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<div class="moz-cite-prefix">If you are working with tablets and an
external GPS connected to the tablet using USB or Bluetooth, you
should have a look at some of the new "GNSS mouse" type GNSS -
receivers that support both both GPS and GLONASS. The are
significantly more accurate and positionally stable than the GPS
only types (in the same price range).<br>
<br>
I have used a HOLUX M-215+ (remember the "+" - it means GLONASS
compatibility) and have a accuracy around 1 meter in the open land
most of the time. <br>
The HOLUX unit cost around 60 Euros.<br>
<br>
Regards <br>
Bo Victor Thomsen<br>
Aestas-GIS<br>
Denmark<br>
<br>
<br>
Den 04-04-2014 04:32, Leo Kris Palao skrev:<br>
</div>
<blockquote
cite="mid:CAMktv+3UJtQANPAtY80D00SyiVLuDn0M0_Rr-ZyPGJb3Mrs4gQ@mail.gmail.com"
type="cite">
<div dir="ltr">Hi Guys,
<div><br>
<div>Thanks all for your valuable insights about my inquiry. I
really appreciate your comments. I can use your comments as
reference on how we will also evaluate GIS applications in
Tablets.</div>
<div><br>
</div>
<div>Our application mainly falls on agriculture. We want to
use the tablets for surveying in Rural areas. And we want to
use QGIS android so we can load our shapefile and raster
maps for validation. On the other hand, we will also want to
use tablets to take location of field corners of farmers
field to get the plot size (this is where accuracy is
important). </div>
<div><br>
</div>
<div>I observe that when there is a wifi the location
significantly increases in tablets. But of course, wifi is
not available in rural areas. So, if we will use tablet we
will just rely on available GPS signal, weather, and the
device.</div>
</div>
<div><br>
</div>
<div>Thank so much, and again I really appreciate the comments,</div>
<div>-Leo</div>
<div class="gmail_extra"><br>
<br>
<div class="gmail_quote">On Fri, Apr 4, 2014 at 2:20 AM,
Michael.Dodd <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:Michael.Dodd@open.ac.uk" target="_blank">Michael.Dodd@open.ac.uk</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">I agree
with the points Richard has made here. I mentioned in an
earlier message on this topic that I'd done a lot of
testing with smartphones vs consumer gps see<br>
<a moz-do-not-send="true"
href="http://www.open.ac.uk/blogs/otih/?p=466"
target="_blank">http://www.open.ac.uk/blogs/otih/?p=466</a>
for details on some of the tests.<br>
<br>
Also tested consumer grade gps and a range of other
surveying techniques with results and discussion shown
here:<br>
<a moz-do-not-send="true"
href="http://oro.open.ac.uk/30066/" target="_blank">http://oro.open.ac.uk/30066/</a><br>
________________________________________<br>
From: Richard McDonnell [<a moz-do-not-send="true"
href="mailto:richard.mcdonnell@opw.ie">richard.mcdonnell@opw.ie</a>]<br>
Sent: Thursday, April 03, 2014 4:09 PM<br>
To: Leo Kris Palao<br>
Cc: QGIS Mailing List<br>
<div class="">Subject: Re: [Qgis-user] Tablet vs GPS
accuracy<br>
<br>
</div>
<div>
<div class="h5">Hi,<br>
It all boils down to the level of accuracy your job
requires, Commercial or Survey Grade GNSS (Global
Navigation Satellite System) now utilises NRTK
(Network Real Time Kinematic) which can produce sub
centimetre accuracies. We have found that the
accuracies is often too good, with our surveys
conflicting with Maps. We have seen +-40mm accuracies
in the field, where a stake in the ground is surveyed
and the kit can take us right back to the point days
later, to within 40mm. it is worth noting that Survey
grade GPS has a stated accuracy of sub meter without
NRTK.<br>
The next step down in accuracies would be GPS enabled
Field Computers, again a dedicated kit but hand held
form factor, the Trimble Geo-Explorer 7 is an example
of one of these. They now also have the ability to
utilise NRTK, bringing there accuracies to within 0.5m
(or better).<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 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.<br>
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>
One other thing you should all note when using a phone
or similar device to record your location, Use the
native Latitude and Longitude to record the position,
don't use the device to transform the coordinates to
some other CRS. Use a dedicated CRS Transformation
tool on a desktop/Laptop computer to convert to your
desired CRS. Handhelds are not suitable for that
purpose.<br>
I hope this helps!!<br>
Regards,<br>
<br>
Richard.<br>
<br>
On 03/04/2014 12:30, Leo Kris Palao wrote:<br>
<br>
Hi QGIS Users,<br>
<br>
I would like to inquire if there are some user that
already assessed the positioning (location) accuracy
of tablet vs commercial gps. We would like to use qgis
android for fieldwork. We would also like to try qmap.<br>
<br>
Thanks,<br>
Leo<br>
<br>
<br>
<br>
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