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

From: Gerry Creager - NOAA Affiliate
Subject: Re: [gpsd-users] Get fix mode with disconnect antenna
Date: Tue, 19 Nov 2013 11:00:14 -0600

Older Motorola PVT6's would continue to output the last valid fix. However, there was at least one NMEA sentence that had a "valid fix" flag, and the Motorola Binary also had a flag for that. Realize I'm working form memory and don't have my notes on the PVT's handy here at work... Aha. GGA has a fix quality, invalid==1, valid GPS==1, DGPS==2. Oh. Fudge. Yakov's already found that. 

In addition, if memory serves, the timestamp on the NMEA output stopped updating when the fix was invalid.

On Tue, Nov 19, 2013 at 1:58 AM, Yakov Shmulevich <address@hidden> wrote:

On Tue, Nov 19, 2013 at 9:21 AM, Gary E. Miller <address@hidden> wrote:
Yo Yakov!

On Tue, 19 Nov 2013 08:15:15 +0200
Yakov Shmulevich <address@hidden> wrote:

> You don't understand me, I disconnect the antenna, so at this time
> the PVT data by sure changed.

Are you sure?  Do you see that in the debug output?  Most GPS will
just stop sending anything when they lose the antenna.
I run gpspipe at this  time and see all periodical NMEA messages come.
And in the GGA message I see GPS Quality Indicator=0 (Fix not available or invalid)
More then, if I reconnect my client by gps_close() and gps_open() I got gpsdata.fix.mode = MODE_NOT_SEEN.
But if I not reconnect my client I continue to get MODE_3D

> But I got the data as before disconnecting antenna, include
> gpsdata.fix.mod=MODE_3D.

Is so, we need to see some debug output to see what is happening.
What debug print you need? I can run the gpsd with -D 7 and send you ? 

> I found the workaround, but it seems me very ugly.
> Now every time that I want to get PVT data, I open the session by
> gps_open(), and after I get the PVT data I close the session by
> gps_close(). Also this solution have some strange behavior - I found
> that after gps_open() I get right PVT data only after 3-5 gps_read().

Sounds like you are not starting gpsd with -n.  Can you confirm how you
are starting gpsd?
gpsd -b -n /dev/ttyUSB1 

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

Gerry Creager
“Big whorls have little whorls,
That feed on their velocity; 
And little whorls have lesser whorls, 
And so on to viscosity.” 
Lewis Fry Richardson (1881-1953)

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