A software program enables a user to track a scene or a spot on Earth from space (such as from the ISS) using an innovative algorithm. This robust and highly accurate software allows a scene to be tracked that can be not only the shifted version of a previous scene, but can also be a distorted one.
A user can choose an M×M-pixel subimage from a previous or older image frame captured by a camera from space, preferably close to the center of the scene to be tracked, where M is preferentially a power of 2, such as 128. Such a subimage, r(x,y), is referred to as a reference cell.
The user can choose N×N-pixel cell, S(x,y), from the current or newer image frame. This cell is called the test cell, where N>M, with N again preferentially a power of 2, such as 256. Then the user calculates the cross-correlation (CC) of the reference cell r(x,y) and the central M×M-pixel subimage, s(x,y), of S(x,y) using FFT (fast Fourier transform). The location of the CC-peak is determined by fitting a quadratic-curve to three points near and including the CC-peak in the x-direction, and doing the same in the y-direction. This is done analytically since there are three data points for three unknown parameters in such a fit. The test cell is shifted by the amount determined in the previous step to match it with the reference cell, using the Fourier-transform of the larger test cell, S(x,y), to avoid wraparound errors.