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<div class="moz-cite-prefix">Hi Steve,</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">I think there are two different aspects
to your question:</div>
<div class="moz-cite-prefix">1) Accuracy of GPS Devices</div>
<div class="moz-cite-prefix">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).</div>
<div class="moz-cite-prefix">So you probably have to stick with your
phone, which is more flexible regarding the software than a
handheld GPS.</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">2) Software</div>
<div class="moz-cite-prefix">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.<br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">Regards,</div>
<div class="moz-cite-prefix">Jochen<br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">Am 22.05.20 um 20:54 schrieb Stephen
Sacks:<br>
</div>
<blockquote type="cite"
cite="mid:cf16f21b-c9a5-dde4-e5db-ad923772264b@earthlink.net">
<p>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. <br>
</p>
<div class="moz-forward-container"><br>
</div>
<div class="moz-forward-container">Message from Neil B:<br>
</div>
<div class="moz-forward-container"><br>
</div>
<div class="moz-forward-container">Hello Stephen.
<div dir="ltr">
<div dir="ltr">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.</div>
<div dir="ltr"><br>
</div>
<div>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.</div>
<div><br>
</div>
<div>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.</div>
<div><br>
</div>
<div>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.</div>
<div><br>
</div>
<div>~Neil B.</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Fri, May 15, 2020 at
7:52 PM Stephen Sacks <<a
href="mailto:sacks44@earthlink.net"
moz-do-not-send="true">sacks44@earthlink.net</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote">
<div>
<p>Hi Neil, <br>
</p>
<p> 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.<br>
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.<br>
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.<br>
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.<br>
Thanks in advance for any advice you might offer.<br>
Steve<br>
<br>
</p>
</div>
</blockquote>
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