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.

This work was done by Erkin Sidick of Caltech for NASA’s Jet Propulsion Laboratory.

This software is available for commercial licensing. Please contact Dan Broderick at This email address is being protected from spambots. You need JavaScript enabled to view it.. Refer to NPO-49156.

NASA Tech Briefs Magazine

This article first appeared in the October, 2015 issue of NASA Tech Briefs Magazine.

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