[SailfishDevel] GPS initially shows old location

christopher.lamb at thurweb.ch christopher.lamb at thurweb.ch
Fri Jan 17 20:49:09 UTC 2014

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

b) Next reading --> GPS Acquired, now in the field next to the railway  
line, close to true location (subsequent readings get even more precise)

--> 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.



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
>> >
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