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).
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.
The HOLUX unit cost around 60 Euros.
Regards
Bo Victor Thomsen
Aestas-GIS
Denmark
Den 04-04-2014 04:32, Leo Kris Palao skrev:
Hi Guys,
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.
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).
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.
Thank so much, and again I really appreciate the comments,
-Leo
On Fri, Apr 4, 2014 at 2:20 AM, Michael.Dodd <michael.d...@open.ac.uk
<mailto:michael.d...@open.ac.uk>> wrote:
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
http://www.open.ac.uk/blogs/otih/?p=466 for details on some of the
tests.
Also tested consumer grade gps and a range of other surveying
techniques with results and discussion shown here:
http://oro.open.ac.uk/30066/
________________________________________
From: Richard McDonnell [richard.mcdonn...@opw.ie
<mailto:richard.mcdonn...@opw.ie>]
Sent: Thursday, April 03, 2014 4:09 PM
To: Leo Kris Palao
Cc: QGIS Mailing List
Subject: Re: [Qgis-user] Tablet vs GPS accuracy
Hi,
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.
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).
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.
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.
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.
I hope this helps!!
Regards,
Richard.
On 03/04/2014 12:30, Leo Kris Palao wrote:
Hi QGIS Users,
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.
Thanks,
Leo
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