INAVerr- Is it the GPS or FC or neither?

Sune Nielsen September 8, 2015 at 2:33pm

I am getting similar behavior, which i posted about here:

http://diydrones.com/group/pixhawk/forum/topics/gps-errors-gps-0-gp...

Maciej Karpinski March 20, 2015 at 3:09am

I've been flying with a 3dr Pixhawk with 3dr GPS for a while without any INAVerrors and yesterad I made two flights with my newly built F450, on this one I have a M8N gps FrSky X8R receiver and during my two first flights yesterday I didn't have any INAVerrors.

My maden flight

https://www.youtube.com/watch?v=V0PlhW6vtwU

tshado March 20, 2015 at 2:15am

@Dan,

This error is also reported with 3DR ublox LEA 6H

some users have also seen with it INAVERR going to it max value of 255

tshado March 19, 2015 at 3:04pm

Hi Dan,

Normal you don't know what INAVERR is as it is not documented anywhere

Randy , aswered that

The Inav errors mean The Inav errors mean that inertial nav has not received a GPS update within 0.3 seconds

http://diydrones.com/xn/detail/705844:Comment:1934458

Three discussions are discussing about this error reported in Performance Monitoring

occuring with 3DR GPS and M8N

giving details, logs, description of errors

logs....

Thorsten in one of them, who did use GPS's for Geomapping described two problems he observed :

-timing jitter (missing samples)

- clock drift or communication latency between the GPS module and the Pixhawk.

see http://diydrones.com/xn/detail/705844:Comment:1931731

But no reactions for any Dev ...I don't know why :(

If it is a false problem please tell us !

Dan Wilson > tshado March 19, 2015 at 3:20pm

Well if INAVerr counts missed gps measurements, it would definitely increment every second with the strange quirk that Im observing on the m8n. However, less consistent, intermittent missed measurements could be a result of interference, which is a separate problem. In my opinion, apm needs to log and display the horizontal and vertical accuracy output of the ublox receivers which gives a much better indication of interference than DOP. I'll post about this in the GPS interference thread
- AKcopter > Dan Wilson March 19, 2015 at 8:17pm
  
  Well, this might explain why the error climbs linearly but if this a not a problem then why log it as an error and if this error has such predictable characteristics then it should be reasonably easy for the devs to mitigate this by appropriate changes in the code....
  - Dan Wilson > AKcopter March 19, 2015 at 8:29pm
    
    This information is quite valuable, for instance, if the GPS dies, this counter will suddenly skyrocket, or if the GPS UART connection is flakey, you may get sudden intermittent increases, or if you lose lock at high attitude you could use INAVerr to confirm this. I think the first thing to do is to play with the M8N by itself, log the output and check the timestamps. Then, play with the configuration using the ublox tools to see if its a config issue. Then, if it seems like its just a quirk of the M8N, you could look at ignoring the consistent missed measurements in the code, but in doing so, you would risk detecting 'real' missed measurements.
    
    I certainly wouldn't be disregarding the M8N though, csgshop have made a great product, I often get 15+ satellites during flight.

Dan Wilson March 19, 2015 at 2:45pm

I don't know what INAVerr means, but I use a csgshop m8n in my own application and have noticed that if it's set to 5 Hz, after receiving 5 measurements it's skips a measurement. I found this by inspecting the derivative of the timestamp where every 5th dt was 400ms. It's so consistent that it's definitely not caused by interference but it shouldn't really be a problem

tshado March 19, 2015 at 11:30am

Hi ,

" if these issues are interfence based that may be a reason"

interferences / EMI flag was raised by 3DR about the M8N

that 3DR didn't want to use M8N because of that ....

BUT

INAVERR is also reporterd with LEA 6 3DR GPS

Today, nobody prooved that INAVERR are caused by interferences ...

"Might be hard coded or something...hard to judge on a beta."

Yes, I agree

We will need to get a released version of this new "variance" reporting

We will need also explanations about their meaning and how to analyze this (these ?) numbers...

Hoping we can still know if GPS updates are missed or not in the 200ms loop

tshado March 19, 2015 at 10:50am

@Stuart,

Yes, as you say very interesting :-)

Was it using 3DR GPS LEA 6H ?

I read the answer of Tandy in Ticket 172

This ticket was asking to go to from a 8 bits to 16 bits counter (ie max value 255 to 65535 for INAVERR)

Answer from Randy

"This is a bit unlikely to get done (at least as stated) because we're moving to the EKF for AC3.3 and errors are reported very differently. Instead of a simple INAV error counter there's extensive (but perhaps not yet well understood by the community) reporting on "variances" which are a 0.0 ~ 1.0 representation of how good the EKF thinks it's various attitude and position estimates are."

Two question I have:

1)INAVERR was indicating clearly "Missed Gps updates"

Now this "Variances" will vary from 0 to 1 , and characterize EKF results about attitude and position estimates

Today we can say :" we have a high occurance a missed GPS updates " impacting EKF results

Tomorrow with 3.3 code: will it be possible to know that the position estimate max variance of 1 will be caused " by missed GPS updates" ...?

2) And more important

Why the missed GPS updates occuring with 3DR GPS ie INAVERR problem has not been investigated in a proper way

Is it caused by GPS or FC or neither?

Has somebody looked at NMEA messages on the UART bus between GPS and Pixhawk to see if this NMEA messages are missing, or bad, or altered ?

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INAVerr- Is it the GPS or FC or neither?

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