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 formationinstructions.  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 columnper field.

If otf=F and scr=F, delmod will provide a listing of the header field records.