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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