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Re: satellites used - NMEA feed

From: Nick Taylor
Subject: Re: satellites used - NMEA feed
Date: Wed, 29 May 2024 11:13:49 +0100
User-agent: Mozilla Thunderbird

Hi Gary

Thought I'd post this to list (following several private exchanges)

Many thanks for all your help - using your fixed release and with code revamp according to your suggestions seems we are now getting beautiful usat count from NMEA feed that isn't including satellite SKY records.

Thanks for all your hard work on this and patience with our understanding of gpslib usage!

Best regards

Nick & team

On 10/05/2024 20:40, Gary E. Miller wrote:
Yo Nick!

On Fri, 10 May 2024 13:14:48 +0100
Nick Taylor <> wrote:

Could you cast your memory back to Dec 2022 - we found that using
NMEA feed we weren't getting satellite data although there was used
satellite count available...
Yeah, Sats Seen and  Sats Used just gets worse and worse.

You kindly made a patch to pick this up as used satellite count if
the satellite data wasn't available (see screenshot attached)
I can'read read your screenshot, my eyes are going bad and that is way
to grainy for me to read.  And I certianly can't cut/paste the
commit number from a course image.

On recently upgrading to latest gpsd release it seems that something
has changed that makes used satellite count disappear again - we pick
this up from gpslib variable gps_data_t.satellites_used
And it is only going to get worse.  Newer receivers can never seem to
report sat counts consistently.  I have one receiver here that reports 4
different sat counts in the same epoch.  Which is correct?

This gets more complicated when the receiver can pick up 3 signals (L1,
L2 and L5) from the same sat.  Should that be reportd as 1 sat, or 3?
For now, gpsd leans to reporting 3, except that not all new multi-frequency
receivers report enough data to know which is which.

I'm also attaching output from gpspipe -R
That looks good.  I'll play with that today.

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703  Tel:+1 541 382 8588

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

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