Re: My GPS-receiver is too good 2

[Håkan Elmqvist]

Hello again,

Returning to this subject I am sorry being a bit slow but I simply didn’t have the time.

Thanks for your advice Gary but regretfully they so far are to no avail.

All the time I get the same position from the receiver, so I took the receiver on a bike-tour resulting in a 10 MB json file. As you can see below I just got a single position in spite of many km pedaled (jq extracts the lat and lon fields, awk with seen eliminates all identical results):

he@x22:~$ jq -r '" \(.lat) \(.lon)"' 4.json |awk '!seen[$0]++'

null null

59.321401029 17.970232032

If I, however, reset the receiver between observations I get a fresh position every time and the values are very reasonable (extracting UTC, lat and lon with awk):

root@pipickle:~# /usr/bin/gpspipe -r -n 9 |/usr/bin/awk -F, '/GPGGA/ { print $2 "\t" $3 "\t" $5; }'

185301.00 5919.2583 01758.2073

root@pipickle:~# /usr/bin/gpspipe -r -n 9 |/usr/bin/awk -F, '/GPGGA/ { print $2 "\t" $3 "\t" $5; }'

185304.00 5919.2583 01758.2073

root@pipickle:~# usbreset 1546:01a7

Resetting u-blox 7 - GPS/GNSS Receiver ... ok

root@pipickle:~# /usr/bin/gpspipe -r -n 9 |/usr/bin/awk -F, '/GPGGA/ { print $2 "\t" $3 "\t" $5; }'

185317.00 5919.2575 01758.2071

The receiver operates in binary mode, switching the receiver to NMEA with gpsctl has no effect other than being confirmed by the software.

gpsd: 3.22 (revision 3.22), receiver u-blox 7 – GPS/GNSS (??).

What is the problem with this receiver, is there anything I can do or is it that simple that I have been deceived buying this cheap gadget?

Regards

Håkan

Ps Pls remember that the fourth fractional decimal digit of a minute in most places corresponds to 1/10000 Nautical Mile (1852 m) and is worth around 18 cm.

Den 2024-05-15 kl. 21:46, skrev Gary E. Miller:

Yo Håkan!

On Wed, 15 May 2024 20:53:50 +0200
Håkan Elmqvist <hakelm@smeden.org> wrote:

Another interesting observation is that in the first position
delivered by gpspipe the minute fraction is given with 5 decimal
digits, all the following with four, se below:

Details matter.
What version gpsd?
What options to gpspipe?
What GNSS receiver?
Is your GNSS receiver set to NMEA, binary, or both?

Any comment?

Not without details.

As my old GPS-receiver died a quiet death I bought a cheap new one 
labeled G-MOUSE.

G-MOUSE is generic.  You never know what you'll get.

lsusb tells me it is a U-Blox AG [u-blox 7] which is confirmed by
dmesg.

Ugh.  You can do a lot better for the price.

Putting the receiver for 5 hours in my garden with a free sky
and sending the output of gpspipe -r to a file and filtering the file

Better yet, grab 5 hours of JSON and/or raw.  Then you can make
scatter plots, sky maps, etc.

I see that the indicated position all the time has stayed the same
not changing a single digit

Then you are not looking at enough digits.

even if the indicated speed all the time
is 0.0724 knots.

Yeah, happens.

My old receiver always wandered around a bit.

In its day, the 7-series was an improvement.  More so for the late
model 7's than the early ones.  But 4 digits not great these days.

Has GNSS become so good and stable or is this some kind of software 
cosmetics or most probably is there something I haven't understood?

The u-blox 7 can, optionally, have smoothing enabled.  And 4 digits
after the decimal place is only 11m resolution.  New $5 receivers
can hold 1m.

RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
	gem@rellim.com  Tel:+1 541 382 8588

	    Veritas liberabit vos. -- Quid est veritas?
    "If you can't measure it, you can't improve it." - Lord Kelvin

-- 
Håkan Elmqvist
Sunnerdahlsv 7
167 62 Bromma
Telefon: +46 (8) 80 18 81, +46 (704) 56 74 81, +46 (176) 84 077
epost: hakelm@smeden.org

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