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Reply to "GPS accuracy for location of a point"

I am copying the posts from the previous thread (which had a title not descriptive of the current discussion) below. Please continue the discussion on this thread.

Admin wrote:
Oscar, I don't understand what you are showing in your photo.

oscarwagner wrote:
I took my iPhone 6 to a manport about 600 feet from my house with the phone OFF. That manport can easily be seen on GE so it could be located later on. I stood on the manport, turned on the phone and started taking pictures about every 4 seconds. Turning on at the port is only important to learn how long it takes to get to GPS lock after travel. I loaded each of the photos onto my Desktop, right clicked, selected properties and clicked the Details tab and scrolled down to lattitude and longtitude. This time all but the first of the photo coordinates were about 15' SE of the manport. To locate them, I opened a "placemark" and maneuvered it till the coords matched the photo. Quick check says 1/100th of a " (second) is about one foot. The U1 chip in the iPhone 11 and 12 is supposed to do much better than a nominal 15'. I want to know how much better.

Admin wrote:
Thanks for the explanation.

Another good test to do would be to go out a couple months after the first test and repeat the process to see how much the points have moved. If they haven't moved much then your device is still useful for locating waypoints you established earlier, even if it has large absolute error.

duanerussell wrote:
It appears that precision is not gained after about 15 seconds of the phone acquiring the satellites. The variation in locations also tells me that 1) there is something nearby causing satellite-signal bounce, or 2) the algorithm doesn't get good accuracy. Close, but not repeatable to great precision. I would have thought it would have taken a bit longer for the phone to have that close of a cluster.

Still, not bad for a phone. It will be interesting to see if someone with a newer model can do the same, but get a tighter cluster of locations. I will have to try it with my Galaxy S7 Android.

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