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<div class="moz-cite-prefix">On 2014/04/03 17:09, Richard McDonnell
wrote:<br>
</div>
<blockquote cite="mid:533D798C.3070009@opw.ie" type="cite">
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<br>
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 <font
color="#006600">multipath (GPS signal bouncing off buildings,
Ground etc.)</font> The number of satellites (the more the
better) Most survey kits wont record a point with less than 5
satellites. <br>
</blockquote>
and<br>
<blockquote cite="mid:533D798C.3070009@opw.ie" type="cite"> 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.<br>
</blockquote>
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.<br>
<br>
The importance of such test is however that it makes the user <u>fully</u>
aware that the coords on the screen are not necessarily the position
the GPS receiver IS actually at (at that time).<br>
<br>
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 <span
class="moz-smiley-s1"><span> :-) </span></span><br>
<br>
<br>
<pre class="moz-signature" cols="72">--
===========================================
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 <a class="moz-txt-link-abbreviated" href="http://www.geograph.co.za">www.geograph.co.za</a>
===========================================</pre>
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