Somehow I did not follow the discussion, but like to add some of our
experience.
We are doing field work in a remote region in the southern Japanese mountains,
archaeological surveys on the ground based on LiDAR data.
A simple Garmin etrex10 is mostly reliable in an area of 40cm by 40cm around a
measured point, if used repeatedly at this point and the point is located in
the middle of a valley. Even cell phones do a good enough job. As soon as we
get closer to the steep slopes, the accuracy of the Garmin is less than 5 to 10
meters. We can check this with the detailed LiDAR based map, and geologists
told us, that even an expensive device could not be more precise under these
conditions. So we decided to measure traditionally on the ground if precise
measure is necessary, otherwise note the GPS data and the location as shown in
the map.
To sum up, we came to the conclusion not to spend money on an expensive GPS
that may not work in the shadow of steep slopes -- or in the streets of New
York. -- I appreciate any additional advice, and hope that this experience can
save Steve's organisation some money...
Best,
Maria
> Am 23.05.2020 um 03:54 schrieb Stephen Sacks <sack...@earthlink.net>:
>
> 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 <sack...@earthlink.net> 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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