[Qgis-user] Tablet vs GPS accuracy
Bo Victor Thomsen
bo.victor.thomsen at gmail.com
Fri Apr 4 01:32:13 PDT 2014
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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