[Qgis-user] Tablet vs GPS accuracy

Thu Apr 24 02:40:22 PDT 2014

I´ve just been introduced to this solutions - might be of interest:
http://swift-nav.com/piksi.html

Lene Fischer
Associate Professor

Department of Geosciences and Natural Resource Management
University of Copenhagen

MOB +45 40115084
lfi at ign.ku.dk<mailto:lfi at ign.ku.dk>

[SCIENCE_bomaerke_UK]

Fra: qgis-user-bounces at lists.osgeo.org [mailto:qgis-user-bounces at lists.osgeo.org] På vegne af Lene Fischer
Sendt: 10. april 2014 08:23
Til: Bo Victor Thomsen; qgis-user at lists.osgeo.org
Emne: Re: [Qgis-user] Tablet vs GPS accuracy

I´ve been looking to the issue using an Android for collecting GPS data.
Try to look at RTKlib http://www.rtklib.com/  An OpenSource program - might give inspiration.
And also this note http://www.diydrones.com/profiles/blogs/rtk-lib-ported-to-android

Regards
Lene Fischer

________________________________
From: qgis-user-bounces at lists.osgeo.org<mailto:qgis-user-bounces at lists.osgeo.org> [qgis-user-bounces at lists.osgeo.org] on behalf of Bo Victor Thomsen [bo.victor.thomsen at gmail.com]
Sent: 04 April 2014 10:32
To: qgis-user at lists.osgeo.org<mailto:qgis-user at lists.osgeo.org>
Subject: Re: [Qgis-user] Tablet vs GPS accuracy
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.Dodd at open.ac.uk<mailto:Michael.Dodd at 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.mcdonnell at opw.ie<mailto:richard.mcdonnell at 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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