Re: [gpsd-users] shared memory and fix.track

[Roger Oberholtzer]

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From: Gary E. Miller address@hidden
Sent: Monday, November 30, 2015 8:44 PM
To: Roger Oberholtzer
Cc: address@hidden
Subject: Re: [gpsd-users] shared memory and fix.track

> Have you verified that your GPS is outputting fix.track but gpsd is not 
> passing it on?  Many GPS output fix.track at a lower rate than the PVT data.

gpsd is parsing NMEA data. The track is known to be in the RMC record, which is 
at least reported each second. As I wrote, I see it in the RMC record myself 
(which I am reading through the gpsd raw data socket). Is fix.track invalidated 
after some period of time by gpsd? Like after less than 1 second? Or is it 
invalidated by each read (which would seem an odd thing to do when there can be 
multiple clients)?  If so, this is problematic because reading the shared 
memory is not tied to when an NMEA record arrives. If it is not invalidating 
it, then why does it fluctuate between NaN and a reasonable value?

> If that is the case then gpsd will massk (NaN) the outdated fix.track when a 
> newer PVT comes in.

> YOu should check the setting in your PGS for fix.track output rate.

> My guess is that gpsd is giving any track.fix it gets, you just need to cache 
> that value until you expire it or get a newer value.


Roger Oberholtzer

RST Systems

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