Deletes model representations in the MS
This utility task is to be used to delete the model visibility
data representations in the MS. The 'otf' representation is
the new (as of v3.4) 'scratch-less' model data, stored as
keywords in the MS header containing model data formation
instructions. It is generated by the setjy, ft, and clean
tasks (usescratch=F), and if present, overrides the
old-fashioned MODEL_DATA column (if present). If a user
wishes to use the MODEL_DATA column _after_ having operated
with the 'otf' representation, this task can be used
to delete the 'otf' represenatation to make the MODEL_DATA
column visible. (Create the MODEL_DATA column by using
usescratch=T in setjy, ft, or clean; or by running the
clearcal task with addmodel=T.)
If otf=T, specific fields can be selected for deletion
using standard field selection semantics. If field='',
all fields' models will be deleted.
For convenience, this method also provides a means for
deleting the MODEL_DATA column by setting scr=T. Note
that it is not possible to delete the MODEL_DATA column
per field.
If otf=F and scr=F, delmod will provide a listing
of the header field records.