Re: [gpsd-users] Garmin 18X-5Hz

[Robin Schwab]

Dear Gary

Am 16.08.2016 um 20:39 schrieb Gary E. Miller:
> On Tue, 16 Aug 2016 09:32:37 +0200
> Miroslav Lichvar <address@hidden> wrote:
> > I mean frequency of the oscillator on which is based the system clock.
> > As the temperature increases the clock slows down and ntpd/chronyd has
> > to tell the kernel to speed up the system clock to compensate for that
> > change.
>
> The temp is no gonna take a steap jump for 10 seconds.  That is the length
> of my spike.

I think you're right when you say you're stubborn. ;-) You tell the list 
there is a random jump roughly every two weeks in your system. But when 
I tell you to try to correlate it with GPS signal quality (in particular 
TDOP) you tell me I must prove my theory to you. I just tried to help. 
If there would be a strong correlation of TDOP with your problem (bird 
sitting on the antenna) then you could find a way to discard the bad 
TDOP data. Otherwise you would at least know that GPS signal quality in 
your case is not the problem and you could focus on software bugs and 
other possible theories.

I was once doing a map survey with expensive Trimble DGPS equipment. 
Even with the super expensive stuff we had a DOP forecast telling us 
which time of the day we could trust the data most. As others said the 
Trimble will even give you a fix inside a metal enclosing. But precision 
will drop.

From a signal theory point of view I would like to know wether I have 
the metal encasing/bird on the antenna or not. This is what DOP provides.

Regards
Robin