[Qgis-user] Tablet vs GPS accuracy

[Zoltan Szecsei]

On 2014/04/03 17:09, Richard McDonnell wrote:
>
> The issue with phones and tablets is that, unlike dedicated systems, 
> you have less control over how the coordinates are recorded. They 
> don't take into account things like multipath (GPS signal bouncing off 
> buildings, Ground etc.)  The number of satellites (the more the 
> better) Most survey kits wont record a point with less than 5 satellites.
and
> There is a way to get an idea of the accuracy for your proposed 
> device. Take several readings over a day (7 or more) of 2 fixed points 
> approx 50m apart,  every day, for a week. Then compare the results. 
> you will have a spread of points, none of which are likely to be 
> perfect, but will give you an idea of the accuracies of the device, 
> the spread of the points being your expected error. A shorter test 
> over a day would yield similar results but over a week, you would have 
> a more comprehensive result. I have seen some tests, where accuracies 
> with an i-Phone were stated as +-3m.
Surely this test is not relevant in any way, as when he is in "the 
field" (which could be a city centre), the accuracies would vary from 
his test site.

The importance of such test is however that it makes the user _fully_ 
aware that the coords on the screen are not necessarily the position the 
GPS receiver IS actually at (at that time).

People often seem to forget that a GPS screen is exactly like a TV 
screen - what you see on it is not necessarily the truth :-)


-- 

===========================================
Zoltan Szecsei PrGISc [PGP0031]
Geograph (Pty) Ltd.
GIS and Photogrammetric Services

P.O. Box 7, Muizenberg 7950, South Africa.

Mobile: +27-83-6004028
Fax:    +27-86-6115323     www.geograph.co.za
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