The position determination accuracy depends on the number of source and background counts and on the position in the Field of View (FOV). Off-axis the collimator blocks some of the source photons and beyond the fully coded FOV (FCFOV) the coding is incomplete.
Figure 6 shows the position resolution for a source on axis as function of energy. The cause of the degradation below 10 keV is the signal-to-noise ratio of the front-end electronics. The energy dependence of the position resolution above 10 keV is determined by the increase of the primary photoelectron range with energy. The position resolution is slightly degraded compared to the ground calibrations.
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