ORB Algorithm: What Is Intensity Centroid? So, I am reading a paper about ORB: An Efficient Alternative to SIFT or SURF and it happens to calculate the direction of  corner from it center . According to Rosin the author of the paper;moments of a patch is given by 



and the centroid is of the patch from the center is calculated using:



The direction of the patch is computed from



My question is what are these value of p and q and why is it out there?
p and q - order of the moments, it is the analogue of the mechanical moments (i.e. of force or inertia). Image moments are very basic properties of image, invariant to rotation, could be used as simple descriptor.

Example,

Moment of inertia Ix= I2 = mass *x_coordinate^2.

Image moment Ix2 = intensity * *x_coordinate^2.

http://en.wikipedia.org/wiki/Moment_(physics)

http://en.wikipedia.org/wiki/Image_moment