[daip] Re: PBCOR

[Eric Greisen]

Neal Miller writes:
 > Hi Eric.
 > 
 > I'm using PBCOR, and I noticed that the more recent
 > versions of AIPS have changed the adverbs. It used to
 > use a "dparm" set of nine, which has been replaced
 > by a "pbparm" set of seven. The explain file is still
 > the old one, and so discusses the dparms. Could you
 > tell me if my understanding is correct here? Here's
 > the mapping as I see it:

So ignore the explain file which I am allergic to changing and so
forgot.  The form of the correction has been changed - it was
1/(the-current-one) and of a somewhat different mathematical form as
well.  Perley's report mentions 3 terms because that is all he thinks
are needed.  The program allows 5 if you insist..

 > 
 > OLD        NEW          Comment
 > 
 > dparm(1)   pbparm(1)    Same - power cutoff of primary
 >                           beam
 > dparm(2)   pbparm(2)    Generally same - if '1' then use
 >                           later parms to describe the
 >                           polynomial coefficients for the
 >                           power pattern. Old: dparm(5-9),
 >                           New: pbparm(3-7)

Yes

 > dparm(3)   -            If set to '0', use information in
 >                           header for pointing center. If
 >                           greater, use coordinates in gpos.
 >                           (In new version, gpos is replaced
 >                           by coordina; if all zeros it uses
 >                           the header, otherwise it uses the
 >                           coordinates specified).

Adverb COORDINA is now used to set the coordinate.  If it is zero then
the header is used.

 > dparm(4)                ?
 > 
 > I don't recall what dparm(4) used to be, but in my notes
 > I had set it to '1'. Has there been some change in the
 > polynomial coefficients (maybe dparm(4) indicated the first
 > term was dparm(4) * X^0, which is now implicitly set to 1)?
 > It is also a bit confusing that the discussion of Perley's
 > results for the polynomial in the explain file are for 
 > three terms, not five.

Yes - the best fit before had the center not = 1.0 !!  But remember
that the parameters PBPARM(3-7) have a different meaning now.  All
tasks use the same parameters now - PBCOR, PATGN, SETFC, FACES, etc.

Eric Greisen