Can you explain the formula for the moment of the contour of an image?

Question

Mathematics

There is a formula for the moment of the contour of the image
Moment is the characteristic of the contour, combined (summed up) with all the pixels of the contour. The moment (p,q) is defined as:

Here p is the order of x, q is the order of y, where the order means, so to speak, the power at which the corresponding component is taken in sum with the other mapped ones.
But I don’t quite understand what exactly X and U mean in the formula. what exactly they should mean.
Knowledgeable people, please explain. On the Internet, I did not find anything other than the same formula and the same explanations.

Answer 1

Isn't it the (x,y)-coordinates of the i-th point of the path?