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*I want to understand what would it mean by easting of ground control points (GCP), and what would it mean to have rmse of x m with a minimum of a m.

The average root mean square errors (RMSE) in the easting and northing of the GCPs were 'x' and 'y' m, respectively, with a minimum value of 'a' m and a maximum value of 'b' m.

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    $\begingroup$ It would be very helpful if you added an online reference to the source of the quote, if possible. If that is not possible, a reference to the source would still be helpful. $\endgroup$ Commented Dec 21, 2022 at 15:36

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Easting and northing provide an alternative to latitude and longitude for specifying a point on the Earth ellipsoid. I suggest you read (for example) the wiki.gis.com pages on the Universal Transverse Mercator (UTM) coordinate system and easting and northing. There are lots of other articles on these topics on the internet.

There are advantages and disadvantages with regard to easting and northing versus latitude and longitude. One key advantage of easting and northing is that for nearby points such as the error in ground control points, easting and northing take advantage of the fact that the surface of the Earth is nearly flat on a local scale. One key disadvantage of easting and northing is that it's rather convoluted.

Because this concept is already well-documented, and because it is rather convoluted, I'm not going to go into details in this answer. I suggest instead that you read up on the topic and ask additional questions when you come up with them.

Regarding the specific issue raised in the question,

The average root mean square errors (RMSE) in the easting and northing of the GCPs were 'x' and 'y' m, respectively, with a minimum value of 'a' m and a maximum value of 'b' m.

Another way to put the first part of the quoted text is that the ground control points have a root mean square error of x meters in the east-west direction and y meters in the north-south direction. I would have to see the relevant text to properly interpret the second part (the part about minimum and maximum errors). I suspect that those are the minimum and maximum of the square roots of the sum of the squares of the easting and northing errors, but that's just a guess.

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  • $\begingroup$ Yes yes, thank you. $\endgroup$
    – kc_nul
    Commented Dec 23, 2022 at 19:22

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