[SailfishDevel] GPS initially shows old location

Marcel marcel at aliquis.de
Fri Jan 17 20:59:02 UTC 2014


Hi Chris,

you can get the timestamp in QML using:

positionSource.position.timestamp

But as said in my last mail, this will not help in this case, as the timestamp 
while waiting for a fix will be 'now'. also the valid-Properties are true 
while receiving the old position.I haven't found any way to detect that the 
device is waiting for a fix. I really hope SatelliteInfoSource will be 
available in the next Sailfish-Update

Am Freitag, 17. Januar 2014 schrieb christopher.lamb at thurweb.ch:
> Hi Juha and Marcel
> 
> Thanks for your valuable hints.
> 
> I should have said that I am using PositionSource from QMl. So unless  
> I have missed something (always possible) I don't get the timestamp.
> 
> The longitudeValid and lattitudeValid are the next things I will test.
> 
> In the future it might be possible to use SatsInView / SatsInUse, but  
> SatelliteInfoSource is not yet available...
> 
> To prove / disprove the indicated behaviour I did a little test
> 
> 1) GPS activated and position acquired in the little big city, then  
> turned off.
> 
> 2) On the train on the way home, at least one city further on, GPS 
reactivated
> 
> a) First reading --> this is still the little-big-city, and 29.5 kms  
> away from the true location
> 47.3937924
> 8.48578765
> 
> b) Next reading --> GPS Acquired, now in the field next to the railway  
> line, close to true location (subsequent readings get even more precise)
> 47.5051796
> 8.84221178
> 
> --> Conclusion: The GPS Location immediately shown is the last  
> reading. Depending on how far the Jolla has travelled since then, this  
> reading may be wildly misleading.
> 
> Grüsse
> 
> chris
> 
> 
> 
> Zitat von Marcel <marcel at aliquis.de>:
> 
> > Hi,
> >
> > I can see the same behaviour, too. The timestamp is not really helpfull, 
as
> > this is the timestamp when you get the position, not when this position 
was
> > seen. And while waiting for a fix you get an updated position every  
> > 30 seconds
> > with a new, current timestamp. Another observation I made is that the
> > horizontal accuracy is always set to 15m and the vertical accuracy is not
> > valid while waiting for a fix.
> >
> > If the fix is found you can get an accurate position like every second. I
> > would expect that while waiting for a fix the Valid-Properties (like
> > langitudeValid) of the Position should be false, and switch to true if 
they
> > are really valid after the GPS fix.
> >
> > Greets,
> > Marcel
> >
> > Am Freitag, 17. Januar 2014 schrieb Juha Siltanen <jsiltane at gmail.com>:
> >> Chris,
> >>
> >> I see the same behaviour. But won't the timestamp method in
> >> QGeoPositionInfo help you? If the stamp differs a lot from current time,
> >> then it is likely to be invalid in your case. At least that is what I see
> >> in my application, the first update has the timestamp set to the time 
when
> >> GPS was last used.
> >>
> >> /jsl
> >>
> >>
> >>
> >> 2014/1/17 <christopher.lamb at thurweb.ch>
> >>
> >> > Hi all
> >> >
> >> > Is it possible that the Jolla GPS / GPS Software stack initially shows 
the
> >> > last location acquired?
> >> >
> >> > This is the behaviour I am observing.
> >> >
> >> > At the moment I am sitting in an office building, which has poor GPS
> >> > reception, yet my app immediately shows GPS Coordinates. By peaking I 
can
> >> > see that the GPS icon is flashing, and thus no fix has been acquired.
> >> >
> >> > Having checked the GPS coordinates with Google Earth, the coords are
> >> > actually for a location several kilometers away - in the middle of a 
set
> > of
> >> > railway tracks that I travel along to and from work. As I do lots of
> > mobile
> >> > development on the train, this is a plausible location for where the 
Jolla
> >> > last got a fix.
> >> >
> >> > By comparison the same app running on my old Nokia N9 gets NaN from the
> >> > GPS for longitude and lattitude until it gets a fix. I can then 
translate
> >> > this into a user friendly text on the GUI "No valid position yet", and
> > stop
> >> > the user from proceeding further into the app until a true fix is
> > acquired.
> >> >
> >> > If my understanding of the behaviour of the Jolla GPS is correct, is 
there
> >> > anyway I can stop it giving me the old fix? It is important to my app 
that
> >> > the coords shown are as accurate as possible, otherwise a recovery 
party /
> >> > rescue helicopter may be mis-directed.
> >> >
> >> > Chris
> >> >
> >> > _______________________________________________
> >> > SailfishOS.org Devel mailing list
> >> >
> > _______________________________________________
> > SailfishOS.org Devel mailing list
> >
> 
> 
> 


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