Re: gpsd Satellite Elev & Azim

[Gary E. Miller]

Yo Nick!

On Tue, 11 Jun 2024 14:56:14 +0100
Nick Taylor <nicktaylor@dataskill.uk> wrote:

> On 10/06/2024 21:23, Gary E. Miller wrote:
> > Without an overlap, I can't say for sure that they even disagree.
> >  
> I reran the dumps at the same time this time!!

Good.

MTK3301:

2024-06-11T13:35:10.000Z to 2024-06-11T13:35:39.000Z

NOE-M8N:

2024-06-11T13:35:11.000Z to 2024-06-11T13:35:39.000Z

> The reason I was checking this was because I was having difficulty
> with SBAS on the NEO but moving receiver higher seems to allow it
> better southern sky view and now both receivers are seeing SB136.

Does it improve the fix quality?  You only need to see one SBS ro
get the SBAS corrections.  And you now see 3 SBAS.

> I still see the quirky numbers eg:
> SIM68M: 49 31 173
> NEO8M : 49 30 173

PRN 49, as in SBAS svid 136?

At 13:35:11, the NEO-M8N:

{"PRN":49," gnssid":1,"svid":136,"az":173.0,"el":31.0,[...]

That mathes the ubxtool output:

UBX-NAV-SAT:
   gnssId 1 svid 136 cno 34 elev  31 azim 173 prRes      0 flags x1916

Both show elevation 31.  In NAV-SAT, the elevation is a 16 bit unsigned
integer, so no rounding happening there.

And the MTK-3301:

{"PRN":49,"gnssid":1,"svid":136,"az":173.0 ,"el":30.0,"ss":33.0,"used":false}

That matches the NMEA:

$GPGSV,3,2,12,32,30,053,44,49,30,173,33,22,25,295,40,08,25,163,26*76

Easy to eyeball that the 30 is from the receiver, and unchanged in the
JSON.

> I assume it could be down to rounding in the receivers?

No assumng needed.  They report the same quantity, with different values.

> In any case
> you say it's not important for the fix calculations...

Yes, never used.  Except against the elevation mask.

> Still weird though...

Don't fall down the rabbit hole...

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

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    "If you can't measure it, you can't improve it." - Lord Kelvin

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