GPS pains

[Willem Ferguson]

I have done quite a bit of testing of the software in land.

1) With 4.6.4.487, the logging of GPS locations proceeded without a 
significant problem. The problems with the previous version of the 
software were obviously related to that specific version on my machine. 
I can stop and restart the GPS logging and it stops and resumes as expected.

2) Logging did not occur at 3 min intervals, but at about 5-min 
intervals. The software behaves almost like the minimum allowed 
between-record interval is 5 minutes and it substitutes my 3-min 
interval with 5-min.

3) Walking at a speed of about 4.5 km/h and the between location 
parameters set at 3 minutes and 100 m, the locations were at longer 
intervals (around 5-11 minutes) compared to walking at a slower speed. 
Walking at about 2 km/h, the records were mostly around 5 min apart. 
Could it be that it captures a moving GPS with less accuracy at speed 
and if one moves faster it takes longer to obtain a valid plot?

4) As far as accuracy is concerned, the error in GPS position was around 
20m, with one record off by around 1.6 km at the fast walking speed. At 
a slow walking speed the accuracy was within 7m.

I have the numeric data behind most of the above.

I think there is room for experimentation with the algorithm that does 
the GPS recording. I suspect that a single plot is obtained from several 
GPS data points and the criteria for determining an accurate plot are 
set quite tight so that data points need to be very close together for 
the software to record a single GPS position in the list of GPS 
positions. If this is the case, then one should experiment with the 
number of repeat points required for a single GPS position as well as 
the degree to which these repeats need to be similar in order to be 
accepted as a valid GPS record. This is the only way in which I can make 
sense of this.

I scratched around in the mobile-widgets, core and Qt-models directories 
to look for the code where the actual GPS recording takes place but I 
have not yet found it. I am not sure at what low level the GPS chip is 
accessible from our code.

Kind regards,
willem