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Fig. 3


Essential part of the A-Projection algorithm relies on the predict step, which transforms a 2D sky image (the projection of the celestial sphere on a plane) into a set of visibilities. We have simulated a dataset having one off-axis source, where the true visibilities (black dashed line) have been estimated using Eq. (1), taking the beam into account. This plot shows the comparison in all measured polarizations between the exact value of the visibility of a given baseline and the A-Projection estimate (gray line). Contrary to a traditional predict step, the visibilities are modulated by the beam amplitude (dotted line), and we have time-dependent polarization leakage. The overplotted graph shows a zoom in the small region shown in the top-right panel. In the degridding step, we use a computationally efficient closest-neighbor interpolation, creating steps in the predicted visibilities.

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