Subtract/Add Model Visibilities

uvsub is a simple task that allows one to subtract or add the MODEL_DATA column to the CORRECTED_DATA column of a given MeasurementSet. It has only 2 parameters: vis and reverse.

If the CORRECTED_DATA column does not exist then it will be created first and the DATA column will be copied into it before the addition/subtraction of the MODEL_DATA is performed.

The MODEL_DATA column can either be the scratch column or a virtual one; either one will work with uvsub. The model visibilities are usually populated by the tasks clean/tclean, ft, and setjy.

Note that uvsub does the subtraction over the whole ms. If only a subsection (say field or spw selection was done whiile using clean or ft) of the MS was used in these tasks that populate the model visibilities, then the uvsub operation will give the expected results for only those parts. The remainder of the MS will get the CORRECTED_DATA added/subtracted with whatever existed originally in the MODEL_DATA. On initialization the model visbilities are 1 for parallel hand and 0 for cross hand.