Martin and list,
To me, in general, I think I would try to go with a Raspberry Pi
based solution. The hardware isn't all that expensive and the
easy ability to do stuff directly with the output of the device
in Python or some other programming language seems to be
preferable to messing around with Android or iOS applications.
One of many articles that may be of interest
https://learn.adafruit.com/adafruit-ultimate-gps-on-the-raspberry-pi?view=all
On Mon, May 25, 2020 at 9:25 AM Martin Weis
<[email protected]
<mailto:[email protected]>> wrote:
Dear list,
I would like to add some things here, since I am trying to
use RTK GPS
in the field with mobile devices.
> 1) Accuracy of GPS Devices
RTK GPS or any more precice GPS technology will be external,
you cannot
get around the missing measurements and lack of algorithms in
consumer
grade chips.
Then it depends on the capabilities of the device to receive
satellites
of all systems (one or multiple frequencies/signals) and be
able to
apply correction data (a question of algorithms). For better
equipment
the prices rise quickly.
There are some low cost devices evolving, a new chip was recently
announced: Skytraq PX1122R for about $100. Could be tested
with a break
out board and antenna, e.g. see board at navspark shop. The
module even
supports PPP, which might be especially interesting where
mobile network
is not available.
https://navspark.mybigcommerce.com/px1122r-evb-px1122r-multi-band-quad-gnss-rtk-evaluation-board/
Other low cost solution were mentioned (emlid/REACH,
Catalyst, etc).
Am 23.05.20 um 21:51 schrieb Michael.Dodd:
> One app that claims to do a lot of what high precions gps
does is> Mobile Topographer Free – Apps on Google Play
> 2) Software
On Android I was able to get the external signal into the
system, you
need the app "Bluetoth GPS" (or similar) or a USB2serial +
app (better
avoid tiny plugs and large cables during field work).
Additionally you
need to override the internal GPS position with the Blue GPS
App in the
developer settings (mock provider).
My impression was, that most Android applications target the
accuracy of
the device only, so e.g.
* you cannot zoom to cm-levels, only ~100m
* not many proper GIS Apps are available, most are expensive
* Tracking usually does not rely on cm-grade positions, so
the apps are
not made for it
One particular thing is, that with high accuracy of the
signal, an
internal computation in single precision float will not
suffice (all
computations must be in double precision), and you may end up
with a cut
off of the last position digits, e.g. if you have 8 digits, 4
before and
4 after the decimal separator (e.g. in DDMM.MMMM format),
then you end
up with coordinates cut down to 2-3 decimeters in the real world
(typical GPS mouse output, not so uncommon).
So, looking into that aspect may be required, and only few
Apps may
implement that (e.g. expensive "surveyor" apps for
professionals? did
not test).
BTW, sponsoring the double accuracy implementation for QField is
welcome, as mentioned ot the webpage. It is already a very
usable and
FLOSS GIS solution for the field, especially useful if you
have a QGIS
workflow already ;)
Finding proper solutions and recommendations still required...
>
------------------------------------------------------------------------
> *From:* Qgis-user <[email protected]
<mailto:[email protected]>> on behalf of
> [email protected] <mailto:[email protected]>
<[email protected] <mailto:[email protected]>>
> *Sent:* 23 May 2020 20:35
> *To:* [email protected]
<mailto:[email protected]> <[email protected]
<mailto:[email protected]>>
> *Subject:* Re: [Qgis-user] wishing for accurate
lattitude/longitude from
> a cell phone
>
>
> Hi Steve,
>
> I think there are two different aspects to your question:
> 1) Accuracy of GPS Devices
> I agree with others that you can't expect a better accuracy
than the 10
> to 30 feet you observed with a smartphone or a simple
handheld GPS. This
> might improve by averaging, but this takes time. Survey
grade GPS
> devices are very expensive. It is possible to get good
modules and
> antennas as components, but building a complete GNSS system
requires
> time and skill. This would reduce cost, but only to several
hundred
> instead of several thousand dollars, so this is no option
in your case.
> Besides, you will still need a correction data service
(usually costly)
> or use two receivers (rover and base).
> So you probably have to stick with your phone, which is
more flexible
> regarding the software than a handheld GPS.
>
> 2) Software
> The accuracy of the recorded position should not depend on
where you tap
> the screen - a good app should allow to record the current
GPS position.
> I am using Locus Map (Asamm Software) for a while now, it
works quite
> well, although it does not allow position averaging. There
is a free
> version, you could try that first.
