MAP_PRECIS Real
Maximum mismatch in pixel at map edge between the true synthesized beam
(which would have been computed using the exact channel frequency) and
the computed synthesized beam with the mean frequency of the channels
sharing the same beam. This is used (with the actual image size) to de-
rive the actual number of channels that can share the same beam, i.e.
the effective value of BEAM_STEP when BEAM_STEP is -1.
Default is 0.1