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It may happen, with ALMA or NOEMA, that some data set result in “tiny” mosaics, where the pointing centers, though different, are very close to each other. This may occur because the specified coordinates changed during the observing sessions, by accident (a typo) or intentionally, for example when observing moving objects.
IMAGER will ignore these pointing differences if the position spread is smaller than MOSAIC_TOLERANCE (in arcseconds). In this case, despite the number of pointings, UV_MAP will proceed as for a single field. Proper handling of the phase centers in this case depends on the reason why the coordinates were changed. This may require a conscious user action to preserve the imaging accuracy. See Sect.16.1 for details.