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Re: ?POLL; responses having wrong ss and used field data

From: Gary E. Miller
Subject: Re: ?POLL; responses having wrong ss and used field data
Date: Fri, 23 Jul 2021 11:01:23 -0700

Yo Niladri!

On Fri, 23 Jul 2021 11:01:31 +0530
Niladri Sekhar Roy <> wrote:

> I am using "gpsd: 3.20 (revision 3.20)"

A bit old.  You should update.

> When I am using <?WATCH={"enable":true}> and <?POLL;> to fetch data
> from daemon

That does not do what you think it does.  I recommend against that.

> I can see all the "ss" and "used" field values of
> satellite objects are 0 and false. In cgps utility, I can see
> non-zero SNR value and true as the used-field value.

Yes, because of limitations in the ?POLL protocol.  cgps does not use

> When I am using <?WATCH={"enable":true,"json":true}> and fetching
> data from daemon I can see all the "ss" and "used" field values are
> consistent with the values showing in cgps utility.

Yes, because then you are doing what cgps is doing.

> I want to read the GPS information on demand that's why I want to use
> the <?POLL;> mechanism.

No, you don't.  ?POLL just gives you the information gathered so far in the
current epoch.  Things like sky view are not even seen in most epochs.

You may as likely do your ?POLL before any data is gathered in the
current epoch.  The odds your ?POLL lands after all data is in
for the epoch, which likely has no skyview, is small.

> Is there any known issue with that?

Many.  Dont do it.

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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