<html>
<head>
<meta content="text/html; charset=ISO-8859-1"
http-equiv="Content-Type">
</head>
<body bgcolor="#FFFFFF" text="#000000">
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:
<blockquote
cite="mid:CAMktv+3rayqub5KjMQzwG1U32Pqpp=YXyxS2os5NWBZ=dqk8DA@mail.gmail.com"
type="cite">
<p dir="ltr">Hi QGIS Users,</p>
<p dir="ltr">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.</p>
<p dir="ltr">Thanks,<br>
Leo</p>
<br>
<fieldset class="mimeAttachmentHeader"></fieldset>
<br>
<pre wrap="">_______________________________________________
Qgis-user mailing list
<a class="moz-txt-link-abbreviated" href="mailto:Qgis-user@lists.osgeo.org">Qgis-user@lists.osgeo.org</a>
<a class="moz-txt-link-freetext" href="http://lists.osgeo.org/mailman/listinfo/qgis-user">http://lists.osgeo.org/mailman/listinfo/qgis-user</a></pre>
</blockquote>
<p><span style="font-family:'Arial';font-size:8pt;"> </span></p>
<p><span style="font-family:'Arial';font-size:8pt;">**********************************************************************</span></p>
<p><span style="font-family:'Arial';font-size:8pt;">Email Disclaimer: http://www.opw.ie/en/disclaimer/ </span></p>
<p><span style="font-family:'Arial';font-size:8pt;">**********************************************************************</span></p>
<p><span style="font-family:'Arial';font-size:8pt;"> </span></p></body>
</html>