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Re: [gpsd-users] CGPS stating fix valid when antenna has been disconnect

From: Gary E. Miller
Subject: Re: [gpsd-users] CGPS stating fix valid when antenna has been disconnected
Date: Tue, 16 Oct 2018 09:52:32 -0700

Yo Giovanni!

On Tue, 16 Oct 2018 15:12:19 +0200
Giovanni Parodi <address@hidden> wrote:

> I'm a user of GPSD (version 3.14).

That's a pretty old version.  3.18 is current.

To be helpful we also need to know what GPS you have, and how it
is configured (NMEA, binary, etc.).

>    7. Here is the problem:
>       1. tool cgps  indicates valid fix, but the timestamp doesn't
> change 2. tool gpsmon indicates fix not valid (and this is the right
>       information)

The key is the timestamp is not changing.  That means your GPS stopped
sending information when the antenna disconnected.

You can confirm this by running "gpspipe -R" to see what the GPS
actually sent.

gpsd only outputs data when it gets data.  When the GPS stopps sending
data, then gpsd has no data to send.  cgps just display the last
data it got.

> Here is my doubt, why the cgps tool always print that the FIX is 3D
> mode?

Because that is what it was told.

> My main issue is that I should implement a custom client in C
> and I would like to copy the code approach in cgps (the one in gpsmon
> is more complicated).

Many ways to skin that cat.  If you like Python then check out the
xgps client.

> However when, at step 7, I read the data using the subroutine
> gps_read
> the structure gps_data_t contains the flag indicating a valid GPS fix
> (while the fix is no valid as stated by gpsmon).

No idea why gpsmon would show different.  That is the most idiosyncrative

> Do you have any idea what's wrong with cgps?

Nothing wrong with cgps, nothing wrong with gpsd.  They are telling you
what the GPS told them.

If you GPS is too lazy to tell you it lost fix, then just add a timeout
in your client for how long before the last fix is declared invalid.

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        address@hidden  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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