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Performance was assessed by comparing the correct translation value,
, used to generate the measured image, to the recovered
translation parameter estimate in the th trial.

A measure of the robustness of the estimated translation is:

where represents the number of elements in set , and
is a moderate tolerance, taken to be 2mm in this case. This
measure represents the fraction of solutions which were not
considered ``close'', where sets the threshold by which
something is considered ``close''.
A measure of the accuracy of the estimated translation is:

This measure is a modified RMS error measurement, where any errors greater
than are replaced by . In this way it downweights the
contribution for very large errors which a non-robust technique can produce
and gives a normalised measure between 0 and 1.
For an ideal method, both measures, and , would be zero.