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Re: [gpsd-users] Get fix mode with disconnect antenna

From: Yakov Shmulevich
Subject: Re: [gpsd-users] Get fix mode with disconnect antenna
Date: Thu, 21 Nov 2013 13:16:22 +0200

Hi Gary,

On Thu, Nov 21, 2013 at 12:15 AM, Gary E. Miller <address@hidden> wrote:
Yo Yakov!

On Wed, 20 Nov 2013 09:23:39 +0200
Yakov Shmulevich <address@hidden> wrote:

> > Can you make a copy of the gpspipe output and annotate it with the
> > remove event?
> >
> > Follow gpspipe output with antenna connected:
> $GPGGA,061139.00,3206.6722,N,03450.3224,E,*1*,09,1.1,-0019.1,M,0018.4,M,,*73
>             |
>             -- GPS Quality Indicator(*1*=GPS SPS Mode, fix valid)
> $GPGSA,A,*3*,12,25,18,21,29,73,79,82,83,,,,1.8,1.1,1.4*30
>                       |
>                       -- Mode(*3*=3D)
> $GPGSV,5,1,17,02,05,047,,05,28,063,,12,30,135,25,18,12,182,31*76
> $GPGSV,5,2,17,21,52,236,30,25,71,138,27,29,58,017,38,31,32,278,33*73
> $GPGSV,5,3,17,65,03,024,26,66,27,068,,67,24,127,,73,15,329,38*70
> $GPGSV,5,4,17,79,36,202,29,80,50,281,,81,30,042,,82,48,336,45*75
> $GPGSV,5,5,17,83,10,273,30*40
> $GPRMC,061139.00,*A*,3206.6722,N,03450.3224,E,000.00000,074.7,201113,,,*A*
> *55
>                                        |
>                                                                  |
>                                        -- Status(*A*=Data Valid)
>                                                  -- Mode
> Indicator(*A*=Autonomous
> mode)
If it were up to me A mode would be NO FIX.  It is saying the GPS is just
guessing about where it is.  You do not really have a 3D fix, you have
a 3D guess.

But I also got  Status(*A*=Data Valid) and Mode(*3*=3D).
For me it is enough indication that I receive good PVT data.
> Follow gpspipe outout with antenna disconnected:
> $GPGGA,061324.00,3206.6721,N,03450.3225,E,*0*,00,9.9,-0018.9,M,0018.4,M,,*7E
>             |
>             -- GPS Quality Indicator(*0*=Fix not available or invalid)
> $GPGSA,A,*1*,,,,,,,,,,,,,9.9,9.9,9.9*30
>                       |
>                       -- Mode(*1*=Fix not available)
> $GPGSV,5,1,17,02,05,047,,05,28,062,,12,30,136,,18,13,181,*73
> $GPGSV,5,2,17,21,53,236,,25,70,139,,29,58,018,,31,32,277,*7F
> $GPGSV,5,3,17,65,02,023,,66,27,067,,67,25,127,,73,16,328,*75
> $GPGSV,5,4,17,79,35,202,,80,50,280,,81,29,043,,82,48,337,*75
> $GPGSV,5,5,17,83,11,274,*45
> $GPRMC,061324.00,*V*,3206.6721,N,03450.3225,E,000.00000,074.7,201113,,,*N*
> *41
>                                        |
>                                                                  |
>                                        -- Status(*V*=Navigation
> receiver warning)                             -- Mode
> Indicator(*N*=Data not valid)

That looks right to me.
It also good for me. But in this situation I expect to get at least some indication in  gpsdata.fix.mode, and not got gpsdata.fix.mode= MODE_3D.
It is also not right not to pay attention to this information: Mode Indicator(N=Data not valid) and GPS Quality Indicator(0=Fix not available or invalid)   

> > > But if I not reconnect my client I continue to get MODE_3D
> >
> > Expected, that means you client has cached the last state.
> >
> Why it is expected?

Well, OK, I should expect nothing about your client.  And that is
part of the problem here.  We are not sure what you are doing.  Can
you share the code with us?

My code is very similar  to cgps code.

Do you see similar with cgps?  If we can all see the issue in cgps
maybe we can converge.

Yes, as I explain  in previous e-mail for cgps:
Then I disconnect the antenna the window with satellites information is cleared, 
but in window with PVT data remained the same information as before antenna disconnecting.

> If so, I am not understand how the libgps works in case of  shared
> memory export.

And libgps out of my area of knowledge as well.  Maybe someone else
can answer to libgps.

O..., Gary,
This is exactly  what I need, because I think that my problem is corresponding to interface to gpsd (libgps).
So, I need expert, better developer of libgps.
I main, who is now responsible of gpsd project?

> > > > Sounds like you are not starting gpsd with -n.  Can you confirm
> > > > how you are starting gpsd?
> > > >
> > > gpsd -b -n /dev/ttyUSB1
> >
> > That is good, except we discourage the use of -b.  That is intended
> > mostly for broken bluetooth GPS.  Why are you using that?
> >
> >
> I am working with GPS module through FT2232H with 1PPS on DCD pin.

Oh, even worse.  -b keeps gpsd from talking to your GPS.  So unless you
have manually configured your GPS for best operation gpsd is stuck
with whatever brken or unbroken state the GPS wwa last put in.

> Is it wrong or can be used?

Very wrong.  Do not use it, As the doc mentions, -b is only when your
device locks up or becomes totally inaccessable.  If your device is
not lking up or becoming totally inaccessible do not use -b.  Using it
seriously degrades how well gpsd can work.

> For cgps:  then I disconnect the antenna the window with satellites
> information is cleared,


> but in window with PVT data remained the same information as before
> antenna disconnecting.

Good.  Until there is new data, the old data stays.
Sorry, but I would define it as BUG.
Why to show not relevant data, if in NMEA messages it is not valid.

So you just need to look at the cgps code and copy it for your code.

As I mentioned, my code is very closed to cgps and this is a problem.

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97701
        address@hidden  Tel:+1(541)382-8588

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