>
> Regards,
> Jochen
>
> Am 22.05.20 um 20:54 schrieb Stephen Sacks:
>>
>> In order to make widely available some wise advice, I'm
sending to
>> this list a message I received from Neil B. In addition to
Neil's
>> message below, I want to mention that Nicolas Cadieux also
provided
>> similar information, saying I'd have to pay around $1,000 for
>> equipment that gives consistently accurate location
coordinates. And
>> thanks, also to Falk Huettmann and Bernd Vogelgesang for
their replies.
>>
>>
>> Message from Neil B:
>>
>> Hello Stephen.
>> Glad that you're having success. I would like to start off
by saying
>> that it is best to always reply to the mailing list and
not directly
>> to the person who submitted the email. Mailing lists work
really well
>> in that there is a pool of people out there who may be
able to offer
>> advice or may have an alternate method to solve the
problem that may
>> turn out to be a better way. On the flip side by
maintaining the email
>> chain through the mailing list, the follow up emails that
provide
>> information are stored in the archives which benefits
anyone searching
>> the internet to have the complete trail of information.
>>
>> As far as your results they are acceptable for the device
you're
>> using. GPS in phones are never built to precision survey
standards and
>> there is no reason for them to be. If you're within 30ft
of where the
>> phone thinks you should be then you can easily navigate
the rest of
>> the way by visual sight. High end equipment to achieve
sub-inch
>> accuracy is probably in the range of thousands of dollars.
One thing
>> to keep in mind is there is a difference between the
accuracy of a
>> device and to what level of precision they display. While
the app on
>> the phone may display 8 decimal places of a lat/long
coordinate and
>> tell you if you have moved a foot, it doesn't help that
the coordinate
>> it is displaying is out +/- 30 feet. The accuracy of a
device can also
>> be affected by the environment where the device is being
operated. In
>> regards to cell phones, they use multiple sources to determine
>> location such as GPS, cell phone towers, and wifi points
to perform
>> the triangulation. Lack of line of sight to satellites,
signals from
>> cell towers bouncing off of surrounding buildings, or
someone's
>> wireless router using inaccurate position information can
all affect
>> the accuracy of what is being displayed on your phone.
>>
>> So the question is how are you determining that the
coordinates are
>> wrong? If you have information that you trust to be
authoritative then
>> adjust your points to those values and carry on. I have no
advice or
>> opinions on inexpensive devices that may help with a more
accurate
>> reading.
>>
>> Please do not respond directly to me. This email account
is not
>> actively monitored and I don't always have the time to
follow up with
>> the emails. All the best with your endeavours.
>>
>> ~Neil B.
>>
>> On Fri, May 15, 2020 at 7:52 PM Stephen Sacks
<[email protected] <mailto:[email protected]>
>> <mailto:[email protected]
<mailto:[email protected]>>> wrote:
>>
>> Hi Neil,
>>
>> With your help, I have successfully brought the
corners of our
>> gardens back from Pennsylvania to the Promenade here
in Brooklyn
>> Heights, New York. Thank you.
>> At the risk of wearing out my welcome, I'm now
asking for more
>> advice. My point features are approximately where
they should be
>> but not exactly, some points are just a few feet off
and some are
>> 10 or even 30 feet off. I imported the data trying
both EPSG 4326
>> and 4269.
>> I'm now convinced that the problem is due to (1) my
Google
>> Pixel 3 cellphone, (2) the app I'm using ("Latitude
Longitude"
>> published by gps-coordinates), and especially (3) my
>> less-than-steady hands. I capture coordinates by
standing at
>> spot, waiting for the blue dot to settle, and then
touching the
>> blue dot. Often I don't touch the screen at exactly
the right
>> place. I tried another app ("GPS Coordinates"
published by
>> Financept) which is better in that it allows me to
zoom in, but
>> I'm still not always getting it right.
>> I'm thinking now that I need specialized equipment.
That is
>> what I want to ask you. Can you recommend some
inexpensive device
>> that will allow me to simply press a button to record
accurately
>> the coordinates of the point where I'm standing? Keep
in mind
>> that this is a community project with no funding. I
live on
>> Social Security and a university pension, but I'm
willing to pay
>> something in the range of $50 or a bit more. Do you
know of
>> anything at such a modest price, or would I have to
pay much
>> more? Or perhaps you know of better software for my
Android Pixel
>> 3 phone.
>> Thanks in advance for any advice you might offer.
>> Steve
>>
>>
>>
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