Yo Greg! On Mon, 10 Nov 2025 08:14:52 -0500 Greg Troxel <[email protected]> wrote:
> The question is then whether the receiver is really outputting values
> that are so high, or if there is a problem in translation.
A quick look with ubxtool will tell you.
> I am saying that the relationship between EPS/C and EPX/Y/V does not
> appear to match the expected standard conversion.
Since they prolly come from the receiver, if you have the proper messages
enable, who knows.
What do you expect?
> The LLh position error estimates are plausible. Yes, I realize that
> 50%, 1 sigma, 2 sigma is not specified and unclear but very broad
> brush that's a factor of 2+, not a factor of 50 or 100.
More like a factor of 20x.
> Reasonable people think they mean *something* but they aren't quite
> sure what.
Exactly what the people that write data sheets want you to think.
> My receiver is currently tracking 6 GPS satellites, and nothing else.
> Reported SNR 16-36 dB. One expects poor performance.
For some definition of poor.
> If I eyeball EP X Y V, and eyeball RMS them, that plausibly matches
> pACC from the XYZ values, this minute around 21m. Whether that's 1
> sigma or 2 sigma I don't really care right now.
Since they are all computed from DOP and URA, you should expect them to
be self consistent.
> If I look at velocities in XYZ, they are all several cm/s, sometimes
> tens of cm/s (the receiver is on a desk).
But, as u-blox tells you. Ignore them unless you are moving.
> But, I'm seeing EPS of 140 km/h. Which is vastly more, and not just
> driving speed, but speeding ticket speed (except maybe on rural
> interstates).
But, as u-blox tells you. Ignore that unless you are moving.
> I would expect vAcc = sqrt ( EPS^2 + EPC^2 ).
Uh, no. vAcc is vertical error. Has nothing to do with speed.
I think you are looking for sAcc, the speed accyracy.
> While it's theoretically possible that ublox intends vAcc to be 50%
> and EPS to be 6 sigma, that doesn't make any sense. Assuming that as
> an explanation is unreasonable.
But, as u-blox tells you. Ignore that unless you are moving.
>
> It's possible that this particular receiver has buggy firmware, and
> it's possible something else is going on.
Seems like every other u-blox 7 or 8 I've ever seen.
> Hence, I was suggesting that other people look at their output and see
> if EPS/EPC are reasonably related to vAcc. If this is just my
> receiver, it's not a gpsd problem. If it's a pattern, then I think
> we should look harder.
But only look at it when actually moving.
Do you have a current gpsprof scaatter plot so you know the acctual
accuracies?
RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
[email protected] Tel:+1 541 382 8588
Veritas liberabit vos. -- Quid est veritas?
"If you can't measure it, you can't improve it." - Lord Kelvin
pgpsT6Buiy92C.pgp
Description: OpenPGP digital signature
