[SailfishDevel] Fwd: Re: QGeoSatelliteInfoSource in Sailfish

christopher.lamb at thurweb.ch christopher.lamb at thurweb.ch
Sun Jan 19 21:32:47 UTC 2014



I am not sure If I have understood your question, but I think you are  
asking about differences in direction from the QtSensors Compass and  
the the QtPositioning PostionSource elements.

1) The Compass Azimuth shows the direction the top of the device is  
pointing to (so it will change as your rotate the device).

2) The PositionSource shows a direction based on the direction the  
device is travelling (irrespective of where the device is pointing).


Similar to 2) The speed shown by a GPS is absolute, irrespective of  
how the device is pointing. Some years ago I was coastal soaring on  
the coast of South Africa when the wind picked up, and got to the  
point where it was at (and possibly just above) the maximum speed of  
my paraglider. Flying fully into the wind, pushing maximum speedbar  
the GPS was showing speeds of 0.5 - 1 Km, and it was very difficult to  
tell if this was fowrards or backwards - but it was most likely the  



Zitat von "Caliste Damien" <dcaliste at free.fr>:

> Bonsoir,
> Le dimanche 12 janvier 2014, christopher.lamb at thurweb.ch a écrit :
>> Marcel used the Compass element from QtSensors for azimuth.
> Ok, I understand, but I'm still wondering :
> - QtSensors and compas will provide the azimuth of the device, so
> acting it like a compas, for instance, top of the device is pointing to
> the north.
> - QGeoPosition is providing GPS info with latitude and longitude, and I
> was thinking that the direction attribute was in fact the first
> derivative of the position, which is different from the compas return
> value, for instance I'm moving west while pointing top of device to the
> north.
> So how to get the first derivative of GPS position, deriving it by
> hand ? Like calling the azimuth method on the two last GPS fix ?
> Have a nice week,
> Damien.

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