UTC](https://discuss.px4.io/t/eph-epv-gps-values/32901 "2023-06-23T10:54:22Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![pordipatrik](https://discuss.px4.io/user_avatar/discuss.px4.io/pordipatrik/32/13037_2.png) [@pordipatrik](https://discuss.px4.io/u/pordipatrik)\
**Post date:** [June 23, 2023, 10:54am UTC](https://discuss.px4.io/t/eph-epv-gps-values/32901/1 "2023-06-23T10:54:22Z")

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Can somebody tell me what do eph and epv s mean?  
Here: [https://danielcjacobs.com/uploads/ECHO\_Memos/ECHO029\_Logged\_GPS\_Data\_Explanation.pdf](https://danielcjacobs.com/uploads/ECHO_Memos/ECHO029_Logged_GPS_Data_Explanation.pdf)  
They considered as standard deviation.  
While here:  
[SensorGps (UORB message) | PX4 User Guide](https://docs.px4.io/main/en/msg_docs/SensorGps.html#sensorgps-uorb-message)  
Accuracy, but it is not detailed.

Also, since eph and epv are used for failsafe:[Parameter Reference | PX4 User Guide](https://docs.px4.io/main/en/advanced_config/parameter_reference.html)  
, I want to use them instead of multiplying the measurement resolution with hdop and vdop.  
Any feedback on the questions above would be appreciated.

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**Author:** ![JulianOes](https://discuss.px4.io/user_avatar/discuss.px4.io/julianoes/32/30_2.png) [@JulianOes](https://discuss.px4.io/u/JulianOes)\
**Post date:** [June 24, 2023, 4:12am UTC](https://discuss.px4.io/t/eph-epv-gps-values/32901/2 "2023-06-24T04:12:29Z")

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For uBlox the value comes from here:

> <https://github.com/PX4/PX4-GPSDrivers/blob/1f850dea2ca80f98a91d96013e2b6cc7da2365de/src/ubx.cpp#L1890>

So it’s UBX-NAV-PVT.hAcc which is described as “Horizontal accuracy estimate” in mm.

See: [https://content.u-blox.com/sites/default/files/products/documents/u-blox8-M8\_ReceiverDescrProtSpec\_UBX-13003221.pdf](https://content.u-blox.com/sites/default/files/products/documents/u-blox8-M8_ReceiverDescrProtSpec_UBX-13003221.pdf)

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<div class="post-metadata">

**Author:** ![pordipatrik](https://discuss.px4.io/user_avatar/discuss.px4.io/pordipatrik/32/13037_2.png) [@pordipatrik](https://discuss.px4.io/u/pordipatrik)\
**Post date:** [June 26, 2023, 7:36am UTC](https://discuss.px4.io/t/eph-epv-gps-values/32901/3 "2023-06-26T07:36:09Z")

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Thank you!  
My problem with this is that accuracy is not defined here neither. In some places it is listed as standard deviation.

It is a bit confusing. Could you clarify this to me?

Many thanks,  
Patrik

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<div class="post-metadata">

**Author:** ![JulianOes](https://discuss.px4.io/user_avatar/discuss.px4.io/julianoes/32/30_2.png) [@JulianOes](https://discuss.px4.io/u/JulianOes)\
**Post date:** [June 26, 2023, 8:51pm UTC](https://discuss.px4.io/t/eph-epv-gps-values/32901/4 "2023-06-26T20:51:37Z")

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My assumption is that it’s a standard deviation but if you want to be sure you might have to talk to uBlox and ask them.